Synthesis and Analysis of Specific Covalent Inhibitors of endo-Xyloglucanases

A series of N-bromoacetylglycosylamines and bromoketone C-glycosides were synthesised from complex xyloglucan oligosaccharide (XyGO) scaffolds as specific active-site affinity labels for endo-xyloglucanases. Compounds based on XXXG (Xyl(3)Glc(4)) and XLLG (Xyl(3)Glc(4)Gal(2)) oligosaccharides exhibited strikingly higher affinities and higher rates of irreversible inhibition than known cellobiosyl and new lactosyl disaccharide congeners when tested with endo-xyloglucanases from two distinct glycoside hydrolase (GH) families. Intact-protein mass spectrometry indicated that inactivation with XyGO derivatives generally resulted in a 1:1 labelling stoichiometry. Together, these results indicate that XyGO-based affinity reagents have significant potential as inhibitors and proteomic reagents for the identification and analysis of diverse xyloglucan-active enzymes in nature, to facilitate industrial enzyme applications.