Stereoselective Glycosylation and Oligosaccharide Synthesis on Solid Support Using a 4-Azido-3-chlorobenzyl Group for Temporary Protection

A versatile and practical methodology for solid-phase synthesis was elaborated in the synthesis of α(1→6)- and β(1→6)-linked oligoglucoses by using thioglycosides having a 4-azido-3-chlorobenzyl (ClAzb) group for temporary protection of hydroxy functions. Highly α-selective glycosylation was achieved by the use of the benzylated thioglycoside 11 and NBS-LiNO₃ as activating reagents on macroporous polystyrene, ArgoPore^TM in Et₂O. Completely β-selective glycosylation was effected by the use of thioglycoside 15 by virtue of the neighboring group participation of a 2-O-benzoyl group. The ClAzb group was satisfactorily stable during the glycosylation, but was easily cleaved on treatment with triphenylphosphine followed by oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone. The proximal saccharide residue was bound to the solid support via an ester-type linker which was cleaved under alkaline conditions. Rapid synthesis of oligosaccharides was readily effected by this methodology.

solid-phase synthesis - macroporous polystyrene - oxidative deprotection - thioglycosides