SYNTHESIS OF 2-O-ETHYL ANALOGS OF 3'-AZIDO-2',3'-DIDEOXYURIDINE AND 3'-FLUORO-2',3'-DIDEOXYURIDINES AND EVALUATION OF THEIR BIOLOGICAL-ACTIVITY AGAINST HIV

2-O-Ethyluracil and 2-O-ethylthymine were silylated with 1,1,1,3,3,3-h examethyldisilazane and condensed in the presence of TMS triflate with 2,3-dideoxy-3-fluoro-D-erythro-pentofuranoside, 3-azido-2,3-dideoxy-D -erythro-pentofuranoside and dideoxy-3-phthalimido-beta-D-erythro-pent ofuranose furanose derivatives to give the corresponding 2-O-ethyl nuc leosides. Deprotection with saturated methanolic ammonia afforded the 2',3'-dideoxy-3'-fluoro-2-O-ethyluridines whereas 3'-azido-2',3'-dideo xy-3-O-ethyluridine was obtained by deprotection with tetrabutylammoni um fluoride in tetrahydrofuran. 3'-Amino-2',3'-dideoxy-3-O-ethyluridin e could be obtained only by treatment of the corresponding 3'-azido nu cleoside with triphenylphosphine in pyridine. 3'-Deoxy-2-O-ethyl-3'-fl uorothymidine (6b) showed moderate activity against HIV-1.