An approach to branched-chain amino sugars, particularly derivatives of -vancosamine (3-amino-2,3,6-trideoxy-3-C-methyl--lyxo-hexose) and its enantiomer, via the cyanohydrin route

Methyl 4,6-O-benzylidene-2-deoxy-α--erythro-hexopyranosid-3-ulose reacted with potassium cyanide under equilibrating conditions to give, initially, methyl 4,6-O-benzylidene-3-C-cyano-2-deoxy-α--ribo-hexopyranoside (7), which, because it reverted slowly to the thermodynamically stable -arabino isomer, could be crystallised directly from the reaction mixture. The mesylate derived from the kinetic product 7 could be converted by published procedures into methyl 3-acetamido-2,3,6-trideoxy-3-C-methyl-α--arabino-hexopyranoside, which was transformed into methyl N-acetyl-α--vancosaminide on inversion of the configuration at C-4. A related approach employing methyl 2,6-dideoxy-4-O-methoxymethyl-α--erythro-hexopyranosid-3-ulose gave the kinetic cyanohydrin and thence, via the spiro-aziridine 27, methyl 3-acetamido-2,3,6-trideoxy-3-C-methyl-α--arabino-hexopyranoside, a known precursor of methyl N-acetyl-α--vancosaminide.