Towards a stable noeuromycin analog with a d-manno configuration: Synthesis and glycosidase inhibition of d-manno-like tri- and tetrahydroxylated azepanes

Noeuromycin is a highly potent albeit unstable glycosidase inhibitor due to its hemiaminal function. While stable d-gluco-like analogs have been reported, no data are available for d-manno-like structures. A series of tri- and tetrahydroxylated seven-membered iminosugars displaying either a d-manno-or a l-gulo-like configuration, were synthesized from methyl α-d-mannopyranoside using a reductive amination-mediated ring expansion as the key step. Screening towards a range of commercial glycosidases demonstrated their potency as competitive glycosidase inhibitors while cellular assay showed selective albeit weak glycoprotein processing mannosidase inactivation.