the compounds of formula i can be prepared by producing a monocarboxylic acid of x -[ cobalamin ], wherein x is cyano -, methyl , adenosyl , and the like . these compounds can be prepared by the mild acid hydrolysis of cyanocobalamin , which has been shown to yield a mixture of mono -, a dicarboxylic acids and one tricarboxylic acid . these carboxylic acids are derived from the propionamide side chains designated b , d and e , as discussed hereinabove , which are more susceptible to hydrolysis than the amide groups on acetamide side chains a , c , and g . the ( b )-, ( d )-, and ( e )- monocarboxylic acids can be separated by column chromatography . see fig1 herein , and fig1 of d . l . anton et al ., j . amer . chem . soc ., 102 , 2215 ( 1980 ). see , also , j . b . armitage et al ., j . chem . soc ., 3349 ( 1953 ); k . bernhauer , biochem . z ., 344 , 289 ( 1966 ); h . p . c . hogenkamp et al ., biochemistry 14 , 3707 ( 1975 ); and l . ellenbogen , in &# 34 ; cobalamin ,&# 34 ; biochem . and pathophysiol ., b . babior , ed ., wiley , n . y . ( 1975 ) at - chapter 5 . the x -[ cobalamin ] [ co 2 h ] can be linked to the metal chelator by means of a linking group , which is preferably a divalent , or &# 34 ; bifunctional &# 34 ; organic linking group . such linking groups comprise two reactive groups , one that is coupled to the co 2 h group , and the other that is coupled to the metal chelator . a variety of homobifinctional and heterobifunctional linking reagents known in the art are useful in the present invention . preferred linkers comprise one or two amino or hydroxyl groups , such as ω - aminoalkanoic acids , e . g ., ε - amino caproic acid ( h 2 n --( ch 2 ) 5 -- cooh ), or alkane diamines including 1 , 4 - diaminobutane , 1 , 5 - diaminopentane and 1 , 6 - diaminohexane , and the like . particularly preferred among the aminoalkanoic acids and similar compounds are those which are soluble in aqueous buffers . det is a chelating group comprising a radionuclide , such as a metallic radioisotope . preferred among these chelating compounds &# 34 ; chelators &# 34 ; or ( chel ) are such polycarboxylic acids as edta , dtpa , dcta , dota , teta , or analogs or homologs thereof . dtpa ( diethylenetriaminepentaacetic acid ) can be attached to cobalamin carboxylic acid ( s ) via reaction of diethylenetriaminepentaacetic dianhydride ( aldrich chem . co .) with a linker comprising a free amino group . this yields a chel group that is 2 -( amidomethyl )- 1 , 1 , 7 , 7 - diethylenetriaminetetraacetic acid . this chelator can be reacted with radionuclides to yield a det moiety of the general formula ## str8 ## wherein m is the radionuclide . the synthetic route to a cobalamin metal ion dtpa complex ( 4 ) is schematically shown in fig2 wherein wsc = water soluble carbodiimide . dcta is a cyclohexane - based metal chelator , wherein r 3 may by ( c 1 - c 4 ) alkyl or ch 2 co 2 --, which may be attached to the y through positions 4 or 5 , or through the group r 3 and which carries from 1 to 4 detectable metal or nonmetal cations ( m ), monovalent cations , or the alkaline earth metals . thus , with metals of oxidation state + 1 , each individual cyclohexane - based molecule may carry up to 4 metal cations ( where both r 3 groups are ch 2 coom ). as is more likely , with higher oxidation states , the number of metals will decrease to 2 or even 1 per cyclohexane skeleton . this formula is not intended to limit the molecule to any specific stereochemistry . in particular , both amino functionalities may be either cis or trans to each other . other macrocyclic carboxylic acid chelators which can be linked to the cobalamin carboxylic acid via bis - amino linking groups include teta 1 , 4 , 8 , 11 - tetraazacyclotetradecane - n , n &# 39 ;, n &# 34 ;, n &# 39 ;&# 34 ;- tetraacetic acid ; 1 , 4 , 7 , 10 - tetrarazcyclododecane - n , n &# 39 ;, n &# 34 ;, n &# 39 ;&# 34 ;- tetraacetic acid ( dota ); 1 , 4 , 8 , 12 - tetraazacyclopentadecane - n , n &# 39 ;, n &# 34 ;, n &# 39 ;&# 34 ;- tetraacetic acid ( 15n4 ); 1 , 4 , 7 - triazacyclononane - n , n &# 39 ;, n &# 34 ;- triacetic acid ( 9n3 ); and 1 , 5 , 9 - triazacyclododecane - n , n &# 39 ;, n &# 34 ;- tnacetic acid ( 12n3 ). bifunctional chelators based on macrocyclic ligands in which conjugation is via an activated arm attached to the carbon backbone of the ligand can be employed as described by m . moi et al ., j . amer . chem ., soc . 