Synthesis, from nojirimycin, of N1-alkyl-d-gluconamidines as potential glucosidase inhibitors

The labile reaction products from nojirimycin (5-amino-5-deoxy-d-glucopyranose, 1) with butyl- and dodecyl-amine were dehydrogenated with iodine to the corresponding N1-alkyl-d-gluconamidines. A major by-product from the direct dehydrogenation of 1 was d-glucono-1,5-lactam. Progress of the reaction and product isolation was monitored by measuring the inhibitory potency of reaction mixtures with mammalian lysosomal and cytosolic β-glucosidases. The latter was tentatively identified as a non-specific β-glucosidase/β-galactosidase in a commercial β-galactosidase preparation from bovine liver by its resistance to conduritol B epoxide and strong inhibition by taurodeoxycholate. Both enzymes were inhibited by the N1-dodecyl derivative > 1000-fold better than by 1. Unsubstituted d-gluconaminidine and its N-benzyl derivative could not be prepared by the method described, because ammonia was immediately transformed into insoluble NI3 and benzylamine was rapidly dehydrogenated. The amidines were stable in aqueous solution at pH ≤ 6, but were hydrolyzed above pH 8 to d-gluconolactam and alkylamine (half-life 24 h at pH 8 and 25 °C). A detailed study with the C12-derivative at pH 10 indicated that the hydrolysis proceeded with formation of the N-dodecylamide of 5-amino-5-deoxy-d-gluconic acid as intermediate which still had considerable inhibitory potency against the cytosolic β-glucosidase. A method is described for the quantification of cyclic amidines based on the reaction of amino groups with ninhydrin before and after hydrolysis with dilute alkali.