Sugars with nitrogen in the ring isolated from the leaves of Morus bombycis

Mulberroside F isolated from the leaves of Morus alba inhibits melanin biosynthesis

The current study was carried out to investigate the in vitro effects of an 85% methanol extract of dried Morus alba leaves on melanin biosynthesis, which is closely related to hyperpigmentation. These extracts inhibited the tyrosinase activity that converts dopa to dopachrome in the biosynthetic process of melanin. Mulberroside F (moracin M-6, 3'-di-O-beta-D-glucopyranoside), which was obtained after the bioactivity-guided fractionation of the extracts, showed inhibitory effects on tyrosinase activity and on the melanin formation of melan-a cells. This compound also exhibited superoxide scavenging activity that is involved in the protection against auto-oxidation. But its activity was low and was weaker than of kojic acid. These results suggest that mulberroside F isolated from mulberry leaves might be used as a skin whitening agent.

New sugar-mimic alkaloids from the pods of Angylocalyx pynaertii

Chromatographic separation of the pod extract of Angylocalyx pynaertii resulted in the isolation of 13 sugar-mimic alkaloids (1-13). The structures of the new alkaloids were elucidated by spectroscopic methods as the 6-O-beta-D-glucoside (10) and N-hydroxyethyl derivative (11) of 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) (1), 1,6-dideoxynojirimycin (12), and 1,3,4-trideoxynojirimycin (13). 2,5-Imino-1,2,5-trideoxy-L-glucitol (7), 2,5-dideoxy-2,5-imino-D-fucitol (8), and beta-homofuconojirimycin (9), isolated from the pods as well as the bark, were very specific inhibitors of alpha-L-fucosidase with no significant inhibitory activity toward other glycosidases. In this work, 1,4-dideoxy-1,4-imino-D-ribitol (6) was found to be a better inhibitor of lysosomal beta-mannosidase than 2,5-imino-1,2,5-trideoxy-D-mannitol (2). N-Hydroxyethyl-1-deoxynojirimycin (miglitol), which is commercially available for the treatment of diabetes, retained its inhibitory potential toward rat intestinal maltase and sucrase, whereas 11 and the synthetic N-hydroxyethyl derivative of 2,5-dideoxy-2,5-imino-D-mannitol markedly lowered or abolished their inhibition toward all enzymes tested.

Calystegine distribution in some solanaceous species

The distribution of eight calystegines (A(3), A(5), B(1), B(2), B(3), B(4), C(1) and N(1)) and their content was investigated by gas chromatography coupled to mass spectrometry (GC-MS) in Datura metel, Atropa belladonna, Hyoscyamus albus, Mandragora autumnalis, Solanum sodomaeum, Withania somnifera, Withania frutescens and Brunfelsia nitida. The most frequently encountered calystegines were A(3), B(1), B(2) and B(3), while distribution of N(1) and C(1) was more limited. In all the investigated samples, calystegines A(5) and B(4) were never detected. This report focuses for the first time on calystegines in Withania and Brunfelsia genera and in Mandragora autumnalis and Solanum sodomaeum species.

Automated multiple development thin layer chromatography for calystegines and their biosynthetic precursors

Automated multiple development thin layer chromatography (AMD-TLC) was used for separation of calystegines, a class of nortropane alkaloids, and of precursors of their biosynthesis. The calystegines differ in the number of hydroxyl groups at the nortropane ring system and in the substitution pattern. A combination of TLC methods allows the separation of the individual calystegines and separation of possible precursors of the biosynthesis. Solvent combination, development time, the number of development steps, the drying time between each run and the preconditioning parameters of the silica gel TLC plates were optimised. Limits of detection were evaluated for several detection reagents.

Polyhydroxylated alkaloids isolated from mulberry trees (Morusalba L.) and silkworms (Bombyx mori L.)

