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

Article

A bicyclo[2.2.2] analogue of the glycosidase inhibitor 1-deoxynojirimycin, 2,6-anhydro-1-deoxymannojirimycin (6), has been synthesized in nine steps from 1,5-anhydro-D-glucitol. This conformationally restricted aza-sugar has been shown to inhibit, albeit weakly, several glycosidase enzymes.Key words: glycosidase, inhibitor, bicyclic, deoxymannojirimycin, deoxynojirimycin.

Enzymatic synthesis of the glycosides of calystegines B1 and B2 and their glycosidase inhibitory activities

Several glycosides of calystegines B1 and B2 were synthesized by use of rice alpha-glucosidase and the whole cells of Rhodotorula lactosa, and their glycosidase inhibitory activities were investigated. Incubation of mixture of calystegine B1 and maltose with rice alpha-glucosidase gave 3-O-alpha-D-glucopyranosylcalystegine B1 (2, 11.3%). An enzymatic beta-transglucosylation reaction of calystegines B1 or B2 with cellobiose using the whole cells of R. lactosa gave 3-O-beta-D-glucopyranosylcalystegine B1 (1) (0.9%) or 4-O-beta-D-glucopyranosylcalystegine B2 (3, 11.2%), respectively, while similar beta-transgalactosylation of calystegine B2 from lactose gave 4-O-beta-D-galactopyranosylcalystegine B2 (4, 10.1%). The glycosylation of calystegines B1 and B2 markedly decreased or abolished their inhibition against beta-glucosidase, alpha- or beta-galactosidase. Compound 4 however retained more or less the potency of calystegine B2 against trehalase. Interestingly, compound 1 was a noncompetitive inhibitor of rice alpha-glucosidase, with a Ki value of 0.9 +/- 0.1 microM.

Specific alpha-galactosidase inhibitors, N-methylcalystegines--structure/activity relationships of calystegines from Lycium chinense

An examination of the roots of Lycium chinense (Solanaceae) has resulted in the discovery of 14 calystegines, a cycloheptane bearing an amino group and three hydroxyl groups, and two polyhydroxylated piperidine alkaloids. Calystegines A7 and B5, in addition to the previously known calystegines A3, A5, A6, B1, B2, B3, B4, C1, C2 and N1, were isolated and determined as 1alpha,2beta,4alpha-trihydroxy-nortropane and 1alpha,2alpha,4alpha,7alpha-tetrahydroxy-nort ropane, respectively. L. chinense also had two polyhydroxytropanes bearing a methyl group on the nitrogen atom, unlike the previously reported nortropane alkaloids. They were established as N-methylcalystegines B2 and C1, and their N-methyl groups were found to be axially oriented from NOE experiments. 1Beta-amino-3beta,4beta,5alpha-trihydroxycyclohepta ne was also present in L. chinense and may be a biosynthetic precursor of the calystegines that occur in this plant. Two polyhydroxypiperidine alkaloids, fagomine and 6-deoxyfagomine, were isolated. Calystegine B2 is a potent competitive inhibitor of almond beta-glucosidase (Ki = 1.9 microM) and coffee bean alpha-galactosidase (Ki = 0.86 microM), while N-methylcalystegine B2 was a more potent competitive inhibitor of the latter enzyme (Ki = 0.47 microM) than the parent compound but showed a marked lack of inhibitory activities towards most other glycosidases. Since this compound is a very specific inhibitor of alpha-galactosidase and inhibits rat liver lysosomal alpha-galactosidase with a Ki of 1.8 microM, it may provide a useful experimental model for the lysosomal storage disorder, Fabry's disease. The addition of a hydroxyl group at C6exo, as in calystegines B1 and C1, enhances the inhibitory potential towards beta-glucosidase and beta-galactosidase but markedly lowers or abolishes inhibition towards alpha-galactosidase. Hence, the N-methylation of calystegine C1 did not enhance its inhibition of alpha-galactosidase. The chemical N-methylation of calystegines A3 and B4 markedly enhanced inhibition of coffee bean alpha-galactosidase, with Ki values of 5.2 microM and 36 microM, respectively, but almost eliminated their inhibitory potential towards beta-glucosidase and trehalase, respectively. Thus, methylation of the nitrogen atom significantly altered the specificity of the inhibitors.