49 , 2639 ( 1989 ) ( 2 - p - nitrobenzyl - 1 , 4 , 7 , 10 - tetraazacyclododecane - n , n &# 39 ;, n &# 34 ;, n &# 39 ;&# 34 ;- tetraacetic acid ); s . v . deshpande et al ., j . nucl . med ., 31 , 473 ( 1990 ); g . ruser et al ., bioconi . chem ., 1 , 345 ( 1990 ); c . j . broan et al ., j . c . s . chem . comm ., 23 , 1739 ( 1990 ); and c . j . anderson et al ., j . nucl . med ., 36 , 850 ( 1995 ) ( 6 - bromoacetamido - benzyl - 1 , 4 , 8 , 11 - tetraazacyclotetadecane - n , n &# 39 ;, n &# 34 ;, n &# 39 ;&# 34 ;- tetraacetic acid ( bat )). any metal capable of being detected in a diagnostic procedure in vivo or in vitro can be employed as m in the det moieties . particularly , any radioactive metal ion capable of producing a diagnostic result in a human or animal body or in an in vitro diagnostic assay may be used in the practice of the present invention . suitable ions include the following : antimony - 124 , antimony - 125 , arsenic - 74 , barium - 103 , barium - 140 , beryllium - 7 , bismuth - 206 , bismuth - 207 , cadmium - 109 , cadmium - 115m , calcium45 , cerium - 139 , cerium - 141 , cerium - 144 , cesium - 137 , chromium - 51 , cobalt - 56 , cobalt - 57 , cobalt - 58 , cobalt - 60 , cobalt - 64 , erbium - 169 , europium - 152 , gadolinium - 153 , gold - 195 , gold - 199 , hafnium - 175 , hafnium - 175 - 181 , indium - 111 , iridium - 192 , iron - 55 , iron - 59 , krypton - 85 , lead - 210 , manganese - 54 , mercury - 197 , mercury - 203 , molybdenum - 99 , neodymium - 147 , neptunium - 237 , nickel - 63 , niobium - 95 , osmium - 185 + 191 , palladium - 103 , platinum - 195m , praseodymium - 143 , promethium - 147 , protactinium - 233 , radium - 226 , rhenium - 186 , rubidium - 86 , ruthenium - 103 , ruthenium - 106 , scandium44 , scandium - 46 , selenium - 75 , silver - 110m , silver - 111 , sodium - 22 , strontium - 85 , strontium - 89 , strontium - 90 , sulfur - 35 , tantalum - 182 , technetium - 99m , tellurium - 125 , tellurium - 132 , thallium - 204 , thorium - 228 , thorium - 232 , thallium - 170 , tin - i 13 , titanium44 , tungsten - 185 , vanadium - 48 , vanadium49 , ytterbium - 169 , yttrium - 88 , yttrium - 90 , yttrium - 91 , zinc - 65 , and zirconium - 95 . the compounds of formula ( i ) are preferable dissolved or dispersed in a nontoxic liquid vehicle , such as physiological saline or a similar aqueous vehicle , to the desired concentration . a preselected analytical , diagnostic or therapeutic unit dose is then administered to the test animal or human patient , by oral administration or ingestion or by parenteral administration , as by intravenous or intraperitoneal infusion or injection , to attain the desired in vivo concentration doses useful for imaging or treating human organs or tumors can be derived , from those found to be effective to image or treat organs in humans in vitro or in animal models , such as those described hereinbelow , or from dosages of other labelled vitamin b 12 molecules , previously employed in animal therapy or imaging . the invention will be further described by reference to the following detailed examples , wherein cyanocobalamin and 1 - ethyl - 3 -( 3 - dimethylaminopropyl ) carbodiimide were purchased from sigma chem . co ., st louis , mo . adenosine , 1 , 4 - diaminobutane dihydrochloride , diethylenetriamine pentaacetic ( dpta ), hexamethylphosphoramide , 1 - hydroxybenzotriazole hydrate , iodomethane and thionylchloride were obtained from aldrich chem - co ., milwaukee , wis . thin layer chromatography ( tlc ) silica gel and pet - cellulose sheets were purchased from e . m . science , gibbstown , n . j . tc 99m and in 111 were obtained from mallinckrodt medical , inc . and gd 153 was obtained from amersham . other inorganic salts and solvents were obtained in the highest purity available . uv - visible spectra were recorded on a hewlett - packard diode array spectrophotometer . dtpa dianhydride and 5 &# 39 ;- chloro - 5 &# 39 ;- deoxyadenosine were synthesized as described by w . c . eckelman et al ., j . pharm . sci ., 64 , 704 ( 1975 ) and k . kikugawa et al ., tetrahedron lett ., 87 ( 1971 ), respectively . the monocarboxylic acids of cyanocobalamin , methylcobalamin - b - carboxylic acid and adenosylcobalamin - b - carboxylic