- An Empirical Understanding of the Glycosylation Reaction
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Reliable glycosylation reactions that allow for the stereo- and regioselective installation of glycosidic linkages are paramount to the chemical synthesis of glycan chains. The stereoselectivity of glycosylations is exceedingly difficult to control due to the reaction's high degree of sensitivity and its shifting, simultaneous mechanistic pathways that are controlled by variables of unknown degree of influence, dominance, or interdependency. An automated platform was devised to quickly, reproducibly, and systematically screen glycosylations and thereby address this fundamental problem. Thirteen variables were investigated in as isolated a manner as possible, to identify and quantify inherent preferences of electrophilic glycosylating agents (glycosyl donors) and nucleophiles (glycosyl acceptors). Ways to enhance, suppress, or even override these preferences using judicious environmental conditions were discovered. Glycosylations involving two specific partners can be tuned to produce either 11:1 selectivity of one stereoisomer or 9:1 of the other by merely changing the reaction conditions.
- Chatterjee, Sourav,Moon, Sooyeon,Hentschel, Felix,Gilmore, Kerry,Seeberger, Peter H.
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- Glycosyl Imidates, 10. - Glycosyl Phosphates from Glycosyl Trichloroacetimidates
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The glycosyl trichloroacetimidates 1-α,β, 8-α, 11-α, 13-α, 15-α, and 17-α directly transfer the glycosyl moiety to phosphoric acid mono- and diesters.The acidity of the phosphoric acid derivatives used was sufficient for the activation of the trichloroacetimidates, therefore an additional acidic catalyst was not required.From the β-imidate 1-β α-glycosyl phosphate and from the α-imidates preferentially β-glycosyl phosphates were obtained.Reaction of dibenzyl phosphate (2a) and cetyl phosphate (2c) with 1-α demonstrated that β/α-anomerization iscatalyzed by traces of acid.The glycosyl phosphates 3a-α, 3a-β - 3c-β, 3f-α, 9a-β, and 9c-β were partly or totally deprotected.The structures of the synthezised compounds were assigned by 1H NMR spectroscopy and by comparison with literature data.
- Schmidt, Richard R.,Stumpp, Michael
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p. 680 - 691
(2007/10/02)
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