Synthesis of crystalline derivatives of 6-deoxy-d-allo- and -l-talo-furanosyl bromide suitable for nucleoside synthesis

6-Deoxy-2,3,5-tri-O-(p-nitrobenzoyl)-β-d-allo- and -α-l-talo-furanosyl bromide (6 and 11) have been synthesized from methyl 2,3-O-isopropylidene-β-d-ribo-pentodialdo-1,4-furanoside (1). Treatment of 1 with methyl Grignard reagent, followed by (p-nitrobenzoyl)ation, afforded two 5-epimers, methyl 6-deoxy-2,3-O-isopropylidene-5-O-(p-nitrobenzoyl)-β-d-allo- and -α-l-talo-furanosides (3 and 8) which were fractionally recrystallized. The l-talo isomer (8) separated first, and was treated with acid to remove the isopropylidene group, the product (p-nitrobenzoyl)ated, and the ester reacted with hydrogen bromide in acetic acid, to afford crystalline compound 11. The mother liquor from the fractional recrystallization was treated with acid, whereby methyl 6-deoxy-5-O-p-nitrobenzoyl)-d-allofuranoside was isolated. It was (p-nitrobenzoyl)ated, and the ester treated with hydrogen bromide in acetic acid, to afford crystalline bromide 6.