Synthesis of 2-O-, 3-O-, and 4-O-β-D-Glucopyranosyl-L-rhamnose, and of 2-O-β-D-Galactopyranosyl-L-rhamnose

Abstract

Reaction of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide with benzyl-α-L-rhamnopyranoside in the presence of silver carbonate yielded benzyl 2-O-, 3-O-, and 4-O-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl)-α-L-rhamnopyranosides in a molar ratio of 1.0:3.6:1.6. The products were separated by preparative t.l.c. Deacetylation followed by hydrogenolysis afforded the unsubstituted disaccharides. Proton magnetic resonance spectra of each derivative and methylation analysis of the disaccharide benzyl glycosides provided confirmation of the structures. The preparation, by a similar method, of benzyl 2-O-β-D-galactopyranosyl-α-L-rhamnopyranoside, characterized as its crystalline acetate, is also described.