there are two main approaches for incorporating radiohalogens into peptides . the first approach is direct labelling of the parent molecule . tyrosine residues , for example , can be labelled through electrophilic iodination 3 , iodogen 4 , or with the bolton - hunter reagent . 5 the main disadvantage of these strategies is that the regioselectivity and stoichiometry of the labelling reaction is often hard to control . the second approach involves reaction of a labelled precursor bearing an activated ester functionality , which will react with pendent amino groups on the peptide . when attention is paid to reaction conditions , the resulting amide bonds can be formed regioselectively . two of the most common labelling agents are , n - succinimidyl 4 -[ 18 f ] fluorobenzoate ([ 18 f ] sfb ) and n - succinimidyl 3 -[ 131 i ] iodobenzoate ( sib ). 6 , 7 the 18 f - and 125 i - derivatives are typically synthesised by nucleophilic substitution and destannylation reactions , respectively ( scheme 1 ). in order to best illustrate the utility of the fluorous synthesis approach for radiopharmaceutical development , a model compound , which was both useful and amenable to different labelling approaches , was chosen . in this way , the target compound became tris ( perfluorohexylethyl ) tin - 3 or 4 - benzoic acid ( compound 2 . 1 or 2 . 2 ). it was hoped that 2 . 1 and / or 2 . 2 would facilitate labelling with a variety of isotopes including ([ 18 f ] f 2 and [ 125 i ] 2 ), and permit conjugation to a variety of amino terminated compounds and biomolecules both prior to and after labelling . the “ fluorous tag ” used throughout this research was bromo [ tris ( 2 - perfluorohexylethyl ) tin ] ( 2 . 3 ), which was prepared following the method of curran et al . 8 compound 2 . 3 was synthesised via the arylstannyl , 2 . 4 , which in turn was prepared using a grignard reaction of phenyltintrichloride and 2 - perfluorohexyl - 1 - iodoethane ( scheme 2 ). removal of the homocoupled impurity by vacuum distillation and subsequent column chromatography yielded 2 . 4 in 75 % yield . the 1 h nmr of 2 . 4 in cdcl 3 showed a singlet at 7 . 33 ppm ( 5h , aromatic ) along with the triplet at 1 . 23 ppm ( with sn satellites 2 j sn , h = 51 . 7 hz ) and multiplet at 2 . 24 ppm corresponding to the methylene protons α and β to the tin . the 13 c nmr shows three aromatic signals at 129 . 06 ppm , 129 . 65 ppm , 136 . 08 ppm . the 13 c nmr resonances at − 1 . 49 ppm and triplet at 27 . 74 ppm ( 3 j f , c = 23 . 5 hz ) correspond to the carbons α and β to tin respectively . the negative ion electrospray mass spectrum of compound 2 . 4 gave peaks at m / z = 1297 [ m + oac − h ] − and m / z = 1283 . 0 [ m + oac − ch 3 ] − . in addition , the ir spectrum reveals strong absorbances corresponding to the aromatic ring at 2962 , 2928 , 2874 , and 2862 cm − 1 . these findings are consistent with literature values . 8 compound 2 . 4 was subsequently reacted with excess bromine and 2 . 3 was purified through vacuum distillation , yielding the desired product in 97 % yield . conversion of 2 . 4 to 2 . 3 was confirmed through disappearance of aromatic resonances in 1 h and 13 c nmr spectra . in addition , substitution of the electronegative bromine shifts 1 h and 13 c signals for the nuclei α to the tin to lower field . the effect is quite dramatic ; the 1 h α chemical shift increases from 1 . 23 ppm to 1 . 57 ppm with sn satellites ( 2 j sn , h = 54 . 1 hz ), while the 13 c α signal shifts from − 1 . 49 ppm to 6 . 11 ppm . the 13 c resonances for the fluorine bearing carbon atoms appear as highly coupled multiplets from 108 . 86 ppm to 121 . 71 ppm . the negative ion electrospray mass spectrum for 2 . 3 gave a single peak at m / z = 1279 . 5 [ m + oac ] − . these results are also consistent with literature findings . 8 four strategies for the synthesis of 2 . 1 were undertaken ( scheme 3 ). each involves nucleophilic attack of an organometallic reagent onto the tin - bromide compound ( 2 . 3 ). in the first approach , a , the procedure of zalutsky et al . 4 , which was used to prepare n - succinimidyl - 3 -( tri - n - butylstannyl ) benzoate , was employed . reaction of 2 . 3 with excess of the dilithiated species ( 2 . 6 ) successfully generated 2 . 1 . purification of the fluorous material was facilitated through a triphasic extraction into fc - 72 ® from dichloromethane and water . unfortunately , the extent of benzoic acid incorporation into the final product was consistently & lt ; 35 % of total available sites . the extent of product ( aryl - stannane ) formation vs . unreacted starting material ( bromo - stannane ) was determined using 1 h nmr . integration of 1 h α , β signals for the two different chemical environments , with respect to one another and to the aromatic protons provides a reasonable assessment of the extent of incorporation ( fig1 ). purification was attempted though column chromatography in accordance with the methods described by curran et al . 9 due to the similarity in r f values between 2 . 1 and 2 . 3 , no level of separation could be attained . approach b involved modifying the procedure described by lequan et al . for the synthesis of p -( phenylmethylisopropylstannyl ) benzoic acid . 10 the mono - anion of p - dibromobenzene was reacted with 2 . 3 , yielding 2 . 8 quantitatively . unfortunately , repeated attempts to lithiate 2 . 8 were unsuccessful , preventing the successive reaction with co 2 . approach c was based on the method reported by milius et al . for the synthesis of 4 - tri - n - butylstannyl - benzoic acid oxazoline . 11 the appeal of the oxazoline protecting group was its stability to grignard reaction conditions , and , more importantly , its ability to be deprotected under mild , non acidic conditions . the precursor , compound 2 . 9 , was synthesised by treatment of p - bromobenzoic acid with thionyl chloride to give the acid chloride . the acid chloride was subsequently reacted with 2 - amino - 2 - methyl - propanol to afford the amide . treatment of the amide with thionyl chloride in the absence of solvent induced cyclization to the oxazoline ring , generating 2 . 9 in 95 % yield . 1 h nmr of compound 2 . 9 showed a singlet at 1 . 42 ppm ( 6h ), singlet at 4 . 17 ppm ( 2h ) and doublets at 7 . 56 ( 2h ) and 7 . 87 ppm ( 2h ). the 13 c nmr and the electron impact mass spectrum ( m / z = 254 ) for 2 . 9 also agree well with the literature . 12 formation of the grignard was sluggish , and necessitated the addition of 1 , 2 - dibromoethane in order to promote the reaction . eventually , 2 . 3 was quantitatively converted to 2 . 10 , which was purified through a triphasic extraction and isolated in a 90 % yield . the 1 h nmr of 2 . 10 showed the typical shift in h α , β to higher field . the 1 h nmr also revealed peaks at 1 . 40 ppm and 4 . 14 ppm from the oxazoline group , and aromatic signals at 7 . 44 ppm and 7 . 97 ppm . similarly , the 13 c nmr showed the c α signal shift to a higher field of − 1 . 25 ppm , in addition to the appearance of methyl carbons at 28 . 5 ppm and aromatic resonances at 128 . 4 ppm and 136 . 0 ppm . the negative ion electrospray mass spectrum gave a peak at m / z = 1394 [ m + oac ] − . in order to facilitate cleavage of the oxazoline group under basic conditions , it was necessary to convert the oxazoline to the oxazolinium ion . in all instances , reaction with methylodide under mild reaction conditions yielded none of the desired quatemerized product . alternatively , under the vigorous reaction conditions suggested by literature , cleavage of the aryl - stannyl bond occurred . 13 approach d required the initial synthesis of a thiol protected intermediate , tripropyl 4 - bromoorthothiobenzoate 2 . 11 . the reaction pathway for d ( scheme 4 ) was applied originally to the synthesis of the analogous silicon fluorous compound . 9 the synthesis of the precursor 2 . 11 involved reaction of p - bromobenzoic acid with t hionyl chloride to generate the acid chloride , which was then reacted with excess propane thiol in the presence of alcl 3 . despite the fact that a great deal of attention was paid to ensuring reagent quality ( alcl 3 was freshly sublimed and propane thiol was freshly distilled ), the crude reaction product consisted of only one or two condensed propane thiol groups . the orthothiobenzoate was never observed as it was described in the paper by studer et al . 9 the successful methodology , approach e ( scheme 4 ), entailed adaptation of research by xizhen , z et al ., who established the feasibility of synthesising arylstannanes using organozinc reagents . 14 the use of the robust organozinc reagents , rather than organolithium reagents , facilitates the incorporation of compounds with electrophilic functionalities , such as esters , nitriles , and ketones . excess 3 - ethoxycarbonylphenylzinc ( 2 . 13 ), which is commercially available through rieke metals inc ., was reacted with 2 . 3 overnight ( scheme 4 ). the product was isolated through a biphasic extraction between fc - 72 ® and methanol in excellent yield ( 99 %). analysis of 1 h nmr for compound 2 . 14 revealed signals corresponding to the ethylene spacer at 1 . 35 ppm ( t , 6h ), and 2 . 33 ppm ( m , 6h ), in addition to peaks at 1 . 39 ppm ( m , 3h ), 4 . 39 ppm ( q , 2h ), and a meta - disubstituted aromatic from 7 . 47 - 8 . 07 ppm ( m , 4h ). the 13 c nmr for 2 . 14 showed four signals at high field — 1 . 12 ppm , 14 . 15 ppm , 27 . 87 ppm ( 2 j f , c = 23 . 3 hz ), and 61 . 32 ppm . at low field the 13 c nmr had resonances corresponding to carbon atoms with attached fluorines ( 106 . 46 ppm to 121 . 17 ppm ) and aromatic resonances , which have yet to be assigned due to difficulty interpreting the spectrum . the negative ion mass spectrum of 2 . 14 gave peaks at m / z = 1279 . 4 [ m - ethyl ] and m / z = 1369 . 5 [ m + oac ] − . saponification of 2 . 14 was achieved using excess base , despite the fact that the substrate was immiscible in the reaction solvent ( methanol / water 4 : 1 ). small amounts of the transesterification product were occasionally observed ; however , this product was removed by way of a second hydrolysis reaction . isolation of the product from fc - 72 ® following several washings with water yields 2 . 2 , presumably as the sodium salt , in 99 % yield . extraction of the sodium salt of 2 . 2 between fc - 72 ®, dichloromethane , and a 1n hcl solution , produced the free acid . the difference in solubility of the salt vs . the acid in cdcl 3 was pronounced . the acid dissolves in chloroform - d 3 to provide well resolved 1 h and 13 c nmr spectra , while the sodium salt was only sparingly soluble . the free carboxylic acid , 2 . 2 , unlike the sodium salt , crystallised over several days yielding a white solid . the 1 h nmr of compound 2 . 2 ( fig2 ) showed an absence of the signals corresponding to the ester group , but was otherwise unchanged from 2 . 14 . similarly , the 13 c nmr lacked the peaks associated with the ester group and had a corresponded shift of the carbonyl carbon to lower field ( 172 . 61 ppm and 172 . 04 ppm ). the 13 c peaks all have a small shoulder peak similar to the carbonyl carbon , which is perhaps a reflection of the presence of a small amount of sodium salt of compound 2 . 2 . the negative ion electrospray mass spectrum of compound 2 . 2 ( fig3 ) shows a peak at m / z = 1279 [ m − h ] − . the ir spectrum of 2 . 2 importantly showed a strong o — h stretch at 3410 cm − 1 , c ═ o stretch at 1632 cm − 1 , and an aromatic stretch at 2950 cm − 1 . dissolving a small quantity of 2 . 2 in pentane , followed by its slow evaporation , produced long needle - like crystals from which an x - ray crystal structure was obtained . this is significant , as it represents the first reported crystal structure of a perfluorostannane species of any variety . compound 2 . 2 crystallised in the triclinic ρ − 1 space group with two independent molecules in the unit cell ( z = 4 ). the structure proved difficult to solve , in large part due to the high level of disorder in one particular perfluorooctyl chain . this is reasonable considering the low barrier of rotation around the c — c bond , which typically leads to the oily property of these compounds . though additional work is still required prior to publishing the x - ray crystal structure , the current structure verifies the presence of compound 2 . 2 ( fig4 ). fluorination of tris ( perfluorohexylethyl ) tin - 3 - benzoic acid ( 2 . 2 ) was initially performed in perfluorinated hexanes ( fc - 72 ®), rather than the more commonly employed hf , or freons such as cfcl 3 . the use of fc - 72 ® is advantageous , since it readily dissolves the precursor , has a suitable freezing and boiling point range (− 100 ° c . and 65 ° c . respectively ) and is not susceptible to degradation by f 2 . the reaction conditions were worked out and optimised through a number of fluorination reactions , where conditions mimic those of the [ 18 f ] f 2 reaction without having to deal with the risks of radiation - exposure . scheme 5 and fig5 illustrates the reaction and apparatus used in a general fluorination reaction , respectively . in general , the substrate 2 . 2 was diluted in fc - 72 ® ( 1 ml ) and transferred to a dried fluoropolymer vessel . the contents of the vessel were cooled to approximately − 85 ° c . in a meoh / n 2 slush bath , after which 180 psi of a 0 . 