CHAIN LENGTHENING OF 1-DEOXY-1-NITROAIDIT OLS BY NITRILE OXIDE CYCLOADDITION - SYNTHESIS OF 4-N-SUBSTITUTED 3,4-DIDEOXY-2-ULOSONIC ACIDS

Treatment of protected nitroalditols 1a or 2 with silylenolpyruvate (3 ) or methyl acrylate leads via nitrile oxide cycloadditon to cycle-tau tomers of oximes, 5 or 4, respectively 4,5-dihydro-isoxazole 6. N-Acet yl-4-deoxy-4-(E/Z)-hydroxyimino-neuraminic acid (7) is obtained by dep rotection of 4. Hydrogenation of 7 yields N-acetyl-4-amino-4-deoxy-neu raminic acid (9) and pentahydroxy-nononic acids 12a,b. The synthesis i s useful for the chain extension of protected nitroalditols 13a and 20 a, to give the corresponding oximes 15 and 22. This work provides a ge neral method for the extension of sugar chains by three C-atoms and th us a novel synthesis of cr-keto acids containing an oxime and amino fu nction. (C) 1998 Elsevier Science Ltd. All rights reserved.