Combinatorial Chemistry Online

Abstract

Current literature highlights Tight-Binding Inhibitors of a-FucosidaseCompounds containing glycosidic bonds are involved in a number of biological and disease processes such as metabolic disorders, viral and bacterial infection and tumour growth and metastasis. As the glycosidic bonds are cleaved by glycosidases, these enzymes are considered important therapeutic targets. Potent glycosidase inhibitors have been sought to treat disease, such as the neuraminidase inhibitor Tamiflu TM and oseltamivir phosphate TM , prescribed to treat influenza virus infection.Amongst members of the glycosidase family, a-fucosidase is involved in removal of nonreducing terminal L L-fucose residues that are connected to oligosaccharides via a1,2-, a1,3-, a1,4-, or a1,6-linkages. Due to the great variety of physiological and pathological events associated with fucose-containing glycoconjugates, certain a-fucosidases have attracted the attention of researchers. An aberrant distribution of a-fucosidases is associated with inflammation, cancer and cystic fibrosis, and these enzymes are recognised as diagnostic markers for the early detection of colorectal and hepatocellular cancers because of the presence of a-fucosidase in the patientsÕ sera. Recently, slow and tight binding inhibitors of afucosidase have been discovered using a combinatorial chemistry approach. 1 This work centred on screening for an optimal aglycon attached to a fuconojirimycin (FNJ)-based structure (i). These FNJ-based structures mimic the transition state of enzymatic glycosidase cleavage.Using 1-aminomethyl FNJ (ii) as the scaffold for diversity-orientated synthesis, a library of amides was prepared by reaction with carboxylic acids. The library compounds were screened without purification, and several potent and competitive inhibitors against a-fucosidase from Corynebacterium sp. were discovered with IC 50 values in the low nM range, including compound (iii) with a K i value of 0.32 nM. It was observed that during prolonged observation of the enzyme inhibition assay there was a time-dependent decrease in the reaction rate as a function of the inhibitor concentration. Upon re-synthesis and purification of a number of library members exhibiting this time-dependent phenomenon, it was shown that the initial collision-complex (E AE I) isomerises to a tighter complex (E AE I*), where E represents free enzyme, I is free inhibitor, E AE I is a rapidly forming preequilibrium complex and E AE I* is the final enzyme-inhibitor complex.Rapid diversity-based synthesis and subsequent in situ screening enables rapid identification of suitable hydrophobic groups that enhance inhibition. Further work to determine the structure of the enzyme-inhibitor complex, allowing an understanding of the mechanism of inhibition is warranted, and the slow-releasing feature of the inhibition process could also provide new directions in drug design.