acid were prepared and isolated as described by h . p . c . hogenkamp , biochemistry , 13 , 2736 ( 1974 ); d . l . anton et al ., j . amer . chem . soc ., 102 , 2215 ( 1980 ); r . h . yamada et al ., j . biol . chem ., 247 , 6266 ( 1972 ) and d . dolphin , methods in enzymology , xville , 34 - 52 ( 1971 ). methylcobalamin , adenosylcobalamin and their derivatives are light sensitive , especially in solution , and all reactions and manipulations were carried out in the dark or in dim light . all images for the in vivo studies were obtained on a ge 500 maxicamera using a leap collimator with a 20 % window about the 140 kev energy peak of technetium , and a medium energy collimator with a 20 % window about the 174 kev and 247 kev energy peaks of indium . a 256 × 256 matrix with a dedicated pinnacle computer system was used to collect and analyze the data . a mixture containing cyanocobalamin - b - carboxylic acid ( 1 . 0 g , 0 . 6 mmol ), hydroxybenzotriazole ( 0 . 81 g , 6 mmol ) and 1 , 4 - diaminobutane dihydrochloride ( 4 . 8 g , 30 mmol ) in 100 ml of water was adjusted to ph 7 . 8 . 1 - ethyl - 3 -( 3 &# 39 ;- dimethylaminopropyl ) carbodiimide ( 1 . 26 g , 6 . 6 mmol ) was then added , the ph was adjusted to 6 . 4 and the reaction stirred at room temperature for 24 h . tlc on silica gel using n - butanol - acetic acid water ( 5 : 2 : 3 ) showed the reaction to be complete . cyanocobalamin - b -( 4 - aminobutyl ) amide was extracted into 92 % aqueous phenol and the phenol layer was washed several times with equal volumes of water . to the phenol extract were added 3 volumes of diethylether and 1 volume of acetone . the desired cobalamin was removed from the organic phase by several extractions with water . the combined aqueous layers were extracted three times with diethylether to remove residual phenol , concentrated to approximately 20 ml in vacuo and crystallized from aqueous acetone . yield 955 mg , 92 %. cyanocobalamin - b -( 4 - aminobutyl ) amide ( 500 mg ), 0 . 3 mmol ) was dissolved in 30 ml sat . sodium bicarbonate and treated with solid dtpa dianhydride ( 1 . 2 g , 3 . 4 mmol ). the progress of the reaction was monitored by tlc on pei plates using n - butanol - acetic acid - water ( 5 : 2 : 3 ) as the solvent . after 30 min incubation at room temperature a second 1 . 2 g of the dianhydride was added . after two additional additions of dianhydride with adjustments of the ph to 8 . 2 the reaction mixture was incubated overnight . cyanocobalamin - dpta adduct was then extracted into 92 % aqueous phenol and purified as described above . the preparation was evaporated to dryness in vacuo and isolated as a glass . yield 460 mg , 77 %. the cyanobalamin - dtpa adduct behaves as a polyanion on paper electrophoresis in 0 . 1 m sodium phosphate buffer ph 7 . 1 . methylcobalamin - b - carboxylic acid ( 1 . 0 g , 0 . 6 mmol ) was reacted with diaminobutane dihydrochloride as described above for the cyano derivative . the cobalamin was purified by extraction through phenol ( see above ) and the resulting aqueous solution was concentrated in vacuo . this solution was chromatographed on ag1 - x2 200 - 400 mesh in the acetate form ( 20 × 2 . 5 cm ) and the pass through collected . the pass through was concentrated to approximately 20 ml and the desired cobalamin crystallized from aqueous acetone . yield 920 mg , 88 %. unreacted methylcobalamin - b - carboxyclic acid was eluted with 1 m acetic acid , concentrated and crystallized from aqueous acetone . yield 60 mg , 6 %. methylcobalarnin - b -( 4 - aminobutyl ) amide ( 500 mg , 0 . 3 mmol ) was dissolved in 30 ml saturated sodium bicarbonate and reacted with solid dtpa dianhydride as described above . the methyl cobalamin - dtpa adduct was purified by extraction through phenol , evaporated to dryness in vacuo and isolated as a glass . yield 600 mg , 96 %. adenosylcobalamin - b - carboxylic acid ( 500 mg , 0 . 3 mmol ) was reacted with diaminobutane dihydrochloride ( 2 . 4 mg , 15 mmol ) as described above . the cobalamin was purified by extraction through phenol ( see above ). the resulting aqueous solution was concentrated in vacuo and applied to ag - 50 × 2 , 200 - 400 mesh , in the hydrogen form ( 20 × 25 cm ). the column was washed thoroughly with water to remove hydroxybenzotriazole and the desired cobalamin eluted with 1 m ammonium hydroxide . after an additional extraction through phenol , adenosylcobalamin - b -( 4 - aminobutyl ) amide was isolated as a glass . yield 366 mg , 77 %. adenosylcobalamin - b -( 4 - aminobutyl ) amide ( 366 mg , 0 . 