an objective of the invention was to use these photosensitizers as a vehicle for delivering the desired conjugate ( chelated with gd or radionuclides ) to tumor . the chelate is “ bifunctional ” because it binds the gd at one end and binds the target specific vehicle at the other . the chelate is a multidentate ligand , which has appropriate ligating groups for coordination to the metal . in a preferred embodiment , our invention includes : development of chlorin and bacteriochlorin - based gd ( iii ) aminophenyl dtpa conjugates with variable lipophilicity as tumor diagnostic agent by mri . development of chlorin and bacteriochlorin - based 111 in aminophenyl dtpa and 99m tc n 2 s 2 conjugates with variable lipophilicity as tumor diagnostic radiopharmaceuticals . a goal has been : ( i ) to successfully bind gadolinium to a tumor - avid porphyrin , originally designed for photodynamic therapy ( pdt ), and to prove that striking tumor uptake at 24 hours enhances the “ signal ” produced by tumor , thus dramatically increasing its conspicuity on mr imaging and ( ii ) to prepare related 99m tc and 111 in labeled radiopharmaceuticals as diagnostic agents for nuclear medicine . this invention includes the synthesis and application of certain chlorin and bacteriochlorin - based bisaminoethanethiol ( n 2 s 2 ) and modified ditetra - triethylamine penta carboxylic acid ( dtpa ) conjugates as mr contrast media and radiopharmaceuticals for diagnosis of primary malignancy and metastatic disease . the following examples describe examples for synthesis and use of magnetic resonance imaging agents . synthesis of hpph - gd ( iii ) aminophenyl - dtpa 14 : for the preparation of the title compound , pyropheophorbide - a 6b was obtained from methylpheophorbide - a 6a ( which in turn was extracted from spirulina algae ) by following the literature procedure . it was then converted into methyl 3 -( hexyloxy ) ethyl analog 9a by following a methodology developed in our laboratory . hydrolysis of the methyl ester functionality with aqueous lioh / methanol / thf produced the corresponding carboxylic acid 9b in quantitative yield . the reaction of 9b with 4 - aminophenyl dtpa penta - tert - butyl esters prepared by following the methodology in fig4 via the carbodiimide approach ( r . k . pandey , f . - y . shiau , a . b . sumlin , t . j . dougherty and k . m . smith , bioorg . med . chem . lett ., 1994 , 4 , 1263 , incorporated herein by reference as background art ) produced the corresponding analog 12 in 57 % yield ( fig5 and 6 ). the structure was confirmed by nmr and mass spectrometry analyses . before preparing the gd ( iii ) complex , the tert - butyl groups of the conjugate were converted into corresponding carboxylic acid by reacting with trifluoroacetic acid ( yield 100 %). for the preparation of gd ( iii ) complex 14 , the conjugate was dissolved in pyridine and gadolinium chloride hexahydrate dissolved in deionized water . the mixture was stirred at room temperature for 2 h . after the completion of the reaction ( monitored by tlc ), pyridine was removed under high vacuum . the residue was washed with water to remove the excess of gadolinium chloride , dried under vacuum and the title compound was isolated in 92 % yield . the structure of the final product was confirmed by mass spectrometry . synthesis of purpurin - 18 - imide - gd ( iii ) aminophenyidtpa 16 : methyl - pheophorbide - a 7a was converted into the hexylether derivative of n - hexyl purpurinimide in 70 % yield . the methyl ester group was then hydrolyzed to the corresponding carboxylic acid 10 by following the methodology as discussed for the preparation of 9b . purpurin - imide 10 was then reacted with aminophenyldtpa penta tert - butyl ester 5 by following a reaction sequence depicted in fig7 and the intermediate conjugate was isolated in 45 % yield . further reaction with trifluoroacetic acid and then with gdcl 3 . 