Cheang Kuan Lee

Synthesis and reactions of tert-butyldiphenylsilyl ethers of sucrose☆

Abstract The reaction of sucrose with 1.1 mol. equiv. of tert-butyldiphenylsilyl (t-BDPS) chloride in pyridine in the presence of 4-dimethylaminopyridine gave the crystalline 6′-t-BDPS ether 1 in 49% yield, without recourse to column chromatography. Compound 1 was transformed into the 4,6,1′-trichloride by using sulphuryl chloride. When the silylation reaction of sucrose was performed with 3 mol. equiv. of the reagent, chromatography gave the crystalline 6,6′-di-t-BDPS ether and the 6,1′,6′-tri-t-BDPS ether 9 in yields of 78 and 18.7%, respectively. Compound 9 was obtained as the major product on treatment of sucrose with 4.6 mol. equiv. of the silylating reagent. Removal of the silyl protecting-group in 6,6′-di-O-tert-butyl-diphenylsilylsucrose hexabenzoate, using tetrabutylammonium fluoride, proceeded smoothly, but with 4→6 migration of the benzoate.

Synthesis of the allo-analogue of trehalose.

Selective benzoylation of HO-2 and HO-2 of 4,6-O-benzylidene-alpha-D-glucopyranosyl 4,6-O-benzylidene-alpha-D-glucopyranoside with N-benzoylimidazole led to the exclusive formation of 2-O-benzoyl-4,6-O-benzylidene-alpha-D-glucopyranosyl 2-O-benzoyl-4,6-O-benzylidene-alpha-D-glucopyranoside. Oxidation of either the dibenzoate or the corresponding ditosylate with methyl sulphoxide--phosphorus pentaoxide gave the 3,3-diulose, and subsequent reduction with borohydride gave the 3,3diepimers having the allo-allo configuration. De-esterification and hydrolysis of the benzylidene substituents gave alpha-D-allopyranosyl alpha-D-allopyranoside.

Stability of sugar acetates in citric acid solution

Abstract The stability of six sugar acetates in 10% citric acid solution was investigated. Quantitative thin-layer chromatography was used to monitor the hydrolysis of acetate groups. The times taken for 50% hydrolysis ( t 0.5 ) varied from 35 h for sucrose octaacetate to 110 h for raffinose hendecaacetate. The stability of sucrose octaacetate was determined at concentrations of 0·5, 1·5, 4 and 10% citric acid. The rate of hydrolysis showed a marked dependence on the pH of the citric acid solution. Primary acetate groups are hydrolysed more readily than secondary acetate groups.