Vinyl Halide‐Modified Unsaturated Cyclitols are Mechanism‐Based Glycosidase Inhibitors

Suitably configured allyl ethers of unsaturated cyclitols act as substrates β-glycosidases, reacting via allylic cation transition states. Incorporation halogens at the vinylic position these carbasugars, along with an activated leaving group, generates potent inactivators β-glycosidases. Enzymatic turnover halogenated (F, Cl, Br) displayed a counter-intuitive trend wherein most electronegative substituents yielded labile pseudo-glycosidic linkages. Structures complexes Sulfolobus β-glucosidase revealed similar enzyme-ligand interactions to those seen in 2-fluorosugar inhibitor, lone exception being displacement tyrosine 322 from active site by halogen. Mutation Y322 Y322F largely abolished glycosidase activity, consistent lost O5, but minimally affected (7-fold) rates carbasugar hydrolysis, yielding more selective enzyme for cyclitol ether hydrolysis.