Branched-chain sugars. Part 17. A synthesis of L-rubranitrose (2,3,6-trideoxy-3-C-methyl-4-O-methyl-3-nitro-L-xylo-hexopyranose)

Abstract

L-Rubranitrose (2,3,6-trideoxy-3-C-methyl-4-O-methyl-3-nitro-L-xylo-hexopyranose)(4) has been elaborated from methyl 3-acetamido-2,3,6-trideoxy-3-C-methyl-α-L-xylo-hexopyranoside (27). N-Deacetylation of the corresponding 4-O-methyl derivative (26), with calcium in liquid ammonia, afforded the amino sugar (25), which was then oxidised to methyl 2,3,6-trideoxy-3-C-methyl-4-O-methyl-3-nitro-α-L-xylo-hexopyranoside (28). Acidic hydrolysis of the latter compound gave L-rubranitrose (4), which proved to be enantiomeric with the novel methyl-branched nitro sugar found in the antibiotic rubradirin.

In another approach to L-rubranitrose (4), methyl 2,6-dideoxy-4-O-methyl-α-L-threo-hexopyranosid-3-ulose (11) was shown to react with cyanide ion under equilibrating conditions to give methyl 3-C-cyano-2,6-dideoxy-4-O-methyl-α-L-xylo-hexopyranoside (12), whereas the corresponding L-lyxo cyanohydrin (22) is the kinetically favoured product.