REACTIONS OF PARTIAL ACYLATED ALDOHEXOPYRANOSIDES .7. AN IMPROVED SYNTHESIS OF EVERNITROSE

Evernitrose (13,2,3,6-trideoxy-3-C-methyl-4-O-methyl-3-nitro-L-arabino-hexopyranose), a constituent of the everninomicin oligosaccharide antibiotics, was synthesised from methyl 2,4-di-O-acetyl-3,6-dideoxy-3-C-methyl-3-nitro-alpha-L-gluco-hexopyranoside (2) in a yield of 16% on a gram scale and avoiding chromatographic separations. Nitro diacetate 2, obtained by the dialdehyde nitroethane cyclisation of methyl alpha-L-rhamnopyranoside (1), was subjected in sequence to hydrogenolysis, N-acetylation, regioselective 2-O-pivaloylation, and 4-O-methylation, to give methyl 3-acetamido-3,6-dideoxy-3-C-methyl-4-O-methyl-2-O-pivaloyl-alpha-L-glucopyranoside (6). Photodeoxygenation (254 nm) of ester 6 in a mixture of hexamethylphosphoric triamide and water gave methyl 3-acetamido-2,3,6-trideoxy-3-C-methyl-4-O-methyl-alpha-L-arabino-hexopyranoside (8). Reductive deprotection of 8 afforded methyl 3-amino-2,3,6-trideoxy-3-C-methyl-4-O-methyl-alpha-L-arabino-hexopyranoside (9), a constituent 4 of antibiotic complex 13-384 component 5. Oxidation of 9 with 3-chloroperoxybenzoic acid furnished the methyl glycoside 11, hydrolysis of which gave 13. Reduction of 11 with zinc/ammonium chloride gave methyl 2,3,6-trideoxy-3-hydroxyamino-3-C-methyl-4-O-methyl-alpha-L-arabino-hexopyranoside (12). Whereas acetamido groups considerably enhanced the rate of photodeoxygenation, nitro groups were not compatible with the reaction conditions.