New polyhydroxylated alkaloids, (2R,3R,4R)-2-hydroxymethyl-3,4-dihydroxypyrrolidine-N-propionamide from the root bark of Morus alba L., and 4-O-alpha-D-galactopyranosyl-calystegine B(2) and 3 beta,6 beta-dihydroxynortropane from the fruits, were isolated by column chromatography using a variety of ion-exchange resins. Fifteen other polyhydroxylated alkaloids were also isolated. 1-Deoxynojirimycin, a potent alpha-glucosidase inhibitor, was concentrated 2.7-fold by silkworms feeding on mulberry leaves. Some alkaloids contained in mulberry leaves were potent inhibitors of mammalian digestive glycosidases but not inhibitors of silkworm midgut glycosidases, suggesting that the silkworm has enzymes specially adapted to enable it to feed on mulberry leaves. The possibility of preventing the onset of diabetes and obesity using natural dietary supplements containing 1-deoxynojirimycin and other alpha-glucosidase inhibitors in high concentration is of great potential interest.

Dihydroxynortropane alkaloids from calystegine-producing plants

Three dihydroxynortropanes, 2alpha,7beta-dihydroxynortropane, 2alpha,3beta-dihydroxynortropane, and 3alpha,7beta-dihydroxynortropane, were isolated from calystegine-producing plants in the families Convolvulaceae and Solanaceae. 2alpha,7beta-Dihydroxynortropane was isolated from six species in the Convolvulaceae whereas only Calystegia soldanella contained it and 2alpha,3beta-dihydroxynortropane. Although neither of these were detectable in three species tested in the Solanaceae, 3alpha,7beta-dihydroxynortropane was, however, isolated from Duboisia leichhardtii.

Iminosugars: potential inhibitors of liver glycogen phosphorylase

The first synthesis of the single isomers (3R,4R,5R); (3S,4S,5S): (3R,4R,5S) and (3S,4S,5R) of 5-hydroxymethyl-piperidine-3,4-diol from Arecolin is reported, including the synthesis of a series of N-substituted derivatives of the (3R,4R,5R)-isomer (Isofagomine). The inhibitory effect of these isomers as well as of a series of N-substituted derivatives of the (3R,4R,5R)-isomer and selected hydroxypiperidine analogues on liver glycogen phosphorylase (GP) showed that the (3R,4R,5R) configuration was essential for obtaining an inhibitory effect at submicromolar concentration. The results also showed that all three hydroxy groups should be present and could not be substituted, nor were extra OH groups allowed if sub-micromolar inhibition should be obtained. Some inhibitory effect was retained for N-substituted derivatives of Isofagomine; however, N-substitution always resulted in a loss of activity compared to the parent compound, IC50 values ranging from 1 to 100 microM were obtained for simple alkyl, arylalkyl and benzoylmethyl substituents. Furthermore, we found that it was not enough to assure inhibitory effect to have the (R,R,R) configuration. Fagomine, the (2R,3R,4R)-2-hydroxymethylpiperidine-3,4-diol analogue, showed an IC50 value of 200 microM compared to 0.7 microM for Isofagomine. In addition, Isofagomine was able to prevent basal and glucagon stimulated glycogen degradation in cultured hepatocytes with IC50 values of 2-3 microM.

Polyhydroxylated alkaloids -- natural occurrence and therapeutic applications

Over one hundred polyhydroxylated alkaloids have been isolated from plants and micro-organisms. These alkaloids can be potent and highly selective glycosidase inhibitors and are arousing great interest as tools to study cellular recognition and as potential therapeutic agents. However, only three of the natural products so far have been widely studied for therapeutic potential due largely to the limited commercial availability of the other compounds.

Novel alpha-L-fucosidase inhibitors from the bark of Angylocalyx pynaertii (Leguminosae)

