Stannylene derivatives in glycoside synthesis. Application to the synthesis of the blood-group B antigenic determinant

Abstract

Condensation of benzyl 2,6-di-O-benzyl-3,4-O-dibutylstannylene-α-D-galactopyranoside (9) with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide in the presence of stannic chloride occurred at the 3- and 4-positions to give the branched trisaccharide (11) with two β-anomeric linkages. A (1→3)-linked ortho ester (13) was selectively obtained by reaction of compound (9) with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl chloride in NN′N″-hexamethylphosphorotriamide; when the solvent was dichloroethane, a mixture of the ortho ester (13) and a branched product (15) with two ortho ester residues was obtained in a 2 : 1 ratio. 2,3,4,6-Tetra-O-benzyl-α-D-galactopyranosyl chloride selectively reacts at the 3-position of compound (9) in the presence of lithium iodide in NN′N″-hexamethylphosphorotriamide to give a 9 : 1 mixture of the α- and β-(1→3)-linked disaccharides (16) and (18) in 82% yield. The latter conditions were applied to the synthesis of the blood-group B antigenic determinant starting from the 2-O-allyl stannylene compound (10). Coupling of 2,3,4-tri-O-benzyl-α-L-fucopyranosyl bromide under bromide-ion catalysis occurred at the 2-position of disaccharide (26) in 32% yield. Hydrogenation afforded the free trisaccharide (29), α-L-Fuc-(1→2)-[α-D-Gal-(1→3)]-D-Gal.