SYNTHESES OF [2-H-2]-5-ETHYNYL-1-(BETA-D-RIDOFURANOSYL) IMIDAZOLE-4-CARBOXAMIDE AND -H-3]-BETA-D-RIBOFURANOSYL)IMIDAZOLE-4-CARBOXAMIDE (EICAR)

Metallation of silyl-beta-D-ribofuranosyl)imidazole-4-carboxamide ((1) under bar) using n-BuLi, deuteration with deuterium oxide and removal of the tert-butyldimethylsilyl protecting groups using tetrabutylammo nium fluroide yielded yl-1-(beta-D-ribofuranosyl)imidazole-4-carboxami de (<(5a)under bar>, 75 atom % deuterium). Regiospecific deprotection of the masked aldehyde N,N'-diphenylethylenediamino synthon <(14)under bar> using DIAION PK212 ion-exchange resin (H+ form) yielded the alde hyde derivative (<(15)under bar>). Reduction of the aldehyde moiety of <(15)under bar> using excess [H-3]NaBH4 gave the carbinol product <(1 7)under bar>. Removal of the ribofuranosyl 2,3-isopropylidene protecti ng group from <(17)under bar> using 90% trifluoroacetic acid afforded -H-3]-beta-D-ribofuranosyl)imidazole-4-carboxamide (<(18)under bar>, 1 9% chemical yield, > 99% radiochemical purity, specific activity 1.56 Ci/mmol).