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 β-D-thiogluco- and galactopyranosides with appropriate acceptors afforded the corresponding disaccharides in good yield. Excellent β-stereoselectivity (β/α≥ 10/1) can be obtained when the glycosylation was realized in CH₃CN at −40 °C. Furthermore, the 6-O-NPPOC thioglucoside 6 can also be readily converted into the corresponding glucopyranose or glucosyl fluoride. The photolysis of 6-O-NPPOC diacetone D-galactose 4 has been studied by UV–vis absorption in CH₃CN in the presence of water or DBU at 365 nm. At 100 µM concentration, photocleavage of 4 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 CH₃CN the presence of water or DBU in more than 87% yield.