(AZT, 1) as donor followed by deprotection gave 2, 6-diamino-9-(3-azido-2, 3-dideoxy-a-and- 0-D-erythro-pento-furanosy1) purines (3 and 4) in low yields. Selective 2'-O-tosylation of 2, 6- diamino-9-(/3-~-ribofuranosyl) purine (2, 6-diaminopurine riboside, DAPR, 5) followed by our lithium triethylborohydride promoted 1, 2-hydride rearrangement gave 2, 6-diamino-9-(2- deoxy-~-~-threo-pentofuranosyl) purine (7). Tritylation of 7 followed by mesylation at 03', ...