23 mmol ) was dissolved in 30 ml saturated sodium bicarbonate and treated with solid dtpa dianhydride ( 1 . 0 g , 2 . 8 mmol ) as described above . the cobalamin was purified through phenol ( see above ). the resulting aqueous solution - as concentrated and applied to ag - 50 × 2 , 200 - 400 mesh , in the hydrogen form ( 6 . 0 × 2 . 5 cm ), the column was washed with water and the desired cobalamin eluted with 0 . 1 m ammonium hydroxide . the solution was evaporated to dryness in vacuo and adenosylcobalamin - b -( 4 - aminobutyl ) amide dtpa isolated as a glass . yield 400 mg , 80 %. under dim light , 1000 μg of the non - labeled methyl -. adenosyl -, and cyanocobalamin - b -( 4 - aminobutyl ) amide - dtpa , as well as 1000 μg of cyanocobalamin and dtpa ( sigma - st . louis , mo . 63178 ), were separately dissolved in 10 ml of normal saline at room temperature . each of the five 1000 μg / 10 ml samples were stored in sealed , aluminum - wrapped 10 ml vials to prevent exposure to light . no buffers were added to the solutions . the ph of the solutions , measured by a beckman 40 ph meter ( beckman instruments , fullerton , calif . ): cyanocobalamin = 5 . 75 , dtpa = 3 . 78 ; cyano , methyl and adenosylcobalamin - dtpa analogues were 5 . 75 , 6 . 10 , and 6 . 19 , respectively . to assess in vitro binding to intrinsic factor ( if ) and transcobalamins ( tc ), the intrinsic factor blocking antibody ( ifba ) and unsaturated vitamin b 12 binding capacity ( ubbc ) assays were performed with serum randomly obtained from five patients being evaluated for pernicious anemia at the mayo clinic . the ifba and ubbc assays were first performed for clinical purposes as previously described by v . f . fairbanks et al ., mayo clin . proc ., 58 , 203 ( 1983 ); intrinsic factor blocking antibody [ 57 co ] radioassay - package insert , diagnostic products corp . ; d . grossowicz et al ., proc . exp . biol . 109 , 604 ( 1962 ) and c . gottlieb et al ., blood 25 , 6 ( 1965 ). next , the serum from the same five patients underwent modified ifba and ubbc assays . specifically , 1 μl of the five previously described solutions were separately incubated with purified if or serum , to potentially saturate all if and tc binding sites . after incubation for 20 minutes at room temperature and for another 20 minutes at 4 ° c . 500 μl of the stock ( 1000 μg / l ) cobalt - 57 - cyanocobalamin ( mallinckrodt medical . inc ., st . louis , mo . 63134 ) solution was added and the usual ifba and ubbc protocols were then followed . all supernatant activity was counted for four minutes on a gamma counter ( micromedix 10 / 20 , huntsville , ala . 35805 ). the results are shown in table i . table i__________________________________________________________________________clinical run cnb . sub . 12 meb . sub . 12 dtpa adb . sub . 12 dtpa cnb . sub . 12 dtpa dtpa__________________________________________________________________________ubbcpt 1 741 & lt ; nsb 17 . 1 54 . 6 222 . 6 731 . 5pt 2 632 & lt ; nsb 26 . 8 62 . 6 216 . 9 913 . 1pt 3 2097 & lt ; nsb 278 . 9 590 . 3 713 . 3 2078 . 9pt 4 1378 & lt ; nsb 60 . 9 126 . 9 433 . 2 1633 . 7pt 5 1682 & lt ; nsb 91 . 1 163 . 9 643 . 2 1418 . 0ifbapt 1 11942 . 5 951 . 5 4279 6758 . 5 5151 11899 ( 0 . 99 ) ( 12 . 48 ) ( 2 . 77 ) ( 2 . 30 ) ( 2 . 30 ) ( 0 . 99 ) pt 2 11656 920 . 5 4082 6841 . 5 5133 . 5 11696 . 5 ( 1 . 02 ) ( 12 . 90 ) ( 2 . 92 ) ( 1 . 74 ) ( 2 . 31 ) ( 1 . 02 ) pt 3 11780 912 . 5 4456 . 5 6828 . 5 5338 . 5 11735 . 5 ( 1 . 01 ) ( 13 . 01 ) ( 2 . 66 ) ( 1 . 74 ) ( 2 . 22 ) ( 1 . 01 ) pt 4 11617 749 4414 7046 . 5 6002 . 5 11909 ( 1 . 02 ) ( 15 . 85 ) ( 2 . 69 ) ( 1 . 64 ) ( 1 . 98 ) ( 1 . 00 ) pt 5 11653 . 5 858 . 5 4381 . 5 7096 . 5 5973 . 5 11778 . 5 ( 1 . 02 ) ( 10 . 91 ) ( 2 . 77 ) ( 1 . 72 ) ( 1 . 99 ) ( 1 . 02 ) __________________________________________________________________________ nsb = nonspecific binding ; counts & lt ; 100 consistent with saturation of transcobalamin proteins negative reference for ifba ; no binding to intrinsic factor (& lt ; 1 . 11 ) positive reference for ifba ; binding to intrinsic factor (& gt ; 1 . 