The extract of bark of Angylocalyx pynaertii (Leguminosae) was found to potently inhibit mammalian alpha-L-fucosidases. A thorough examination of the extract resulted in the discovery of 15 polyhydroxylated alkaloids, including the known alkaloids from seeds of this plant, 1,4-dideoxy-1,4-imino-D-arabinitol (DAB), 1-deoxymannojirimycin (DMJ) and 2,5-imino-1,2,5-trideoxy-D-mannitol (6-deoxy-DMDP). Among them, eight sugar-mimic alkaloids showed the potent inhibitory activity towards bovine epididymis alpha-L-fucosidase and their Ki values are as follows: 6-deoxy-DMDP (83 microM), 2,5-imino-1,2,5-trideoxy-L-glucitol (0.49 microM), 2,5-dideoxy-2,5-imino-D-fucitol (17 microM), 2,5-imino-1,2,5-trideoxy-D-altritol (3.7 microM), DMJ (4.7 microM), N-methyl-DMJ (30 microM), 6-O-alpha-L-rhamnopyranosyl-DMJ (Rha-DMJ, 0.06 microM), and beta-L-homofuconojirimycin (beta-HFJ, 0.0053 microM). We definitively deduced the structural requirements of inhibitors of alpha-L-fucosidase for the piperidine alkaloids (DMJ derivatives). The minimum structural feature of alpha-L-fucosidase inhibitors is the correct configuration of the three hydroxyl groups on the piperidine ring corresponding to C2, C3 and C4 of L-fucose. Furthermore, the addition of a methyl group in the correct configuration to the ring carbon atom corresponding to C5 of L-fucose generates extremely powerful inhibition of alpha-L-fucosidase. The replacement of the methyl group of beta-HFJ by a hydroxymethyl group reduced its inhibitory potential about 80-fold. This suggests that there may be a hydrophobic region in or around the active site. The existence or configuration of a substituent group on the ring carbon atom corresponding to the anomeric position of L-fucose does not appear to be important for the inhibition. Interestingly, Rha-DMJ was a 70-fold more potent inhibitor of alpha-L-fucosidase than DMJ. This implies that the lysosomal alpha-L-fucosidase may have subsites recognizing oligosaccharyl structures in natural substrates.

Use of borate complexation for the separation of non-UV-absorbing calystegines by capillary electrophoresis

A capillary zone electrophoresis method was developed for the simultaneous analysis of seven closely related polyhydroxyalkaloids called calystegines. Successful results were obtained with a fused-silica capillary, 80 mM sodium tetraborate at pH 9.2 and temperature of 50 degrees C. Detection of non-UV-absorbing calystegines was achieved through in-situ complexation with borate ions. To further improve method sensitivity, a capillary with a bubble cell was used and detection performed at low wavelength (191 nm). Effects of buffer concentration, pH and temperature on migration times and efficiency are discussed. Migration behavior of selected compounds was significantly affected by their chemical structure (i.e., number and position of hydroxy groups). Under optimized conditions, baseline separation of the selected compounds was achieved in less than 12 min. Precision was evaluated by measuring repeatability and intermediate precision of migration times and corrected peak areas. Finally, the method was applied to the qualitative analysis of calystegines in plant extracts and results were confirmed by GC-MS.

Alkaloidal sugar mimetics: biological activities and therapeutic applications

Alkaloids mimicking the structures of sugars inhibit glycosidases because of a structural resemblance to the sugar moiety of the natural substrate. Glycosidases are involved in a wide range of important biological processes, such as intestinal digestion, post-translational processing of glycoproteins and the lysosomal catabolism of glycoconjugates. The realization that alkaloidal sugar mimics might have enormous therapeutic potential in many diseases such as viral infection, cancer and diabetes led to increasing interest and demand for these compounds. In this review, the structural basis of the specificity of alkaloidal sugar mimics and their current and potential applications to biomedical problems are reviewed.

Polyhydroxylated pyrrolidine and piperidine alkaloids from Adenophora triphylla var. japonica (Campanulaceae)

Adenophora triphylla var. japonica (Campanulaceae) yielded two new alkaloids, the 6-C-butyl derivative of 2R,5R-bis(hydroxymethyl)-3R,4R-dihydroxypyrrolidine (DMDP) and alpha-1-C-ethyl-fagomine, together with the known alkaloids 1,4-dideoxy-1,4-imino-D-arabinitol, 1-deoxynojirimycin, and 1-deoxymannojirimycin. 6-C-Butyl-DMDP showed inhibitory activity toward almond beta-glucosidase (IC50 = 68 microM), whereas alpha-1-C-ethyl-fagomine inhibited bovine liver beta-galactosidase (IC50 = 29 microM).