5 % f 2 in ne solution were bubbled through the solution over a 20 - 30 minute period . the solvent was transferred to a vial along with methanol , which was used to rinse the reaction vessel . the entire mixture was evaporated by rotary evaporation , dissolved in acetonitrile : water ( 1 : 1 ) and passed down a fluorous column . fractions ( 3 × 3 ml ) were collected and characterised using 19 f nmr , hplc and ms spectroscopy . the 19 f nmr of the reaction product 2 . 15 showed roughly a quartet at − 112 . 00 ppm ( 3 j f , h = 5 . 76 hz ) when run in meoh : chcl 3 , consistent with an authentic m - fluorobenzoic acid standard and literature values . 15 , 16 the negative ion electrospray mass spectrum of compound 2 . 15 gave the requisite peak at m / z = 139 . 1 [ m − h ] − . hplc of the purified reaction mixture produced a single peak at 4 . 22 min , consistent with the authentic standard . the immiscibility of perfluorocarbons with most organic solvents has led to the development of a new approach to synthesis known as the fluorous biphasic system ( fbs ). in this approach , molecules containing appreciable fluorine content ( fluorous compounds ) can be selectively separated from non - fluorinated compounds . common separation techniques include biphasic extraction , triphasic extraction or application of fluorous reversed phase silica gel . the latter technique takes advantage of the tendency of fluorous substrates to interact strongly with the fluorous solid phase thereby dramatically increasing their retention time compared to non - fluorous materials . the fluorous biphasic approach can be used as a means of preparing radiolabeled substrates in high apparent specific activity . the technique entails binding a substrate to a fluorous - support in such a manner that the fluorous component is released upon reaction with the radionuclide of choice . the target radiochemical can then be readily separated from the fluorous support ( and any fluorous byproducts ) by passing the material through a plug of fluorous silica , or other suitable solid material , or by liquid - liquid extraction . this approach can yield iodine and fluorine labelled compounds in high chemical and radiochemical yields in a time and resource efficient manner . in particular , the fluorous approach can be used to prepare iodo and fluoro - labelled benzoic acids , which are important substrates for labelling proteins . initially in this research , fluorous silica synthesised in our laboratory was used in the purification process . it proved , however , to be less effective at retaining fluorous material than commercially available fluorous modified silica manufactured by silicycle ®. the improved retention of the commercial variety , which was attributed to improved loadings , facilitated a more rapid purification . in the case of the “ home - made ” and commercial fluorous silica we also observed that the use of alcoholic solvents as a mobile phase resulted in substantial breakthough of the fluorous impurities . in order to remedy this , an acetonitrile : water ( 1 : 1 ) eluent system was used , and appears to have prevented any migration of the perfluorotin impurity . elution of the product 2 . 15 , however occurs rapidly and is obtained (& gt ; 99 %) within the first 9 ml of eluent . in the initial reaction mixtures , two extraneous peaks were consistently found in the 19 f nmr spectrum (− 74 ppm and − 153 ppm ), in addition to the product peak at − 112 ppm . initially , it was believed that these additional peaks were the result of fc - 72 ®, which is composed of multiple isomers of perfluorinated hexanes . however , subjecting fc - 72 ® to the same fluorination and purification conditions yielded no observable peaks in the fluorine spectrum . it was later found that the peak at − 74 ppm was not present when medical grade sterile water replaced the laboratories own distilled - deionized water . further , the peak at − 153 ppm was found to originate from the use of silicycle ® brand fluorous silica . replacement of this brand of silica with that prepared by fluorous technologies ® proved to remove this peak from the fluorine spectrum . the reaction temperature also proved to influence the products generated in these reactions . when the reactions were carried out at higher temperatures , & gt ;− 65 ° c ., it was found that an occasionally small peak at − 105 ppm ( unresolved coupling ) could be seen in the spectrum . this could be the result of ortho substitution or a di - fluorinated ring , both of which would result in deshielding of the attached fluorine . this small impurity , however , was not seen when the reaction was carried out at lower temperature (− 85 ° c . to − 75 ° c .). in the course of these cold fluorinations , the yield of m - fluorobenzoic acid was optimised . the ratio of substrate to f 2 was varied between 0 . 7 to 3 . 0 in all cases , using 180 psi ( 0 . 5 % f 2 ) which corresponds to 1 . 18 × 10 − 4 mol of f 2 , similar to the amount used in a 18 f [ f 2 ] reaction . the percent yield of 2 . 15 with respect to f 2 decreased from 18 % to 16 % when 0 . 65 and 2 . 9 equivalents were used respectively . the yield analysis was based on comparison with calibration curves . it was found that the yield of 2 . 15 with respect to f 2 reached a maximum at approximately 24 % when the ratio of substrate to f 2 was 1 . 2 : 1 . since the reactions were run in equivalent volumes of fc - 72 ®, the decreasing yield may be a result of a visibly increasing viscosity in the more concentrated samples . the successful cold labelling and purification of 2 . 15 using the precursor 2 . 2 prompted the investigation of [ 18 f ] f 2 labelling . the reaction scheme is shown in scheme 6 . fluorine - 18 was produced at mcmaster university hospital by the 18 o ( p , n ) 18 f nuclear reaction using a siemens rds 112 proton cyclotron operating at 11 mev by the “ double shoot ” method . 17 the “ double shoot ” method entails diluting 18 f , which remains largely bound to the target wall following the 18 o ( p , n ) 18 f reaction with f 2 . irradiation results in fluoride exchange and releases 15 - 20 μmol of carrier - added 18 f [ f 2 ]. the 18 f [ f 2 ] in neon was carried through a teflon tube and was bubbled through the 1 ml solution of 2 . 2 in fc - 72 ® at − 85 ° c . the fluorination reaction was carried out in a fep ( perfluoroethylenepropylene co - polymer ) tube , and the outlet gas was bubbled through a 0 . 1 n naoh solution . assessment of [ 18 f ] f 2 consumed in the reaction was determined by measuring the total radioactivity in the vessel , compared to that in the naoh trap . work - up involved transferring the contents of the vessel to another vial using pressure generated by a syringe . the vessel was then rinsed with hplc grade methanol and the combined solvents were evaporated in a hot water bath under a rapid flow of nitrogen . to the resulting residue was added 3 × 3 ml of acetonitrile : water ( 1 : 1 ), and each aliquot successively transferred to the fluorous column . fractions of 3 ml were collected and characterised . in total , five [ 18 f ] f 2 fluorinations of 2 . 2 were carried out . fig6 shows the typical hplc chromatograms which were generated . analysis was carried out on a c 18 analytical column , eluted with a 1 : 1 acetonitrile : water ( 0 . 2 % tfa ) at 2 ml / min . the uv trace of compound 2 . 16 generated a single peak eluting at 4 . 18 minutes , which is identical to that of an authentic standard . integration of the peak area and comparison to the calibration curve indicates a 19 . 4 % yield of labelled product ( 18 f & amp ; 19 f ). the radioactive trace for compound 2 . 16 shows a single peak eluting at 4 . 99 min . the later elution time is consistent with the time delay between the uv lamp and radiation detector . in the last two reactions , the radiochemical yield and specific activity of 2 . 16 was assessed . in these instances , the decay corrected radiochemical yield of 2 . 16 was 30 . 2 % and 11 . 2 %; the lower yield was attributed to the vial walls not being rinsed effectively prior to purification . the theoretical maximum yield for this synthesis is 50 %, as half of the activity is lost as tris ( perfluorohexylethyl ) tin -[ 18 f ] fluoride . this is comparable to the [ 18 f ] f 2 destannylation reactions where 6 -[ 18 f ] fluoro - l - dopa and 6 -[ 18 f ] fluoro - l - m - tyrosine were generated with radiochemical yields of 33 % and 23 % respectively . 18 , 19 the specific activity of 2 . 16 following purification in the two experiments was 1966 and 2899 mci / mmol , respectively . the discrepancy can , in part , be attributed to the shorter purification times of the second vs . the first ( 27 min . vs 49 min .). the specific activity is dependent on the amount of f 2 mixed in the target gas , and as such it is difficult to make a direct comparison to other fluorodestannylation reactions . however , the obtained specific activities are reasonably high when compared to other electrophilic fluorination reactions . for example , various direct electrophilic fluorination approaches to generate 6 -[ 18 f ] fluoro - l - dopa give specific activities of ≦ 2000 mci / mmol . 20 , 21 though similar specific activities were obtained , this fluorous approach did not require hplc purification . the 19 f nmr spectra of the crude reaction products from an analogous cold fluorination and the purified reaction ( 2 . 16 ) products are shown in fig7 and 8 , respectively . the 19 f nmr was obtained after allowing sufficient time for decay of 18 f - labeled 2 . 16 . in the 19 f nmr of crude reaction , the sensitivity of the fluorine nucleus to detection by nmr is evident in the clarity obtained following only a few scans . the crude spectrum shows six clearly resolved peaks corresponding to the six fluorine containing carbons atoms along three equivalent n - octyl chains . there was no discernible shift in these peaks prior to or following the fluorination reaction . the 19 f nmr spectrum of the purified reaction ( fig8 ) shows only a single peak at − 110 . 10 ppm ( 3 j f , h = 7 . 24 hz ) when run in acetonitrile : water ( 1 : 1 ). the peak position and coupling is consistent with an authentic standard of m - fluorobenzoic acid in which the 19 f - signal appears at − 109 . 8 ppm , and is also consistent with literature values . 16 furthermore , it is important to note the absence of peaks associated with the fluorous “ tag ”, which is a testament of the efficiency of the fluorous purification method . the negative ion electrospray mass spectrum of a crude fluorination reaction and the purified reaction of 2 . 16 are shown in fig9 and fig1 , respectively . the electrospray mass spectrum of the reaction mixture prior to purification shows the product peak at m / z = 139 . 1 [ m − h ] − and the fluorous “ tag ” impurity around m / z = 1319 . 2 , 1345 . 2 . however , the purified reaction ( fig1 ) shows only a single peak corresponding to the product at m / z = 139 . 0 [ m − h ] − , with no trace of any impurity . as mentioned previously , the highest radiochemical yield ( eob ) obtained was 30 . 2 %. however , it should be noted that approximately 20 mci of radioactivity ( or ≈ 11 %) was lost during evaporation of the fc - 72 ® solvent . it is possible that the substitution of h - atoms in fc - 72 ® by [ 18 f ] fluoride accounts for this loss of activity post evaporation . de vries et al . observed a 61 - 73 % loss of radioactivity to the reaction solvent when they switched from cfcl 3 to the more environmentally appropriate chcl 3 or ch 3 cn . 18 this reduced the radiochemical yield of 6 -[ 18 f ] fluoro - l - dopa , obtained through fluorodestannylation , from 33 % to 5 % ( chcl 3 ) and 17 % ( ch 3 cn ). it appears , despite the loss of activity , that fc - 72 ® permits higher overall radiochemical yields compared with other reaction solvents . in developing these [ 18 f ] f 2 reactions , it quickly became evident that a workup procedure needed to be devised to permit a more “ hands - free ” or automated approach . the challenge with this work - up is that the fluorophilic solvent ( fc - 72 ®/ methanol ) needed to be exchanged with a fluorophobic solvent ( acetonitrile / water ). rotary evaporation required too much manual manipulation . alternatively , solvent evaporation in a hot water bath under a rapid flow of nitrogen took too long and often dispersed the product . in an attempt to improve upon these procedures , a u - tube like apparatus was constructed ( fig1 ). following the fluorination reaction , the vessel contents could be transferred to the u - tube via syringe pressure . applying a weak vacuum to the top of the u - tube facilitated removal of the solvent at room temperature within a couple of minutes . addition of 3 × 3 ml of acetonitrile : water ( 1 : 1 ), followed successively with applied syringe pressure , transferred the contents to the fluorous sep - pak and into the collection vial . in a trial cold reaction this apparatus appeared to facilitate a more suitable “ hands - free ” workup . the facile synthesis and purification of 2 . 16 demonstrates that the fluorous strategy shows promise as a convenient route for the preparation of 18 f [ f 2 ] labelled radiopharmaceuticals . there is a complete removal of the fluorous “ tag ” through a quick and simple fluorous column purification , which requires less than a minute . this approach therefore would be appealing in certain applications , as it avoids time intensive purification , reduces exposure , and can increase overall specific activity when compared to standard methods . with the success of the fluorination reactions , we explored labelling benzoic acid with iodine . the cold iodinolysis of the fluorous “ tagged ” model compound ( 2 . 