A range of new C-1 modified derivatives of the powerful glucosidase inhibitor 2,5-dideoxy-2,5-imino-D-mannitol has been synthesised and their biological activities probed with the beta-glucosidase from Agrobacterium sp. Ki values are compared with those of previously prepared close relatives. Findings suggest dramatic effects exerted by the aglycon binding site on substrate/inhibitor binding.