Synthesis of 4-nitrophenyl beta-D-fucofuranoside and beta-D-fucofuranosyl-(1 -> 3)-D-mannopyranose: modified substrates for studies on catalytic requirements of beta-D-galactofuranosidase

Syntheses of 4-nitrophenyl beta-D-fucofuranoside (6) and beta-D-fucofuranos yl-(l --> 3)-D-mannopyranose (10) are reported. These compounds, as analogu es of galactofuranosides, were used for studying the influence of the hydro xyl group at C-6 in the interaction of the substrate with beta-D-galactofur anosidase. For the synthesis of the fucofuranosides, 2,3,5-tri-O-benzoyl-6- bromo-6-deoxy-D-galactono-1,4-lactone (1) was the key intermediate, which u pon reduction of the lactone group with diisoamylborane, acetylation of the anomeric hydroxyl group, and catalytic hydrogenoiysis of the bromine at C- 6, led to 1-O-acetyl-2,3,5-tri-O-benzoyl-alpha,beta-D-fucofuranose (4), a c onvenient derivative for the preparation of fucofuranosides. Compound 4 was glycosylated in the presence of SnCl4, either with 4-nitrophenol for the p reparation of 6, or with 2,5,6-tri-O-benzoyl-D-mannono-1,4-lactone (7), for the synthesis of disaccharide 10, via the glycosyl-aldonolactone approach. The synthetic route developed for the beta-D-fucofuranosides is simple and efficient. Compound 6 was not hydrolyzed by incubation with the exo beta-D -galactofuranosidase from Penicillium, fellutanum, showing that HO-6 is ess ential for interaction of the substrate with the enzyme. (C) 2000 Elsevier Science Ltd. All rights reserved.