2 ) was carried out in order to assess the capacity for introducing 125 i , 131 i , and 123 i . in addition to being interested in simple product generation , optimising reaction conditions was also an important goal . the iododestannylation reaction of 2 . 2 using excess iodine is shown in scheme 7 . the iodination reaction was carried out using excess 12 dissolved in methanol , which was added to a sizeable ( 1 × 10 − 4 mol ) sample of 2 . 2 . the reaction was allowed to proceed overnight , after which sodium metabisulfite was added to quench any unreacted iodine . methanol was removed under reduced pressure and the residue was dissolved in 5 × 5 ml volumes of hplc grade acetonitrile : water ( 1 : 1 ), and each washing was eluted through a fluorous column . in this case , purification utilised a 3 . 9 g sample of loose fluorous silica ( silicycle ®), packed into a 40 cm narrow column . the 5 ml aliquots were assessed for purity through hplc ( fig1 ) and electrospay mass spectrometry ( fig1 ). the hplc chromatogram contained three peaks , corresponding to salts ( solvent front ) and 2 . 17 ( t r = 9 . 9 min ). the peak at 9 . 9 min was shown to be 2 . 17 through comparison to a standard sample of 3 - iodobenzoic acid . the negative ion electrospray mass spectrum showed a single peak above background at m / z = 246 . 9 [ m − h ] − , which is consistent with the formation of 2 . 17 . there was no evidence of the fluorous “ tag ” which would be seen at m / z & gt ; 1000 . the iodinolysis reactions discussed above used an excess of iodine and 10 − 4 moles of substrate , and are therefore not representative of radioiodination reactions . in order to develop a labelling approach towards 2 . 18 , reactions with cold na 127 i at concentrations that mimic those that would be used with iodine radionuclides were undertaken ( scheme 8 ). in an attempt to optimise the cold iodination reaction a number of reaction conditions were investigated . first , a wide range of oxidants , which are commonly used in radioiododestannylation reactions , were screened . these included chloramine - t ( n - monochloro - p - toluenesulfonamide ), n - chlorosuccinimide , and peracetic acid . peracetic acid showed the highest conversions , which is consistent with literature reports . 22 the choice of solvent can also dramatically impact the radiochemical yields . f or the most part , methanol was utilised because of its ability to dissolve 2 . 2 and has been shown to be compatible with the other reagents and reaction conditions . iodination reactions are also highly dependent on the ph of the solvent , generally being promoted in an acetic medium and sometimes arresting when the ph increases towards neutrality . 23 for this reason , researchers often add small quantities of hcl or acetic acid to the reaction ; however , it was found that the oxidant ( 32 % peracetic acid in acetic acid ) was adequately acidic to promote the aforementioned reaction . in addition to optimising the reaction conditions , detection of the very small quantity of product ( 2 . 18 ) being generated necessitated optimising the hplc conditions . it was found through lengthy trial and error that separation of 2 . 18 from salts in solution could not be exacted using a c - 8 analytical column . this problem was rectified by switching to a c - 18 analytical column which facilitated significant separation . in the end , the optimum reaction involved dissolving compound 2 . 2 ( na + salt ) ( 4 × 10 − 6 mol ) in methanol ( 200 μl ) with stirring . to this solution was added nai ( 4 μl , 1 . 8 × 10 − 7 mol ) in 0 . 1 n naoh , which was followed immediately by the addition of freshly prepared peracetic acid solution ( 2 μl ). the reaction was quenched after 2 hours with excess sodium metabisulfite and diluted to 1 ml with distilled deionized water . the hplc chromatogram of compound 2 . 18 shows two primary peaks with elution times of 4 . 8 - 6 . 3 min . and 10 . 3 minutes , corresponding to salts ( solvent front ) and 2 . 18 respectively ( fig1 ). an authentic standard of 3 - iodobenzoic acid under the same elution conditions produced a peak at 10 . 2 minutes , confirming the peak assignment . the advantage to developing this chemistry using a cold isotope , similar to the case of fluorine , was that reactions could be conducted and handled without risk of exposure . however , the difficulty in developing radiochemical labelling procedures with representative quantities of na 127 i for na 125 i , was that detection had to be based solely on ultraviolet absorption . comparatively , the use of 400 μci ( approx . 1 . 8 × 10 − 7 mol ) na 125 i would result in an extremely intense peak on a gamma detector , although a very small , if visible , ultraviolet absorbance . recall that the maximal incorporation of iodine into the target molecule is ≦ 50 % of the total ; therefore , in an analogous 400 μci reaction , the maximum product yield is ≦ 9 × 10 − 8 moles . the successful cold labeling of 2 . 2 using cold nai prompted the corresponding radioiododestannylation using na 125 i ( scheme 9 ). the reaction was conducted in a similar fashion to the cold iododestannylation reactions . compound 2 . 2 ( na + salt ) ( 9 × 10 − 4 mol ) was dissolved in 200 μl of methanol with stirring , prior to the addition of na 125 i ( 44 μci ) in approximately 200 μl of 0 . 1 n naoh solution , and 2 μl of fresh peracetic acid . the reaction was allowed to stir for 29 min prior to quenching with sodium metabisulfite ( 100 μl ). a 20 μl aliquot of the crude reaction mixture was injected onto the hplc for analysis . the uv trace revealed only a single peak corresponding to the solvent front , while the radioactivity chromatogram showed several peaks ( fig1 ). the peak at 5 . 3 min is coincident with the solvent front and presumably represents free 125 i . the peak at 17 . 1 min was confirmed to be 2 . 19 through injection of the standard 3 - iodobenzoic acid . however , the identity of the other extraneous peaks , particularly the large peak at 24 . 9 min could not be assigned at the time of the reaction . although the quality of the crude reaction mixture containing 2 . 19 is less than ideal , a simple purification was undertaken to illustrate our capacity to remove any unreacted free 125 i in solution . the aforementioned crude reaction mixture was diluted with 500 μl of water and added to a conditioned c 18 sep - pak . the sep - pak was eluted with 2 ml of distilled deionized water to remove unbound 125 i , followed by elution with 1 ml of methanol . hplc analysis of a 20 μl aliquot of the methanol fraction is shown in fig1 . the chromatogram reveals that essentially all of the radioactive impurities up to 2 . 19 ( t r = 16 . 9 min ) are removed by washing the column with water . further , taking into account dilution , most of 2 . 19 was eluted with the 1 ml of methanol . however , the then unidentified peak at 24 . 5 minutes was still present . the less - than favourable results obtained in the above reaction prompted another reaction with a fresh source of na 125 i . in this reaction , compound 2 . 2 ( na + salt ) ( 1 . 1 × 10 − 6 mol ) was dissolved in 200 μl of methanol with stirring , prior to the addition of na 125 i ( 32 μci ) in approximately 5 μl of 0 . 1 mm naoh solution , followed by 2 μl of a freshly prepared solution of peracetic acid . the reaction was allowed to stir for 47 min , prior to quenching with excess sodium metabisulfite ( 20 μl ) and dilution with 300 μl of distilled - deionized water . a 20 μl aliquot of the crude reaction mixture was injected onto the hplc for analysis . the uv trace revealed only a peak representative of the solvent front , while the radioactivity chromatogram showed a peak with a retention time of 16 . 91 min ( fig1 ). the peak is consistent with the formation of 2 . 19 , confirmed by injection of 3 - iodobenzoic acid , which elutes at 15 . 86 min . the difference in retention times is a result of the time delay between the uv and radiation detectors . the radioactivity chromatogram of the crude reaction mixture illustrates that 2 . 19 was essentially generated in quantitative yield with no significant contribution of unbound / unreacted iodine . the radiochemical purity of crude 2 . 19 was ≧ 90 %. this level of incorporation and purity in a crude iododestannylation reactions is uncommon , especially given the short reaction time . although there is a little evidence for the presence of unbound iodine or radiolabelled salts in the reaction mixture , a short purification was undertaken to indicate that they could in the future be removed from the product . the reaction solution was diluted with approximately 1 . 5 ml of water and passed down a c 18 sep - pak column , conditioned with methanol . the column was further washed with 1 . 5 ml of water , and these fractions combined . the sep - pak was then eluted with 2 ml of acetonitrile and collected into a separate vial . the acetonitrile faction contained 72 % of the activity , and further elution of the column with acetonitrile released only small additional amounts of activity . a total of 4 μci was bound to the sep - pak column , likely the more highly retained and radiolabelled fluorous “ tag ” ( r 3 sn 125 i ). the other activity was found in the water ( 3 μci ), the reaction vessel ( 1 μci ), and in an additional 1 ml washing of the sep - pak with acetonitrile ( 1 μci ). hplc analysis of the fraction containing the majority of the activity displayed a single peak in the radiochromatogram corresponding to 2 . 19 at 16 . 59 minutes . the final radiochemical yield of purified 2 . 19 was 75 % with respect to the total na 125 i activity utilised . yields of this magnitude are uncommon , considering that the maximum theoretical radiochemical yield should be less than or equal to 50 %. the results of hunter et al . are fairly representative of a radioiododestannylation reaction . they observed a 50 . 8 % radiochemical yield of [ 131 i ] mibg ; 44 % of the activity was bound to tin and 5 . 1 % was free 131 i − in solution . 23 given the high radiochemical yield , it became important to quantify the purity of [ 125 i ]- 3 - iodobenzoic acid with regards to any labelled or unlabelled precursor 2 . 2 . as mass spectrometry and 19 f nmr are not feasible for 125 i labelled compounds , we had to rely on hplc analysis . elution of the precursor 2 . 2 on a c 18 analytical column with 100 % acetonitrile generated a uw peak at 6 . 61 minutes . similarly hplc analysis of the sep - pak purified faction exhibited peaks at 3 . 19 - 4 . 17 min , corresponding to the solvent front , and 6 . 38 - 6 . 72 min , likely corresponding to 2 . 2 ( fig1 ). the radioactivity chromatogram showed only a single peak at the solvent front , 4 . 46 min , corresponding to the 2 . 19 . a radioactivity peak corresponding to a labelled fluorous “ tag ” product would be predicted to elute in a similar position to 2 . 2 ; however , this is not seen . this indicates that our previous radiochemical yield of 75 % is accurate , though there appears to be some unreacted 2 . 2 present in this reaction solution . it has previously been established that even large quantities (& gt ; 200 mg ) of the “ fluorous tag ” can readily be removed using a fluorous column and an acetonitrile : water ( 1 : 1 ) mobile phase . this system can therefore readily facilitate the removal of the much smaller quantities of substrate ( 1 . 4 mg ) used in this and other typical radioiodination reactions . in order to demonstrate this purification approach , 2 . 19 in acetonitrile was diluted with an equal volume of distilled - deionized water and passed down a conditioned fluorous column . washing the column with an additional 4 μl of acetonitrile : water ( 1 : 1 ) liberated all the activity ( 19 μci ). analysis of an aliquot of this solution showed , upon expansion of the chromatogram , a solvent peak at 3 . 055 min and a small peak at 6 . 53 min ( fig1 ). because we have shown that the fluorous sep - pak can remove large quantities of the fluorous “ tag ”, the peak at 6 minutes likely arose through another source . one possibility is that the fluorous column , which had been recycled from another reaction , might not have been adequately cleaned . alternatively , since fluorous material is prone to sticking to the hplc loop , it is possible that accumulated material was released into this injection . a method was developed to prepare tris ( perfluorohexylethyl ) tin - 3 - benzoic acid and to label this material with fluorine and iodine . the fluorous approach using both hot and cold f 2 and 12 was effective in generating the desired products . additional experiments are needed to optimise the reactions , particularly with respect to purification protocols . initially , the rationale behind the synthesis of 2 . 2 lied in permitting the facile radiolabelling of peptides / biomolecules through coupling to labelled benzoic acid . the successful synthesis and labelling of 2 . 16 and 2 . 19 encouraged the synthesis of more complex compounds . one such approach that would benefit from , and extend the utility of , compound 2 . 