Patent Application: US-25894803-A

Abstract:
the invention describes the synthesis of a panel of novel carbon - carbon linked carboranyl - containng 5 , 10 , 15 , 20 - tetraphenylporphyrins bearing 25 - 44 % boron by weight . preliminary in vitro evaluation of several of these compounds , using both rat and human brain tumor cell lines , shows that these compounds display very low cytotoxicities , are capable of delivering substantial amounts of boron intracellularly , and are retained for long periods of time .

Description:
the present invention is directed to the synthesis and use of porphyrin compounds , which contain carboranyl groups attached to the porphyrin compound by a carbon - carbon linkage . the porphyrin compound generally corresponds to general formula i : where m is 2h or a divalent metal ion ; r1 and r2 are each independently hydrogen , alkyl or hydoxyalkyl ; and r3 through r6 are hydrogen or a substituted phenyl group . where r7 through r11 are hydrogen , a hydrophilic group or a carboranyl group . the carboranyl group is attached to the phenyl group by a carbon - carbon linkage . typically , either one or two of r7 through r11 are hydrophilic or carboranyl groups . examples of hydrophilic groups include hydroxyl , nme 3 + , pmeph 2 + , po ( oh ) 2 , so 3 h , cooh or nh 2 . at least one of r3 through r6 is a phenyl group of general formula ii having at least one carboranyl group attached by a carbon - carbon linkage . more preferably , two of r3 through r6 are phenyl groups of general formula ii , each having at least one carboranyl group . most preferably , r3 through r6 are all phenyl groups of general formula ii , each having at least one carboranyl group . in a preferred embodiment of the porphyrin compound the carboranyl group is 1 - methyl - o - carboranyl or o - carboranyl . in another preferred embodiment the compound is at least about 15 % boron by weight ; most preferably about 25 % to about 44 % boron by weight . the present invention also includes a method of making the foregoing carboranyl - containing porphyrin compounds . the first step of the method is providing a reaction mixture , which includes ( 1 ) a pyrrole or a dipyrrole , and ( 2 ) a benzaldehyde , both dissolved in a suitable solvent . the pyrrole or dipyrrole can be unsubstituted or substituted with alkyl groups ; and the benzaldehyde is of general formula iii where r7 through r11 are each hydrogen , a hydrophilic group or a carboranyl group attached to the benzaldehyde by a carbon - carbon linkage . hydrophilic groups can include hydroxyl , nme 3 + , pmeph 2 + , po ( oh ) 2 , p ( ch 2 oh ) 2 , so 3 − , cooh , co 2 − or nh 2 . the next step of the method is to subject the reaction mixture to an acidic ph until the benzaldehyde and the pyrrole , or the benzaldehyde and the dipyrrole , are converted to a porphyrin compound . in one preferred version of the method , the reaction mixture is subjected to an acidic ph by the addition of tfa . preferred versions of the method also include oxidation of the reaction mixture with tetrachloroquinone or dichlorodicyanobenzoquinone . optionally , the method can include complexing the porphyrin compound with a divalent metal ion , e . g . by treating the free base of the porphyrin compound with zinc choride to form a zn ( ii ) complex . moreover , the solubility of the porphyrin compound can be improved by forming a salt of the porphyrin compound . the present invention also includes an intermediate for use in the synthesis of porphyrin compounds , namely the aforementioned benzaldehyde of general formula iii where r7 through r11 are each hydrogen , a hydrophilic group or a carboranyl group attached to the benzaldehyde by a carbon - carbon linkage ; and either one or two of r7 through r11 are carboranyl groups . we anticipate that the carboranyl - containing porphyrins of the present invention will be of use in cancer treatments involving boron neutron capture therapy ( bnct ). accordingly , the present invention includes a method of delivering an effective amount of a neutron capture agent to tumor cells , which involves contacting the tumor cells with a carboranyl - containing porphyrin compound of the present invention . in vivo , the method includes administering the carboranyl - containing porphyrin compound to a patient , which is then selectively taken up by the tumor cells . to be effective in bnct , the amount of porphyrin compound taken up by the tumor cells is an amount sufficient for cytotoxicity when the tumor cells are irradiated by thermal neutrons . preferably , the tumor cells are brain tumor or melanoma cells our preliminary results , described in greater detail in the examples below , show that the carboranyl - containing porphyrins of the present invention will also be of use in cancer treatments involving photodynamic therapy ( pdt ). thus , the present invention includes a method of delivering an effective amount of a photosensitizing agent to tumor cells , similar to the method for bnct . in the pdt method , an effective amount of the porphyrin compound is an amount sufficient for cytotoxicity when the tumor cells are irradiated by red light . the present invention also includes compositions for use in boron neutron capture therapy comprising an effective amount of a carboranyl - containing porphyrin compound of the present invention , and a pharmaceutically acceptable carrier or excipient . an effective amount for bnct is an amount sufficient for selective uptake , retention and damage to tumor cells when the tumor cells are irradiated by thermal neutrons . similarly , the present invention includes compositions for use in photodynamic therapy comprising the carboranyl - containing porphyrin compounds of the present invention and a pharmaceutically acceptable carrier or excipient . the effective amount of the porphyrin compound for pdt is an amount sufficient for selective uptake , retention and cytotoxicity to tumor cells when the tumor cells are irradiated by red light . [ 0034 ] fig1 through 6 describe , in very few steps , the total synthesis of carboranylated 5 , 10 , 15 , 20 - tetraphenylporphyrins . these meso - phenylporphyrin compounds contain carbon - carbon linkages between the carboranyl groups and the meso - phenylporphyrin ring for increased chemical in vitro and in vivo stability over existing drugs . in addition , the high solubility of these new drugs in aqueous solution allows for their easy administration into the blood stream ( via a concentrated saline solution of the drug ), and avoids the use of a co - solvent . in vitro and in vivo biological activities of the new drugs show that these new compounds are very promising drugs for both the bnct and the pdt modalities for cancer treatment . [ 0035 ] fig7 describes the compounds that can be synthesized using the same synthetic methodology as for compound 26 ( fig6 ). these unsymmetrical compounds contain carbon - carbon linked hydrophobic o - carboranyl cages and hydrophilic groups ( oh ) to warrant solubility in aqueous solution . fig8 describes additional compounds that can be synthesized using the carborane building blocks described in fig5 . these compounds will be analogues of compound 24 , and will bear other hydrophilic groups ( neutral , positive and negative , e . g . — nme 3 + , — pmeph 2 + , — p ( ch 2 oh ) 2 , so 3 − , co 2 − ). in summary , all drugs in the present invention contain carbon - carbon linkages between the porphyrin ring and the carboranyl groups , and amphiphilic properties for both adequate solubility into the blood stream and interaction with cell membranes . [ 4 -( 1 - methyl - o - carboranyl ) methyl ] bromobenzene ( 1 ): a two - necked round bottom flask containing 1 - methyl - o - carborane ( 5 . 