Iminosugar C-Glycosides Work as Pharmacological Chaperones of NAGLU, a Glycosidase Involved in MPS IIIB Rare Disease**

Mucopolysaccharidosis type IIIB is a devastating neurological disease caused by a lack of the lysosomal enzyme, α-N-acetylglucosaminidase (NAGLU), leading to a toxic accumulation of heparan sulfate. Herein we explored a pharmacological chaperone approach to enhance the residual activity of NAGLU in patient fibroblasts. Capitalizing on the three-dimensional structures of two modest homoiminosugar-based NAGLU inhibitors in complex with bacterial homolog of NAGLU, CpGH89, we have synthesized a library of 17 iminosugar C-glycosides mimicking N-acetyl-D-glucosamine and bearing various pseudo-anomeric substituents of both α- and β-configuration. Elaboration of the aglycon moiety results in low micromolar selective inhibitors of human recombinant NAGLU, but surprisingly it is the non-functionalized and wrongly configured β-homoiminosugar that was proved to act as the most promising pharmacological chaperone, promoting a 2.4 fold activity enhancement of mutant NAGLU at its optimal concentration.