2 would be its conversion to biologically active derivatives . radioiodobenzamides , or n - alkyl - iodobenzamides , constitute a new class of important radiopharmaceuticals . 24 exhibiting a high affinity towards σ 1 and σ 2 receptors , radioiodobenzamides are currently the best known radiopharmaceuticals for the diagnosis of cutaneous melanoma and its metastases . 24 this class of compounds have also been found to bind strongly to dopamine receptors , and are therefore effective imaging agents for diagnosis of parkinson &# 39 ; s and schizophrenia . 25 one of the most clinically relevant compounds is [ 123 i ]— n -( 2 - diethylaminoethyl )- 4 - iodobenzamide ( 123 i - bza ), which possesses ideal properties for melanoma scintigraphy . 26 currently , the most facile route to 123 i - bza involves an isotope exchange reaction ( 123 i for 127 i ). this method affords a carrier - added product resulting in reduced image quality . a more ideal strategy , which would lead to a no - carrier - added product , is radioiododestannylation of a trialkyltin precursor , which has been developed by moreau et al 26 with this in mind , the fluorous synthesis approach would seem suited for synthesis of radiolabelled benzamides and would avoid the need for exhaustive purification . the aim of this project was the synthesis of iodobenzamide , 2 . 20 , through an iododestannylation reaction of a corresponding fluorous “ tagged ” precursor ( 2 . 21 ) ( scheme 10 ). the synthesis of 2 . 20 requires the development of a new coupling methodology . the approach towards the synthesis of 2 . 21 concentrated on adapting traditional peptide synthesis procedures . the success of these reactions was qualified through 1 h - nmr and electrospray mass spectrometry . integration of the ethylene protons ( nch 2 ch 2 n ) with respect to the protons positioned α and β to tin served to quantify the extent of derivatization . initially , carbodiimide activating agents such as diisopropylcarbodiimide ( dic ) and edc were employed ; however , they led to little detectable product formation . it was difficult to determine if the lack of reaction was due to the reagent or the reaction solvent . in most instances , good solvents for the coupling reagents proved to be poor solvents for 2 . 2 , and visa versa . while coupling reactions were promoted in polar aprotic solvents such as acetonitrile and dmf , compound 2 . 2 was generally solvated by only extremely non - polar solvents . solvents such as thf , which solvated both 2 . 2 and dic , did not result in conversion to 2 . 21 . edc had another drawback . edc contains an ammonium salt which proved acidic enough to result in the cleavage of & gt ; 30 % of the tin aryl bonds . successful synthesis of 2 . 21 employed the use of the coupling reagent hbtu ( 2 -( 1h - benzotriazol - 1yl )- 1 , 1 , 3 , 3 - tertramethyluronium hexafluorophosphate ) in dmf ( scheme 11 ). hbtu promotes couplings by readily generating an activated intermediate concurrent with the formation of a urea byproduct . this activated complex reacts with amines with the subsequent loss of 1 - hydroxybenzotriazole ( hobt ) ( scheme 12 ). reaction of hbtu and compound 2 . 2 ( na + salt ) was carried out in dmf in the presence of dipea for 5 min , prior to addition of the amine . experiments have shown that this incubation leads to a dramatic improvement in coupling rates and yields . 27 following addition of excess n , n - dimethylethylenediamine in an equivalent of dipea , the reaction was allowed to stir for 16 hours . due to the high solubility of 2 . 21 in dmf , water was added to facilitate extraction of fluorous compounds into dichloromethane and fc - 72 ®. the more organic 2 . 21 could then be selectively extracted into dichloromethane from fc - 72 ®. several more extractions into dichloromethane yielded pure 2 . 21 , while unreacted 2 . 2 remained in fc - 72 ®. compound 2 . 21 , a dark yellow oil , was obtained in satisfactory yield ( 74 %). the substantial difference in r f values between 2 . 21 and 2 . 2 ( 0 ; 0 . 21 ), suggests that chromatographic purification would likely be a more appropriate and higher yielding purification method for the future . the 1 h nmr spectrum of compound 2 . 21 ( fig2 ) revealed a triplet at 1 . 31 ppm with sn satellites ( 2 j sn , h = 54 . 8 hz ) and a partially obstructed multiplet at approximately 2 . 33 ppm , corresponding to the protons positioned α and β to the tin respectively . in addition , the 1 h nmr showed a broad singlet at 2 . 31 ppm ( 6h ), a pseudo triplet at 2 . 59 ppm ( 2h ), a pseudo quartet at 3 . 55 ppm ( 2h ), and the expected aromatic peaks from 7 . 39 - 8 . 01 ppm ( 4h ). the 13 c nmr of 2 . 21 showed at low field peaks at − 1 . 43 ppm , 27 . 55 ppm ( 2 j f , c = 23 . 4 hz ), 37 . 11 ppm , 44 . 87 ppm , and 57 . 75 ppm . the 13 c nmr at higher field had resonances from 104 . 80 ppm to 120 . 03 ppm corresponding to the carbon atoms with attached fluorines and aromatic signals which have yet to be assigned . the ir of compound 2 . 21 showed aromatic stretches at 2900 cm − 1 in addition to the c ═ o absorption at 1650 cm − 1 n — h stretch at 3338 cm − 1 . the mass spectrum of 2 . 21 ( fig2 ) showed , in the positive ion mode , a single peak at m / z = 1353 [ m + h ] + . importantly , the negative ion mass spectrum of the same compound did not show the precursor peak at m / z = 1279 [ m − h ] − . the iododestannylation of compound 2 . 21 and purification of the product 2 . 20 was carried out in a similar manner to that used for compound 2 . 2 ( scheme 13 ). an excess of iodine was added to a small quantity ( 2 . 37 μmol ) of 2 . 21 and the reaction was stirred for 1 hour at room temperature . the reaction solution was quenched with sodium metabisulfite and placed on the rotary evaporator to remove methanol . the vial was washed with 1 ml of acetonitrile : water ( 50 : 50 ) and passed down a conditioned fluorous column . an additional 1 ml was used to rinse the vial and added to the column . the combined fractions were analysed through hplc ( fig2 ) and electrospray mass spectrometry ( fig2 ). the hplc chromatogram for compound 2 . 20 shows three principle peaks eluting at 6 . 6 , 16 . 6 , and 18 . 9 minutes . the earliest peak was assigned as the solvent front , while the later eluting peaks were presumably the protonated and deprotonated states of 2 . 20 , respectively . the positive ion electrospray mass spectrum of compound 2 . 20 showed a peak at m / z = 319 . 0 [ m + h ] + . the purity of the 2 . 20 was again confirmed , as the negative ion mode showed no peak corresponding at m / z = 247 [ m − h ] − , which would be present had unreacted 2 . 2 existed . the cold fluorination of 2 . 21 was undertaken in a similar manner employed for 2 . 2 . preliminary results from the electrospray mass spectrum reveal the product peak m / z = 211 [ m + h ] + ( fig2 ). the negative ion mode did not reveal any of the possible impurity , 3 - fluorobenzoic acid , at m / z = 139 ( m − h ) − . these initial cold experiments clearly indicate the potential to label 2 . 21 with 18 f [ f 2 ] and na 125 i , following the method used to label 2 . 2 . success would provide a facile route to radiolabelled benzamides for both spect and pet , and thereby increase their clinical utility . the development of a coupling procedure will allow us to prepare a diverse array of benzamides and related compounds for future radiolabelling . with the success attained at producing labelled benzoic acid and derivatives , we sought to expand the fluorous synthesis method to benzylamines and related derivatives . this would provide a complementary nucleophilic derivative to the electrophilic halobenzoic acids . in addition it would expand the potential variety of compounds which could be coupled to the fluorous “ tag ” and then radiolabelled . derivatives of benzylamine have been used to label biomolecules , 28 and are precursors to the synthesis of [ 131 i ] and [ 123 i ] meta - iodobenzylguanidine ( mibg ), 29 which is a valuable but synthetically challenging radiopharmaceutical . there are scarce examples in the literature describing the synthesis and / or labelling of trialkyltin bound benzylamine . vaidyanathan , g et al . synthesised 3 -( tri - n - butylstannyl ) benzylamine in a 30 % yield using n - buli , 3 - bromobenzylamine , and a two - fold excess of tributyltin - chloride . 30 this approach was not considered for the synthesis of 3 . 0 , due to the poor yield obtained and the generation of a large excess of fluorous by - products . rather , a method reported by hunter et al . for the preparation of a polymer bound 3 - benzylamine was adapted for the synthesis of 3 . 0 . 31 hunter &# 39 ; s method utilised the precursor , 3 . 1 , an azadisilolidine protected derivative of 3 - bromobenzylamine . this silicon - based protecting group is stable to n - buli , allowing for the synthesis of the corresponding monolithium salt , 3 . 2 . synthesis of 3 . 1 entailed the reaction of 3 - bromobenzylamine in triethylamine with 1 , 1 , 4 , 4 - tetramethyl - 1 , 4 - dichlorosilethylene at room temperature for 1 . 5 hours ( scheme 14 ). pouring the crude solution into aqueous sodium dihydrogen phosphate , followed by distillation of the crude organic extract , provided the product in moderate yield ( 64 %). the 1 h nmr of compound 3 . 1 revealed three singlets at 0 . 00 ppm ( 12h ), 0 . 78 ppm ( 4h ), and 4 . 06 ppm ( 2h ), in addition to the aromatic peaks appearing at 7 . 20 - 7 . 48 ppm ( 4h ). the 13 c nmr of 3 . 1 had resonances at − 0 . 26 ppm , 8 . 01 ppm , 45 . 59 ppm , 122 . 15 ppm , 126 . 10 ppm , 129 . 35 ppm , 129 . 53 ppm , 130 . 69 ppm , and 146 . 01 ppm . the electron impact mass spectrum of 3 . 1 gave a peak at m / z = 312 . these spectra are consistent with data reported in the literature . 4 , 32 the synthesis of 3 . 3 ( scheme 15 ) involved reaction of 3 . 1 with n - buli in thf at − 78 ° c . for a period of 35 minutes to generate 3 . 2 . compound 2 . 3 in thf was then added to 3 . 2 dropwise . the reaction was kept at − 78 ° c . for 2 hours , where upon fc - 72 ® was added and the mixture stirred for 10 minutes . the reaction was subsequently quenched through the addition of methanol ( 30 ml ). following the addition of methanol , the reaction was extracted with fc - 72 ®, water , and dichloromethane . the fc - 72 ® was removed on the rotary evaporator , providing 3 . 3 in 89 % yield . hydrolysis of 3 . 3 ( scheme 16 ) involved stirring the compound overnight in methanol with sufficient 1 m hcl to give a ph ≈ 3 . the product was extracted into fc - 72 ®, and concentrated to give 3 . 0 as a light yellow oil in 97 % yield . the 1 h nmr of compound 3 . 0 ( fig2 ) showed a triplet at 1 . 31 ppm ( 6h ) with sn satellites ( 2 j sn , h = 54 . 2 hz ), a multiplet at 2 . 31 ppm ( 6h ), a singlet at 3 . 88 ppm , and aromatic peaks from 7 . 22 - 7 . 46 ppm . trace amounts of the silicon protecting group can be seen in the baseline from 0 . 1 - 0 . 2 ppm . the 13 c nmr showed a peak at − 1 . 37 ppm ( 1 j sn , c = 347 hz ), 27 . 94 ppm ( t , 1 j f , c = 23 . 4 hz ), and 46 . 62 ppm . the multiplets corresponding to carbon atoms bonded to fluorine were seen from 106 . 17 - 121 . 17 ppm , and the peaks associated with the aromatic region have yet to be definitively assigned . the positive ion electrospray mass spectrum of compound 3 . 0 ( fig2 ) shows a single peak at m / z = 1268 . 5 [ m + h ] + . the ir showed strong absorbances corresponding to c — h stretches at 2850 and 2955 cm − 1 , and for the primary amine at 3354 cm − 1 . these results are all consistent with formation of the desired product . the quantitative conversion of the stannylbromide precursor ( 2 . 3 ) to 3 . 3 proved extremely difficult . early on it was appreciated that the azadisilolidine protected 3 - bromobenzylamine ( 3 . 1 ) was not particularly stable . synthesis and purification of 3 . 1 had to be immediately followed by reaction with n - buli to generate 3 . 2 . if these measures were not taken , incomplete conversion of 2 . 3 would result . hunter and coworkers reported that reaction of 3 . 2 with the chlorostannane polymer for 7 hours at − 78 ° c ., followed by stirring at room temperature for 2 hours , resulted in quantitative functionalization of sn — cl bonds . 4 in contrast with these results , it was found that under similar reaction conditions only 50 - 67 % of sn — br sites were converted to product ( 3 . 3 ). through extensive trials it was appreciated that the product was extremely prone to decomposition if the reaction solution was allowed to warm to room temperature . the complete conversion of 2 . 3 to 3 . 3 , therefore , could only be facilitated if the reaction was kept at − 78 ° c ., prior to immediate extraction into fc - 72 ® and quenching with methanol . iododinolysis of 3 . 0 was carried out in order to further characterise the product bound to the fluorous tag and to ensure its purity ( scheme 17 ). compound 3 . 0 was reacted with an excess of iodine in acetonitrile overnight , followed by quenching with sodium metabisulfite . the solution was diluted with water and passed down a conditioned fluorous column with an acetonitrile : water eluent ( 1 : 1 ). aliquots ( 3 × 5 ml ) were collected and the products characterised using hplc and mass spectrum . the hplc chromatogram ( fig2 ) of the purified solution ( 3 . 4 ) generated two principle peaks at 1 . 78 and 6 . 