Extension of chains of 1-deoxy-1-nitroalditols by nitrile oxide cycloaddition. Synthesis of 4-N-substituted 3,4-didesoxy-2-ulosonic acids

Article abstract of DOI:10.1016/S0040-4020(98)00168-9

Treatment of protected nitroalditols 1a or 2 with silylenolpyruvate (3) or methyl acrylate leads via nitrile oxide cycloadditon to cyclo-tautomers of oximes, 5 or 4, respectively 4,5-dihydro-isoxazole 6. N-Acetyl-4-deoxy-4- (E/Z)-hydroxyimino-neuraminic acid (7) is obtained by deprotection of 4. Hydrogenation of 7 yields N-acetyl-4-amino-4-deoxy-neuraminic acid (9) and pentahydroxy-nononic acids 12a,b. The synthesis is useful for the chain extension of protected nitroalditols 13a and 20a, to give the corresponding oximes 15 and 22. This work provides a general method for the extension of sugar chains by three C-atoms and thus a novel synthesis of α-keto acids containing an oxime and amino function.