Deactivating Influence of 3-O-Glycosyl Substituent on Anomeric Reactivity of Thiomannoside Observed in Oligomannoside Synthesis

摘要: It has been long recognized that, in chemical glycosylation, the anomeric reactivity of glycosyl donor can be influenced greatly by protecting groups. As opposed to effects groups, we report herein a finding on how O-glycosyl substituent affect oligosaccharyl donor, which turn should have impact convergent assembly oligosaccharide. During our synthetic efforts toward Pichia holstii oligomannoside, type α-1,3-linked dimannosyl thioglycosides was found exhibit unexpected low activation NIS/TMSOTf. This observation prompted us perform series comparative studies, attributed deactivation presence 3-O-glycosyl substituent, comparison with O-acetyl group and O-glycosidic linkages at C-4/C-6 positions. To rationalize unusual phenomenon, hypothesize that moiety C-3 could destabilize oxocarbenium ion intermediate additionally increasing O2–C2–C3–O3 torsion...