00 g , 31 . 65 mmol ) in dry dme ( 150 ml ) was cooled down to 0 ° c . under argon . n - buli ( 20 . 0 ml , 1 . 6 m in hexane ) was added dropwise and the resulting mixture was stirred at 0 ° c . for 30 minutes . a solution of 4 -( bromomethyl ) bromobenzene ( 7 . 91 g , 31 . 65 mmol ) in dry dme ( 15 ml ) was added dropwise . after stirring at 0 ° c . for 10 minutes , the final reaction mixture was warmed to room temperature and subsequently refluxed for 12 hours under argon . the solvent was then removed under vacuum and the crude solid obtained was purified by recrystallization from dichloromethane / methanol to give the title compound ( 7 . 80 g , 75 . 4 % yield ) as white crystals . ms ( ei ) m / e 327 . 1 ( m + ); 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 3 - 3 . 0 ( br , 10h , bh ), 2 . 15 ( s , 3h , ch 3 ), 3 . 41 ( s , 2h , ch 2 ), 7 . 06 ( d , 2h , arh , j = 8 . 1 hz ), 7 . 48 ( d , 2h , arh , j = 8 . 1 hz ). [ 4 -( 1 - methyl - o - carboranyl ) methyl ] benzaldehyde ( 2 ): a solution of compound 1 ( 4 . 00 g , 12 . 23 mmol ) in thf ( 150 ml ) under argon was cooled to − 78 ° c . ( acetone / dry ice bath ). n - buli ( 7 . 6 ml , 1 . 6 m in hexane ) was added dropwise while maintaining the temperature at − 78 ° c . the reaction mixture was stirred for 30 minutes at − 78 20 c . before dry dmf ( 5 . 0 ml , 64 . 6 mmol ) was slowly added . the final mixture was stirred at − 78 ° c . for 15 minutes and then warmed up slowly to room temperature . a 2n hcl solution ( 150 ml ) was added end the reaction mixture stirred for 2 h at room temperature . the solution was then reduced to a volume of 200 ml and extracted with dichloromethane ( 4 × 50 ml ). the organic extracts were washed once with an aqueous saturated solution of nahco 3 , once with water and dried over anhydrous na 2 so 4 . after removal of the solvent under vacuum , the oily residue was purified by column chromatography on silica gel ( dichloromethane / petrbleum ether 1 : 1 ), yielding the title compound ( 2 . 1 g , 62 % yield ) as a white solid . ms ( ei ) m / e 276 . 2 ( m + ); 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 5 - 3 . 0 ( br , 10h , bh ), 2 . 19 ( s , 3h , ch 3 ), 3 . 54 ( s , 2h , ch 2 ), 7 . 38 ( d , 2h , arh , j = 8 . 0 hz ), 7 . 89 ( d , 2h , arh , j = 8 . 0 hz ), 10 . 04 ( s , 1h , cho ). meso - tetra [ 4 ( 1 - methyl - o - carboranyl ) methylphenyl ] porphyrin ( 3 ): a solution of aldehyde 2 ( 1 . 16 g , 4 . 19 mmol ) and freshly distilled pyrrole ( 0 . 30 ml , 4 . 32 mmol ) in dry dichloromethane ( 420 ml ) was purged with argon for 15 minutes . tfa ( 0 . 25 ml , 3 . 15 mmol ) was added to the solution and the final mixture was stirred at room temperature under argon for 20 hours ( complete disappearance of starting compound 2 by tlc ). after addition of p - chloranil ( 0 . 788 g , 3 . 14 mmol ) the final reaction mixture was stirred at room temperature for 2 hours . the solution was concentrated under vacuum to 200 ml , then washed once with an aqueous saturated solution of nahco 3 , and once with water before being dried over anhydrous na 2 so 4 . the residue obtained after removal of the solvent under vacuum was purified by column chromatography ( dichloromethane / petroleum ether 1 : 1 ) and the fastest running porphyrin fraction was collected and recrystallized from dichloromethane / methanol , yielding 0 . 289 g ( 21 % yield ) of the title compound as purple crystals , m . p .& gt ; 300 ° c . ; ms ( maldi ) m / e 1296 . 0 ( m + ); 1 h - nmr ( cdcl 3 ) δ ppm : − 2 . 80 ( br , 2h , nh ), 1 . 6 - 3 . 1 ( br , 40h , bh ), 2 . 34 ( s , 12h , ch 3 ), 3 . 81 ( s , 8h , ch 2 ), 7 . 59 ( d , 8h , arh , j = 8 . 0 hz ), 8 . 20 ( d , 8h , arh , j = 8 . 0 hz ), 8 . 85 ( s , 8h , β - h ). uv - vis ( chcl 3 ) λ max : 418 nm ( ε 467 , 700 ), 514 ( 16 , 867 ), 550 ( 8 , 132 ), 590 ( 5 , 470 ), 646 ( 4 , 028 ). meso - tetra [ 4 -( 1 - methyl - nido - carboranyl ) methylphenyl ] porphyrin tetrapotassium salt ( 4 ): porphyrin 3 ( 0 . 050 g , 0 . 0386 mmol ) was dissolved in a 3 : 1 mixture of pyridine and piperidine ( 4 . 0 ml ), and stirred at room temperature in the dark for 36 hours , under argon . the solvent was completely removed under vacuum , the residue re - dissolved in a 60 % acetone aqueous solution and passed slowly through a dowex 50w2 - 100 resin in the potassium form . the porphyrin fraction was collected , dried under vacuum , re - dissolved in a 30 % acetone aqueous solution and again passed through the ion - exchange resin . after removal of the solvent under vacuum , the tetraanionic porphyrin was recrystallized from methanol / diethyl ether , yielding 0 . 051 g ( 94 % yield ) of the title compound , m . p .& gt ; 300 ° c . 1 h - nmr ( cd 3 cocd 3 ) δ ppm : − 2 . 70 ( s , 2h , nh ), − 2 . 45 to − 1 . 90 ( br , 4h , bh ), 0 . 9 - 2 . 4 ( br , 32h , bh ), 1 . 59 ( s , 12h , ch 3 ) 3 . 50 ( s , 8h , ch 2 ), 7 . 81 ( d , 8h , arh , j = 8 . 0 hz ), 8 . 08 ( d , 8h , arh , j = 8 . 0 hz ), 8 . 90 ( s , 8 , β - h ). uv - vis ( acetone ) λ max : 420 nm ( ε 349 , 700 ), 516 ( 13 , 595 ), 554 ( 12 , 410 ), 594 ( 4 , 130 ), 650 ( 5 , 990 ). zn ( ii )- meso - tetra [ 4 -( 1 - methyl - o - carborane ) methylphenyl ] porphyrin ( 5 ): to a solution of porphyrin 3 ( 0 . 150 g , 0 . 110 mmol ) in dichloromethane ( 150 ml ), thf ( 10 ml ), and pyridine ( 0 . 5 ml ) was added zncl 2 . 2h 2 o ( 0 . 075 mg , 0 . 435 mmol ), and the final mixture was stirred at room temperature under argon overnight . the mixture was then washed once with water , dried over anhydrous na 2 so 4 , and the solvent evaporated under vacuum . the residue was purified by column chromatography ( dichloromethanelpetroleum ether 1 : 1 . 5 ), the pink color fraction collected and recrystallized from dichloromethane / methanol , to give 0 . 135 g ( 92 % yield ) of the title compound as purple crystals , m . p .& gt ; 300 ° c . ; ms m / e 1358 . 6 ; 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 6 - 3 . 0 ( br , 40h , bh ), 2 . 33 ( s , 12h , ch 3 ), 3 . 80 ( s , 8h , ch 2 ), 7 . 57 ( br s , 8h , arh ), 8 . 19 ( br s , 8h , arh ), 8 . 95 ( br s , 8h , β - h ). uv - vis ( chcl 3 ) λ max : 424 nm ( ε 577 , 000 ), 554 ( 20 , 102 ), 596 ( 6 , 380 ). zn ( ii )- meso - tetra [ 4 -( 1 - methyl - nido - carboranyl ) methylphenyl ] porphyrin tetrapotassium salt ( 6 ): the zn ( ii ) complex 5 ( 0 . 075 g , 0 . 