Preparative route to N-glycolylneuraminic acid phenyl 2-thioglycoside donor and synthesis of Neu5Gc-alpha-(2 -> 3 ')-lactosamine 3-aminopropyl glycoside

The spacer-armed trisaccharide, Neu5Ge-alpha-(2-->3')-lactosamine 3-aminopropyl glycoside, was synthesized by regio- and stereoselective sialylation of the suitably protected triol acceptor. 3-trifluoroacetamidopropyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-(6-O-benzyl-beta-D-galactopyranosyl)-beta-D-glucopyranoside, with the donor methyl [phenyl 5-acetoxyacetamido-4.7,8.9-tetra-O-acetyl-3.5-dideoxy-2-thio-D-glycero-alpha,beta-D-galacto-2-nonulopyranosid]onate. The donor was obtained. in turn, from methyl [phenyl 5-acetamido-4,7,8.9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-alpha,beta-D-galacto-2-nonulopyranosid]onate by N-tert-butoxycarbonylation of the acetamido group followed by total N- and O-deacetylation, per-O-acetylation, subsequent Boc group removal, and N-acetoxyacetylation. (C) 2002 Elsevier Science Ltd. All rights reserved.