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Structural, Mechanistic, and Computational Analysis of the Effects of Anomeric Fluorines on Anomeric Fluoride Departure in 5-Fluoroxylosyl Fluorides

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posted on 2011-10-12, 00:00 authored by Seung Seo Lee, Ian R. Greig, David J. Vocadlo, John D. McCarter, Brian O. Patrick, Stephen G. Withers
The effects of fluorine substitution at the C-5 center of pyranosyl fluorides on the reactivity at the C-1 anomeric center was probed by studying a series of 5-fluoroxylosyl fluoride derivatives. X-ray structures of their per-O-acetates detailed the effects on the ground-state structures. First-order rate constants for spontaneous hydrolysis, in conjunction with computational studies, revealed that changes in the stereochemistry of the 5-fluorine had minimal effects on the solvolysis rate constants and that the observed rate reductions were broadly similar to those caused by additional fluorine substitution at C-1 but significantly less than those due to substitution at C-2. Differences in the trapping behavior of 5- versus 2-fluoro-substituted glycosyl fluorides with α- and β-glycosidases arise more from differences in steric effects and hydrogen-bonding interactions than from intrinsic reactivity differences.

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