ta通过2硫缩醛制备KDO及其2糖.pdfVIP

TETRAHEDRON: ASYMMETRY Pergamon Tetrahedron: Asymmetry 11 (2000) 3737–3746 Synthetic approach to 3-deoxy-D-manno -oct-2-ulosonic acid (Kdo) -disaccharides via a ketene dithioacetal† Jacek Ml ynarski and Anna Banaszek* Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44 52, 01 -224 Warsaw, Poland Received 27 July 2000; accepted 14 September 2000 Abstract A unique strategy for the synthesis of Kdo -disaccharides based on the ketene dithioacetal 4 (precursor of Kdo) as a ‘glycosyl donor’ has been developed. Direct, fully stereoselective addition of 6-, 7-, or 8-OH unprotected sugar units to the exo -anomeric double bond in 4, promoted by trimethylsilyl triflate, led to the corresponding O-disaccharides 12 with the dithioacetal residue intact. Subsequent hydrolysis of the later afforded the title compounds in high yields. © 2000 Elsevier Science Ltd. All rights reserved. 1. Introduction 3-Deoxy-D-manno -oct-2-ulosonic acid (Kdo) is a key component of the core region lipo- polysaccharides (LPS) of Gram-negative bacteria.1 Kdo--(2 6)-GlcN disaccharide forms the glycosidic linkage between lipid A and inner core region,2 which is composed of Kdo and L- and D-glycero -D-manno -heptoses.3 Kdo units in this region are connected by -(2 4) linkage, forming trisaccharides,3 or by -(2 8) linkage, as it occurs in the terminal part of LPS of Chlamydia.4 Synthetic analogues of Kdo and its disaccharides have attracted interest as potential inhibitors of Kdo inco