Conformational and Electronic Variations in 1,2-and 1,5a-Cyclophellitols and their Impact on Retaining -Glucosidase Inhibition

Glycoside hydrolases (glycosidases) take part in myriad biological processes and are important therapeutic targets. Competitive and mechanism-based inhibitors are useful tools to dissect their biological role and comprise a good starting point for drug discovery. The natural product, cyclophellitol, a mechanism-based, covalent and irreversible retaining beta-glucosidase inhibitor has inspired the design of diverse alpha- and beta-glycosidase inhibitor and activity-based probe scaffolds. Here, we sought to deepen our understanding of the structural and functional requirements of cyclophellitol-type compounds for effective human alpha-glucosidase inhibition. We synthesized a comprehensive set of alpha-configured 1,2- and 1,5a-cyclophellitol analogues bearing a variety of electrophilic traps. The inhibitory potency of these compounds was assessed towards both lysosomal and ER retaining alpha-glucosidases. These studies revealed the 1,5a-cyclophellitols to be the most potent retaining alpha-glucosidase inhibitors, with the nature of the electrophile determining inhibitory mode of action (covalent or non-covalent). DFT calculations support the ability of the 1,5a-cyclophellitols, but not the 1,2-congeners, to adopt conformations that mimic either the Michaelis complex or transition state of alpha-glucosidases. Twenty configurational and functional cyclophellitol analogues were synthesized and evaluated on their potency as retaining alpha-glucosidase inhibitors. The inhibitory properties of the focused library of compounds were determined on human alpha-glucosidases after which we mapped the conformational free energy landscapes of the most active compounds. Our results add to the growing list of covalent and competitive alpha-glucosidase inhibitors and may pave the way towards the design of new therapeutics targeting these enzymes. image