43 ) indeterminate reference value ( 1 . 11 → 1 . 43 ) clinical run = patients supernatant counts from ubbc and ifba assays dtpa = diethylenetriamine pentaacetic acid cnb . sub . 12 = cyanocobalamin meb . sub . 12 dtpa = methylcobalaminb -( 4 - aminobutyl )- amide - dtpa adb . sub . 12 dtpa = adenosylcobalaminb -( 4 - aminobutyl )- amide - dtpa cnb . sub . 12 dtpa = cyanocobalaminb -( 4 - aminobutyl )- amide - dtpa the ifba assay demonstrated that dtpa does not significantly bind to if ( values less than the negative reference ), whereas cyanocobalamin and the cobalamin - dtpa analogs do , in varying degrees , competitively inhibit co - 57 cyanocobalamin from binding to intrinsic factor . by using the counts of the clinical run divided into the counts of the five solutions , the efficacy of binding to intrinsic factor can be estimated . the averaged percent binding of the five solutions to if was : cyanocobalamin = 92 . 5 %; methylcobalamin - b -( 4 - aminobutyl )- amide - dtpa = 63 . 2 %; cyanocobalamin - b -( 4 - aminobutyl )- amide - dtpa = 52 . 9 %; adenosylcobalamin - b -( 4 - aminobutyl )- amide - dtpa = 41 . 0 % and 0 . 8 % for dtpa . this is in contrast to the disclosure in houts ( u . s . pat . no . 4 , 465 , 775 ) that the ( b )- monocarboxylic acid of vitamin b 12 and its radioiodinated derivative exhibit very low binding to if . likewise the averaged percent binding of the five solutions to the transcobalamin proteins was : cyanocobalamin = 100 %, methylcobalamin - b -( 4 - aminobutyl ) amide - dtpa = 94 . 0 %, adenosylcobalamin - b -( 4 - aminobutyl ) amide - dtpa = 90 . 4 %, cyanocobalamin - b -( 4 - aminobutyl ) amide - dtpa = 66 . 4 % and 3 . 6 % for dtpa . thus , the attachment of dtpa to vitamin b 12 does alter its binding to the carrier proteins . as expected , non - labeled cyanocobalamin had the greatest affinity for if and the transcobalamin proteins . methylcobalamin - b -( 4 - aminobutyl ) amide - dtpa was next , followed by adenosylcobalamin - b -( 4 - aminobutyl ) amide - dtpa , and finally cyanocobalamin - b -( 4 - aminobutyl ) amide - dtpa . there was also some nonspecific binding of dtpa to the carrier proteins ( 0 . 8 % and 3 . 6 %). under dim light , 1000 μg of methyl -, adenosyl -, and cyanocobalamin - b -( 4 - aminobutyl ) amide - dtpa were separately dissolved in 200 μl of normal saline . next , 500 μci of indium - 111 or 250 μci of gadolinium - 153 were added to the cobalamin - dtpa solutions . the reactions were carried out at room temperature and room air . for the chelation of technetium , the dissolved cobalamin dtpa complexes were separately placed into sealed 2 ml vials . next , 200 μl of stannous chloride solution ( 1000 μg / ml normal saline ) were added to each vial . the vials were purged with nitrogen gas for 5 minutes . after this time , 1 - 5 mci of technetium - 99m was added to the n 2 purged vials . each vial underwent further nitrogen purging for 5 minutes . all chelation reactions were mixed gently for 5 minutes . control mixtures of 1000 μg of cyanocobalamin were dissolved in 200 μl of normal saline . cyanocobalamin was mixed with tc - 99m at room temperature and room air , as well as within nitrogen purged vials containing 200 μl of the described stannous chloride solution . additionally , the cobalamin - dtpa complexes underwent tc - 99m labeling in open vials at room air in the absence of the stannous chloride . specific activity was assessed by mixing 100 μl aliquots of methyl and adenosyl cobalamin - b -( 4 - aminobutyl ) amide - dtpa ( 5 μg / 100 μl normal saline ) with 50 μl stannous chloride solution ( 1 μg / 50 μl normal saline ) in nitrogen purged 2 ml vials . technetium - 99m in 10 , 25 , 50 , 75 , and 100 mci allotments of activity were added to the vials . the vials underwent gentle mixing and continuous nitrogen purging for five minutes after the addition of technetium . efficiency of chelation and specific activity were assessed via thin layer chromatography ( tlc ). thin layer chromatographic strips ( grade 31 et chr - thickness 0 . 50 mm , flow rate ( water ) 225 mm / 30 min , whatman lab sales , hilsboro , oreg . 97123 ) were developed in acetone in dim light . the dry strips were placed on film ( ektascan - mc1 , eastern kodak -. rochester , n . y . 