Chemoenzymatic and Protecting-Group-Free Synthesis of 1,4-Substituted 1,2,3-Triazole-α-<scp>d</scp>-glucosides with Potent Inhibitory Activity toward Lysosomal α-Glucosidase

Abstract

α-Glucosyl triazoles have rarely been tested as α-glucosidase inhibitors, partly due to inefficient synthesis of their precursor α-d-glucosylazide (<b>αGA1</b>). Glycosynthase enzymes, made by nucleophile mutations of retaining β-glucosidases, produce <b>αGA1</b> in chemical rescue experiments. <i>Thermoanaerobacterium xylanolyticus</i> glucosyl hydrolase 116 β-glucosidase (<i>Tx</i>GH116) E441G nucleophile mutant catalyzed synthesis of <b>αGA1</b> from sodium azide and <i>p</i>NP-β-d-glucoside (<i>p</i>NPGlc) or cellobiose in aqueous medium at 45 °C. The <i>p</i>NPGlc and azide reaction product was purified by Sephadex LH-20 column chromatography to yield 280 mg of pure <b>αGA1</b> (68% yield). <b>αGA1</b> was successfully conjugated with alkynes attached to different functional groups, including aryl, ether, amine, amide, ester, alcohol, and flavone via copper-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry reactions. These reactions afforded the 1,4-substituted 1,2,3-triazole-α-d-glucoside derivatives <b>AGT2-14</b> without protection and deprotection. Several of these glucosyl triazoles exhibited strong inhibition of human lysosomal α-glucosidase, with IC₅₀ values for <b>AGT4</b> and <b>AGT14</b> more than 60-fold lower than that of the commercial α-glucosidase inhibitor acarbose.