055 mmol ) was dissolved in a 3 : 1 mixture of pyridine and piperidine ( 4 . 0 ml ), and stirred at room temperature in the dark for 36 hours , under argon . the solvent was completely removed under vacuum , the residue re - dissolved in a 60 % acetone aqueous solution and passed slowly through a dowex 50w2 - 100 resin in the potassium form . the porphyrin fraction was collected , dried under vacuum , re - dissolved in a 30 % acetone aqueous solution and again passed through the ion - exchange resin . after removal of the solvent under vacuum , the tetra - anionic porphyrin was recrystallized from methanovdiethyl ether , yielding 0 . 078 g ( 96 . x % yield ) of the title compound , m . p .& gt ; 300 ° c . 1 h - nmr ( cd 3 cocd 3 ) δ ppm : − 2 . 48 to − 1 . 95 ( br , 4h , bh ), 0 . 9 - 2 . 4 ( br , 32h , bh ), 1 . 59 ( s , 12h , ch 3 ), 3 . 50 ( s , 8h , ch 2 ), 7 . 77 ( d , 8h , arh , j = 8 . 0 hz ), 8 . 11 ( d , 8h , arh , j = 8 . 0 hz ), 8 . 92 ( s , 8h , β - h ). uv - vis ( acetone ) λ max : 422 nm ( ε 479 , 000 ), 554 ( 13 , 870 ), 596 ( 6 , 595 ). [ 3 -( 1 - methyl - o - carboranyl ) methyl ] bromobenzene ( 7 ): a two - necked round bottom flask containing 1 - methyl - o - carborane ( 3 . 00 g , 18 . 99 mmol ) in dry thf ( 150 ml ) was cooled down to 0 ° c . under argon . n - buli ( 12 . 0 ml , 1 . 6 m in hexane ) was added dropwise and the resulting mixture was stirred at 0 ° c . and then cooled down to − 10 ° c . a solution of anhydrous lii ( 0 . 350 g , 2 . 61 mmol ) in thf ( 2 . 5 ml ) was added , followed by a solution of 3 -( bromomethyl ) bromobenzene ( 5 . 00 g , 20 . 00 mmol ) in thf ( 10 ml ). after stirring at − 10 ° c . for 15 minutes , the final reaction mixture was warmed to room temperature and stirred for 12 hours under argon . the reaction mixture was then washed with water ( 2 × 25 ml ), extracted with diethyl ether ( 3 × 25 ml ) and dried over na 2 so 4 . the solvent was then removed under vacuum and the crude solid obtained was purified by column chromatography ( silica gel , dichloromethane / petroleum ether 1 : 9 ) to give the title compound ( 4 . 25 g , 65 . 0 % yield ). ms ( ei ) m / e 327 . 1 ( m + ); 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 3 - 3 . 1 ( br , 10h , bh ), 2 . 16 ( s , 3h , ch 3 ), 3 . 42 ( s , 2h , ch 2 ), 7 . 13 ( d , 1h , arh , j = 7 . 8 hz ), 7 . 23 ( t , 1h , arh , j = 7 . 8 hz ), 7 . 33 ( s , 1h , arh ), 7 . 47 ( d , 1h , arh , j = 7 . 8 hz ). [ 3 -( 1 - methyl - o - carboranyl ) methyl ] benzaldehyde ( 8 ): a solution of compound 7 ( 1 . 00 g , 3 . 06 mmol ) in thf ( 25 ml ) under argon was cooled to − 78 ° c . ( acetone / dry ice bath ). n - buli ( 2 . 0 ml , 1 . 6 m in hexane ) was added dropwise while maintaining the temperature at − 78 ° c . the reaction mixture was stirred for 30 minutes at − 78 ° c . before dry dmf ( 1 . 0 ml , 17 . 5 mmol ) was slowly added . the final mixture was stirred at − 78 ° c . for 15 minutes and then warmed up slowly to room temperature . a 2n hcl solution ( 25 ml ) was added and the reaction mixture stirred for 2 h at room temperature . the solution was then reduced to a volume of 200 ml and extracted with dichloromethane ( 4 × 50 ml ). the organic extracts were washed once with an aqueous saturated solution of nahco 3 , once with water and dried over anhydrous na 2 so 4 . after removal of the solvent under vacuum , the oily residue was purified by column chromatography on silica gel ( dichloromethane / petroleum ether 1 : 1 ), yielding the title compound ( 0 . 668 g , 79 . 1 % yield ) as a white solid . ms ( ei ) m / e 276 . 2 ( m + ); 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 4 - 3 . 1 ( br , 10h , bh ), 2 . 19 ( s , 3h , ch 3 ), 3 . 55 ( s , 2h , ch 2 ), 7 . 48 ( d , 1h , arh , j = 7 . 8 hz ), 7 . 56 ( t , 1h , arh , j = 7 . 8 hz ), 7 . 70 ( s , 1h , arh ), 7 . 85 ( d , 1h , arh , j = 7 . 8 hz ), 10 . 04 ( s , 1h , cho ). meso - tetra [ 3 -( 1 - methyl - o - carboranyl ) methylphenylporphyrin ( 9 ): a solution of aldehyde 8 ( 0 . 660 g , 2 . 39 mmol ) and freshly distilled pyrrole ( 0 . 18 ml , 2 . 59 mmol ) in dry dichloromethane ( 240 ml ) was purged with argon for 45 minutes . tfa ( 0 . 15 ml , 1 . 89 mmol ) was added to the solution and the final mixture was stirred at room temperature under argon for 18 hours . after addition of p - chloranil ( 0 . 440 g , 1 . 77 mmol ) the final reaction mixture was stirred at room temperature for 3 hours . the organic solution was washed once with an aqueous saturated solution of nahco 3 , and once with water before being dried over anhydrous na 2 so 4 . the residue obtained after removal of the solvent under vacuum was purified by column chromatography ( dichloromethane / petroleum ether 1 : 1 ) and the porphyrin fraction was collected and recrystallized from dichloromethane / methanol , yielding 0 . 252 g ( 33 % yield ) of the title compound as purple crystals , m . p .& gt ; 300 ° c . ; ms ( maldi ) m / e 1296 . 0 ( m + ); 1 h - nmr ( cdcl 3 ) δ ppm : − 2 . 84 ( br , 2h , nh ), 1 . 5 - 3 . 0 ( br , 40h , bh ), 2 . 20 ( s , 12h , ch 3 ), 3 . 74 ( s , 8h , ch 2 ), 7 . 62 ( d , 4h , arh ), 7 . 74 ( d , 4h , arh ), 8 . 05 ( d , 4h , arh ), 8 . 18 ( d , 4h , arh ), 8 . 84 ( s , 8h , β - h ). uv - vis ( chcl 3 ) λ max : 419 nm , 516 , 548 , 590 , 646 . meso - tetra [ 3 -( 1 - methyl - nido - carboranyl ) methylphenyl ] porphyrin tetrapotassium salt ( 10 ): porphyrin 9 ( 0 . 049 g , 0 . 0378 mmol ) was dissolved in a 3 : 1 mixture of pyridine and piperidine ( 4 . 0 ml ), and stirred at room temperature in the dark for 36 hours , under argon . the solvent was completely removed under vacuum , the residue re - dissolved in a 60 % acetone aqueous solution and passed slowly through a dowex 50w2 - 100 resin in the potassium form . the porphyrin fraction was collected , dried under vacuum , re - dissolved in a 30 % acetone aqueous solution and again passed through the ion - exchange resin . after removal of the solvent under vacuum , the tetraanionic porphyrin was recrystallized from methanol / diethyl ether , yielding 0 . 050 g ( 94 % yield ) of the title compound , m . p .& gt ; 300 ° c . uv - vis ( acetone ) λ max : 431 nm , 511 , 546 , 590 , 647 . 4 - ethynylbenzaldehyde ( 11 ): to a solution of 4 - bromobenzaldehyde ( 10 . 00 g , 54 . 08 mmol ) and triphenylphosphine ( 0 . 500 g , 1 . 91 mmol ) in anhydrous triethylamine ( 80 ml ) under angon , were added ethynyltrimethylsilane ( 6 . 00 g , 61 . 09 mmol ) and palladium ( ii ) acetate ( 0 . 100 g , 0 . 445 mmol ). the final mixture was heated to reflux for 2 hours , and then it was cooled down to room temperature and filtrated . the filtrate was concentrated under vacuum to a thick oil , which was purified by column chromatography ( dichloromethane / petroleum ether 1 : 4 ) and recrystallized from cold cyclohexane to give 10 . 5 g ( 96 . 1 % yield ) of 4 -( trimethylsilylethynyl ) benzaldehyde ; ms m / e 187 . 2 ( m + ); 1 h - nmr ( cdcl 3 ) δ ppm : 0 . 27 ( s , 9h , sime 3 ), 7 . 60 ( d , 2h , arh , j = 8 . 1 hz ), 7 . 82 ( d , 2h , arh , j = 8 . 1 hz ), 10 . 