Novel oxidatively removable protecting groups and linkers for solid-phase synthesis of oligosaccharides

Several new para-substituted benzyl- or phenyl-type protecting groups and their application to linkers for solid-phase synthesis are described. p-Acylaminobenzyl groups have higher acid stability than the p-methoxybenzyl (MPM) group, but are readily cleaved with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ). The p-azidobenzyl (Azb) group also has higher acid stability than the MPM group and can be removed much faster than the MPM group by DDQ oxidation after conversion of the azide group into the corresponding iminophosphorane. The acid stability of the p-azido-m-chlorobenzyl group (Cl-Azb) is higher than that of the Azb group. The former can be readily removed by DDQ oxidation after conversion of the azide group into the iminophosphorane. The p-acylaminophenyl glycoside linker can be readily obtained from p-nitrophenyl glycoside and can be readily cleaved by ammonium cerium(IV) nitrate (CAN) oxidation. This type of linker should be useful not only for the solid-phase synthesis of oligosaccharides but also for general solid-phase synthesis.