6h 2 o produced the gd ( iii ) complex 16 in & gt ; 90 % yield . the structures of the conjugates were confirmed by nmr and mass spectrometry . synthesis of purpurin - 18 - imide - gd ( iii ) aminophenyldtpa 16 : methylpheophorbide - a 7a was converted into the hexylether derivative of n - hexyl purpurinimide in 70 % yield . the methyl ester group was then hydrolyzed to the corresponding carboxylic acid 10 by following the methodology as discussed for the preparation of 9b . purpurin - imide 10 was then reacted with aminophenyldtpa penta tert - butyl ester 5 by following a reaction sequence depicted in fig7 and the intermediate conjugate was isolated in 45 % yield . further reaction with trifluoroaceticacid and then with gdcl 3 . 6h 2 o produced the gd ( iii ) complex 16 in & gt ; 90 % yield . the structures of the conjugates were confirmed by nmr and mass spectrometry . in our attempt to investigate the effect of the position of the gd ( iii ) conjugate in the macrocycle , purpurin - imide 7 was converted into the related carboxylic acid analog 11 by conventional procedures . reaction of 10 with aminophenyl dtpa 5 will produce gd ( iii ) aminophenyl dtpa conjugate 15 , purpurin 18 - 3 - devinyl - 3 [ 4 ′- amidophenyl gadolinium ( iii ) dtpa ]- n - hexylimide . in this series of compounds , the overall lipophilicity of the molecule can be altered by varying the length of the carbon chain of either the alkyl ether substituents and / or n - substituted alkyl chain . thus , these compounds provide a unique opportunity to investigate the correlation of tumor uptake and lipophilicity . bacteriochlorins are a class of tetrapyrroles in which the two pyrrole units diagonal to each other are reduced . starting from n - hexyl - purpurin imide 7 we have prepared ketobacteriochlorin 20 by following a reaction sequence illustrated in fig9 . in our approach purpurinimide 7 containing a vinyl group at position 3 was converted into the 3 - devinyl - 3 - ethyl analog 17 ( can also be named as meso - n - hexyl - purpurin - 18 - imide ) by reacting with hydrogen using pd / c as a catalyst . it was then reacted with osmium tetroxide / pyridine / h 2 s ( a . n . kozyrev . t . j . dougherty and r . k . pandey , tetrahedron lett ., 1996 , 37 , 3781 , incorporated herein by reference as background art ) and the corresponding vic - dihydroxybacteriochlorin 18 was isolated in 75 % yield as a mixture of diasteriomers ( cis - hydroxy groups up or down relative to trans - reduced ring d ). the dihydroxy analog as a diasteriomeric mixture was treated with sulfuric acid under pinacolpinacolone reaction conditions , ( r . k . pandey , t . tsuchida , s . constantine , g . zheng , c . medforth , a . kozyrev , a . mohammad , m . a . j . rodgers , k . m . smith and t . j . dougherty , j . med . chem ., 1997 , 40 , 2770 , incorporated herein by reference as background art ) and the keto - bacteriochlorin , containing a keto - group either at 7 - ( compound 20 ) or 8 - position ( compound 19 ) respectively were isolated in 70 % yield . among these bacteriochlorins , the 7 - keto analog 20 showed high tumor uptake as determined by in vivo reflectance spectroscopy in mice model transplanted with rif tumor ( see fig3 ). the structures of bacteriochlorins 19 and 20 were confirmed by nmr and mass spectrometry analyses . our next step was to hydrolyze the methyl ester group in purpurinimide 20 into carboxylic acid 21 before converting it into the corresponding 4 - aminophenyldtpa conjugate 22 by following the methodology discussed previously for the preparation of related hpph and purpurin - imide analogs . synthesis of hpph - based bisaminoethanethiol conjugates 27 : for preparing the 99m tc labeled radiopharmaceuticals , two bisaminoethanethiols 23 and 24 were prepared by following the methodology developed in our laboratory ( g . li , q . ma , b . ma , z . d . grossman and r . k . pandey ( 1999 ) heterocycles 51 ( 12 ): 2849 - 2854 ; and g . li , b . ma , j . r . missert , z . d . grossman and r . k . pandey ( 1999 ) heterocycles 51 ( 12 ): 2855 - 2860 ; incorporated herein by reference as background art ). for the synthesis of n 2 s 2 