00 ( s , 1h , cho )]. this compound ( 8 . 00 g , 39 . 59 mmol ) was treated with k 2 co 3 ( 0 . 500 g ) in methanol ( 50 ml ) at 25 ° c . for 2 hours , under argon . the solvent was removed under vacuum and the residue dissolved in dichloromethane ( 100 ml ). this solution was washed once with an aqueous saturated solution of nahco 3 and once with water , before being dried over anhydrous na 2 so 4 and the solvent evaporated under vacuum . the yellow residue was purified by column chromatography using dichloromethane / petroleum ether 1 : 4 for elution and recrystallization from cold cylohexane to give 4 . 40 g ( 85 . 5 % yied ) of the title compound ; ms ( ei ) m / e 130 . 0 ; ( m + ). 1 h - nmr ( cdcl 3 ) δ ppm : 3 . 30 ( s , 1h , ch ), 7 . 64 ( d , 2h , arh , j = 8 . 1 hz ), 7 . 84 ( d , 2h , arh , j = 8 . 1 hz ), 10 . 02 ( s , 1h , cho ). 4 -( o - carboranyl ) benzaldehyde ( 12 ): bf 3 . oet 2 ( 0 . 654 g , 4 . 62 mmol ) was added at 0 ° c . and under argon , to a solution of 4 - ethynylbenzaldehyde ( 11 ) ( 6 . 00 g , 46 . 15 mmol ) and 1 , 2 - ethanedithiol ( 5 . 00 g , 53 . 09 mmol ). this mixture was stirred at room temperature under argon for 15 minutes . the reaction mixture was then washed once with a 10 % aqueous naoh solution , and once with an aqueous saturated solution of nacl , before being dried over anhydrous na 2 so 4 and the solvent evaporated under vacuum . purification of the resulting residue by column chromatography ( dichloromethane / petroleum ether 1 : 4 ) gave p - ethynylbenzyl ( 1 , 3 - dithiane ) ( 7 . 5 g , 79 % yield ) as a yellow solid [ ms ( ei ) m / e 206 . 0 ( m + ); 1 h - nmr ( cdcl 3 ) □ ppm : 3 . 07 ( s , 1h , ch ), 3 . 38 and 3 . 51 ( m , 2h each , ch 2 ch 2 ), 5 . 61 ( s , 1h , sch ), 7 . 42 ( d , 2h , arh , j = 8 . 1 hz ), 7 . 47 ( d , 2h , arh , j = 8 . 1 hz )]. decaborane ( 3 . 00 g , 24 . 59 mmol ), ethyl sulfide ( 5 . 00 g , 55 . 44 mmol ) and dry toluene ( 50 ml ) were combined in a schlenk tube equipped with a stir bar . this solution was heated at 40 ° c . for 3 hours and at 60 ° c . for 2 hours , and then allowed to cool down to room temperature . to this mixture was added a solution of p - ethynylbenzyl ( 1 , 3 - dithiane ) ( 5 . 00 g , 24 . 26 mmol ) in dry toluene ( 10 ml ), and the final reaction mixture was slowly warmed up to 80 ° c . and stirred at this temperature for 3 days . after cooling to room temperature , the mixture was concentrated under vacuum and the resulting oil was dissolved in methanol ( 250 ml ) and heated to reflux until liberation of hydrogen ceased ( approximately 60 minutes ). at room temperature a 50 % aqueous hcl solution ( 2 to 3 ml ) was cautiously added and the mixture was again heated to reflux until the hydrogen evolution was complete ( approximately 30 minutes ). after cooling down to room temperature , the reaction mixture was diluted with ethanol and excess ethylsulfide was removed by ethanol - ethylsulfide co - distillation . the remain residue was concentrated under vacuum . to a solution of the resulting residue in benzene ( 100 ml ) at 50 ° c ., was added 100 ml of a cold 10 % aqueous naoh solution , and the final mixture stirred vigorously for 15 minutes . the organic layer was separated , washed with water ( 3 × 25 ml ) and dried over anhydrous na 2 so 4 . after evaporation of the solvent , the residue obtained was purified by column chromatography ( dichloromethane / petroleum ether 1 : 4 ), yielding 5 . 25 g ( 66 . 8 % yield ) of p -( o - carboranyl ) benzyl ( 1 , 3 - dithiane ) [ ms ( ei ) m / e 324 . 1 ( m + ); 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 6 - 3 . 3 ( br , 10h , bh ), 3 . 36 and 3 . 47 ( m , 2h each , ch 2 ch 2 ), 3 . 91 ( br s , 1h , o - carborane - ch ), 5 . 56 ( s , 1h , sch ), 7 . 40 ( d , 2h , arh , j = 8 . 1 hz ), 7 . 46 ( d , 2h , arh , j = 8 . 1 hz )]. to a solution of the latter compound ( 5 . 00 g , 15 . 43 mmol ) in 5 % aqueous thf ( 25 ml ) under argon , was added dropwise a solution of hgclo 4 ( 12 . 50 g , 31 . 29 mmol ) in thf ( 15 ml ). the final mixture was stirred at room temperature for 15 minutes , before being filtered and the precipitate washed 3 times with 25 ml of diethyl ether . the filtrate was washed with an aqueous saturated solution of na 2 co 3 ( 3 × 25 ml ) and with water ( 2 × 25 ml ), before being dried over anhydrous na 2 so 4 . the residue obtained after evaporation of the solvent was purified by column chromatography ( dichloromethane / petroleum ether 1 : 4 ) to give the title compound ( 3 . 27 g , 85 . 6 % yield ); ms ( ei ) m / e 248 . 2 ( m + ); 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 60 - 3 . 2 ( br , 10h , bh ), 4 . 03 ( br s , 1h , o - carborane - ch ), 7 . 65 ( d , 2h , arh , j = 8 . 4 hz ), 7 . 86 ( d , 2h , arh , j = 8 . 4 hz ), 10 . 04 ( s , 1h , cho ). meso - tetra [ 4 -( o - carboranyl ) phenyl ] porphyrin ( 13 ): a solution of aldehyde 12 ( 1 . 05 g , 4 . 23 mmol ) and freshly distilled pyrrole ( 0 . 30 ml , 4 . 32 mmol ) in dry dichloromethane ( 430 ml ) was purged with argon for 30 minutes . tfa ( 0 . 20 ml , 2 . 52 mmol ) was added to the solution and the final mixture was stirred at room temperature under argon for 24 hours . after addition of p - chloranil ( 0 . 780 g , 3 . 14 mmol ) the final reaction mixture was stirred at room temperature for 3 hours . the solution was concentrated under vacuum to 300 ml , then washed once with an aqueous saturated solution of nahco 3 , and once with water before being dried over anhydrous na 2 so 4 . after evaporation of the solvent under vacuum , the resulting residue was purified by column chromatography ( dichloromethane / petroleum ether 1 : 2 ) and the fastest running porphyrin fraction was collected and recrystallized from dichloromethane / methanol , yielding 0 . 220 g ( 17 . 7 % yield ) of the title compound as purple crystals , m . p .& gt ; 300 ° c . ; ms ( maldi ) m / e 1184 . 5 ( m + 1 ); 1 h - nmr ( cdcl 3 ) δ ppm : − 2 . 89 ( br , 2h , nh ), 1 . 7 - 3 . 5 ( br , 40h , bh ), 4 . 28 ( br s , 4h , o - carborane - ch ), 7 . 89 ( d , 8h , arh , j = 8 . 0 hz ), 8 . 17 ( d , 8h , arh , j = 8 . 0 hz ), 8 . 78 ( s , 8h , β - h ). 1 h - nmr ( d - tfa / cdcl 3 ) δ ppm : − 0 . 97 ( br , 4h , nh ), 1 . 8 - 3 . 4 ( br , 40h , bh ), 4 . 31 ( br s , 4h , o - carborane - ch ), 8 . 13 ( d , 8h , j = 8 . 0 hz ), 8 . 51 ( d , 8h , j = 8 . 0 hz ), 8 . 68 ( s , 8h , β - h ). uv - vis ( chcl 3 ) λ max : 418 nm ( ε 464 , 700 ), 514 ( 17 , 165 ), 550 ( 8 , 300 ), 590 ( 5 , 635 ), 646 ( 4 , 035 ). meso - tetra [ 4 -( nido - carboranyl ) phenyl ] porphyrin tetrapotassium salt ( 14 ): porphyrin 13 ( 0 . 0500 g , 0 . 0423 mmol ) was dissolved in a 3 : 1 mixture of pyridine and piperidine ( 4 . 0 ml ), and stirred at room temperature in the dark for 36 hours , under argon . the solvent was completely removed under vacuum , the residue re - dissolved in a 60 % acetone aqueous solution and passed slowly through a dowex 50w2 - 100 resin in the potassium form . the porphyrin fraction was collected , dried under vacuum , re - dissolved in a 30 % acetone aqueous solution and again passed through the ion - exchange resin . after removal of the solvent under vacuum , the tetraanionic porphyrin was recrystallized from methanol / diethyl ether , yielding 0 . 