Synthesis of glycosyl amino acids by light-induced coupling of photoreactive amino acids with glycosylamines and 1-C-aminomethyl glycosides

The glycosylamines of O-acetyl-protected GlcNAc and chitobiose, as well as two partially unprotected 1-C-aminomethyl glucosides, were photochemically coupled with orthogonally protected N-aspartyl-5-bromo-7-nitroindoline derivatives. The reactions proceeded under neutral conditions by irradiation with near-UV light. The glycosyl asparagines with N- or C-glycosyl linkages were afforded in 60-85% yield on a 10-70 mg scale. Moreover, the ability of a highly photoreactive N-glutamyl-4-methoxy-7-nitroindoline derivative to acylate amino saccharides was tested. Upon irradiation in the presence of a dimeric 1-C-aminomethyl glycoside, or a glycosylamine, the corresponding glycosyl glutamines were obtained in 50% and 30% yield, respectively. Preparations of the photoreactive aspartates and the 1-C-aminomethyl glycosides are also described.