46 minutes , corresponding to the solvent front and 3 - iodobenzylamine , respectively . an authentic standard of 3 - iodobenzylamine under similar elution conditions produced a peak at 6 . 47 minutes . positive ion electrospray ( fig2 ) mass spectrum of the reaction solution produced a single peak at m / z = 233 . 9 [ m + h ] + , with no evidence of the fluorous impurity at approximately m / z & gt ; 1200 . these results are consistent with formation of 3 . 4 . during the past two decades , radioiodinated mibg ( m - iodobenzylguanidine ) has been used extensively in nuclear medicine . 33 it is used primarily for diagnostic scintigraphy and therapy of neural crest tumours such as phaeochromocytoma and neurblastoma . 34 in addition , it is increasingly being used to assess the status of adrenergic nerves in the heart muscle . 6 the most widely employed synthesis method for production of [ 123 i ] or [ 131 i ] mibg involves the cu + catalyzed exchange process . unfortunately , this method yields a low specific activity product ( 50 mci / mg for [ 123 i ]) necessitating an increased dose , which in turn results in poorer quality images . 4 consequently , several routes to a no - carrier - added product have been investigated ; however , none have found widespread application . 35 a fluorous strategy for the synthesis of mibg may ameliorate the aforementioned synthetic limitations . furthermore , if a convenient labelling method were available , there is substantial interest in generating a positron emitting migb - related radiopharmaceutical . for example , zalutsky et al . synthesised meta -[ 18 f ] fluorobenzylguanidine and para -[ 18 f ] fluorobenzylguanidine in three steps with a fluoro for nitro exchange reaction . they reported lower than desirable radiochemical yields of 10 - 15 % ([ 18 f ] mfbg ) and 50 - 55 % [ 18 f ] pfbg , and difficulty removing impurities . 36 the next section describes the development of a fluorous strategy for the preparation of [* 1 ] mibg and [ 18 f ] mfbg . in order to produce tris ( perfluorohexylethyl ) tin - 3 - benzylguanidine , 3 . 5 , several synthetic routes were attempted . the first approach , approach a ( scheme 18 ), applied the method developed by wieland et al . for synthesis of 3 . 5 . 37 wieland &# 39 ; s method involves the reaction of m - iodobenzylamine with cyanimide at 100 ° c . for 4 hours . unfortunately , the synthesis of 3 . 5 through various adapted procedures would only yield trace amounts of the product , as indicated by electrospray mass spectrometry . the failure of this reaction method to generate 3 . 5 is likely a result of the precursor 3 . 0 not being protonated . although hydrolysis of the silicon - protecting group to generate 3 . 0 occurred at a ph of 3 , the expected benzylammonium chloride was not formed . the benzylammonium chloride is necessary in order to activate cyanimide to nucleophilic attack ( scheme 19 ). any further attempts at protonating 3 . 0 resulted in protodestannylation . similarly , the addition of catalytic amounts of hcl ( 0 . 05 eq ) resulted in protodestannylation under the reaction conditions ( 54 ° c .). these results mirror the findings of vaidyanathan et al ., who were unable to convert 3 -( tri - n - butylstannyl ) benzylamine to the guanidine . 8 rather , they were forced to synthesize [ 131 ] mibg from r adioiododestannylation of ( trialkylstannyl ) benzylamine , followed by its subsequent reaction with cyanimide . approach b entailed the adaptation of research by jursic et al . for their preparation of n - formamidinylamino acids . 38 here , the reaction of formamidinesulfinic acid [ hn ═ c ( nh 2 ) so 2 h ] with a substituted amino acid ( d , l - phenylalanine ) in aqueous sodium hydroxide leads to the generation of d , l - n - formamidinephenylalanine ( scheme 20 ). application of this approach towards 3 . 5 was found to be most successful when 3 . 0 was stirred with 2 . 0 equivalents of foramidinesulfinic acid in methanol overnight at room temperature . the methanol was removed on the rotary evaporator , prior to a triphasic extraction . the white viscous oil obtained following removal of fc - 72 ® was heated in chloroform and subsequently decanted to remove any unreacted 3 . 0 . the product , a viscous white oil , was obtained in good yield ( 86 %). the positive ion electrospray mass spectrum of compound 3 . 5 ( synthesised using foramidinesulfinic acid ) showed a peak at m / z = 1310 . 2 [ m + h ] + , in addition to peaks at m / z = 1325 . 1 and m / z = 1293 . 1 ( fig2 ). the 1 h nmr and 13 c nmr for compound 3 . 5 could not be acquired , as no suitable solvent could be found . compound 3 . 5 was treated with cold i 2 and f 2 , and a similar peak pattern in the elctrospray mass spectrum was found for the cleaved products . the peak associated with the product was typically the most intense , flanked on either side with a peak of +/− 15 mass units . as the resulting peak pattern could not be rationalized , other routes to the synthesis of 3 . 5 were investigated . approach c involved adaptation of the research by mosher et al ., who converted several primary amines to the corresponding guanidines . 39 the conversions were accomplished by reacting aminoimino - methanesulfonic acid with a primary amine for two hours at room temperature to generate the corresponding guanidine in moderate yield ( 22 - 80 %). this method appeared applicable for the synthesis of 3 . 5 , as a free amine could be converted to the guanidine under mild conditions ( ph = 3 . 1 ). aminoiminomethanesulfonic acid ( h 2 n — c (═ nh ) so 3 h ) ( 3 . 7 ) was synthesized in high yield through reaction of foramidinesulfinic acid ( 3 . 6 ) with peracetic acid , following the procedure of mosher ( scheme 21 ). 12 the melting point of compound 3 . 7 was consistent with literature findings of 125 - 126 ° c . 12 compound 3 . 7 was first reacted with m - iodobenzylamine in order to assess the products formed and to obtain a standard sample of mibg ( scheme 22 ). equivalent molar quantities of 3 . 7 and 3 . 8 were combined in methanol and refluxed overnight . the resulting product ( 3 . 9 ) was characterized without further purification . the 1 h nmr showed a singlet at 4 . 22 ppm , and aromatic peaks between 6 . 90 - 7 . 56 ppm . the 13 c nmr showed a peak at 48 . 9 ppm , 99 . 3 ppm , 131 . 6 ppm , 135 . 7 ppm , 141 . 0 ppm , 141 . 9 ppm , 144 . 3 ppm , and 162 . 65 ppm . the positive ion electrospray mass spectrum showed a peak at m / z = 276 . 1 [ m + h ] + corresponding to 3 . 9 , and a extremely small peak at m / z = 233 . 9 [ m + h ] + corresponding to 3 . 8 . the hplc analysis of compound 3 . 9 generated only one principle peak at t r = 24 . 54 minutes ( 86 % of total peak area ). this data is consistent with literature reports , and confirms formation of the desired product . 40 the synthesis of compound 3 . 9 using 3 . 7 prompted the application of this procedure toward the synthesis of 3 . 5 ( scheme 23 , approach c ). compound 3 . 0 was combined with 1 . 1 equivalents of 3 . 7 in methanol and refluxed overnight . incomplete conversion occurred if the reaction was carried out at room temperature as suggested by mosher et al . 12 extraction of the crude reaction mixture into fc - 72 ® from methanol generated the product as a milky white oil in acceptable yield ( 88 %). positive ion electrospray mass spectrometry ( fig3 ) showed a single peak at m / z = 1309 . 9 [ m + h ] + , which is consistent with the formation of 3 . 5 . the electrospray spectrum did not show any peaks that were associated with the precursor ( 3 . 0 ), which had a m / z value of 1268 , nor the peaks corresponding to m / z +/− 15 , which had been seen using approach b . currently , resolved 1 h nmr and 13 c nmr spectra for compound 3 . 5 have not yet been obtained , a result of the compounds poor solubility . the cold iodination of 3 . 5 was undertaken in order to assess the products and reaction conditions for eventual use of na 125 , ( scheme 24 ). a sample of 3 . 5 ( 3 . 90 μmol ), synthesised through approach c , was dissolved in methanol . to the stirring solution was added nai ( 4 . 6 × 10 − 7 mmol ), which was followed promptly by addition of the peracetic acid oxidant . the reaction was stirred for 2 hours and then quenched with 100 μl of a 10 % sodium metabisulfite solution . purification of the dilute reaction solution was not attempted , though it has been established that fluorous material can easily be removed from the cleavage products . the positive ion electrospray mass spectrum of compound 3 . 10 revealed a peak at m / z = 275 . 9 [ m + h ] + which is consistent with the product ( fig3 ). hplc a 100 μl aliquot of compound 3 . 10 showed peaks with retention times of 7 . 2 , 14 . 7 , and 24 . 9 minutes ( fig3 ). the peaks eluting at 7 minutes and 24 . 9 minutes were assigned to the solvent front and product 3 . 10 , respectively . the standard preparation of mibg eluted with a similar retention time of 24 . 5 minutes . the peak at 14 . 7 minutes accounted for & lt ; 1 % of total migb and the nature of the compound giving rise to the peak remains unknown . the encouraging results for the iodine labelling of 3 . 5 prompted us to investigate the possibility of synthesising m - fluorobenzylguanidine ( mfbg ). the fluorodestannylation reaction for the synthesis of mfbg ( 3 . 11 ) is shown in scheme 25 . the cold fluorination reaction of compound 3 . 5 proceeded in a manner analogous to those of previous reactions ( 3 - fluorobenzoic acid and 3 - fluorobenzamide ). to an fep tube containing 3 . 5 dissolved in fc - 72 ® at − 93 ° c . was bubbled approximately 0 . 7 equivalents of f 2 ( 0 . 6 % in ne ). following the reaction , the fc - 72 ® from the reaction along with methanol used to rinse the vessel were removed on rotary evaporator , prior to diluting with acetonitrile : water ( 1 : 1 ) and eluting down a conditioned fluorous column . the positive ion electrospray mass spectrum for compound 3 . 11 showed a single peak at m / z = 168 . 0 [ m + h ] + ( fig3 ). the mass spectrum showed no evidence of any fluorous impurity at m / z = 1000 or evidence of 3 - fluorobenzylamine at m / z = 126 [ m + h ] + . the hplc chromatogram of compound 3 . 11 contains peaks at the solvent front ( t r = 2 - 6 min .) and peaks eluting at 25 . 3 min ., 30 . 3 min ., and 35 . 0 minutes ( fig3 ). there are no peaks corresponding to 3 - fluorobenzylamine which has a retention time of 15 . 8 minutes under these elution conditions . the elution conditions are the same as those used for mibg , and it is therefore surprising that the principle peak ( 61 +%) eluting at 35 minutes is more highly retained than mibg . the longer retention time might suggest a di - fluorinated or a bi - guanidinium species ; however , peaks corresponding to these products are not found in the electrospray mass spectrum . unfortunately , at the time of these experiments , an authentic standard of mfbg was not available to better interpret these results . the 19 f nmr of compound 3 . 11 shows three peaks ( fig3 ). the two principle peaks are centred at − 109 . 5 ppm and − 110 . 3 ppm , with 3 j h , f coupling of 9 . 2 hz and 8 . 7 hz respectively . these peak positions and coupling constants are consistent with a meta or para - fluorinated aryl compound . the smaller coupling constants initially suggest that a 1 . 2 or 1 . 4 difluorinated species is not present . the varying peak positions , rather than being attributed to isomers , could be the results of varying protonation states , which has been shown to markedly affect fluorine shifts . 41 the poor resolution of the spectrum can be attributed to the dilute sample , obtained without further concentrating the eluent . concentration of the sample on the lyophilizer was avoided as it appeared this resulted in loss of product on several occasions . as mentioned in chapter 2 , short peptide sequences have been used to target radionuclides to specific receptors . for receptor specific agents of this type , it is important that all unreacted material is separated from the radiopharmaceutical . it would be advantageous therefore to develop the fluorous approach for labelling peptides . in this chapter preliminary steps towards these goals were taken . in particular , a method of coupling the carboxylic acid terminus of a model oligopeptide to the fluorous “ tagged ” benzylamine was developed . the chemotactic peptide n - formyl - met - leu - phe - gly , 3 . 12 is a bacterial product which binds to polymorphonuclear leucocytes and mononuclear macrophages . fischman et al . have shown that radiolabelled derivatives of this peptide are effective for imaging sites of abscesses and inflammation . 42 the severe toxicity of chemotactic peptides in higher doses has hampered their clinical application ; consequently it is essential that any unlabelled material be removed . the coupling strategy developed for the synthesis of fluorous “ tagged ” benzamide should be applicable to the current objective . in this case , however , the peptides carboxylic acid terminus will be activated ( hbtu ) for nucleophilic attack by benzylamine ( 3 . 0 ). synthesis of compound 3 . 13 ( scheme 26 ) entailed combining 3 . 0 and 3 . 12 in dmf , followed by addition of the acylating reagent ( hbtu ) and base . the reaction was stirred at room temperature overnight , diluted with water , and extracted into fc - 72 ®. the fc - 72 ® layer was found to contain only a small quantity of product 3 . 13 along with unreacted 3 . 