Antioxidative flavonoids from the leaves of Morus alba

Nine flavonoids (1-9) were isolated from the leaves of Morus alba (Moraceae). The structures of compounds were determined to be kaempferol-3-O-beta-D-glucopyranoside (astragalin, 1) kaempferol-3-O-(6"-O-acetyl)-beta-D-glucopyranoside (2), quercetin-3-O-(6"-O-acetyl)-beta-D-glucopyranoside (3), quercetin-3-O-beta-D-glucopyranoside (4), kaempferol-3-O-alpha-L-rhamnopyranosyl-(1-->6)-beta-D-glucopyranoside (5), quercetin-3-O-alpha-L-rhamnopyranosyl-(1-->6)-beta-D-glucopyranoside (rutin, 6), quercetin-3-O-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (7), quercetin-3,7-di-O-beta-D-glucopyranoside (8) and quercetin (9) on the basis of spectroscopic and chemical studies. Compounds 7 and 9 exhibited significant radical scavenging effect on 1,1-diphenyl-2-picrylhydrazyl radical.

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.

Fagomine isomers and glycosides from Xanthocercis zambesiaca

50% aqueous MeOH extracts from the leaves and roots of Xanthocercis zambesiaca (Leguminosae) were subjected to various ion-exchange column chromatographic steps to give fagomine (1), 3-epi-fagomine (2), 3,4-di-epi-fagomine (3), 3-O-beta-D-glucopyranosylfagomine (4), and 4-O-beta-D-glucopyranosylfagomine (5). Their structures were determined by spectroscopic analyses, particularly by extensive 1D and 2D NMR studies. Compounds 3 and 4 are new natural products. Compound 1 is a good inhibitor of isomaltase and certain alpha- and beta-galactosidases. Whereas 2 is a more potent inhibitor of isomaltase and beta-galactosidases than 1, it does not inhibit alpha-galactosidase. Compounds 3-5 exhibited no significant inhibition against the glycosidases used.

Biological activities of the nortropane alkaloid, calystegine B2, and analogs: structure-function relationships

Calystegines, polyhydroxy nortropane alkaloids, are a recently discovered group of plant secondary metabolites believed to influence rhizosphere ecology as nutritional sources for soil microorganisms and as glycosidase inhibitors. Evidence is presented that calystegines mediate nutritional relationships under natural conditions and that their biological activities are closely correlated with their chemical structures and stereochemistry. Assays using synthetic (+)- and (-)-enantiomers of calystegine B2 established that catabolism by Rhizobium meliloti, glycosidase inhibition, and allelopathic activities were uniquely associated with the natural, (+)-enantiomer. Furthermore, the N-methyl derivative of calystegine B2 was not catabolized by R. meliloti, and it inhibited alpha-galactosidase, but not beta-glucosidase, whereas the parent alkaloid inhibits both enzymes. This N-methyl analog therefore could serve to construct a cellular or animal model for Fabry's disease, which is caused by a lack of alpha-galactosidase activity.

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)

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

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-D-arabinitol (5), 1,4-dideoxy-1,4-imino-D-ribitol (6), calystegin B2 (1 alpha,2 beta,3 alpha,4 beta-tetrahydroxy-nor-tropane, 7), calystegin C1 (1 alpha,2 beta,3 alpha,4 beta,6 alpha-pentahydroxy-nor-tropane, 8), 1,4-dideoxy-1,4-imino-(2-O-beta-D-glucopyranosyl)-D-arabinitol (9), and nine glycosides of 1. These glycosides consist of 2-O- and 6-O-alpha-D-galactopyranosyl-1-deoxynojirimycins (10 and 11, respectively), 2-O-, 3-O- and 4-O-alpha-D-glucopyranosyl-1-deoxynojirimycins (12, 13, and 14, respectively), and 2-O-, 3-O-, 4-O- and 6-O-beta-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 A3 is the trihydroxy-nor-tropane, and calystegins B1 and B2 are the tetrahydroxy-nor-tropane. Calystegin C1, a new member of calystegins, is the first naturally occurring pentahydroxy-nor-tropane alkaloid. The inhibitory activities of these compounds were investigated against rat digestive glycosidases and various commercially available glycosidases.