Nitrogen-containing furanose and pyranose analogues from Hyacinthus orientalis

The inhibitory action of pyrrolidine alkaloid, 1,4-dideoxy-1,4-imino-D-ribitol, on eukaryotic DNA polymerases

The pyrrolidine alkaloids mimicking the structures of pentose with nitrogen in the ring are known to be inhibitors of glycosidases. We report here that a compound belonging to this category is an inhibitor of eukaryotic DNA polymerases. Among the eight naturally occurring pyrrolidine alkaloids we tested, only one compound, 1,4-dideoxy-1,4-imino-D-ribitol (DRB), which was purified from the mulberry tree (Morus alba), strongly inhibited the activities of eukaryotic DNA polymerases with IC50 values of 21-35 microM, and had almost no effect on the activities of prokaryotic DNA polymerases, nor DNA metabolic enzymes such as human immunodeficiency virus type 1 reverse transcriptase, T7 RNA polymerase, and bovine deoxyribonuclease I. Kinetic studies showed that inhibition of both DNA polymerases alpha and beta by DRB was competitive with respect to dNTP substrate. Whereas DNA polymerase alpha inhibition was noncompetitive with the template-primer, the inhibition of DNA polymerase beta was found to be competitive with the template-primer. The K(i) values of DNA polymerases alpha and beta for the template-primer were smaller than those for dNTP substrate. Therefore, the affinity of DRB was suggested to be higher at the template-primer binding site than at the dNTP substrate-binding site, although DRB is an analogue of deoxyribose consisting of dNTP. Computational analyses of the eight pyrrolidine alkaloids revealed a remarkable difference in the distribution of positive and negative electrostatic charges on the surface of molecules. The relationship between the structure of DRB and the inhibition of eukaryotic DNA polymerases is discussed.

New polyhydroxylated pyrrolidine, piperidine, and pyrrolizidine alkaloids from Scilla sibirica

Chromatographic separation of an extract of the bulbs of Scilla sibirica resulted in the isolation of five pyrrolidines, two pyrrolidine glycosides, six piperidines, one piperidine glycoside, and eight pyrrolizidines. 2,5-Dideoxy-2,5-imino-glycero-d-manno-heptitol (homoDMDP, 1) is a common alkaloid in all plants of the Hyacinthaceae examined to date and was also found in S. sibirica. The structures of the new alkaloids were elucidated by spectroscopic methods as 7-deoxy-homoDMDP (4), 2,5-dideoxy-2,5-imino-glycero-d-galacto-heptitol (5), the 4-O-beta-d-mannoside (6) and the 4-O-beta-d-mannobioside (7) of 6-deoxy-homoDMDP (2), 7-deoxyhomonojirimycin (12), 7-deoxyhomomannojirimycin (13), and polyhydroxypyrrolizidines, hyacinthacines A(4) (15), A(5) (16), A(6) (17), A(7) (18), B(4) (20), B(5) (21), and B(6) (22). HomoDMDP (1) is a potent inhibitor of beta-glucosidase and beta-galactosidase, while 6-deoxy-homoDMDP (2) showed significantly less inhibition. However, 7-deoxygenation of 1, leading to 4, showed no effect on the inhibitory activity toward both enzymes. Although 2 is not an inhibitor of alpha-l-fucosidase, the monomannoside of 2 shows inhibitory activity toward alpha-l-fucosidase. Elongation of the beta-mannopyranosyl chain of 6 to give 7 enhanced the inhibitory activity.

Polyhydroxy alkaloids: chromatographic analysis

Polyhydroxy alkaloids are a burgeoning category of natural products that encompass several structural types and generally exhibit potent activity as inhibitors of glycosidases. As presently defined the group consists of monocyclic or bicyclic aLkaloids of the pyrrolidine, piperidine, pyrrolizidine, indolizidine and tropane classes, bearing two or more hydroxyl groups. These structural features render the compounds highly water soluble and frequently quite insoluble in non-hydroxylic solvents, so that their isolation and analysis by chromatographic means are consequently difficult. This problem is further confounded by the lack of a chromophore which would permit their detection by UV absorption. This review presents chromatographic techniques that have been successfully applied to the problem of isolating, purifying, detecting and analyzing polyhydroxy alkaloids.

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.

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).

