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

Abstract

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.