SYNTHESIS OF O-BETA-L-FUCOPYRANOSYL-(1-]3)-O-BETA-D-GALACTOPYRANOSYL-(1-]4)-D-GLUCOPYRANOSE (3'-O-BETA-L-FUCOPYRANOSYLLACTOSE)

Isopropylidenation of lactose with 2,2-dimethoxypropane in N,N-dimethylformamide afforded 4′,6′-O-isopropylidenelactose as the main product. Its constitution was proved by permethylation and hydrolysis giving 2,3-di-O-methyl-D-galactose. By standard procedures, the β-hexaacetate and the β-hexabenzoate of the cyclic acetal were obtained, and removal of the isopropylidene group gave 1,2,3,6,2′,3′-hexa-O-acetyl-β-lactose (4) and 1,2,3,6,2′,3′-hexa-O-benzoyl-α-lactose, respectively. Koenigs-Knorr condensation of 4 with 2,3,4-tri-O-acetyl-α-L-fucopyranosyl bromide involved an acetyl migration from O-3′ and gave a crystalline nonaacetate 6 (that could be acetylated to a decaacetate) of O-β-L-fucopyranosyl-(1→3)-O-β-D-galactopyranosyl-(1→4)-D-glucose (8). The free trisaccharide 8 was obtained from 6 by Zemplén deacetylation, and its constitution was established by permethylation, followed by hydrolysis which produced 2,4,6-tri-O-methyl-D-galactose. A simplified synthesis of the latter compound from methyl α-D-galactopyranoside is also described. © 1979.