the arylsilane intermediate of this invention is prepared quickly and conveniently from conventional starting materials , in a high degree of purity . it is quickly converted to the binding ligands described in the parent application for tracing ( spect or pet ) if desired , by iodination using icl . the invention is exemplified herein with the identities of substituents r 1 - r 5 , a and n , selected so as to give the prototypical and commercialized radioactive binding ligand rti - 55 , which has the formula ## str6 ## as those of skill in the art will recognize , the identities for r 1 - r 5 , y and a may be readily substituted into the starting materials used to prepared rti - w148 - 1 , as the starting material , the methylester , is readily substituted on , see , e . g ., clarke , j . med . chem . 16 , 1260 ( 1973 ). p - iodophenyltrimethylsilane was synthesized according to literature procedures . 1 the aryl halide ( 1 . 633 g , 6 . 02 mmol ) was added gradually to mg turnings ( 0 . 317 g , 13 . 04 mmol ) and an i 2 crystal under n 2 . once the vigorous reaction had subsided , the grignard was refluxed for 0 . 5 hr . the reagent was cooled to room temperature and transferred into a round bottom flask under n 2 . the standard procedure for the synthesis of other 3β -( phenyl ) tropane analogues was used as follows : 2 the reaction vessel was cooled to - 40 ° c . and a solution of anhydroecgonine methyl ester ( 0 . 226 g , 1 . 24 mmol ) in 15 ml anhydrous ether was added dropwise over 10 min . the reaction was cooled to - 78 ° c . and a solution of trifluoroacetic acid ( 1 ml ) in 10 ml eto was added dropwise over 10 minutes . the reaction mixture was warmed to 0 ° c . and water ( 25 ml ) was added . if necessary , the aqueous layer was acidified to ph 2 ( with conc . hcl ) and the layers were separated . the aqueous layer was basified to ph 11 with nh 4 oh and filtered through celite . the aqueous layer was extracted with et 2 o ( 4 × 50 ml ). the organic layers were combined and dried over mgso 4 . the solvent was removed under reduced pressure to afford 0 . 40 g of a cloudy oil . purification was accomplished using flash chromatography ( 9 / 1 et 2 o / et 3 n diluted with 50 % hexanes ). the fractions were pooled to give 0 . 202 g ( 49 . 3 % yield ) of the rti - w148 - 1 as a white solid . a second fraction ( 0 . 023 g ) contained a mixture of the α and β - isomers . recrystallization of the β - isomer ( 0 . 182 g ) from petroleum ether afforded 0 . 155 g of product , mp . 117 - 119 ° c . to a solution of 58 mg of rti - 148 - 1 in 4 ml of methanol was added 124 mg of silver tetrafluoroborate . the mixture was cooled to 0 ° c ., and 0 . 64 ml of a 1 . 0 m solution of icl in methanol was added . the reaction was allowed to warm to 25 ° c . and kept at that temperature for 2 h . the reaction mixture was diluted with water , basified with nh 4 oh , and extracted with ch 2 cl 2 . evaporation of the solvent gave 70 mg of rti - 55 . flash chromatography gave 60 mg ( 90 %) of rti - 55 . this invention has been described in both generic terms , and by reference to a specific description . no specific description or example is considered binding , unless so identified . alternate forms and conditions will occur to those of ordinary skill in the art , without the exercise of inventive faculty , and remain within the scope of this invention , save as limited by the claims set forth below .
an improved method for preparation of cocaine receptor binding ligands is provided . the method calls for the preparation of the silylaryl intermediate prepared from phenyl trimethylsilane and a anhydroecgonine methyl ester appropriately substituted . the intermediate is prepared in high purity and can be directly converted to the binding ligand by iodine substitution .