N-containing sugars from Morus alba and their glycosidase inhibitory activities

Abstract

The reexamination of N-containing sugars from the roots of Morus alba by improved purification procedures led to the isolation of eighteen N-containing sugars, including seven that were isolated from the leaves of Morus bombycis. These N-containing sugars are 1-deoxynojirimycin ( 1), N-methyl-1-deoxynojirimycin ( 2), fagomine ( 3), 3- epi-fagomine ( 4), 1,4-dideoxy-1,4-imino-pD-arabinitol ( 5), 1,4-dideoxy-1,4-imino-pD-ribitol ( 6), calystegin B 2 (1α,2β,3α,4β-tetrahydroxy- nor-tropane, 7), calystegin C 1, (1α,2β,3α,6α-pentahydroxy- nor-tropane, 8), 1,4-dideoxy-1,4-imino-(2- O-β-pD-glucopyranosyl)- d-glucopyranosyl)- d-arabinitol ( 9), and nine glycosides of 1. These glycosides consist of 2- O- and 6- O-α- d-galactopyranosyl-1-deoxynojirimycins ( 10 and 11, respectively), 2- O-, 3- O- and 4- O-α- d-glucopyranosyl-1-deoxynojirimycins ( 12, 13, and 14, respectively), and 2- O-, 3- O-, 4- O- and 6- O-β- D-glucopyranosyl-1-deoxynojirimycins ( 15, 16, 17, and 18, respectively). Compound 4 is a new member of polyhydroxylated piperidine alkaloids, and the isolation of 6 is the first report of its natural occurrence. It has recently been found that the polyhydroxy- nor-tropane alkaloids possess potent glycosidase inhibitory activities. Calystegin A 3 is the trihydroxy- nor-tropane, and calystegins B 1 and B 2 are the tetrahydroxy- nor-tropane. Calystegin C 1, a new member of calystegins, is the first naturally occurring pentahydroxy- nor-tropane alkaloid. The inhibitory activities of these compounds are investigated against rat digestive glycosidases and various commercially available glycosidases.