Inversion at the anomeric carbon

Family 45 contains five endocellulases from bacteria and fungi. The structure of Humicola insolens endoglucanase V has been solved and consists of a six-stranded P-barrel domain with a long open groove across the surface. This enzyme catalyzes hydrolysis with inversion at the anomeric carbon atom [36,37, 61]. 

Alcoholysis of acyclic sugar dithioacetals1,4,5 in the presence of mer-cury(II) oxide and mercury(II) chloride leads to the formation of glycosides. The reaction of phenyl 1-thioglycosides with alcohols in the presence of mercury(II) salts gives the glycosides with inversion of the configuration at the anomeric carbon atom.53... 

Rhind-Tutt and Vernon149 found that the methanolysis of 2,3,4,6-tetra-O-methyl-a-D-glucopyranosyl chloride proceeds by an SnI mechanism, and mainly gives methyl tetra-0-methyl-j3-D-glucopy-ranoside (with inversion of configuration at the anomeric carbon atom). 

Extensive studies have been performed to enable understanding of the mechanism of hydrogenation of o-fructose on copper catalysts. Experiments performed with deuterium showed clearly that the enediol form is not involved in hydrogenation and D-fructose is assumed to be preferentially hydrogenated via its furanose form by attack of a copper hydride-like species at the anomeric carbon, with inversion of configuration [22]. The proposed mechanism could explain the diaster-... 

Lysozyme has two catalytic groups at the active site Glu 35 and Asp 52. The discovery that the enzyme-catalyzed reaction takes place with retention of configuration at the anomeric carbon indicates that it caimot be a one-step Sn2 reaction. (Recall that an Sn2 reaction takes place with inversion of configuration Section 9.1.) Therefore, the reaction must involve either two sequential Sn2 reactions or an SnI reaction with the enzyme blocking one face of an oxocarbenium ion intermediate to nucleophilic... 

The experimental evidence obtained for the azide nucleophilic substitution in fluorides 3 and 5 suggests that the reaction follows a different mechanism in each case. a-Glucopyranosyl fluoride 3 yields die substitution product 4 with inversion of the configuration at the anomeric carbon, which is die expected result for a Sn2-type reaction (Scheme 13.5). 

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