0 , as determined by electrospray mass spectrometry . the majority of 3 . 13 was in fact partitioned between fc - 72 ® and dmf / h 2 o . evidently , the polar nature of the peptide is significant enough to make the product no longer completely soluble in the fluorous solvent , while the fluorous “ tag ” prevents the peptide from dissolving in the h 2 o phase . this result is somewhat favourable , as it permits facile purification of the fluorophobic product ( 3 . 13 ) from any unreacted fluorophilic precursor ( 3 . 0 ) by collecting the interfacial emulsion . isolating the resulting white emulsion was followed by re - extraction from fc - 72 ® to remove any unreacted 3 . 0 . the yield ( 33 %) of the resulting thick , gummy , white solid was compromised so as to ensure the isolation of a pure sample . fig3 shows the positive ion electrospraymass spectrum of compound 3 . 13 . the peak pattern is characteristic of the product with m / z = 1744 [ m + h ] + , m / z = 1761 [ m + nh 4 ] + , and m / z = 1766 [ m + na ] + . the spectrum revealed no peak at m / z = 1268 corresponding to the precursor 3 . 0 . in order to characterize the fluorous “ tagged ” compound ( 3 . 13 ) further , it was cleaved through an iodinolysis reaction ( scheme 27 ). a purified sample of 3 . 13 was reacted with excess iodine in methanol and chloroform overnight . the excess iodine was quenched with sodium metabisulfite and the solution was concentrated on the rotary evaporator . the resulting residue was diluted with acetonitrile : water ( 1 : 1 ) and characterised using electrospray ( fig3 ) and hplc ( fig3 ). the positive ion mass spectrum of compound 3 . 14 reveals peaks corresponding to the desired product at m / z = 710 [ m + h ] + , m / z = 727 [ m + nh 4 ] + , and m / z = 732 [ m + na ] + . there is no peak corresponding to the possible impurity , 3 - iodobenzylamine , at m / z = 234 . the hplc chromatogram of compound 3 . 14 shows two sizeable peaks with retention times of 3 . 3 minutes and 19 . 4 minutes , presumably the solvent front and product respectively . the hplc chromatogram of the gflm ( f ) under the same elution conditions has a t r = 13 . 6 and 14 . 8 minutes , while an authentic standard of 3 - iodobenzoic acid has a t r = 6 . 5 minutes . the chromatogram of 3 . 14 therefore seems to confirm product formation , with a longer retention time compared to gflm ( f ) and no indication of the impurity at t r = 6 . 5 minutes . the synthesis of tris ( perfluorohexylethyl ) tin - 3 - benzylamine ( 3 . 0 ) should facilitate the synthesis and labelling of a wider array of biomolecules . initial results appear to confirm the successful synthesis of mibg ( 3 . 10 ) and mfbg ( 3 . 11 ) through the corresponding fluorous “ tagged ” precursor ( 3 . 5 ). further detailed characterisation of the precursor and products is required however , including expanding the labelling experiments to include [ 18 f ] f 2 and na 125 i . the synthesis of fluorous “ tagged ” peptides through compound 3 . 0 , has also been shown using standard coupling methodology . the differences in solubility allow for purification of the peptide coupled product ( 3 . 13 ) from any unreacted fluorous substrate by simple extraction . this coupling protocol should permit for a wide array of short peptides to be coupled to the fluorous support in the future . the preliminary labelling of 3 . 13 with iodine will have to be expanded to [ 18 f ] f 2 and na 125 i in the future . the techniques presented herein can be used as a novel means of preparing radiopharmaceuticals . it allows for the facile synthesis of labelled compounds , without the need for extensive purification , in high radiochemical and chemical yields and in high specific activities . this is particularly important for receptor targeted radioimaging and therapy agents . this approach can also be used in pharmaceutical and radiopharmaceutical discovery research . there are numerous advantages of the reported technology compared to traditional and resin - based labelling methods . the aforementioned techniques can be used to prepare radiolabelled compounds more efficiently , safely and more conveniently than traditional radiolabelling techniques . the approach can be adapted for a wide variety of isotopes including 99m tc , 94m tc , 186 re , 105 rh , 18 f , 11 c , 125 i , 123 i , 131 i , 76 br , and 111 at and is easily automatable . the fluorous - tagged compounds are readily soluble in per - fluorinated solvents . these solvents are particularly useful for carrying out labelling reactions because they are stable to reactive compounds like 18 f - 19 f ( i . e . f 2 ). furthermore , gases , such as 11 co 2 and 11 co , are highly soluble in perfluorinated solvents , which will lead to an increase in product yields compared to reactions carried out in conventional solvents . for example , it is possible to prepare carbon - 11 labelled benzophenone from a fluorous tin substrate as shown in scheme 28 . the reaction was complete in less than five minutes generating labelled benzophenone as the major product . this approach will be particularly applicable to drug development research where pet is being used to perform biodistribution studies . the use of fluorous supports broadens the number of compounds that can be labelled compared to the approach using insoluble polymer supports . conventional synthetic methods can be used to attach compounds to the fluorous supports without the need for forceful reaction conditions . impurities can be removed ( unlike polymer supported methods ) using standard chemical techniques . furthermore , fluorous - labelled substrates can be readily characterized using traditional methods , which is important when getting compounds and / or techniques approved for medical use . the reported approach can also be used to develop libraries of radiopharmaceuticals , which will facilitate the rate and efficiency with which new imaging agents are discovered . the invention now being generally described , it will be more readily understood by reference to the following examples , which are included merely for purposes of illustration of certain aspects and embodiments of the present invention , and are not intended to limit the invention . analytical tlc was performed on silica gel 60 - f 254 ( merck ) with detection by long wavelength ultraviolet light . hplc experiments ( cold ) utilized a varian prostar hplc system with a pda detector and c - 8 or c - 18 reverse phase column ( where mentioned ). hplc analysis of fluorine - 18 labeled 3 - fluorobenzoic acid employed a waters 490e programmable multiwavelength detector and a beckman radioisotope detector ( model 170 ). gradient or isocratic elution was performed as indicated with acetonitrile and distilled - deionized water as the mobile phase ( buffered / acidified where indicated ). 1 h , 13 c and 19 f nmr spectra were recorded on the bruker avance ac - 200 or drx - 500 spectrometers . the x - ray structure was collected using mo kα radiation on a siemens rotating anode instrument fitted with a ccd detector . electrospray mass spectrometry ( esms ) were performed on a fisons platform quadrupole instrument . chemical ionisation mass spectra ( cims ) were measured at 70 ev with a source temperature of 200 ° c . on a vg instruments analytical zab - e mass spectrometer equipped with a vg11 - 250 data system . ir spectra were run on a bio - radfts - 40ft ftir spectrometer . melting points were determined using a fisher - john melting point apparatus . fluorine - 18 labelled f 2 was produced by the 18 o ( p , n ) 18 f nuclear reaction using a siemens rds 112 proton cyclotron operating at 11 mev by the “ double shoot ” method . 18 all commercial reagents were used as supplied with the following exceptions : thf was distilled from sodium and benzophenone ; toluene was distilled from calcium hydride . enriched [ 18 o ] o 2 ( 18 o , 95 . 87 at %, eurisotope , st . aubin , france ), neon ( 99 . 999 %, air products ), 1 % f 2 in neon ( canadian liquid air ), hplc grade solvents ( calcdon ), reagent grade fc - 72 ® ( 3m corporation ), and perfluorooctyliodide , phenyltintrichloride , 3 -( ethoxycarbonyl ) phenylzin solution , and benzotrifluoride were all purchased from aldrich . tris [( 2 - perfluorohexyl ) ethyl ] phenyltin ( 2 . 4 ). the procedure developed by masahide et al . was followed . 43 to magnesium turnings 2 . 308 g ( 94 . 9 mmol ) was added 22 . 501 g ( 47 . 5 mmol ) of perfluorooctyliodide in 10 ml of dry ether . the reaction mixture was stirred at reflux for 25 min and then 1 . 95 ml ( 11 . 9 mmol ) phenyltintrichloride was added in 20 ml of dry toluene . the reaction was stirred at 70 ° c . for 4 h and then at room temperature overnight . the reaction mixture was quenched with a 40 ml of ammonium chloride solution , and washed with three 200 ml portions of a 5 % sodium thiolsulfate solution . the combined aqueous layers were additionally extracted with three 100 ml portions of diethylether . the combined organic fractions were then dried ( mgso 4 ) and concentrated under reduced pressure . vacuum distillation removed the homocoupled impurity at 82 ° c . (≈ 0 . 2 mm hg ) and the residue was purified by flash chromatography on neutral alumina . elution with hexane gave 2 . 4 as a colorless oil : yield 11 . 031 g ( 75 %). tlc r f 0 . 89 ( 6 : 1 hexanes - diethylether ). 1 h nmr ( 200 mhz , cdcl 3 ): δ 1 . 23 ( t , 6h ) with sn satellites ( 2 j sn , h = 51 . 7 hz ), 2 . 24 ( m , 6h ), 7 . 33 ( s , 5h ). 13 c nmr ( 50 . 3 mhz , cdcl 3 ): δ − 1 . 49 , 27 . 74 ( t , 3 j f , c = 23 . 5 hz ), 129 . 06 , 129 . 65 , 136 . 08 . ms ( esms ), ( ipa , 2 mm nh 4 oac ): m / z 1297 . 0 [ m + oa − h ] − , m / z = 1283 . 0 [ m + oac − ch 3 ] − . ir ( thin film ): 2962 , 2928 , 2875 , 2862 , 1241 , 1146 , 497 cm − 1 . bromotris [( 2 - perfluorohexyl ) ethyl ] tin ( 2 . 3 ). to a solution containing 15 . 860 g ( 12 . 8 mmol ) of 2 . 4 in 20 ml of diethylether at 0 ° c . was added slowly a solution containing 670 μl ( 13 mmol ) of bromine in 20 ml of diethylether . the reaction solution was stirred at 0 ° c . for 2 h and then at room temperature overnight . the reaction solution was concentrated under diminished pressure . vacuum distillation at 162 ° c . (≈ 0 . 2 mmhg ) gave 2 . 3 as a colorless oil : yield 15 . 487 g ( 97 %). 1 h nmr ( 500 mhz , cdcl 3 ): δ 1 . 57 ( t , 6h ) with sn satellites ( 2 j sn , h = 54 . 1 hz ), 2 . 46 ( m , 6h ). 13 c nmr ( 126 mhz , cdcl 3 ): δ 6 . 11 with sn satellites ( 1 j sn , c = 374 hz ), 27 . 60 ( t , 3 j f , c = 22 . 9 hz ), 108 . 86 - 120 . 71 ( m , cf 2 , cf 3 ). ms ( esms , ipa 2 mm nh 4 oac ): m / z 1279 . 5 [ m + oac ] − . ir ( thin film ): 3472 , 3417 , 2949 , 1442 , 1146 cm − 1 . synthesis of tris [ 2 - perfluorohexylethyl ] tin - 4 - bromobenzene ( 2 . 8 ). the procedure was adapted from that used by lequan et al . 44 to 37 mg ( 1 . 52 mmol ) of magnesium turnings was slowly added a solution containing 390 mg ( 1 . 66 mmol ) p - dibromobenzene in 8 ml of thf . the reaction mixture was refluxed for 2 h at which time a solution containing 820 mg ( 0 . 662 mmol ) of 2 . 3 in 6 ml of thf was added . the reaction solution was stirred overnight and then concentrated under reduced pressure . the residue was extracted with three ( 3 ml ) portions of fc - 72 ® from dichloromethane and water . the combined fc - 72 ® layers were extracted again from dichloromethane and then concentrated under reduced pressure to give 2 . 8 as a clear colourless oil : yield 0 . 538 mmol ( 81 %). 1 h nmr ( 200 mhz , cdcl 3 ): δ 1 . 30 ( t , 6h ), 2 . 30 ( m , 6h ), 7 . 24 ( d , 2h ), 7 . 56 ppm ( d , 2h ). ms ( esms ): m / z 1375 . 0 [ m + oac ] + , and 1297 . 1 [ m + oac − br ] + . 4 - bromobenzyloxazoline ( 2 . 9 ). the procedure was adapted from that used by hughes , a . et al . 45 a mixture of 4 . 00 g ( 19 . 9 mmol ) in 7 . 0 ml ( 96 mmol ) thionyl chloride was refluxed for 2 h prior to concentration under reduced pressure . to the product dissolved in 10 ml of dichloromethane at 0 ° c . was slowly added 3 . 8 ml ( 40 mmol ) of 2 - amino - 2 - methyl - 1 - propanol in 10 ml of dichloromethane . the reaction solution was allowed to warm gradually overnight , filtered , and extracted from two 10 ml portions of water and dried over mgso 4 . the solution was concentrated under reduced pressure and to 4 . 850 g ( 17 . 82 mmol ) of the solid was added 6 ml ( 80 mmol ) of thionyl chloride . the reaction mixture was stirred for 45 min followed by addition of a large volume of diethylether to precipitate a white solid . the solid was filtered and extracted into diethylether from 3 n naoh , and washed with an additional three 10 ml portions of 3 n naoh . the combined organic layer was dried over mgso 4 , filtered and concentrated under reduced pressure to give 2 . 9 as a clear solid : yield 4 . 810 g ( 95 %). 1 h nmr ( 200 mhz , cdcl 3 ): δ 1 . 42 ( s , 6h ), 4 . 17 ( s , 2h ), 7 . 56 ( d , 2h ), 7 . 87 ( d , 2h ). 13 c nmr ( 50 . 3 mhz , cdcl 3 ): δ 28 . 26 , 67 . 58 , 79 . 32 , 125 . 99 , 126 . 68 , 129 . 80 , 131 . 53 , 161 . 48 . mass spectra ( ei ): m / z 254 . synthesis of tris [ 2 - perfluorohexylethyl ] tin - benzyloxazoline ( 2 . 10 ). the procedure was adapted from that used by milius et al . 46 to 215 mg ( 8 . 83 mmol ) of magnesium turning was slowly added a solution containing 1 . 122 g ( 4 . 415 mmol ) of 2 . 9 in 18 ml of thf . to the stirring mixture was added 1 , 2 - dibromoethane ( 20 drops ) and allowed to reflux for 1 h . this solution was added to a solution containing 547 mg ( 4 . 