We report the synthesis of two novel families of iminosugars as glycosidase inhibitors involving an intramolecular cyclization between an N-alkoxyamino group and a latent aldehyde of a reducing sugar as the key step. Using this methodology we have prepared the hitherto unknown bicyclic polyhydroxylated N-(methoxy, benzyloxy)anhydroazepanes and N-benzyloxy-D-xylonojirimycin; all these novel compounds turned out to be moderate β-glucosidase inhibitors in a pH-dependent manner.