Synthesis of 3-deoxy-D-manno-2-octulosonic acid (Kdo) and D-glycero-D-talo-2-octulosonic acid (Ko) and their α-glycosides

Reaction of 2,3:5,6-di-O-isopropylidene-D-mannofuranose 1 with C-2 lithio derivatives of glyoxylate mercaptal in the presence of MgBr2 afforded D-glycero-D-galacto-2-octulosonates 2 and 3, respectively. Their 3-O-deoxygenation led to Kdo. N-Iodosuccinimide treatment of 3 gave thioglycoside 11 directly, which was transformed into Ko derivative 12 via epimerisation of the 3-hydroxy group. 3-O-Benzoylation of 12 and then transformation into phosphite furnished 15, an efficient glycosyl donor. Reaction of 15 with 6-O-unprotected glucosamine derivative 22 as acceptor gave alpha-glycoside 23, which was successfully transformed either into Kdo-disaccharide 27 or into Ko-disaccharide 29. (C) 2000 Elsevier Science Ltd. All rights reserved.