ANOMERIC O-ALKYLATION .7. O-ALKYLATION AT THE ANOMERIC CENTER FOR THE STEREOSELECTIVE SYNTHESIS OF KDO-ALPHA-GLYCOSIDES

O-Alkylation at the anomeric centre of the dianion of 4,5:7,8-di-O-cyclohexylidene-3-deoxy-N-methyl-α-d-manno- octulopyranosonamide (1) with several triflates led diastereoselectively to the α-glycosides. In this way, lipopolysaccharide building-blocks containing α-Kdo-(2→6)-GlcN and α-Kdo-(2→6)-β-GlcN-(1→6)-GlcN moieties were obtained and deployed in the synthesis of decyl 4,5,7,8-tetra-O-acetyl-3-deoxy-N-methyl-α-d-manno-2- octulopyranosidonamide (18), 2,3-di-O-tetradecanoyl-d-glycer-1-yl 4,5,7,8-tetra-O-acetyl-3-deoxy-N-methyl-α-d-manno-2- octulopyranosid-onamide (22), methyl 2,3,4-tri-O-acetyl-6-O-(methyl 4,5,7,8-tetra-O-acetyl-3-deoxy-α-d-manno-2- octulopyranosylonate)-α-d-glucopyranoside (28), 1-O-acetyl-2-deoxy-6-O-(methyl 4,5,7,8-tetra-O-acetyl-3-deoxy-α-d-manno-2-octulopyranosylonate)-2-tetradecanoylamino-α-d-glucopyranose (33), tert-butyldimethylsilyl O-(methyl 4,5:7,8-di-O-cyclohexylidene-3-deoxy-α-d-manno-2-octulopyranosylonate)-(2→6)- O-(3,4-di-O-benzyl-2-deoxy-2-tetradecanoylamino-β-d-glucopyranosyl)-(1→6)-3,4-di-O-benzyl-2-deoxy-2-tetradecanoylamino-α-d- glucopyranoside (36). © 1990.