One-pot synthesis of Lewis X oligosaccharide derivatives using "armed-disarmed" coupling method

A stereocontrolled synthesis of Le ^x oligosaccharide derivatives using a facile one-pot, two-step glycosylation based on the "Armed-Disarmed" concept are described. The first coupling of phenyl O-(2,6-di-O-benzoyl-3,4-O-isopropylidene-β-D-galactopyranosyl)-(1→4)- 2,6-di-O-benzoyl-1-thio-β-D-glucopyranoside (2) with phenyl 2,3,4-tri-O-benzyl-1-thio-β-L-fucopyranoside (3) using N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) gave the trisaccharide (8) which was subjected to the second condensation without purification with several acceptors such as ethyl 2,4,6-tri-O-benzyl-β-D-galactopyranoside (4), ethyl 2,6-di-O-benzoyl-β-D-galactopyranoside (5), ethyl O-(2,6-di-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl- β-D-glucopyranoside (6), and ethyl O-(2,6-di-O-benzoyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzoyl- β-D-glucopyranoside (7), to afford the desired Le ^x tetra- and pentasaccharides in good yields, respectively.