STANNYLENE DERIVATIVES IN GLYCOSIDE SYNTHESIS - APPLICATION TO THE SYNTHESIS OF THE BLOOD-GROUP-B ANTIGENIC DETERMINANT

Condensation of benzyl 2,6-di-O-benzyl-3,4-O-dibutylstannylene-.alpha.-D-galactopyranoside (9) with 2,3,4,6-tetra-O-acetyl-.alpha.-D-glucopyranosyl bromide in the presence of stannic chloride occurred at the 3- and 4-positions to give the branched trisaccharide (11) with 2 .beta.-anomeric linkages. A (1 .fwdarw. 3)-linked ortho ester (13) was selectively obtained by reaction of compound (9) with 2,3,4,6-tetra-O-acetyl-.beta.-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 2 ortho ester residues was obtained in a 2:1 ratio. 2,3,4,6-Tetra-O-benzyl-.alpha.-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 .alpha.- and .beta.-(1 .fwdarw. 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-.alpha.-L-fucopyranosyl bromide under bromide-ion catalysis occurred at the 2-position of disaccharide (26) in 32% yield. Hydrogenation afforded the free trisaccharide (29), .alpha.-L-Fuc-(1 .fwdarw. 2)-[.alpha.-D-Gal-(1 .fwdarw. 3)]-D-Gal.