In order to obtain agenta with therapeutic indices superior to those of AZT, FLT, or D4T, several analogues of anti-HIV-1 nucleosides were synthesized. These include 2', 3'-dideoxy- 2', 3'-difluoro-5-methyluridine (13), ita arabino analogue 19, arabino-5-methylcytosine analogue 21, 3'-deoxy-2', 3'-didehydro-2'-fluorothymidine (25), Y-azido-2', 3'-dideoxy-2'- fluoro-5-methyluridine (29), 2'-azido-3'-fluoro-2', 3'-dideoxy-5-methyluridine (31), and 2', 3' ...