Stereoselective glycosylation and oligosaccharide synthesis on solid support using a 4-azido-3-chiorobenzyl group for temporary protection

A versatile and practical methodology for solid-phase synthesis was elabora ted in the synthesis of alpha(1-->6)- and alpha(1-->6)-linked oligoglucoses by using thioglycosides having a 4-azido-3-chlorobenzyl (CLAzb) group for temporary protection of hydroxy functions. Highly cc-selective glycosylatio n was achieved by the use of the benzylated thioglycoside 11 and NBS-LiNO3 as activating reagents on macroporous polystyrene, ArgoPore(TM) in Et2O. Co mpletely beta-selective glycosylation was effected by the use of thioglycos ide 15 by virtue of the neighboring group participation of a 2-O-benzoyl gr oup. The ClAzb group was satisfactorily stable during the glycosylation, bu t was easily cleaved on treatment with triphenylphosphine followed by oxida tion with 2,3-dichloro-5,6-dicyanobenzoquinone. The proximal saccharide res idue was bound to the solid support via an ester-type linker which was clea ved under alkaline conditions. Rapid synthesis of oligosaccharides was read ily effected by this methodology.