14650 ) for autoradiography ( ar ). chromatographic and autoradiographic results were visually compared . all the radiolabeled cobalamin - dtpa complexes underwent tlc and ar to confirm 100 % labeling prior to in vivo administration . under acetone development , free tc - 99m migrates to the top of the chromatographic strip , whereas in - 111 and gd - 153 diffusely spread over the lower two - thirds of the strip . tlc and ar analysis demonstrated that there was 100 % labeling of all three cobalamin - dtpa complexes with tc - 99m , in - 111 , and gd - 153 . specifically , all radioactivity was confined to the chromatographic distribution of the cobalamin analogues . since methyl and adenosyl cobalamin could potentially have greater uptake in malignant tissue , the chelation of tc - 99m , in - 111 , and gd - 153 by methyl and adenosylcobalamin - b -( 4 - aminobutyl ) amide - dtpa underwent greater scrutiny . the chromatographic and autoradiographic images were consistently coincident . in contrast , unmodified cyanocobalamin did not demonstrate any affinity for binding the three radionuclides . as expected , there was minimal labeling of the cobalamin - dtpa complexes with tc - 99m in the absence of stannous chloride and hypoxic conditions . at a concentration of 5 μg / 100 μl the red color of the cobalamin - dtpa analogues is barely discernible in the aqueous state , and undetectable on tlc . however , the ar distribution is the same when compared to the more concentrated cobalamin analogue solutions with lower specific activity . methyl and adenosyl cobalamin - b -( 4 - aminobutyl ) amide - dtpa can chelate up to 50 mci of technetium - 99m per 5 μg with 100 % efficiency . this results in a specific activity of 10 mci / μg for the cobalamin - dtpa analogue . a . biodistribution : methylcobalamin - b -( 4 - aminobutyl ) amide - dtpa in a concentration of 300 μg / 100 μl normal saline was labeled with 3 mci of indium - 111 . the labeled vitamin b 12 analogue was diluted with normal saline to a final volume of 1000 μl . via intraperitoneal injection ( ip ), five 12 week old female balb - c mice ( harlan , sprague , dawley , indianapolis , ind . 46229 ) each received 200 μl ( 500 μci ) of the methylcobalamin - dtpa - 111 in complex . for comparison , indium - 111 - dtpa having the same concentration and specific activity of the methylcobalamin - dtpa analogue , was injected ip into three mice . all mice were sacrificed at 24 hours via co 2 inhalation . the pancreas . spleen , kidneys , and heart were dissected in their entirety . a portion of the liver , lung , left quadricep muscle , and flank fat were also harvested . all tissue samples and organs were weighed wet , minced in 2 . 0 ml normal saline , and counted for five minutes in a gamma well counter ( minaxi autogamma 5000 , packard instrument , downers grove , ill . 60515 ). b . gastrointestinal absorption : methylcobalamin - b -( 4 - aminobutyl )- dtpa and dtpa alone were labeled as described above , with the exception that the 3 mci indium / 300 μg / 100 μl normal saline solutions were not diluted . two groups of three mice had a few drops of either 111 in - dtpa or methylcobalamin - b -( 4aminobutyl )- dtpa - in - 111 placed in their oral cavities . the mice were sacrificed at 24 hrs , dissected , and studied as described above . a modified schillings test was performed on two mice . specifically , each mouse received via subcutaneous and intraperitoneal administration , a 1000 μg loading dose of non - labeled methylcobalamin - b -( 4 - aminobutyl ) amide - dtpa analogue . at 24 hrs , the mice were fed 2 - 3 drops of indium - labeled methylcobalamin - b -( 4 - aminobutyl ) amide - dtpa - complex . urine and feces were collected from the three groups of mice after oral administration . the mice were sacrificed at 24 hours after ingestion of tracer and images and biodistribution data were obtained at that time . c . tumor imaging : at 24 hours , there was a significant amount of adenosylcobalamin - b -( 4 - aminobutyl ) amide - dtpa - in - 111 uptake within the transplanted sarcoma both visually and by gamma well counting ( table ii ). table ii__________________________________________________________________________kidney liver spleen pancreas heart lung fat muscle tumor__________________________________________________________________________mouse 13717 . 5 943 . 3 433 . 1 304 . 2 134 . 7 130 . 9 101 . 