0494 g ( 90 . 2 % yield ) of the title compound , m . p .& gt ; 300 ° c . 1 h - nmr ( cd 3 cocd 3 ) δ ppm : − 2 . 78 ( s , 2h , nh ), − 2 . 45 to − 1 . 90 ( br , 4h , bh ), 0 . 8 - 2 . 4 ( br , 32h , bh ), 2 . 57 ( br s , 4h , nido - carborane - ch ), 7 . 66 ( d , 8h , arh , j = 8 . 0 hz ), 7 . 97 ( d , 8h , arh , j = 8 . 0 hz ), 8 . 87 ( s , 8h , β - h ). uv - vis ( acetone ) λ max : 420 nm ( ε 302 , 900 ), 516 ( 11 , 560 ), 554 ( 10 , 580 ), 594 ( 3 , 335 ), 650 ( 4 , 875 ). zn ( ii )- meso - tetra [ 4 -( o - carboranyl ) phenyl ] porphyrin ( 15 ): to a solution of porphyrin 13 ( 0 . 085 g , 0 . 072 mmol ) in dichloromethane ( 50 ml ), thf ( 4 . 0 ml ), and pyridine ( 0 . 5 ml ) was added zncl 2 . 2h 2 o ( 0 . 30 g ), and the final mixture was stirred at room temperature under argon overnight . the mixture was then washed once with water , dried over anhydrous na 2 so 4 , and the solvent evaporated under vacuum . the residue was purified by column chromatography ( dichloromethane / cyclohexane 1 : 2 ), the pink color fraction collected and recrystallized from dichloromethane / methanol , to give 0 . 085 g ( 94 . 7 % yield ) of the title compound as purple crystals , m . p .& gt ; 300 ° c . ; ms ( maldi ) m / e 1246 . 7 ( m + ); 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 6 - 3 . 6 ( br , 40h , bh ), 4 . 30 ( br s , 4h , o - carborane - ch ), 7 . 91 ( br s , 8h , arh ), 8 . 17 ( br s , 8h , arh ), 8 . 88 ( br s , 8h , β - h ). uv - vis ( ch 2 cl 2 ) λ max : 424 nm ( ε 607 , 400 ), 554 ( 22 , 566 ), 594 ( 6 , 781 ). zn ( ii )- meso - tetra [ 4 -( nido - carboranyl ) phenyl ] porphyrin tetrapotassium salt ( 16 ): the zn ( ii ) complex 15 ( 0 . 0600 g , 0 . 0481 mmol ) was dissolved in a 3 : 1 mixture of pyridine and piperidine ( 4 . 0 ml ), and stirred at room temperature in the dark for 36 hours , under argon . the solvent was completely removed under vacuum , the residue re - dissolved in a 60 % acetone aqueous solution and passed slowly through a dowex 50w2 - 100 resin in the potassium form . the porphyrin fraction was collected , dried under vacuum , re - dissolved in a 30 % acetone aqueous solution and again passed through the ion - exchange resin . after removal of the solvent under vacuum , the tetraanionic porphyrin was recrystallized from methanoldiethyl ether , yielding 0 . 0615 g ( 94 . 0 % yield ) of the title compound ; 1 h - nmr ( cd 3 cocd 3 ) δ ppm : − 2 . 54 to − 1 . 78 ( br , 4h , bh ), 0 . 6 - 2 . 2 ( br , 32h , bh ), 2 . 58 ( br s , 4h , nido - carborane - ch ), 7 . 64 ( d , 8h , arh , j = 8 . 1 hz ), 7 . 95 ( d , 8h , arh , j = 8 . 1 hz ), 8 . 88 ( s , 8h , β - h ). uv - vis ( acetone ) λ max : 426 nm ( ε 432 , 000 ), 558 ( 14 , 380 ), 598 ( 9 , 513 ). 3 - ethynylbenzaldehyde ( 17 ): to a solution of 3 - bromobenzaldehyde ( 10 . 00 g , 54 . 08 mmol ) and triphenylphosphine ( 0 . 500 g , 1 . 91 mmol ) in anhydrous triethylamine ( 100 ml ) under argon , were added ethynyltrimethylsilane ( 6 . 00 g , 61 . 09 mmol ) and palladium ( ii ) acetate ( 0 . 100 g , 0 . 445 mmol ). the final mixture was heated to reflux for 2 hours , and then it was cooled down to room temperature and filtered . the filtrate was concentrated under vacuum to a thick oil , which was purified by column chromatography ( dichloromethane / petroleum ether 1 : 4 ) to give 8 . 52 g ( 78 . 0 % yield ) of 3 -( trimethylsilylethynyl ) benzaldehyde [ 1 h - nmr ( cdcl 3 ) δ ppm : 0 . 26 ( s , 9h , sime 3 ), 7 . 47 ( t , 1h , arh , j = 7 . 5 hz ), 7 . 70 ( d , 1h , arh , j = 7 . 5 hz ), 7 . 82 ( d , 1h , arh , j = 7 . 5 hz ), 7 . 96 ( s , 1h arh ), 9 . 98 ( s , 1h , cho )]. this compound ( 5 . 00 g , 24 . 74 mmol ) was treated with k 2 co 3 ( 0 . 500 g ) in methanol ( 50 ml ) at 25 ° c . for 2 hours , under argon . the solvent was removed under vacuum and the residue dissolved in dichloromethane ( 100 ml ). this solution was washed once with an aqueous saturated solution of nahco 3 and once with water , before being dried over anhydrous na 2 so 4 and the solvent evaporated under vacuum . the yellow residue was purified by column chromatography using dichloromethane / petroleum ether 1 : 4 for elution and recrystallization from cyclohexane to give 2 . 80 g ( 87 . 1 % yied ) of the title compound ; ms ( ei ) m / e 130 . 0 ; ( m + ). 1 h - nmr ( cdcl 3 ) δ ppm : 3 . 20 ( s , 1h , ch ), 7 . 51 ( t , 1h , arh , j = 7 . 8 hz ), 7 . 74 ( d , 1h , arh , j = 7 . 8 hz ), 7 . 87 ( d , 1h , arh , j = 7 . 8 hz ), 7 . 99 ( s , 1h , arh ), 10 . 02 ( s , 1h , cho ). 3 -( o - carboranyl ) benzaldehyde ( 18 ): bf 3 . oet 2 ( 0 . 11 g , 0 . 77 mmol ) was added at 0 ° c . and under argon , to a solution of 3 - ethynylbenzaldehyde ( 17 ) ( 1 . 00 g , 7 . 69 mmol ) and 1 , 2 - ethanedithiol ( 0 . 73 g , 7 . 75 mmol ). this mixture was stirred at room temperature under argon for 15 minutes . the reaction mixture was then washed once with a 10 % aqueous naoh solution , once with an aqueous saturated solution of nahco 3 and once with water , before being dried over anhydrous na 2 so 4 and the solvent evaporated under vacuum . purification of the resulting residue by column chromatography ( dichloromethane / petroleum ether 1 : 4 ) gave 1 . 28 g ( 80 . 7 % yield ) of m - ethynylbenzyl ( 1 , 3 - dithiane ) [ ms ( ei ) m / e 206 . 0 ( m + ); 1 h - nmr ( cdcl 3 ) □ ppm : 3 . 07 ( s , 1h , ch ), 3 . 37 and 3 . 50 ( m , 2h each , ch 2 ch 2 ), 5 . 59 ( s , 1h , sch ), 7 . 27 ( t , 1h , arh j = 7 . 8 hz ), 7 . 38 ( d , 1h , arh , j = 7 . 8 hz ), 7 . 50 ( d , 1h , arh , j = 7 . 8 hz ), 7 . 66 ( s , 1h , arh )]. decaborane ( 0 . 0500 g , 4 . 10 mmol ), ethyl sulfide ( 0 . 750 g , 8 . 32 mmol ) and dry toluene ( 25 ml ) were combined in a schlenk tube equipped with a stir bar . this solution was heated at 40 ° c . for 3 hours and at 60 ° c . for 2 hours , and then allowed to cool down to room temperature . to this mixture was added a solution of m - ethynylbenzyl ( 1 , 3 - dithiane ) ( 0 . 800 g , 3 . 88 mmol ) in dry toluene ( 5 ml ), and the final reaction mixture was slowly warmed up to 80 ° c . and stirred at this temperature for 3 days . after cooling to room temperature , the mixture was concentrated under vacuum and the resulting oil was dissolved in methanol ( 100 ml ) and heated to reflux until liberation of hydrogen subsisted ( approximately 60 minutes ). at room temperature a 50 % aqueous hci solution ( 1 . 0 ml ) was cautiously added and the mixture was again heated to reflux until the hydrogen evolution was complete ( approximately 30 minutes ). after cooling down to room temperature , the reaction mixture was diluted with ethanol and the excess ethylsulfide was removed by ethanol - ethylsulfide co - distillation . the remaining residue was concentrated under vacuum . to a solution of the resulting residue in benzene ( 50 ml ) at 5 ° c ., was added 100 ml of a cold 10 % aqueous naoh solution , and the final mixture stirred vigorously for 15 minutes . the organic layer was separated , washed with water ( 3 × 15 ml ) and dried over anhydrous na 2 so 4 . after evaporation of the solvent , the residue obtained was purified by column chromatography ( dichloromethane / petroleum ether 1 : 4 ), yielding 0 . 