First Total Synthesis of 5'- O -α-d-Glucopyranosyl Tubercidin

The first total synthesis of 5'- -α-d-glucopyranosyl tubercidin was successfully developed. It is a structurally unique disaccharide 7-deazapurine nucleoside exhibiting fungicidal activity, and was isolated from blue-green algae. The total synthesis was accomplished in eight steps with 27% overall yield from commercially available 1- -acetyl-2,3,5-tri- -benzoyl-β-d-ribose. The key step involves stereoselective α- -glycosylation of the corresponding 7-bromo-6-chloro-2',3'- -isopropylidene-β-d-tubercidin with 2,3,4,6-tetra- -benzyl-glucopyranosyl trichloroacetimidate. All spectra are in accordance with the reported data for natural 5'- -α-d-glucopyranosyl tubercidin. Meanwhile, 5'- -β-d-glucopyranosyl tubercidin was also prepared using the same strategy.