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 anom eric mixtures of the tetraacetates which can be separated and crystallized. The tetraacetates were deprotected to give alpha/beta mixtures of the pare nt compounds which were evaluated as inhibitors of the hydrolysis of maltos e by glucoamylase G2 (GA). A transferred NOE NMR experiment with an alpha/b eta mixture of 7 in the presence of GA showed that only the alpha isomer is bound by the enzyme. The K-i values, calculated on the basis of specific b inding of the a isomers, are 0.47 mM for p-methoxy-N-phenyl-5-thio-D-glucop yranosylamine (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 fo r p-trifluoromethyl-N-phenyl-5-thio-D-glucopyranosylamine (10); and the K-m values for the substrates maltose and p-nitrophenyl alpha-D-glucopyranosid e are 1.2 and 3.7 mM, respectively. Methyl 4-amino-4-deoxy-4-N-(5'-thio-alp ha-D-glucopyranosyl)-alpha-D-glucopyranoside (11) is a competitive inhibito r of GA wild-type (K-i 4 mu M) and the active site mutant Trp120 --> Phe GA (K-i 0.12 mM). Compounds 7, 8, and 11 are also competitive inhibitors of a lpha-glucosidase from brewer's yeast, with K-i values of 1.05 mM, > 10 mM, and 0.5 mM, respectively. Molecular modeling of the inhibitors in the catal ytic site of GA was used to probe the ligand-enzyme complementary interacti ons and to offer insight into the differences in inhibitory potencies of th e ligands. (C) 1999 Elsevier Science Ltd. All rights reserved.