905 g ( 72 . 0 % yield ) of m -( o - carboranyl ) benzyl ( 1 , 3 - dithiane ) [ 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 40 - 3 . 20 ( br , 10h , bh ), 3 . 39 and 3 . 49 ( m , 2h each , ch 2 ch 2 ), 3 . 97 ( br s , 1h , o - carborane - ch ), 5 . 58 ( s , 1h , sch ), 7 . 28 ( t , 1h , arh , j = 7 . 8 hz ), 7 . 39 ( d , 1h , arh , j = 7 . 8 hz ), 7 . 55 ( d , 1h , arh , j = 7 . 8 hz ), 7 . 63 ( s , 1h , arh )]. to a solution of the latter compound ( 1 . 00 g , 3 . 09 mmol ) in 5 % aqueous thf ( 10 ml ) under argon , was added dropwise a solution of hgclo 4 ( 2 . 50 g , 6 . 26 mmol ) in thf ( 5 . 0 ml ). the final mixture was stirred at room temperature for 15 minutes , before being filtered and the precipitate washed with 25 ml of diethyl ether . the filtrate was then washed with an aqueous saturated solution of na 2 co 3 ( 3 × 10 ml ) and with water ( 2 × 10 ml ), before being dried over anhydrous na 2 so 4 . the residue obtained after evaporation of the solvent was purified by column chromatography ( dichloromethane / petroleum ether 1 : 4 ) to give the title compound ( 0 . 677 g , 88 . 5 % yield ); 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 5 - 3 . 3 ( br , 10h , bh ), 4 . 04 ( br s , 1h , o - carborane - ch ), 7 . 56 ( t , 1h , arh , j = 7 . 8 hz ), 7 . 79 ( d , 1h , arh , j = 7 . 8 hz ), 7 . 91 ( d , 1h , arh , j = 7 . 8 hz ), 7 . 96 ( s , 1h , arh ), 10 . 02 ( s , 1h , cho ). meso - tetra [ 3 -( o - carboranyl ) phenyl ] porphyrin ( 19 ): a solution of aldehyde 18 ( 0 . 702 g , 2 . 83 mmol ) and freshly distilled pyrrole ( 0 . 200 ml , 2 . 88 mmol ) in dry dichloromethane ( 285 ml ) was purged with argon for 30 minutes . tfa ( 0 . 100 ml , 1 . 26 mmol ) was added to the solution and the final mixture was stirred at room temperature under argon for 18 hours . after addition of p - chloranil ( 0 . 522 g , 2 . 10 mmol ) the final reaction mixture was stirred at room temperature for 3 hours . the solution was concentrated under vacuum to 200 ml , then washed once with water , once with an aqueous saturated solution of nahco 3 , and again once with water before being dried over anhydrous na 2 so 4 . after evaporation of the solvent under vacuum , the resulting residue was purified by column chromatography ( dichloromethane / petroleum ether 1 : 2 ) and the fastest running porphyrin fraction was collected and recrystallized from dichloromethane / methanol , yielding 0 . 140 g ( 16 . 7 % yield ) of the title compound as purple crystals ; ms ( maldi ) m / e 1184 . 1 h - nmr ( cdcl 3 ) δ ppm : − 2 . 88 ( br , 2h , nh ), 1 . 6 - 3 . 5 ( br , 40h , bh ), 4 . 19 ( br s , 4h , o - carborane - ch ), 7 . 78 ( m , 4h , arh ), 7 . 94 ( m , 4h , arh ), 8 . 27 ( m , 4h , arh ), 8 . 33 ( m , 4h , arh ), 8 . 80 ( s , 8h , β - h ), uv - vis ( chcl 3 imax : 418 nm , 512 , 549 , 588 , 644 . meso - tetra [ 3 - nido - carboranyl ) phenyl ] porphyrin tetrapotassium salt ( 20 ): porphyrin 19 ( 0 . 010 g , 0 . 008 mmol ) was dissolved in a 3 : 1 mixture of pyridine and piperidine ( 4 . 0 ml ), and stirred at room temperature in the dark for 36 hours , under argon . the solvent was completely removed under vacuum , the residue re - dissolved in a 60 % acetone aqueous solution and passed slowly through a dowex 50w2 - 100 resin in the potassium form . the porphyrin fraction was collected , dried under vacuum , re - dissolved in a 30 % acetone aqueous solution and again passed through the ion - exchange resin . after removal of the solvent under vacuum , the tetraanionic porphyrin was recrystallized from methanol / diethyl ether , yielding 0 . 0108 g ( 98 . 1 % yield ) of the title compound , m . p .& gt ; 300 ° c . 1h - nmr ( cd 3 cocd 3 ) d ppm : − 2 . 70 ( s , 2h , nh ), − 2 . 40 to − 1 . 90 ( br , 4h , bh ), 0 . 8 - 2 . 3 ( br , 32h , bh ), 2 . 48 ( br s , 4h , nido - carborane - ch ), 7 . 49 ( m , 4h , arh ), 7 . 65 ( m , 4h , arh ), 7 . 84 ( m , 4h , arh ), 8 . 15 ( m , 4h , arh ), 8 . 88 ( s , 8h , b - h ). uv - vis ( acetone ) imax : 416 nm ( e 326 , 300 ), 512 ( 14 , 300 ), 547 ( 8 , 000 ), 590 ( 4 , 300 ), 646 ( 4 , 300 ). bis -( 3 , 5 - bromomethyl ) bromobenzene ( 21 ): to a refluxing solution of 3 , 5 - dimethylbromobenzene ( 4 . 63 g , 25 . 0 mmol ) in dry ccl 4 ( 300 ml ) under argon , were added nbs ( 9 . 79 g , 55 . 0 mmol ) and benzoyl peroxide ( 0 . 80 g , 3 . 30 mmol ) in portions , over a one hour period . the final reaction mixture was refluxed with stirring and under argon for 16 hours . after cooling to room temperature , the reaction mixture was filtered and the filtrate washed once with an aqueous saturated solution of nahco 3 and once with water . the organic solution was dried over anhydrous na 2 so 4 and the solvent evaporated under vacuum . the resulting residue was purified by column chromatography using dichloromethane / petroleum ether 1 : 9 for elution , and the main product collected and recrystallized from n - hexane , yielding 2 . 83 g ( 33 % yield ) of the title and literature known compound ; 1 h - nmr ( cdcl 3 ) δ ppm : 4 . 40 ( s , 2h , ch2 ), 7 . 34 ( s , 1h ), 7 . 47 ( s , 2h ). bis [ 3 , 5 -( 1 - methyl - o - arboranyl ) methyl ] bromobenzene ( 22 ): n - buli ( 5 . 2 ml , 1 . 6 m in hexane ) was added dropwise to a solution of methyl - o - carborane ( 1 . 39 g , 8 . 80 mmol ) in dry thf ( 80 ml ), at a temperature between − 5 ° and 0 ° c ., under argon . the mixture was stirred at this temperature range for one and a half hours , then cooled to − 15 °-− 20 ° c . ( ice / salt bath ). a solution of lii ( 0 . 166 g , 1 . 27 mmol ) in dry thf ( 15 ml ) and a solution of compound 21 ( 1 . 37 g , 4 . 00 mmol ) in dry thf ( 20 ml ) were added and the final reaction mixture allowed to warm up to room temperature and stirred for 16 hours . after quenching the reaction with water the resulting mixture was extracted with diethyl ether . the organic extracts were washed once with water , once with brine , dried over anhydrous na 2 so 4 and the solvent removed under vacuum . the crude product was purified by column chromatography using dichloromethane / petroleum ether 2 : 8 for elution , and the main product collected and recrystallized from n - hexane to give 1 . 26 g ( 63 % yield ) of the title compound ; ms m / e 497 . 3 ; 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 4 - 3 . 0 ( br , 20h , bh ), 2 . 17 ( s , 6h , ch 3 ), 3 . 43 ( s , 4h , ch 2 ), 6 . 96 ( s , 1h ), 7 . 31 ( s , 2h ). bis [ 3 , 5 -( 1 - methyl - o - carboranyl ) m thyl ] benzaldehyde ( 23 ): a solution of compound 22 ( 0 . 994 g , 2 . 00 mmol ) in thf ( 20 ml ) under argon was cooled to − 78 ° c . n - buli ( 1 . 4 ml , 1 . 6 m in hexane ) was added dropwise via syringe . after stirring the reaction mixture for 30 minutes at − 78 ° c ., dry dmf ( 0 . 