3'-Azido-3'-deoxy-5'-O-isonicotinoylthymidine AIDS-070696 AIDS070696 AZT-Iso AZT-prodrug Isonicotinic acid 3-azido-5-(5-methyl-2,4-dioxo-tetrahydro-pyrimidin-1-yl)-tetrahydro-furan-2-ylmethyl ester-