The Role of Sugar Substituents in Glycoside Hydrolysis
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- 作者：Mark N. Namchuk ; John D. McCarter ; Adam Becalski ; Trevor Andrews ; and Stephen G. Withers
- 刊名：Journal of the American Chemical Society
- 出版年：2000
- 出版时间：February 23, 2000
- 年：2000
- 卷：122
- 期：7
- 页码：1270 - 1277
- 全文大小：273K
- 年卷期：v.122,no.7(February 23, 2000)
- ISSN：1520-5126
文摘
A series of monosubstituted deoxy and deoxyfluoro 2,4-dinitrophenyl (DNP) 
-D-glycopyranosideswas synthesized and used to probe the mechanism of spontaneous -glycoside hydrolysis. Their relative ratesof hydrolysis followed the order 2-deoxy > 4-deoxy > 3-deoxy 
6-deoxy > parent > 6-deoxy-6-fluoro >3-deoxy-3-fluoro > 4-deoxy-4-fluoro > 2-deoxy-2-fluoro. Hammett correlations of the pH-independenthydrolysis rates of each of the 6-, 4-, 3-, and 2-position substituted glycosides with the 
I value for the sugarring substituent were linear (r = 0.95 to 0.999, 
I = -2.2 to -10.7), consistent with hydrolysis rates beinglargely dictated by field effects on an electron-deficient transition state. The relative rates of hydrolysis of theDNP glucosides can be rationalized on the basis of the stabilities of the oxocarbenium ion-like transitionstates, as predicted by the Kirkwood-Westheimer model. The primary determinant of the rate of hydrolysiswithin a series appears to be the field effect of the ring substituent on O5, the principal center of chargedevelopment at the transition state. Differences in the rates of hydrolysis between different series ofhexopyranosides may not arise solely from field effects and likely also reflect differences in steric factors orsolvation.
-D-glycopyranosideswas synthesized and used to probe the mechanism of spontaneous -glycoside hydrolysis. Their relative ratesof hydrolysis followed the order 2-deoxy > 4-deoxy > 3-deoxy 6-deoxy > parent > 6-deoxy-6-fluoro >3-deoxy-3-fluoro > 4-deoxy-4-fluoro > 2-deoxy-2-fluoro. Hammett correlations of the pH-independenthydrolysis rates of each of the 6-, 4-, 3-, and 2-position substituted glycosides with the I value for the sugarring substituent were linear (r = 0.95 to 0.999, I = -2.2 to -10.7), consistent with hydrolysis rates beinglargely dictated by field effects on an electron-deficient transition state. The relative rates of hydrolysis of theDNP glucosides can be rationalized on the basis of the stabilities of the oxocarbenium ion-like transitionstates, as predicted by the Kirkwood-Westheimer model. The primary determinant of the rate of hydrolysiswithin a series appears to be the field effect of the ring substituent on O5, the principal center of chargedevelopment at the transition state. Differences in the rates of hydrolysis between different series ofhexopyranosides may not arise solely from field effects and likely also reflect differences in steric factors orsolvation.