77 ml , 10 . x mmol ) was slowly added . the resulting yellow mixture was stirred at − 78 ° c . for 30 minutes and then warmed to 0 ° c . and stirred at this temperature for one hour . temperature . a 5 % aqueous hcl solution was added until the ph of the reaction mixture was between 2 and 3 , and the final mixture stirred at room temperature for 30 minutes . the aqueous layer was extracted 4 times with diethyl ether , the organic fraction dried over anhydrous mgso 4 and the solvent evaporated under vacuum . purification by column chromatography ( dichloromethane / petroleum ether 2 : 3 ), afforded the title compound ( 0 . 632 g ) in 70 . 9 % yield ; ms m / e 446 . 4 ; 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 5 - 3 . 0 ( br , 20h , bh ), 2 . 20 ( s , 6h , ch 3 ), 3 . 55 ( s , 4h , ch 2 ), 7 . 30 ( d , 1h , j = 1 . 6 hz ), 7 . 67 ( d , 2h , j = 1 . 6 hz ), 10 . 03 ( s , 1h , cho ). meso - tetra [ bis - 3 , 5 -( 1 - methyl - o - carboranyl ) methylphenyl ] porphyrin ( 24 ): a solution of aldehyde 23 ( 0 . 243 g , 0 . 54 mmol ) and freshly distilled pyrrole ( 0 . 050 ml g , 0 . 72 mmol ) in dry dichloromethane ( 55 ml ) was purged with argon for 15 minutes . tfa ( 0 . 03 ml , 0 . 377 mmol ) was added and the final solution was stirred at room temperature overnight ( until complete disappearance of the starting aldehyde and formation of 2 new spots by tlc ). after oxidation with p - chloranil ( 0 . 102 g , 0 . 41 mmol ) for 6 hours at room temperature , the final reaction mixture was washed once with an aqueous saturated solution of nahco 3 and once with water , before being dried over anhydrous na 2 so 4 . the residue obtained after removal of the solvent was purified by column chromatography using dichloromethane / petroleum ether 1 : 2 for elution . the porphyrin fraction obtained was recrystallized from dichloromethane / methanol , to give 0 . 30 g ( 12 % yield ) of the title compound ; ms m / e 1977 . 3 1 h - nmr ( d - tfa / cdcl 3 ) δ ppm : − 0 . 80 ( br , nh ), 1 . 5 - 3 . 1 ( br , 80h , bh ), 2 . 31 ( s , 24h , ch 3 ), 3 . 91 ( s , 16h , ch 2 ), 7 . 72 ( s , 4h ), 8 . 33 ( s , 8h ), 8 . 74 ( s , 8h , β - h ). 5 , 15 - bis [ bis - 3 , 5 -( 1 - methyl - o - carboranyl ) methylphenyl ] porphyrin ( 26 ): a solution of aldehyde 23 ( 0 . 446 g , 1 . 00 mmol ) and dipyrromethane 25 ( 0 . 146 g , 1 . 00 mmol ) in dry dichloromethane ( 100 ml ) was purged with argon for 15 minutes and cooled down to 0 ° c . tfa ( 0 . 05 ml , 0 . 629 mmol ) was added to the solution and the final mixture was stirred at 0 ° c . for 2 hours and then at room temperature overnight . after oxidation with p - chloranil ( 0 . 277 g , 1 . 13 mmol ) for 6 hours at room temperature , the final reaction mixture was washed once with an aqueous saturated solution of nahco 3 , once with water , and once with brine , before being dried over anhydrous mgso 4 . the residue obtained after removal of the solvent was purified by column chromatography ( alumina ) using dichloromethane for elution . the porphyrin fraction obtained was recrystallized from acetone to give 33 . 6 % yield ( 0 . 192 g ) of the title compound ; ms m / e 1144 . 0 ; 1 h - nmr ( d - tfa / cdcl 3 ) δ ppm : − 1 . 92 ( br , nh ), 1 . 4 - 3 . 2 ( br , 40h , bh ), 2 . 30 ( s , 12h , ch 3 ), 3 . 89 ( s , 8h , ch 2 ), 7 . 71 ( s , 2h ), 8 . 34 ( s , 4h ) β - h , j = 4 . 5 hz ), 9 . 61 ( d , 4h , β - h , j = 4 . 5 hz ), 10 . 98 ( s , 2h , meso - h ). 5 , 15 - bis [ bis - 3 , 5 -( 1 - methyl - nido - carboranyl ) methylphenyl ] porphyrin tetrapotassium salt ( 27 ): porphyrin 26 ( 0 . 100 g , 0 . 087 mmol ) was dissolved in a 3 : 1 mixture of pyridine and piperidine ( 4 . 0 ml ), and stirred at room temperature in the dark for 36 hours , under argon . the solvent was completely removed under vacuum , the residue re - dissolved in a 60 % acetone aqueous solution and passed . slowly through a dowex 50w2 - 100 resin in the potassium form . the porphyrin , fraction was collected , dried under vacuum , re - dissolved in a 30 % acetone aqueous solution and again passed through the ion - exchange resin . after removal of the solvent under vacuum , the tetraanionic porphyrin was recrystallized from methanol / diethyl ether , yielding 0 . 102 g ( 92 . 8 % yield ) of the title compound . 1 h - nmr ( cd 3 cocd 3 ) δ ppm : − 2 . 84 ( s , 2h , nh ), − 2 . 45 to − 1 . 85 ( br , 4h , bh ), 0 . 9 - 2 . 4 ( br , 32h , bh ), 1 . 66 ( s , 12h , ch 3 ), 3 . 52 ( s , 8h , ch 2 ), 7 . 67 ( s , 1h , arh ), 7 . 74 ( s , 1h , arh ), 8 . 37 ( s , 4h , arh ), 9 . 53 ( dd , 4h , β - h ), 9 . 61 ( dd , 4h , β - h ), 10 . 58 ( s , 2h , meso - h ). uv - vis ( acetone ) λ max : 406 nm ( ε 312 , 600 ), 502 ( 13 , 400 ), 536 ( 7 , 800 ), 576 ( 6 , 100 ), 630 ( 3 , 100 ). zn ( ii )- 5 , 15 - bis [ bis - 3 , 5 -( 1 - methyl - o - carboranyl ) methylphenyl ] porphyrin ( 28 ): to a solution of porphyrin 26 ( 0 . 065 g , 0 . 057 mmol ) in dichloromethane ( 100 ml ) and thf ( 10 ml ), was added zncl 2 . 2h 2 o ( 0 . 031 g , 0 . 288 mmol ), and the final mixture was stirred at room temperature under argon overnight . the mixture was then washed once with water , dried over anhydrous na 2 so 4 , and the solvent evaporated under vacuum . the residue was purified by column chromatography ( dichloromethane / cyclohexane 2 : 1 ), the pink color fraction collected and recrystallized from dichloromethane / methanol , to give 0 . 061 g ( 89 . x % yield ) of the title compound ; ms ( maldi ) m / e 1206 . 6 . 1 h - nmr ( cdcl 3 ) δ ppm : 1 . 4 - 3 . 0 ( br , 40h , bh ), 2 . 11 ( s , 12h , ch 3 ), 3 . 64 ( s , 8h , ch 2 ) 7 . 33 ( s , 2h , arh ), 7 . 98 ( s , 4h , arh ), 8 . 98 ( d , 4h , β - h , j = 4 . 5 hz ), 9 . 41 ( d , 4h , β - h , j = 4 . 5 hz ), 10 . 25 ( s , 2h , meso - h ). zn ( ii )- 5 , 15 - bis [ bis - 3 , 5 -( 1 - methyl - nido - carboranyl ) methylphenyl ] porphyrin tetrapotassium salt ( 29 ): the zn ( ii ) complex 28 ( 0 . 050 g , 0 . 041 mmol ) was dissolved in a 3 : 1 mixture of pyridine and piperidine ( 4 . 0 ml ), and stirred at room temperature in the dark for 36 hours , under argon . the solvent was completely removed under vacuum , the residue redissolved in a 60 % acetone aqueous solution and passed slowly through a dowex 50w2 - 100 resin in the potassium form . the porphyrin fraction was collected , dried under vacuum , re - dissolved in a 30 % acetone aqueous solution and again passed through the ion - exchange resin . after removal of the solvent under vacuum , the tetraanionic porphyrin was recrystallized from methanol / diethyl ether , yielding 0 . 052 g ( 94 . 8 % yield ) of the title compound ; 1 h - nmr ( cd 3 cocd 3 ) δ ppm : − 2 . 45 to − 1 . 85 ( br , 4h , bh ), 0 . 9 - 2 . 4 ( br , 32h , bh ), 1 . 65 ( s , 12h , ch 3 ), 3 . 50 ( s , 8h , ch 2 ), 7 . 66 ( s , 1h , arh ), 7 . 73 ( s , 1h , arh ), 8 . 28 ( s , 4h , arh ), 9 . 41 ( dd , 4h , β - h ), 9 . 47 ( dd , 4h , β - h ), 10 . 33 ( s , 2h , meso - h ). uv - vis ( acetone ) λ max : 412 nm ( ε 263 , 100 ), 496 ( 1 , 400 ), 542 ( 9 , 900 ), 580 ( 1 , 070 ), ms ( maldi ) m / e 1319 . 