Synthesis Of Isomaltose Analogues

Preparation of the alpha-glucosides 11, 12, 13 and 14 were accomplished through glycosylation of racemic trans-1-hydroxy-2-(hydroxymethyl)cyclohexane using 2-thiopyridyl tetra-O-benzyl-glucoside as the glycosyl donor in acceptable overall yield for alpha-selectivity, but with poor regioselectivity. Glycosylation under thermodynamic control using tetrabenzyl glucopyranose acetate and trimethylsilyl triflate as the promotor gave similar results. The unprotected glucosides 12 and 13 were separated and characterized by NMR spectroscopy. Similarly methyl 4-deoxy-alpha-isomaltoside (5a) was prepared through halide catalyzed glycosylation of methyl 2,3-di-O-benzoyl-4-deoxy-alpha-D-glucopyranoside (15) in acceptable yield and the unprotected compound characterized by NMR spectroscopy. Compounds 5a, 12a, 13a and the mixture-11a and 14a were all tested as substrates for the enzyme glucoamylase from Aspergillus niger and proved to be very poor substrates for the enzymic hydrolysis.