Oxygen-sulfur exchange at the C-4 carbonyl of several modified pyrimidine nucleosides, including 3 '-azido-3 '-deoxythymidine (AZT), is described in an effort to enhance the lipophilicity and, thereby, the delivery to the central nervous system of the sulfur analogues without compromising the anti-HIV activities of the parental structures. Preparation of 3'- azido-3'-deoxy-4-thiothymidine (3) proceeded from 4-thiothymidine (1) and utilized the ...