415 mmol ) of 2 . 3 in 3 ml of fc - 72 ® and 14 ml of benzotrifluoride . the reaction solution was stirred overnight at room temperature , and then concentrated under reduced pressure . the residue was extracted with three ( 3 ml ) portions of fc - 72 ® from dichloromethane and water . the combined fc - 72 ® layers were re - extracted with dichloromethane and concentrated under reduced pressure to give 2 . 10 as a clear colorless oil : yield 528 mg ( 90 %). 1 h nmr ( 200 mhz , cdcl 3 ): δ 1 . 32 ( t , 6h ), 1 . 40 ( s , 6h ), 2 . 30 ( m , 6h ), 4 . 14 ( s , 2h ), 7 . 44 ( d , 2h , j = 8 . 2 hz ), 7 . 97 ( d , 2h , j = 8 . 1 hz ). 13 c nmr ( 50 mhz , cdcl 3 ): δ − 1 . 25 , 27 . 68 ( t , 3 j f , c = 23 . 4 hz ), 28 . 47 , 67 . 71 , 79 . 46 , 128 . 36 , 135 . 97 . ms ( esms ): m / z 1394 . 2 [ m + oac ] + . tris [ 2 - perfluorohexylethyl ] tin - 3 - ethylbenzoate ( 2 . 14 ). to a solution containing 8 . 523 g ( 6 . 879 mmol ) of 2 . 3 in 10 ml of thf at 0 ° c . was slowly added 41 . 2 ml ( 20 . 6 mmol ) of a 0 . 5 m 3 -( ethoxycarbonyl ) phenylzinc solution in thf . the solution was warmed to room temperature over 2 h and stirred overnight at r . t . the reaction solution was concentrated under diminished pressure . the residue was extracted with four 5 ml portions of fc - 72 ® from 20 ml of methanol . the combined fc - 72 ® layers were concentrated under reduced pressure and dried under high vacuum to give 2 . 14 as a colorless oil : yield 8 . 903 g ( 98 . 9 %). tlc r f 0 . 58 ( 6 : 1 hexane : diethylether ). 1 h nmr ( 500 mhz , cdcl 3 ): δ 1 . 35 ( t , 6h ), 1 . 39 ( m , 3h ), 2 . 33 ( m , 6h ), 4 . 39 ( q , 2h , j = 7 . 1 hz ), 7 . 49 ( t , 1h , j = 7 . 0 hz ), 7 . 57 ( d , 1h , j = 7 . 2 hz ), 8 . 05 ( d , 1h ), 8 . 07 ( s , 1h ). 13 c nmr ( 50 . 3 mhz , cdcl 3 ): − 1 . 12 , 14 . 20 , 27 . 87 ( t , 1 j f , c = 23 . 3 hz ), 61 . 17 , 108 . 92 - 118 . 84 ppm ( m , cf 2 , cf 3 ), 128 . 90 , 129 . 54 , 130 . 79 , 131 . 13 , 131 . 84 , 136 . 06 , 136 . 97 , 137 . 34 , 140 . 30 , 143 . 46 , 166 . 67 . ms ( esms , epa 2 mm nh 4 oac ): m / z 1369 . 5 [ m + oac ] − , m / z = 1279 . 4 [ m − oet ] − . tris [ 2 - perfluorohexylethyl ] tin - 3 - benzoic acid ( 2 . 2 ). a mixture of 8 . 903 g ( 6 . 801 mmol ) of 2 . 14 and 34 ml of 1n naoh in 34 ml of methanol was refluxed for 24 h . methanol was removed under diminished pressure and the residue was extracted with four 5 ml portions of fc - 72 ®. the combined fc - 72 ® layers were then extracted twice from 20 ml of dichloromethane and 10 ml of 1n hcl . the combined fc - 72 ® layers were concentrated under diminished pressure to give 2 . 2 as a colourless oil : yield 8 . 584 g ( 98 %). after several days 2 . 2 crystallised as a white solid . dissolving approximately 100 mg of 2 . 2 in 1 ml of pentane followed by slow evaporation over one week gave 2 . 2 as colourless needles . tlc r f 0 . 21 ( 6 : 1 hexane - diethylether ). 1 h nmr ( 200 mhz , cdcl 3 ): δ 1 . 34 ppm ( t , 6h ) with sn satellites ( 2j sn , h = 53 . 4 hz ), 2 . 31 ( m , 6h ), 7 . 51 ( t , 1h , j = 7 . 7 hz ), 7 . 62 ( d , 1h , j = 7 . 1 hz ), 8 . 11 ( d , 1h ), 8 . 12 ( s , 1h ). 13 c nmr ( 126 mhz , cdcl 3 ): δ − 1 . 53 - 1 . 06 , 27 . 42 ( t , 1 j f , c = 24 . 40 hz ), 108 . 49 - 118 . 51 ( m , cf 2 , cf 3 ), 128 . 66 , 129 . 02 , 129 . 73 , 130 . 01 , 130 . 39 , 131 . 08 , 131 . 34 , 134 . 00 , 135 . 906 , 136 . 16 , 137 . 53 , 141 . 00 , 141 . 23 , 172 . 61 , 172 . 04 . ms ( esms , ipa ): m / z 1279 . 1 [ m − h ] − . ir ( thin film ): 3410 , 2981 , 2950 , 1631 , 1610 , 1593 cm − 1 . general procedure : 3 - fluorobenzoic acid from f 2 reaction ( 2 . 15 ). to 0 . 191 g ( 0 . 149 mmol ) of 2 . 2 in 1 ml of fc - 72 ® at − 85 ° c . in a fep tube was bubbled 118 μmol of 0 . 5 % f 2 in ne . the f 2 was steadily released into the solution over 35 min . the reaction solution along with three 3 ml portions of methanol used to rinse the vessel were concentrated in a large vial . the residue was washed with three 3 ml portions of 1 : 1 acetonitrile : water and eluted down a conditioned fluorous reverse phase column ( 1 g ) to give 2 . 15 . yield 28 . 2 μmol ( 24 %). hplc analysis was carried out on an analytical ( 250 mm × 4 . 6 mm ) c 8 reversed - phase column . a retention time of 4 . 22 min . consistent with the standard was produced when flow rate = 1 ml / min , eluent : 50 % water ( 0 . 2 % tfa ): 50 % acetonitrile ( 0 . 2 % tfa ), λ = 280 nm . 19 f nmr ( 188 . 16 mhz , meoh : chcl 3 ): δ − 112 . 00 ( d , 3 j f , h = 5 . 65 hz ). ms [ esms , 1 : 1 ipa :( acn : h 2 o )]: m / z 139 . 1 [ m − h ] − . general procedure : [ 18 f ] 3 - fluorobenzoic acid ( 2 . 16 ). to 0 . 124 g ( 97 . 2 μmol ) of 2 . 2 in 1 ml fc - 72 ® at − 85 ° c . in a fep tube was bubbled [ 18 f ] f 2 ( 15 - 20 μmol ) in ne over 10 min . the reaction solution and two 2 ml portions of methanol used to rinse the vessel were combined and evaporated on a hot water bath under a stream of n 2 . the residue was rinsed with three 3 ml portions of 1 : 1 acetonitrile : water and eluted down a fluorous reverse phase column ( 1 g ). hplc analysis was carried out on an analytical ( 250 mm × 4 . 6 mm ) c 8 reversed - phase column . a retention time of 4 . 18 min , consistent with the standard , was produced when flow rate = 1 ml / min , eluent : 50 % water ( 0 . 2 % tfa ): 50 % acetonitrile ( 0 . 2 % tfa ), λ = 280 nm . the chromatogram using a γ detector produced a single peak with a retention time of 4 . 99 min , which is consistent with the delay times between instruments . 19 f nmr ( 188 . 16 mhz , ch 3 cn : h 2 o ): δ − 110 . 10 ( d , 3 j f , h = 7 . 24 hz ). ms [ esms , 1 : 1 ipa :( acn : h 2 o )]: m / z 139 . 0 [ m − h ] − . 3 - iodobenzoic acid ( 12 reaction ) ( 2 . 17 ). to a mixture containing 0 . 127 g ( 99 . 1 μmol ) of 2 . 2 in 2 ml acetonitrile was added 1 ml ( 0 . 1 mmol ) iodine in methanol . the reaction mixture was stirred for 16 hr and then quenched with a crystal of sodium metabisulfite . the reaction was diluted with 2 . 5 ml of distilled deionized water and the total volume added to a fluorous column ( 3 . 9 g ), pre - conditioned with 1 : 1 acetonitrile : water . the column was eluted with 25 ml of 1 : 1 acetonitrile : water to give 2 . 17 in solution . hplc analysis was carried out on an analytical ( 250 mm × 4 . 6 mm ) c 8 reversed - phase column . a retention time of 9 . 90 minutes , which is consistent with a standard of 3 - iodobenzoic acid , was observed when the flow rate = 1 ml / min , eluent : 80 % water ( 0 . 1 % hfba ): 20 % acetonitrile , λ = 254 μm ). alternatively , varying elution conditions to a flow rate = 1 ml / min : 80 % water ( ph = 7 . 4 ): 20 % acetonitrile , λ = 254 nm resulted in elution of 2 . 17 at 2 . 9 minutes , also consistent with the authentic standard . ms ( esms ), m / z 246 . 9 [ m − h ] + . 3 - iodobenzoic acid ( na 127 i reaction ) ( 2 . 18 ). to a solution containing 5 . 4 mg ( 4 . 15 μmol ) of 2 . 2 in 200 μl of methanol was added 4 μl ( 0 . 184 nmol ) nai in 0 . 1 n naoh , followed by 2 μl of peracetic acid ( 32 % in acetic acid ). the reaction was quenched at 2 h with 100 μl of a 10 % sodium metabisulfite solution and diluted to 1 ml with distilled deionized water . hplc analysis was carried out on an analytical ( 250 mm × 4 . 6 mm ) c 18 reversed - phase nucleosil column . hplc analysis of a 100 μl aliquot gave a retention of 10 . 2 minutes , analogous to an authentic standard ( flow rate = 1 ml / min : 50 % water ( 0 . 2 % formic acid ): 50 % acetonitrile ( 0 . 2 % formic acid ), λ = 254 nm ). [ 125 ] 3 - iodobenzoic acid ( na 125 i reaction ) ( 2 . 19 — no impurities ). to a solution containing 1 . 4 mg ( 1 . 07 μmol ) of 2 . 2 in 200 μl of methanol was added 5 μl ( 32 μci ) na 125 i in 0 . 01 n naoh , followed by 2 μl of peracetic acid ( 32 % in acetic acid ). the reaction was stirred for 47 min followed by quenching with 20 μl of a 10 % solution of sodium metabisulfite and dilution with 300 μl of distilled - deionized water . hplc analysis was carried out on an analytical ( 250 mm × 4 . 6 mm ) c 18 reversed - phase nucleosil column . hplc analysis of a 20 μl aliquot gave a retention time of 16 . 91 min on the chromatogram using the γ detector . there was no visible uv absorbance other than the solvent front . the retention time was consistent with an authentic standard of 3 - iodobenzoic acid ( flow rate = 0 . 5 ml / min , 50 % water ( 0 . 2 % formic acid ): 50 % acetonitrile ( 0 . 2 % formic acid ), λ = 254 nm ). the solution was diluted with 1 ml of distilled deionized water and eluted through a waters c 18 sep - pak previously conditioned with water . the column was eluted with an additional 1 . 5 ml of distilled deionized water and the combined fractions showed an activity of 3 μci . the column was then washed with 2 ml of hplc grade acetonitrile and released 23 μci of activity . an additional washing of the column with 1 ml of acetonitrile resulted in only 1 μci of activity being released . the remaining activity was found in the sep - pak ( 4 μci ) and original reaction vessel ( 1 μci ). hplc analysis was carried out on an analytical ( 250 mm × 4 . 6 mm ) c 18 reversed - phase nucleosil column . hplc analysis of a 20 μl aliquot gave a retention of 16 . 586 min on the γ detector and no visible uv peak . the retention time was consistent with an authentic standard of 3 - iodobenzoic acid ( flow rate = 0 . 5 ml / min : 50 % water ( 0 . 2 % formic acid ): 50 % acetonitrile ( 0 . 2 % formic acid ), λ = 254 nm ). modification of the elution conditions to a flow rate = 1 ml / min : 100 % acetonitrile , and λ = 254 nm resulted in a peak at 4 . 458 min on the γ detector and two peaks at 6 . 379 min and 6 . 720 m in on the u v chromatogram . these two peaks have a similar retention time as 2 . 2 , 6 . 613 min , under similar elution conditions . the acetonitrile solution ( approx . 2 ml ) was diluted with 2 ml of distilled deionized water and passed down a fluorous technologies ® sep - pak . a total of 9 μci was released in the eluting volume . washing the column with an additional 4 ml of ( 1 : 1 ) acetonitrile : water yielded a total 19 μci when combined with the previous fraction . no additional activity was found in either the fluorous sep - pak or previous vial . hplc analysis was carried out on an analytical ( 250 mm × 4 . 6 mm ) c 18 reversed - phase nucleosil column . hplc analysis of a 20 μl aliquot gave a small peak at 6 . 532 min v chromatogram ( flow rate = 1 . 0 ml / min : 100 % acetonitrile , and λ = 254 nm ). tris [ 2 - perfluorohexylethyl ] tin - 3 - benzamide ( 2 . 21 ). to a reaction solution containing 294 mg ( 226 μmol ) of 2 . 2 in 2 . 5 ml of dmf was added 0 . 130 g ( 344 μmol ) of hbtu , followed by 90 μl ( 517 μmol ) diisopropylethylamine ( dipea ). the reaction solution was stirred for 5 min prior to addition of 251 μl ( 2 . 29 mmol ) of n , n - dimethylethylenediamine and 400 μl ( 2 . 30 mmol ) of dipea . the reaction solution was then stirred for 16 h . the solution was diluted with 20 ml of water and extracted into 50 ml of dichloromethane and 10 ml of fc - 72 ®. the fc - 72 ® layer was re - extracted with three additional 10 ml portions of dichloromethane . the combined organic layers were re - extracted with 20 ml of water prior to concentration under reduced pressure to give 2 . 21 as a dark orange oil : yield 227 mg ( 74 %). tlc r f 0 . 00 ( 6 : 1 hexane - diethylether ). 1 h nmr ( cdcl 3 , 200 mhz ): δ 1 . 31 ( t , 6h ) with sn satellites ( 2 j sn , h = 54 . 8 hz ), 2 . 31 ( 6h ), 2 . 33 ( m , 6h ), 2 . 59 ( dt , 2h ), 3 . 55 ( q , 2h ), 7 . 14 - 7 . 90 ( m , 4h ). 13 c nmr ( cdcl 3 , 50 . 3 mhz ): δ − 1 . 43 , 27 . 55 ( t , 3 j f , c = 23 . 4 hz ), 37 . 11 , 44 . 87 , 57 . 75 , 104 . 80 - 120 . 03 ( m , cf 2 , cf 3 ), 127 . 04 , 127 . 71 , 128 . 66 , 134 . 70 , 134 . 82 , 136 . 01 , 137 . 53 , 138 . 69 , 167 . 16 , 167 . 41 . ir ( thin film ): 3338 , 2950 , 2831 , 1650 cm − 1 . ms ( esms ), m / z 1353 . 0 [ m + h ] + . 3 - iodobenzamide ( 12 reaction of 2 . 21 ) ( 2 . 20 ). to a solution containing 3 . 2 mg ( 2 . 37 μmol ) of 2 . 21 in 200 μl methanol was added 30 μl ( 3 . 0 μmol ) of 0 . 1 m iodine . the reaction solution was stirred for 1 h prior to quenching with 100 μl of a 10 % solution of sodium metabisulfite . the solution was diluted with 700 μl of distilled - deionized water and analysed on a nucleosil c 18 reversed - phase column . a retention time of 16 . 6 min and 18 . 9 min was observed ( flow rate = 2 ml / min , 80 % h 2 o ( 0 . 01 m nah 2 po 4 ): 20 % ch 3 cn , and λ = 254 nm ). ms ( esms ), m / z 319 [ m + h ] + . 3 - fluorobenzamide ( f 2 reaction of 2 . 21 ). to 180 mg ( 133 μmol ) of 2 . 21 in 1 ml of fc - 72 ® at − 90 ° c . in a fep tube was bubbled 131 μmol of 0 . 5 % f 2 in ne . the f 2 was steadily released into the solution over 25 min . the reaction solution along with two 3 ml portions of fc - 72 ® used to rinse the vessel were concentrated in a large vial . the residue was washed with three 3 ml portions of acetonitrile and eluted down a conditioned fluorous reversed - phase column ( 1 g ). ms ( esms ), m / z 211 . 1 [ m + h ] + , 193 . 1 [ m − f + h ] + . tris [ 2 - perfluorohexylethyl ] tin - 3 - benzylamine ( 3 . 0 ). a mixture containing 3 . 990 g ( 2 . 84 mmol ) of 3 . 3 in 125 ml of 9 : 1 methanol : water with sufficient 0 . 5 n hcl to give a ph = 3 . 