The product is employed for the characterization of GH 20 β-N-acetylhexosaminidases.298 Its complex (Ki 2.7 μM) with Streptomyces plicatus β-N-acetylhexosaminidase (PDB 1JAK) shows the “typical isofagomine-type” 4C1 chair, with the exocyclic nitrogen as well as 3-OH ａnd the hydroxymethyl group all in equatorial orientations. When compared with the corresponding complex with GlcNAc-thiazoline 140 (PDB 1HP5),299 the ring nitrogen atom is positioned in “aza-sugar binding mode” close to the location of C-1. A strong interaction of the general acid–base Glu 314 was observed, with the equatorial proton of the ionized ring nitrogen.