Branched-chain sugars. Part 10. Some approaches to the synthesis of L-evernitrose (2,3,6-trideoxy-3-C,4-O-dimethyl-3-nitro-L-arabino-hexopyranose)

Abstract

3-Acetamido-4-O-acetyl-3,6-dideoxy-3-C-methyl-L-glucal (6) reacted with methanol in the presence of boron trifluoride etherate to give a separable mixture of methyl 3-acetamido-4-O-acetyl-2,3,6-trideoxy-3-C-methyl-α-L-arabino-hexopyranoside (7) and the corresponding β-2-deoxyglycoside (8). The α-2-deoxyglycoside (7) can also be prepared, though less efficiently, by deoxygenation of methyl 3-acetamido-4-O-acetyl-3,6-dideoxy-3-C-methyl-α-L-mannopyranoside (12), which was obtained in three steps from methyl 3-acetamido-3,6-dideoxy-3-C-methyl-α-L-glucopyranoside (9). O-Deacetylation of the α-2-deoxyglycoside (7), followed by methylation of the resulting alcohol (15), gave methyl 3-acetamido-2,3,6-trideoxy-3-C,4-O-dimethyl-α-L-arabino-hexopyranoside (16), a precursor of the antibiotic sugar L-evernitrose (1). Another route to this precursor, via deoxygenation of methyl 3-acetamido-3,6-dideoxy-3-C,4-O-dimethyl-α-L-glucopyranoside (21) at C-2, was less satisfactory.

An attempt to convert methyl 3-acetamido-2,3,6-trideoxy-3-C-methyl-α-L-arabino-hexopyranoside (15) into a derivative (29) of L-vancosamine (3-amino-2,3,6-trideoxy-3-C-methyl-L-lyxo-hexose), by an oxidation-reduction sequence, was unsuccessful, since reduction of methyl 3-acetamido-2,3,6-trideoxy-3-C-methyl-α-L-threohexopyranosid-4-ulose (30) with sodium borohydride in methanol regenerated (15).