Homonojirimycin analogues and their glucosides from Lobelia sessilifolia and Adenophora spp. (Campanulaceae)

2,6-Dideoxy-7-O-(beta-D-glucopyranosyl) 2,6-imino-D-glycero-L-gulo- heptitol (7-O-beta-D-glucopyranosyl-alpha-homonojirimycin, 1) was isolated from the 50% methanol extract of the whole plant of Lobelia sessilifolia (Campanulaceae), which was found to potently inhibit rice alpha-glucosidase. Adenophorae radix, roots of Adenophora spp. (Campanulaceae), yielded new homonojirimycin derivatives, adenophorine (2), 1-deoxyadenophorine (3), 5-deoxyadenophorine (4), 1-C-(5-amino-5-deoxy-beta-D-galactopyranosyl)butane (beta-1-C-butyl-deoxygalactonojirimycin, 5), and the 1-O-beta-D-glucosides of 2 (6) and 4 (7), in addition to the recently discovered alpha-1-C-ethylfagomine (8) and the known 1-deoxymannojirimycin (9) and 2R,5R-bis(hydroxymethyl)-3R,4R- dihydroxypyrrolidine (DMDP, 10). Compound 4 is a potent inhibitor of coffee bean alpha-galactosidase (IC50 = 6.4 microM) and a reasonably good inhibitor of bovine liver beta-galactosidase (IC50 = 34 microM). Compound 5 is a very specific and potent inhibitor of coffee bean alpha-galactosidase (IC50 = 0.71 microM). The glucosides 1 and 7 were potent inhibitors of various alpha-glucosidases, with IC50 values ranging from 1 to 0.1 microM. Furthermore, 1 potently inhibited porcine kidney trehalase (IC50 = 0.013 microM) but failed to inhibit alpha-galactosidase, whereas 7 was a potent inhibitor of alpha-galactosidase (IC50 = 1.7 microM) without trehalase inhibitory activity.

A Versatile Synthetic Strategy for the Preparation and Discovery of New Iminocyclitols as Inhibitors of Glycosidases

A series of iminocyclitols was prepared using a versatile synthetic strategy, and their inhibition of glycosidases was evaluated using capillary electrophoresis. The study has demonstrated that remarkable specificities in enzyme inhibition can be achieved with small modifications on the aglycon side chain and the ring nitrogen. Among the compounds synthesized, (2R,3R,4R,5R)-N-methyl-2-(acetamidomethyl)-3,4-dihydroxy-5-(hydroxymethyl)pyrrolidine was found to be very potent against β-N-acetylhexosaminidase P with the K_i value of 80 nM.

Polyhydroxylated pyrrolidine and pyrrolizidine alkaloids from Hyancinthoides non-scripta and Scilla campanulata

Aqueous ethanol extracts from the immature fruits and stalks of bluebell (Hyacinthoides non-scripta) were subjected to various ion-exchange column chromatographic steps to give 1,4-dideoxy-1,4-imino-D-arabinitol (1),2(R),5(R)-bis(hydroxymethyl)-3(R),4(R)-dihydroxypyrrolidine (DMDP) (2), 6-deoxy-6-C-(2,5-dihydroxyhexyl)-DMDP (3),2,5-dideoxy-2,5-imino-DL-glycero-D-manno-heptitol (homoDMDP)(4),homoDMDP-7-O-apioside (5), homoDMDP-7-O-beta-D-xylopyranoside (6), (1S*,2R*,3R*,5R*,7aR*)-1,2-dihydroxy-3,5- dihydroxymethylpyrrolizidine (7), and (1S*,2R*,3R*,5R*,6R*,7R*,7aR*)-3-hydroxymethyl-5-methyl-1,2,6,7 tetrahydroxypyrrolizidine (8). Bulbs of Scilla campanulata (Hyacinthaceae) yielded (1S*,2R*,3R*,5S*,7aR*)-1,2-dihydroxy-3,5-dihydroxy-methylpyrrol izidine (9) in addition to compounds 1-7. Compounds 3,6,7,8, and 9 are new natural products. Compound 4 is a potent competitive inhibitor with K(i) values of 1.5 microM for Caldocellum saccharolyticum beta-glucosidase and 2.2 microM for bovine liver beta-galactosidase. The 7-O-beta-D xyloside 6 was a stronger competitive inhibitor than 4 of C saccharolyticum beta-glucosidase and rat intestinal lactase, with K(i) values of 0.06 and 0.07 microM, respectively, but a weaker inhibitor of bovine liver beta-galactosidase. Furthermore, compound 4 is also a competitive inhibitor (K(i) = 1.8 microM) of porcine kidney trehalase, but 6 was inactive against this enzyme.