Submitted to: Pacifichem Symposium
Publication Acceptance Date: December 19, 2000
Publication Date: N/A
Abstract only

Technical Abstract: Based on kinetics of deacetylation of diacetates of methyl beta-D-xylopyranoside by acetylxylan esterase from Streptomyces lividans which shows regioselectivity for acetyl groups at positions two and three, it has been hypothesized that the mechanism of deacetylation of the positions two and three when the neighboring positions three and two are non-acetylated, might involve an enzyme-catalyzed formation of a five-membered transition state from which acetyl group is released (Biely et al., FEBS Lett. 27, 19, 1996). To verify the hypothesis, 3-deoxy- and 3-deoxy-3-fluoro-2,4-di-O-acetyl-methyl-beta-D-xylopyranoside were synthesized as model substrates. The rate of deacetylation of diacetates was found to be dramatically reduced with the deoxy derivative but not with deoxy-fluoro derivative. The absence of hydroxyl group in position three seems to prevent the formation of the five-membered transition state while fluorine atom seems to function in the reaction mechanism similarly as a hydroxyl group.