Synthesis of methyl 4-acetamido-N-acetyl-4-deoxy-α- and β-4-epi-neuraminic acids

Methyl 5-acetamido-7,8,9-tri-O-acetyl-4-azido-2,3-didehydro-2,3,4,5-tetradeoxy-d-glycero-d-talo-nonulopyranosonate with N-bromosuccinimide in methanol gave methyl (methyl 5-acetamido-7,8,9-tri-O-acetyl-4-azido-3-bromo-3,4,5-trideoxy-α-d-glycero-d-talo-nonulopyranosid)onate and methyl (methyl 5-acetamido-7,8,9-tri-O-acetyl-4-azido-3-bromo-3,4,5-trideoxy-β-d-glycero-d-talo-nonulopyranosid)onate, which on reductive acetylation with H2PdC in acetic anhydride-ethyl acetate yielded the corresponding 4-acetamido analogues. Debromination with Bu3SnHAIBN in toluene, followed by hydrolysis, gave methyl 4-acetamido-N-acetyl-4-deoxy-α-and β-4-epi-neuraminic acids.