07 was stirred overnight . to the reaction mixture was added 20 ml 1 n naoh solution , which was followed by removal of methanol under reduced pressure . the reaction mixture was subsequently extracted with four ( 3 ml ) portions of fc - 72 ®. the fc - 72 ® layers were combined and re - extracted from 5 ml of dichloromethane . the solvent was concentrated under reduced pressure to give 3 . 0 as a light yellow oil : yield 3 . 482 g ( 97 %). tlc r f 0 . 22 ( 6 : 1 hexane - diethylether ). 1 h nmr ( 200 mhz , cdcl 3 ): δ 1 . 31 ( t , 6h ) with sn satellites ( 2 j sn , h = 54 . 2 hz ), 2 . 31 ( m , 6h ), 3 . 88 ( s , 2h ), 7 . 22 - 7 . 46 ( m , 4h ). 13 c nmr ( 126 mhz , cdcl 3 ): δ − 1 . 37 with sn satellites ( 1 j sn , c = 347 hz ), 27 . 94 ( t , 1 j f , c = 23 . 4 hz ), 46 . 62 , 106 . 17 - 121 . 17 ( m , cf 2 , cf 3 ), 128 . 63 , 129 . 19 , 129 . 72 , 134 . 60 , 134 . 90 , 135 . 56 , 135 . 66 , 136 . 96 , 138 . 42 , 140 . 08 , 143 . 89 , 162 . 09 . ir ( thin film ), 3386 , 2944 , 2870 , 1647 , 1250 cm − 1 . ms ( esms , ipa ): m / z 1268 . 5 [ m + h ] + . 1 -( 3 - bromobenzyl )- 2 , 2 , 5 , 5 - tetramethyl - 1 , 2 , 5 - azadisilolidine ( 3 . 1 ). the procedure developed by magnus et al . was followed . 5 to a solution containing 2 . 228 g ( 11 . 98 mmol ) of 3 - bromobenzylamine in 10 ml of dichloromethane was added 3 . 4 ml ( 24 mmol ) of triethylamine . the solution was stirred for 30 min and then treated with a solution containing 2 . 579 g ( 11 . 98 mmol ) of 1 , 1 , 4 , 4 - tetramethyl - 1 , 4 - dichlorosilethylene in 5 ml of dichloromethane . the reaction mixture was stirred for 3 h and then poured into 100 ml of saturated sodium dihydrogen phosphate . the reaction mixture was extracted with three 50 ml portions of dichloromethane , then dried ( mgso 4 ), and concentrated under reduced pressure . the residue was distilled at 160 ° c . to give 3 . 1 as a clear colourless oil : yield 2 . 510 g ( 64 %). 1 h nmr ( 200 mhz , acetone - d 6 ): δ 0 . 00 ( s , 12h ), 0 . 78 ( s , 4h ), 4 . 06 ( s , 2h ), 7 . 20 - 7 . 48 ( m , 4h ). 13 c nmr ( 50 . 3 mhz , acetone - d6 ): δ − 0 . 26 , 8 . 01 , 45 . 59 , 122 . 15 , 126 . 10 , 129 . 35 , 129 . 53 , 130 . 69 , 146 . 01 . ir ( thin film ): 3388 , 2953 , 1666 , 1251 , and 1132 cm − 1 . ms ( ci ): m / z = 312 . tris [ 2 - perfluorohexylethyl ] tin -( 3 - bromobenzyl )- 2 , 2 , 5 , 5 - tetramethyl - 1 , 2 , 5 - azadisilolidine ( 3 . 3 ). to a solution containing 4 . 301 g ( 13 . 1 mmol ) of 3 . 1 in 30 ml of thf at − 78 ° c . was slowly added 5 . 24 ml ( 13 . 1 mmol ) of 2 . 5 m n - buli . the reaction solution was stirred for 40 minutes , followed by addition of a solution containing 4 . 3662 g ( 3 . 521 mmol ) of 2 . 3 in 20 ml of thf . the reaction solution was stirred at − 78 ° c . for 2 h and then diluted with 5 ml of fc - 72 ® and 30 ml of methanol . the reaction solution was extraction with three 4 ml portions of fc - 72 ®. the combined fluorous layers were concentrated under reduced pressure to give 3 . 3 as a light yellow oil : yield 4 . 732 g ( 96 %). 1 h nmr ( 200 mhz , cdcl 3 ): δ 0 . 01 - 0 . 21 ( s , 12h ), 0 . 80 ( s , 4h ), 1 . 34 ( t , 6h , 2 j sn , c - h = 27 . 5 hz ), 2 . 35 ( m , 6h ), 3 . 96 - 4 . 06 ( s , 2h ), 7 . 28 - 7 . 39 ( m , 4h ). ir ( thin film ), 3354 , 2955 , 2849 , 1256 , and 442 cm − 1 . ms ( esms , ipa ): m / z 1268 . 3 [ m -( 2 , 2 , 5 , 5 - tetramethyl - 1 , 2 , 5 - azadisilolidine + h ] + . 3 - iodobenzylamine ( 12 reaction with 3 . 0 ) ( 3 . 4 ). to a mixture of 0 . 164 g ( 129 μmol ) of 3 . 0 in 2 ml of acetonitrile was added 1 . 5 ml of 0 . 1 m iodine in methanol . the reaction mixture was stirred for 16 h prior to quenching with a crystal of sodium thiosulfate and dilution with 3 ml of deionized distilled water . the reaction mixture was purified by flash chromatography using silicycle ® fluorous silica ( 3 . 9 g ). elution with 1 : 1 acetonitrile - water and collection of four 5 ml fractions gave 3 . 4 in solution . hplc analysis was carried out on an analytical ( 250 mm × 4 . 6 mm ) c 8 reversed - phase column . a retention time of 6 . 461 min , consistent with a standard , was generated when the column was eluted with 80 % h 2 o ( ph ≈ 7 . 4 ): 20 % ch 3 cn at a flow rate of 1 . 5 ml / min and λ = 254 nm . ms ( esms ), m / z 233 . 9 [ m + h ] + . tris [ 2 - perfluorohexylethyl ] tin - 3 - benzylguanidine using formamidine sulfinic acid ( 3 . 5 — approach b ). to a mixture containing 1 . 964 g ( 1 . 549 mmol ) of 3 . 0 in methanol ( 15 ml ) was added 0 . 184 g ( 1 . 704 mmol ) of 3 . 7 . the reaction mixture was stirred for 16 h and then methanol was decanted from the resulting viscous oil . the oil was washed with three ( 10 ml ) portions of hot chloroform and then two portions of hot water . the residue was extracted into 5 ml of fc - 72 ® from dichloromethane and residual water . the solvent was concentrated to give 3 . 5 as a clear orange oil : yield 1 . 654 g ( 82 %). mass spectrum ( esms ), m / z 1310 . 2 [ m + h ] + , 1293 . 0 [ m + h − 15 ] + , and 1325 . 0 [ m + h + 15 ] + . tris [ 2 - perfluorohexylethyl ] tin - 3 - benzlguanidine using aminoimino - methanesulfinic acid ( 3 . 5 — approach c ). to a mixture containing 518 mg ( 409 μmol ) of 3 . 0 in 1 ml of methanol was added 55 . 8 mg ( 450 μmol ) of aminoiminomethanesulfonic acid . the reaction mixture was then refluxed for 16 h . the reaction mixture was extracted into 5 ml of fc - 72 ® from 10 ml of methanol . the solvent was concentrated under reduced pressure to give 3 . 5 as an orange oil : yield 468 mg ( 88 %). tlc r f 0 . 25 ( 6 : 1 hexane - diethylether ). ir ( thin film ), 3349 , 3197 , 2946 , 1647 , 1449 , 1239 , 446 cm − 1 . mass spectrum ( esms ), m / z 1309 . 9 [ m + h ] + . aminoiminomethanesulfonic acid ( 3 . 7 ). the procedure developed by mosher et al . was followed . 12 to a mixture containing 0 . 633 g ( 5 . 85 mmol ) of 3 . 6 in 3 . 0 ml of glacial acetic acid at 0 ° c . was slowly added 1 . 56 ml of 32 % peracetic acid . the reaction mixture was then stirred for 16 h at room temperature . the precipitate was filtered and washed with five 5 ml portions of absolute ethanol and dried to give 3 . 7 as a white crystalline solid : yield 596 mg ( 82 %). mp 125 - 126 ° c . 3 - iodobenzylguanidine ( 3 . 9 ). to a solution containing 168 mg ( 721 μmol ) of 3 . 8 in 1 ml of methanol was added 90 . 1 mg ( 726 μmol ) of 3 . 7 . the reaction solution was refluxed for 16 h and then concentrated under reduced pressure to give 3 . 9 as a viscous yellow gum : yield 258 mg . hplc analysis was preformed using a nucleosil c 18 reversed - phase column . a retention time of 24 . 54 min was generated when the column was eluted with 80 % h 2 o ( 0 . 01 m nah 2 po 4 ): 20 % ch 3 cn at a flow rate of 2 . 0 ml / min and λ = 231 nm . 1 h nmr ( meoh , 200 mhz ): δ 4 . 22 ( s , 2h ), 6 . 99 ( t , 1h ), 7 . 22 ( d , 1h ), 7 . 49 ( d , 1h ), 7 . 56 ( s , 1h ). 13 c nmr ( meoh , 50 . 3 mhz ): δ 48 . 95 , 99 . 31 , 131 . 64 , 135 . 72 , 141 . 05 , 141 . 93 , 144 . 30 , 162 . 65 . ir ( thin film ): 3407 , 3192 , 1653 , 1115 cm − 1 . ms ( esms , methanol ), m / z 276 . 1 [ m + h ] + . 3 - iodobenzylguanidine ( nai reaction with 3 . 5 ) ( 3 . 10 ). to a reaction mixture containing 5 . 1 mg ( 3 . 90 μmol ) of 3 . 5 in 200 μl of methanol was added 10 μl ( 0 . 460 nmol ) of nai followed by 2 μl of solution of peracetic acid ( 35 % in acetic acid ). the reaction mixture was stirred for 2 h and then quenched with 100 μl of sodium metabisulfite ( 10 %) solution , prior to dilution to 1 ml with distilled deionized water . hplc analysis was performed with a nucleosil c 18 analytical column . a retention time of 24 . 89 min was observed ( 80 % h 2 o ( 0 . 01 m nah 2 po 4 ): 20 % ch 3 cn at a flow rate of 2 . 0 ml / min and λ = 231 nm ). ms ( esms ), m / z 276 . 0 [ m + h ] + . fluorination of 3 . 5 using [ f 2 ] ( 3 . 11 ). to 0 . 334 g ( 0 . 255 mmol ) of 3 . 5 in 1 ml of fc - 72 ® at − 95 ° c . in a fep tube was bubbled 172 μmol of 0 . 63 % f 2 in ne . the f 2 was steadily released into the solution over 35 min . the reaction solution along with two 3 ml portions of fc - 72 ® used to rinse the vessel were concentrated in a large vial . the residue was washed with three 3 ml portions of 1 : 1 acetonitrile : water and eluted down a conditioned fluorous reversed - phase column ( 1 g ) to give 3 . 11 in solution . hplc analysis was carried out on a nucleosil analytical ( 250 mm × 4 . 6 mm ) c 18 reversed - phase column . a retention time of 34 . 98 min was observed ( 80 % h 2 o ( 0 . 01 m nah 2 po 4 ): 20 % ch 3 cn at a flow rate of 2 . 0 ml / min and λ = 231 nm ). 19 f nmr ( acn : h 2 o , 470 . 493 hz ): δ − 110 . 3 ( 3 j f , h = 8 . 7 hz ), − 109 . 5 ( 3 j f , h = 9 . 2 hz ). ms ( esms ), m / z 168 . 0 [ m + h ] + . tris [ 2 - perfluorohexylethyl ]- 3 - benzylamine - gflm ( f ) ( 3 . 13 ). to a reaction solution containing 137 mg ( 108 μmol ) of 3 . 0 and 84 mg ( 170 μmol ) of gflm ( f ) in 5 ml of dmf was added 71 mg ( 187 μmol ) hbtu . to the reaction solution was added 97 μl of dipea and allowed to stir at for 16 h . the solution was diluted with 20 ml of water and extracted with 5 ml of fc - 72 ®. the emulsion partitioning fc - 72 ® and the aqueous layer was extracted and washed with three 3 ml portions of fc - 72 ®. the residual solvent was removed under reduced pressure to give 3 . 12 as a milky white oil : yield 63 mg ( 33 %). ms ( esms ), m / z 1744 [ m + h ] + , 1761 [ m + nh 4 ] + , 1766 [ m + na ] + . 3 - iodobenzyl - gflm ( f ) ( i 2 reaction with 3 . 13 ) ( 3 . 14 ). to a reaction mixture containing 50 mg ( 28 . 7 μmol ) of 3 . 13 in 3 ml of chloroform was added 1 . 5 ml ( 150 μmol ). the reaction mixture was stirred for 16 h prior to quenching with a sodium thiosulfate solution . the chloroform was removed under reduced pressure , and the mixture was diluted with 10 ml of 5 : 1 acetonitrile : water . the reaction solution was washed with three 1 . 5 ml portions of fc - 72 ® and the aqueous layer was isolated and assessed for the presence of 3 . 14 . hplc analysis was carried out on a nucleosil c 18 reversed - phase analytical column ( 250 mm × 4 . 6 mm ). a retention time of 19 . 4 min was observed ( 80 % h 2 o ( 0 . 01 m nah 2 po 4 ): 20 % ch 3 cn at a flow rate of 2 . 0 ml / min and λ = 254 nm ). ms ( esms ), m / z 319 [ m + h ] + . synthesis and purification of n - hydroxysuccinimidyl 3 - iodobenzoate . the n - hydroxysuccinimidyl tri ( fluoroalkyl ) stannylbenzoate , which was prepared following the method shown below in the scheme , was reacted with 125 i − in the presence of chloramine - t following the method of lindegren et al . lindegren , s . ; skamemark , g . ; jacobsson , l . ; karlsson , b . nuc . med . biol . 1998 , 25 , 659 . the reaction was stopped prematurely to compare the ability of two separate purification methods to remove impurities . the initial method involved extraction with perflourinated hexanes ( fc - 72 ) following dilution of the reaction mixture with water . the hplc trace of the aqueous layer ( fig3 ) showed the desired product , its hydrolysis product m -[ 125 i ] iodobenzoic acid and some unreated 125 i − . the second purification method , which is more convenient and more easily automated than extraction , involved passing the reaction mixture down a commercially available fluorous sep - pak . the purification protocol involved washing with 100 % water to remove unreacted iodide , which was immediately followed with 80 / 20 methanol - water which caused the desired product to elute . the hplc of the methanol - water eluent ( fig4 ) showed one major peak , which corresponds to the desired product . the fluorous labeling method has a number of advantages over traditional labeling methods , including ease of automation , sterilization and the fact that all of the precursors can be purified and characterized by traditional methods . all of the patents and publications cited herein are hereby incorporated by reference . those skilled in the art will recognize , or be able to ascertain using no more than routine experimentation , many equivalents to the specific embodiments of the invention described herein . such equivalents are intended to be encompassed by the following claims . 1 blok , d . ; feitsma , r . i . j . ; vermeij , p . ; pauwels , e . j . k . eur j nucl med . 1999 , 26 , 1511 . 2 krenning , e . p . ; bakker , w . h . ; breeman , w . a . lancet . 1989 , i , 242 . 3 hunter , r . m . ; greenwood , f . c . nature . 1962 , 194 , 495 . 4 fracker , p . j . ; speck , j . c . biochem . biophys . res . commun . 1987 , 80 , 849 . 5 bolton , a . m . ; hunter , r . m . biochem . j . 1973 , 133 , 529 . 6 okarvi , s . m . eur . j . nucl . med . 2001 , 28 , 929 . 7 okarvi , s . m . eur . j . nucl . med . 2001 , 28 , 929 . 8 hoshino , m . ; degenkolb , p . ; curran , d . p . j . org . chem . 1997 , 62 , 8341 . 9 studer , a ; jeger , p . ; wipf , p . ; curran , d . p . j . org . chem . 1997 , 62 , 2917 . 10 lequan , m . ; meganem , f . j . organometallic chem . 1975 , 94 , c1 - 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one aspect of the present invention relates to a method of purifying radiolabelled compounds comprising a ) loading onto a fluorous polymer a radiolabelled compound precursor comprising a fluoroalkyl tin moiety ; b ) reacting the radiolabelled compound precursor with a radiolabel delivering compound to give a radiolabelled compound , wherein the fluoroalkyl tin moiety is replaced by a radiolabel ; and c ) eluting the radiolabelled compound from the fluorous polymer .