4 93 . 6 -- mouse 23299 . 5 823 . 4 405 . 3 319 . 9 189 . 4 180 . 1 147 . 3 51 . 4 -- mouse 33462 . 7 768 . 6 366 . 8 310 . 3 171 . 2 113 . 1 102 . 8 43 . 9 -- mouse 4224 . 0 56 . 9 44 . 1 13 . 4 10 . 3 6 . 2 12 . 6 5 . 4 -- mouse 5130 . 2 41 . 5 26 . 2 13 . 0 6 . 9 6 . 0 19 . 5 5 . 6 -- mouse 6281 . 6 66 . 1 57 . 7 14 . 1 12 . 5 10 . 5 18 . 8 5 . 0 -- mouse 7621 . 4 126 . 4 67 . 8 40 . 0 35 . 0 38 . 4 -- 13 . 6 -- mouse 8700 . 5 111 . 7 66 . 6 39 . 3 29 . 8 51 . 2 -- 12 . 4 -- mouse 9601 . 2 115 . 8 66 . 3 41 . 2 31 . 3 40 . 6 -- 12 . 0 -- mouse 10119 . 4 24 . 0 19 . 5 6 . 0 5 . 6 5 . 4 -- 8 . 9 -- mouse 11117 . 3 25 . 5 19 . 0 6 . 7 5 . 0 5 . 3 -- 2 . 6 -- mouse 12110 . 1 23 . 2 18 . 1 5 . 9 4 . 8 5 . 0 -- 3 . 7 -- mouse 134 . 3 0 . 82 0 . 67 0 . 75 0 . 54 1 . 1 & lt ; bkg & lt ; bkg -- mouse 144 . 1 0 . 80 0 . 70 0 . 76 0 . 54 0 . 33 & lt ; bkg & lt ; bkg -- mouse 153 . 1 0 . 73 0 . 65 1 . 1 0 . 50 0 . 44 & lt ; bkg & lt ; bkg -- mouse 160 . 64 0 . 28 0 . 62 0 . 93 & lt ; bkg & lt ; bkg & lt ; bkg & lt ; bkg -- mouse 170 . 54 0 . 21 0 . 67 0 . 96 & lt ; bkg & lt ; bkg & lt ; bkg & lt ; bkg -- mouse 180 . 59 0 . 30 0 . 48 0 . 61 & lt ; bkg & lt ; bkg & lt ; bkg & lt ; bkg -- mouse 193886 . 9 691 . 0 576 . 3 445 . 0 165 . 0 318 . 8 76 . 0 70 . 1 954 . 7mouse 203115 . 6 464 . 8 309 . 5 242 . 7 134 . 8 230 . 0 170 . 4 81 . 9 1426 . 0mouse 213592 . 8 675 . 0 478 . 3 439 . 0 157 . 8 335 . 2 198 . 0 166 . 5 1183 . 1mouse 22116 . 5 19 . 7 17 . 3 7 . 1 5 . 0 4 . 5 13 . 7 7 . 2 52 . 8mouse 23180 . 7 40 . 9 22 . 8 11 . 3 8 . 0 9 . 2 17 . 9 6 . 4 69 . 3mouse 24231 . 2 60 . 3 46 . 1 13 . 9 9 . 7 8 . 5 19 . 2 6 . 8 73 . 1mouse 25543 . 9 116 . 5 54 . 7 38 . 4 21 . 7 34 . 4 39 . 5 23 . 5 135 . 5mouse 26240 . 8 56 . 2 25 . 8 21 . 3 11 . 4 19 . 9 13 . 5 15 . 5 60 . 4mouse 27459 . 2 107 . 6 37 . 1 30 . 3 16 . 9 21 . 3 17 . 8 14 . 5 120 . 3mouse 2814 . 0 1 . 6 1 . 9 1 . 4 0 . 94 1 . 7 0 . 93 . 68 5 . 0mouse 299 . 9 1 . 3 1 . 4 8 . 2 0 . 61 0 . 87 0 . 75 . 60 2 . 8mouse 3010 . 2 1 . 4 1 . 6 3 . 1 0 . 85 0 . 9 0 . 79 . 63 3 . 4__________________________________________________________________________ mice 1 - 3 and 19 - 21 = 500 μci adenosylcobalaminb -( 4 - aminobutyl )- amide - dtpa -. sup . 111 ln injected intraperitoneal mice 4 - 6 and 22 - 24 = 500 μci dtpa . sup . 111 in injected intraperitoneal mice 7 - 9 = 500 μci adenosylcobalaminb -( 4 - aminobutyl )- amide - dtpa -. sup . 111 in injected subcutaneously mice 10 - 12 = 500 μci dtpa . sup . 111 in injected subcutaneously mice 13 - 15 = approximately 30 μci methylcobalaminb -( 4 - aminobutyl )- amide - dtpa -. sup . 111 in administered orall mice 16 - 18 = approximately 30 μci dtpa . sup . 111 in administered orally mice 25 - 27 = approximately 100 μci methylcobalaminb -( 4 - aminobutyl )- amide - dtpa -. sup . 111 in tailvein injection mice 28 - 30 = approximately 100 μci dtpa . sup . 111 in tailvein injection despite the difference in the amount of activity injected between ip and iv routes , the degree of uptake within the tumor was consistently second behind the kidneys . the tumors had two to four times greater activity than the liver , spleen , and pancreas , with 4 - 12 times greater activity than that of the heart , lungs , fat , and muscle . as expected , no activity was seen to localize in the left flank of the control mice . usual uptake in the liver and spleen was again seen . gross pathology of the dissected masses demonstrated fat encapsulated tumors . microscopically , by h & amp ; e stain , the tumors were solid masses of blue stained cells consistent with a sarcoma . no areas of necrosis were noted . although dtpa - 111 in demonstrated uptake within the transplanted tumors , its concentration was 10 - 20 times less than that of adenosylcobalamin - dtpa - 111 in . d . intravenous administration : one milligram of either methyl or adenosylcobalamin - b -( 4 - aminobutyl ) amide - dtpa was labeled with 5 mci of 99m tc as described above . several mice were sacrificed via co 2 inhalation at varying time intervals after tailvein injection . the fist urine passed was collected and analyzed via tlc and ar . the organ and tissue distribution of the methyl and adenosylcobalamin - dtpa analogs at 24 hours was similar despite the route of administration ( table ii ). the kidneys were first , followed by the liver and spleen . the pancreas