6-Azathymidine-4'-thionucleosides: synthesis and antiviral evaluation

The synthesis of dideoxy-6-azathymidine 4'-thionucleoside 1-(2,3-dideoxy-4-thio-beta-D-erythro-pentofuranosyl)-(6-azathymidine) (2), and the L-nucleoside, 1-(4-thio-beta-L-erythro-pentofuranosyl)-(6-azathymidine) (3) and their evaluation against a wide panel of antiviral assays are described. The L-thionucleoside (3) was devoid of antiviral activity. The dideoxy-thionucleoside (2) was moderately active against vaccinia virus (VV) and the herpes simplex virus strains HSV-1 (strain KOS) and HSV-2 (strain G) (MIC 12 microM) and retained inhibitory activity vs a thymidine kinase-deficient strain HSV-1/TK(-), suggesting that (2) is not dependent on viral TK-catalysed phosphorylation for antiviral activity and/or may use an alternative metabolic activation pathway.