Reactions of Glucosides

An efficient, stereocontrolled synthesis of a- or yS-l-C-alkyl-imino-L-arabinols (6) depends on the nucleophilic addition of pentose-derived imines generated from enan-tiopure f-butanesulfinamide. The stereoselectivity of this key step can be controlled 0 either by the sugar moiety or by the stereogenic sulfur centre. 

Evidence for a very short-lived oxocarbenium species in an enzymatic glycosyl transfer that proceeds with retention of configuration has been obtained via QM/MM 

Mechanisms of glycosyltransferases have been reviewed. l-/3-0-Acyl glucoside conjugates of phenylacetic acids have been synthesized, and their acyl migration and hydrolysis kinetics have been compared with the corresponding acyl glucoronides.  

The isomerization of glyceraldehyde [HOCH2CH(OH)CHO] to dihydroxyacetone at the surface of Lewis acidic zeolites has been studied theoretically, focusing on the rate-determining 1,2-hydride shift involved.  

The mechanism of the entry of fructose into the Maillard reaction (a series of sugar/amino acid processes in vivo) has been studied by DFT the order of reactivity for the isomers is predicted as a- /3- open-chain. Heyns rearrangement products are most favourable under basic conditions, possible under neutral conditions, but unfeasible at or below glycine s isoelectric point. Kinetic and activation parameters have been reported for the corresponding glucose/proline reaction.  

Proton affinities and have been calculated for various tautomers of o-glucose and d- 

A review surveys the catalysts and mechanistic approaches to alter the reactivity of hydroxyl groups in carbohydrates, thus facilitating regioselective manipulation.  

A DFT Study of the acid catalysis of the mutarotation of erythrose and threose has looked at reaction in the gas phase, and in a continuum water model.Sodium cation can act as an inhibitor, whereas borane acts as a Lewis acid catalyst. Brpnsted acids H+ and HjO are particularly effective, with the activation energy being further lowered using H30 with one bridging H2O. 

MP2 and B3LYP methods have been used to examine the mechanisms of the Lewis acid-catalysed isomerization and epimerization of xylose to xylulose and lyxose, respectively.  

Activation of 0-glycosyl trichloroacetimidates as glycosyl donors typically requires moderately strong acids, such that a simple A/,A/ -diarylthiourea, ArNHC(=S)NHAr [e.g., Ar = 3,5-bis(trifluoromethyl), = 8-5], would not be expected to catalyse the process. However, it can act as a co-catalyst with simple Brpnsted acids such as benzoic (p. = 4). The system gives significant rate and yield enhancements, and good selectivity for the / -anomer. A multiply hydrogen-bonded complex of reactants and catalysts is proposed. 

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For more references to Imines, see sections titled Formation and Reactions of Acetals and Related Species , Reactions of Glucosides , Reactions of Ketenes , and... 

For more references to Aldols, see section titled Reactions of Glucosides . 

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