4 . the zn ( ii ) complex of carboranyl compound 30 of fig7 bearing four hydrophobic o - carboranes and four hydrophilic 3 - hydroxypropyl side chains , was prepared from dipyrromethane 31 and benzaldehyde 23 , in 28 % overall yield . the benzyl ester groups of 31 were removed by catalytic hydrogenation ( h 2 — pd / c ), followed by decarboxylation using trifluoroacetic acid ( tfa ). condensation of the resulting 1 , 9 - diunsubstituted dipyrromethane with benzaldehyde 23 , using lindsey - type conditions ( tfa as the acid catalyst and p - chloranil as the oxidizing agent ), produced a tetra - propionic ester porphyrin in 40 % yield . metalation of this compound using zinc ( ii ) chloride in dichloromethane , at room temperature , quantitatively produced the corresponding zn ( ii ) porphyrin . reduction of the methyl ester groups with 5 . 2 equivalents of lithium aluminum hydride in tetrahydrofuran at 0 ° c ., gave the zn ( ii ) complex of porphyrin 30 in 70 % yield . the zn ( ii ) complex of 30 is soluble in methanol but only partially soluble in water . in vitro studies using rat 9l gliosarcoma cells , mouse b16 melanoma cells and human u - 373mg glioblastoma cells have been performed . we found that all compounds studied have very low dark cytoxicities , are readily taken up and retained by cells and localize in specific cell organelles , mostly in close proximity to the cell nucleus . our biological results to date indicate that these compounds have very low in vivo toxicities . so far we have determined maximum tolerated doses ( mtd ) for 8 of our compounds using healthy female balb / c mice , and for all compounds tested we found mtd & gt ; 300 mg per kg of body weight . we have also done a biodistribution study with 2 of our compounds , using male fisher 344 rats bearing 9l glioma tumors , and achieved tumor to normal brain boron concentration ratios of 5 and higher . this compares favorably with drugs currently in bnct clinical trials — bsh and bpa — which both show lower selectivities , i . e . smaller ratios . human glioblastoma u373 mg and mouse melanoma b16 cells were obtained from atcc . the rat gliosarcoma line was kindly provided by the ucsf brain tumor research group . all cells were maintained in log phase monolayer cultures with rpmi 1640 supplemented with 10 % fetal bovine and 2 mm glutamine . cells were seeded in 96 - well culture plates , allowed to settle and attach for 24 - 48 hours , and then triplicate wells were exposed to two fold serial dilutions of test compounds at concentrations up to 250 μm . compounds 4 , 6 , 10 , and the zn ( ii ) complex of 10 in crystalline form were carefully weighed and dissolved in 100 % dmso to prepare stock solutions ; subsequent dilutions were done directly into the culture medium just prior to administration to cells . after short term ( 2 hours ) or long term ( 24 - 48 hours ) exposure , cells were washed and wells refilled with fresh culture medium . for dark toxicity trials cells were allowed to proliferate for an additional 48 - 72 hours . for phototoxicity trials , washed cells were irradiated for 10 minutes with broad spectrum ( 600 - 700 nm ) red light and then returned to an incubator for 48 - 72 hours . exposure to drug for 2 hours followed by drug wash - out did not inhibit proliferation of any of the three cells types . exposure for 24 hours was inhibitory only at higher concentrations ( ic 50 -≧ 150 μm ) for 9l and u - 373 mg cells , but b16 viability was unaffected . whereas the metal free porphyrins 4 and 10 display nearly identical ic 50 values (˜ 150 μm ) in the affected cells , their zn ( ii ) complexes were found to be about 20 % less toxic ( ic 50 ˜ 180 - 185 μm ), thus , the nido - carboranylporphyrin compounds of the present invention display low dark toxicity . for carboranylprorphyrin 4 , irradiation with broad spectrum light caused cytotoxicity at 2 hours ( ic 50 = 50 μm ) and 24 hours exposure ( ic 50 = 1 . 5 μm ). as observed for the dark toxicity experiments , the corresponding zn ( ii ) complex 6 was about 20 - fold less phototoxic . these phototoxicity results indicate that the carboranylporyphin compounds of the present invention would be active in pdt . as with dark toxicity , b16 cells were more resistant that the other two cell types . the concentration - dependent uptake of compounds 4 , 6 , 10 and the corresponding zn ( ii ) complex of 10 was investigated in cells exposed to 1 , 5 , and 10 μm of the porphyrins for 24 hours . the concentration of intracellular - bound porphyrin was determined by chemical extraction of washed cell monolayers , followed by spectrophotometric and / or imp - ms determinations . the uptake values for 9l and u - 373mg cells were very similar and exceeded that of b16 cells . the porphyrin accumulation invariably increased with increasing exogenous drug concentration and the uptake of nido - carboranylprophyrins 4 and 10 was approximately 4 - times greater than that of the corresponding zn ( ii ) complexes . the uptake of carboranylporphyrins by log phase cells was also shown to be time - dependent . cells exposed to 5 μm drug concentrations contained increasing amounts of extractable porphyrin over the 24 - hour uptake period examined in these studies . while 9l and u - 373mg cells had similar uptake levels , b16 cell cultures consistently accumulated 60 - 70 % less drug on a per cell basis . cell - bound porphyrin that could not be removed by rinsing the cells with hanks balanced salt solution ( hbss ) was detectable as early as 1 hour after introducing drug to the cell culture . in experiments using 9l cell s exposed to a 10 μm concentration of free - base porphyrins 4 and 10 , intracellular levels & gt ; 60 μg of boron per billion cells ( or gram of wet tissue ) were achieved , following a 24 hour exposure to drug . confocal fluorescence microscopy was used to examine the intracellular localization of nido - carboranylporphyrin 4 in live cells . rat 9l tumor cells and human normal keratinocyte line hacat were used in these studies . hacat cells were included in these particular experiments because they adhere and spread nicely on glass cover slips , thus facilitating the imaging process . cells exposed to 2 μm concentration of porphyrin 4 for either 6 or 24 hours were examined at a magnification of 200 × for intracellular fluorescence using excitation / emission wavelengths optimized for this type of compound . the 9l and hacat cells showed a similar intracellular fluorescent pattem . in both cases , 100 % of the cells were labeled and the cells exposed to drug for 24 hours were slightly brighter than those exposed for 6 hours . the punctuate fluorescence was predominantly perinuclear , with many cells having an additional local area of concentration that appeared to be adjacent to the nuclear membrane . no fluorescent signal was detectable in the plasma membranes of isolated individual cells nor in the intercellular junctions of confluent cells . male fisher 344 rats with bilateral subcutaneous 9l tumors were injected i . v . 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