O-GlcNAcylation is a dynamic post-translational modification mediated by O-linked β-N-acetylglucosamine transferase (OGT) and O-GlcNAc hydrolase (OGA), that adds or removes a single β-N-acetylglucosamine (GlcNAc) moiety to or from serine/threonine residues of nucleocytosolic and mitochondrial proteins, respectively. The perturbed homeostasis of O-GlcNAc cycling results in several pathological conditions. Human OGA is a promising therapeutic target in diseases where aberrantly low levels of O-GlcNAc are experienced, such as tauopathy in Alzheimer's disease. A new class of potent OGA inhibitors, 2-acetamido-2-deoxy-d-glucono-1,5-lactone (thio)semicarbazones, have been identified. Eight inhibitors were designed and synthesized in five steps starting from d-glucosamine and with 15-55% overall yields. A heterologous OGA expression protocol with strain selection and isolation has been optimized that resulted in stable, active and full length human OGA (hOGA) isomorph. Thermal denaturation kinetics of hOGA revealed environmental factors affecting hOGA stability. From kinetics experiments, the synthesized compounds proved to be efficient competitive inhibitors of hOGA with Ki-s in the range of ∼30-250 nM and moderate selectivity with respect to lysosomal β-hexosaminidases. In silico studies consisting of Prime protein-ligand refinements, QM/MM optimizations and QM/MM-PBSA binding free energy calculations revealed the factors governing the observed potencies, and led to design of the most potent analogue 2-acetamido-2-deoxy-d-glucono-1,5-lactone 4-(2-naphthyl)-semicarbazone 6g (Ki = 36 nM). The protocol employed has applications in future structure based inhibitor design targeting OGA.

Inhibition of the human O-linked β-N-acetylglucosaminidase (hOGA, GH84) enzyme is pharmacologically relevant in several diseases such as neurodegenerative and cardiovascular disorders, type 2 diabetes, and cancer. Human lysosomal hexosaminidases (hHexA and hHexB, GH20) are mechanistically related enzymes; therefore, selective inhibition of these enzymes is crucial in terms of potential applications. In order to extend the structure–activity relationships of OGA inhibitors, a series of 2-acetamido-2-deoxy-d-glucono-1,5-lactone sulfonylhydrazones was prepared from d-glucosamine. The synthetic sequence involved condensation of N-acetyl-3,4,6-tri-O-acetyl-d-glucosamine with arenesulfonylhydrazines, followed by MnO₂ oxidation to the corresponding glucono-1,5-lactone sulfonylhydrazones. Removal of the O-acetyl protecting groups by NH₃/MeOH furnished the test compounds. Evaluation of these compounds by enzyme kinetic methods against hOGA and hHexB revealed potent nanomolar competitive inhibition of both enzymes, with no significant selectivity towards either. The most efficient inhibitor of hOGA was 2-acetamido-2-deoxy-d-glucono-1,5-lactone 1-naphthalenesulfonylhydrazone (5f, K_i = 27 nM). This compound had a K_i of 6.8 nM towards hHexB. To assess the binding mode of these inhibitors to hOGA, computational studies (Prime protein–ligand refinement and QM/MM optimizations) were performed, which suggested the binding preference of the glucono-1,5-lactone sulfonylhydrazones in an s-cis conformation for all test compounds.