conjugate 26 , hpph was reacted with n 2 s 2 chelate 23 and the thioprotected , hpph conjugate 25 was isolated in 40 % yield . subsequent deprotection of the thiols with triethylsilane / tfa afforded the corresponding bis - aminoethanethiol 26 in quantitative yield . the structure of the newly synthesized compound was confirmed by nmr and mass spectrometry analyses . the tc - 99m complex 27 was prepared by ligand - exchange reaction with 99m tc pertechnatate reduced by sn ( ii ) glucoheptonate by following the methodology of kung and coworkers ( s . k . meegalla , k . plossl , m - p . kung , s . chumpradit , d . a . stevenson , s . a . kushner , w . t . mcelgin , p . d . mozley and h . f . kung . j . med . chem ., 1997 , 40 , 9 , incorporated herein by reference as background art ). the radiolabeling yield was & gt ; 80 %. the purity of the tc - 99m complex was & gt ; 95 %, by chromatography . for the preparation of the title compound , the hpph - aminophenyldtpa 13was reacted with 111 in ( iii ) chloride , following the methodology reported by low and coworkers ( s . wang j . juo , d . a . lantrip , d . a . waters , c . j . mathias , w . a . green , p . l . fuchs and p . s . low , bioconjugate chem ., 1997 , 8 , 673 , incorporated herein by reference as background art ) for the preparation of 111 in - dtpa - folate and the 111 in - labeled compound was obtained in 82 % yield . following the synthesis of gd - labeled hpph , a series of three rats were injected intravenously and studied immediately after injection , at 1 hour , and at 24 hours , to establish whether the gd - hpph remained in the circulation longer than the current standard contrast medium ( magnavist or gd - dtpa ). whereas magnavist clears rapidly from the mammalian circulation by glomerular filtration , with a circulatory half - time of 16 - 20 minutes , the newly - synthesized contrast medium gd - hpph , was evident in the cerebral circulation at 1 hour . subsequently , to establish whether the gd - hpph is tumor - avid , a single rat with a subcutaneously - implanted ward colon carcinoma was imaged , 24 hours after intravenous gd - hpph . a second tumor - bearing rat was imaged 24 hours after injection of magnavist ( see fig1 and 2 ). clearly , the enhanced tumor signal after gd - hpph injection indicated that gd - hpph 14 has potential as a contrast medium for mri . hpph ( a chlorophyll - a derivative ) represents the vehicle by which the gd complex is carried into the tumor . addition of the gd chelate to hpph does not hinder its ability to form singlet oxygen producing efficacy , so this contrast medium also has the potential for dual action : enhanced localization on mr imaging ( diagnosis ), followed by directed light exposure with tumor injury ( treatment ). also , because of its excellent tumor selectivity and high fluorescence , the newly synthesized conjugate can be used for ir imaging . also , indium or other radionuclides like tc - 99m ( the latter conjugated by an n 2 s 2 ligand ) bound to chlorins and bacteriochlorins synthesized and proposed in this invention have potential as imaging agents for nuclear medicine .
compositions that are a chemical combination of porphyrins , chlorins , bacteriochlorins , and related tetra - pyrrolic compounds with radioactive elements such as technetium 99 , gadolinium , indium 111 and radioactive iodine . when the element can form cations , the compound is usually a chelate with the porphyrin or chlorin structure . when the element forms anions , the compound is usually a direct chemical combination of the radioactive element into the porphyrin or chlorin structure . the invention further includes the method of using the compounds of the invention for diagnostic imaging of hyperproliferative tissue such as tumors and new blood vessel growth as is associated with the wet form of age related macular degeneration and methods of making the compounds . compounds for mri contrast imaging of the invention are usually tc 99 , in 111 or gd complexes of compounds of the formula :