Novel disaccharides containing sulfur in the ring and nitrogen in the interglycosidic linkage. Conformation of methyl 5'-thio-4-N-maltoside bound to glucoamylase and its activity as a competitive inhibitor

The syntheses of novel heteroanalogues of methyl maltoside and methyl kojibioside containing sulfur in the nonreducing ring and nitrogen in the interglycosidic linkage are described. The compounds are substrate analogues for glucosidases and are of interest as potential inhibitors of these enzymes. The synthesis relied upon the acid-catalyzed condensation of 5-thio-D-glucose with either methyl 4-amino-4-deoxy-α-D-glucopyranoside or methyl 2-amino-2-deoxy-β-D-glucopyranoside in methanol solvent. Thus, the interconverting anomeric mixtures, methyl 5’-Thio-4-N-α-maltoside (5α), methyl 5’-Thio-4-N-α-cellobioside (5β) and methyl 5’-Thio-4-N-β-kojibioside 6α, methyl 5’-Thio-2-N-β-sophoroside 6β, were synthesized in 55% and 52% yield, respectively. Acetylation of the anomeric mixtures yielded anomers which were separable and did not mutarotate. A comparison of NOE data for free 5α and transferred NOE data for a mixture of 5α and glucoamylase G1 suggests that 5α is bound by the enzyme in a conformation in the area of the global energy minimum of free 5α. These NMR data also suggest that 5α may be an inhibitor of glucoamylase. Kinetic studies indicate that a mixture of 5α/5β is a competitive inhibitor of maltose binding by glucoamylase G2, with a Ki value for 5α of 4 ± 0.3 μM.