usually was next followed by the lungs , fat , heart , and muscle . the differences in activity between the pancreas , heart , lung , fat , and muscle was less significant after oral , subcutaneous , and intravenous administration . however , the ratio of uptake between the kidneys to liver , liver to spleen , and spleen to pancreas was relatively constant . the route of administration ( iv , ip , po ) did not have any obvious effect on the chelation of tc - 99m or in - 111 by these complexes . the greatest amount of dtpa - 111 in uptake was in the kidneys . the distribution of dtpa was similar to the cobalamin analogs , especially after intraperitoneal injection . despite their similarities , dtpa - 111 in had 5 - 12 times less activity per organ or tissue sample when compared to the methyl and adenosylcobalamin analogs . methylcobalamin - b -( 4 - aminobutyl ) amide - dtpa - in - 111 was absorbed from the gastrointestinal tract after oral administration . the majority of activity was localized in the kidneys , liver , and spleen on delayed imaging . in the mice that were not &# 34 ; flushed &# 34 ; with oral and intraperitoneal doses of non - labeled methylcobalamin - b -( 4 - aminobutyl ) amide - dtpa , no discernable activity was detected in the urine by gamma well counting . however , the mice that underwent the &# 34 ; modified schillings test &# 34 ; had detectable radioactivity within their urine at one hour . imaging at 24 hours of these &# 34 ; flushed &# 34 ; mice demonstrated significantly less activity throughout the body when compared to the &# 34 ; non - flushed &# 34 ; mice . fecal radioactivity became detectable at 2 hours in both groups receiving the radioactive cobalamin analogs orally . dtpa - 111 in was also absorbed from the gastrointestinal tract , but to a lesser degree . no activity was detected in the heart lungs , muscle , or fat tissue samples . radioactivity was detected in urine and stool by two hours . micturition occurred at approximately 15 and 45 minutes after intravenous and intraperitoneal injections , respectively . the first passed urine after intravenous or intraperitoneal administration was always radioactive . tlc and ar analysis of the collected urine showed no evidence of dissociation of the tc - 99m or in - 111 from the cobalamin - dtpa complexes . images at 5 minutes and 4 hours after tailvein injection demonstrated focal early uptake in the kidneys which became obscured by the liver and spleen activity on the delayed images . at 24 hours , there was a significant amount of adenosylcobalamin - b -( 4 - aminobutyl ) amide - dtpa - in - 111 uptake within the transplanted sarcoma both visually and by gamma well counting ( table ii ). despite the difference in the amount of activity injected between ip and iv routes , the degree of uptake within the tumor was consistently second behind the kidneys . the tumors had two to four times greater activity than the liver , spleen , and pancreas , with 4 - 12 times greater activity than that of the heart , lungs , fat , and muscle . as expected , no activity was seen to localize in the left flank of the control mice . usual uptake in the liver and spleen was again seen . gross pathology of the dissected masses demonstrated fat encapsulated tumors . microscopically , by h & amp ; e stain , the tumors were solid masses of blue stained cells consistent with a sarcoma . no areas of necrosis were noted . although dtpa - 111 in demonstrated uptake within the transplanted tumors , its concentration was 10 - 20 times less than that of adenosylcobalamin - dtpa - 111 in . all publications , patents and patent documents are incorporated by reference herein , as though individually incorporated by reference . the invention has been described with reference to various specific and preferred embodiments and techniques . however , it should be understood that many variations and modifications may be made while remaining within the spirit and scope of the invention .
a compound useful for in vivo imaging of organs and tumors is provided of formula : ## str1 ## wherein ## str2 ## is a cobalamin , ## str3 ## is derived from a corrin carboxylic acid group of said cobaltmin , y is a linking group and x is a chelating group , optionally comprising a detectable radionuclide or a paramagnetic metal ion , and n is 1 - 3 .