In order to probe the active-site requirements of the human N-terminal subunit of maltase-glucoamylase (ntMGAM), one of the clinically relevant intestinal enzymes targeted for the treatment of type-2 diabetes, the syntheses of two new inhibitors are described. The target compounds are structural hybrids of kotalanol, a naturally occurring glucosidase inhibitor with a unique five-membered ring sulfonium-sulfate inner salt structure, and miglitol, a six-membered ring antidiabetic drug that is currently in clinical use. The compounds comprise the six-membered ring of miglitol and the side chain of kotalanol or its de-O-sulfonated derivative. Inhibition studies of these hybrid molecules with human ntMGAM indicated that they are inhibitors of this enzyme with comparable K(i) values to that of miglitol (kotalanol analogue: 2.3±0.6μM; corresponding de-O-sulfonated analogue: 1.4±0.5μM; miglitol: 1.0±0.1μM). However, they are less active compared to kotalanol (K(i)=0.19±0.03μM). These results suggest that the (3)T(2) enzyme-bound conformation of the five-membered thiocyclitol moiety of the kotalanol class of compounds more closely resembles the (4)H(3) conformation of the proposed transition state for the formation of an enzyme-substrate covalent intermediate in the glycosidase hydrolase family 31 (GH31)-catalyzed reaction.
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