Regioselective Protection of Hydroxy Groups in Sugars

Glycosyl acceptors that contain a specific free hydroxy group are essential in the synthesis of oligosaccharides. However, the regioselective protection and deprotection of the numerous hydroxy groups present in oligosaccharides is challenging. For example, hexopyranoses contain one primary hydroxy group at the 6-position and three secondary hydroxy groups at the 2-, 3- and 4-positions. Selective modification of the primary hydroxy group, which is more reactive and less sterically hindered than the secondary hydroxy groups, is achieved by using bulky protecting groups (for example, tert-butyldiphenylsilyl and trityl) or a controlled amount of an electrophile.