Calystegine B4, a novel trehalase inhibitor from Scopolia japonica

GLC-MS analysis has been developed for screening plants of the family Solanaceae for new calystegines. GLC-MS analyses of the extract of Scopolia japonica showed the presence of a new tetrahydroxy-nor-tropane alkaloid in addition to the known calystegines A3, A5, B1, B2, B3, and C1. We gave this new alkaloid the trivial name calystegine B4. The structure of calystegine B4 was determined as 1 alpha, 2 beta, 3 alpha, 4 alpha-tetrahydroxy-nor-tropane from a variety of NMR spectral data. Calystegines B1, B2, and C1 are potent competitive inhibitors with Ki values ranging from 10(-6) to 10(-7) M for almond beta-glucosidase, while calystegine B4 inhibited this enzyme in a competitive manner, with a Ki value of 7.3 microM. Calystegine B2 is also a potent inhibitor of green coffee bean alpha-galactosidase, whereas calystegine B4 exhibited no significant activity for this enzyme. Among rat intestinal glycosidases, only trehalase was potently inhibited by calystegine B4, with an IC50 value of 9.8 microM. Furthermore, calystegine B4 potently inhibited pig kidney trehalase in a competitive manner, with a Ki value of 1.2 microM, but it was almost inactive against yeast and fungal trehalases.

Calystegins of Physalis alkekengi var. francheti (Solanaceae). Structure determination and their glycosidase inhibitory activities

Five calystegins were extracted from the roots of Physalis alkekengi var. francheti (Solanaceae) with hot water and purified to homogeneity by the combination of a variety of ion-exchange column chromatographies. Their structures have been determined from the 1H- and 13C-NMR spectral data, and two of the compounds were identified as calystegins A3 and B2, which have been isolated from the roots of Calystegia sepium (Convolvulaceae). Two of the remaining three were found to be 1 alpha, 3 alpha, 4 beta-trihydroxy-nor-tropane and 1 alpha, 2 alpha, 3 alpha, 4 beta-tetrahydroxy-nor-tropane and given the trivial name calystegins A5 and B3, respectively. The last calystegin was assigned as 1 alpha, 2 beta, 3 alpha, 6 alpha-tetrahydroxy-nor-tropane, which was the same as the relative configuration proposed in the literature for calystegin B1 isolated from C. sepium. However, the 13C-NMR spectral data for the compound from C. sepium differed substantially from our results. From a personal communication with the authors of the original paper on calystegins, it was clarified that the 13C-NMR chemical shifts of calystegin B1 in the original paper had been erroneous. Since their corrected 13C-NMR data of calystegin B1 and its 1H-NMR chemical shifts in the original paper are very close to our present data, we concluded that both compounds from C. sepium and P. alkekengi are identical. Calystegin B2 has been known to be a potent competitive inhibitor of almond beta-glucosidase (Ki = 1.2 microM) and coffee bean alpha-galactosidase (Ki = 0.86 microM). In this study calystegin B1 (1 alpha, 2 beta, 3 alpha, 6 alpha-tetrahydroxy-nor-tropane) proved to be a potent competitive inhibitor of almond beta-glucosidase (Ki = 1.9 microM) and bovine liver beta-galactosidase (Ki = 1.6 microM), but not an inhibitor of alpha-galactosidases. Calystegin A3 was found to be a weaker inhibitor compared to calystegin B2 but with the same inhibitory spectrum. Calystegin A5, a 2-deoxy derivative of calystegin B2, showed no activity against any glycosidases tested. Since calystegin B3, a 2-epimer of calystegin B2, also exhibited only a weak inhibitory activity, it was concluded that the equatorially oriented OH group at C2 is the essential feature for recognition and strong binding by the active site of glycosidases.(ABSTRACT TRUNCATED AT 400 WORDS)