Synthesis and glycosidase inhibitory activity of 5-thioglucopyranosylamines. Molecular modeling of complexes with glucoamylase

The synthesis of a series of 5-thio-d-glucopyranosylarylamines by reaction of 5-thio-d-glucopyranose pentaacetate with the corresponding arylamine and mercuric chloride catalyst is reported. The products were obtained as anomeric mixtures of the tetraacetates which can be separated and crystallized. The tetraacetates were deprotected to give α/β mixtures of the parent compounds which were evaluated as inhibitors of the hydrolysis of maltose by glucoamylase G2 (GA). A transferred NOE NMR experiment with an α/β mixture of 7 in the presence of GA showed that only the α isomer is bound by the enzyme. The Ki values, calculated on the basis of specific binding of the α isomers, are 0.47 mM for p-methoxy-N-phenyl-5-thio-d-glucopyranosylamine (7), 0.78 mM for N-phenyl-5-thio-d-glucopyranosylamine (8), 0.27 mM for p-nitro-N-phenyl-5-thio-d-glucopyranosylamine (9) and 0.87 mM for p-trifluoromethyl-N-phenyl-5-thio-d-glucopyranosylamine (10), and the Km values for the substrates maltose and p-nitrophenyl α-d-glucopyranoside are 1.2 and 3.7 mM, respectively. Methyl 4-amino-4-deoxy-4-N-(5′-thio-α-d-glucopyranosyl)-α-d-glucopyranoside (11) is a competitive inhibitor of GA wild-type (Ki 4 μM) and the active site mutant Trp120→Phe GA (Ki 0.12 mM). Compounds 7, 8, and 11 are also competitive inhibitors of α-glucosidase from brewer’s yeast, with Ki values of 1.05 mM, >10 mM, and 0.5 mM, respectively. Molecular modeling of the inhibitors in the catalytic site of GA was used to probe the ligand–enzyme complementary interactions and to offer insight into the differences in inhibitory potencies of the ligands.