Synthesis, glycosylation and photolysis of photolabile 2-(2-nitrophenyl)propyloxycarbonyl (NPPOC) protected glycopyranosides

Abstract

The photolabile NPPOC group has been successfully introduced into the 6-position of various glycopyranosides in 91-97% yield. Glycosylation of NPPOC-protected phenyl beta-D-thiogluco- and galactopyranosides with appropriate acceptors afforded the corresponding disaccharides in good yield. Excellent beta-stereoselectivity (beta/alpha>or= 10/1) can be obtained when the glycosylation was realized in CH(3)CN at -40 degrees C. Furthermore, the 6-O-NPPOC thioglucoside can also be readily converted into the corresponding glucopyranose or glucosyl fluoride. The photolysis of 6-O-NPPOC diacetone D-galactose has been studied by UV-vis absorption in CH(3)CN in the presence of water or DBU at 365 nm. At 100 microM concentration, photocleavage of was accomplished after 5 min irradiation, with t(1/2) = 37 s (10% water), 75 s (1 equiv. DBU) or 87 s (0.05 M DBU). The formation of the nitroso byproduct can be avoided in the presence of 0.05 M DBU. All the NPPOC-protected mono- or disaccharides can be readily removed by photolysis at 365 nm in CH(3)CN the presence of water or DBU in more than 87% yield.