Identification of a regiospecific S-oxygenase for the production of marasmin in traditional medicinal plant Tulbaghia violacea.

Marasmin [S-(methylthiomethyl)-L-cysteine-4-oxide] is a pharmaceutically valuable sulfur-containing compound produced by the traditional medicinal plant, Tulbaghia violacea. Here, we report the identification of an S-oxygenase, TvMAS1, that produces marasmin from its corresponding sulfide, S-(methylthiomethyl)-L-cysteine. The amino acid sequence of TvMAS1 showed high sequence similarity to known flavin-containing S-oxygenating monooxygenases in plants. Recombinant TvMAS1 catalyzed regiospecific S-oxygenation at S4 of S-(methylthiomethyl)-L-cysteine to yield marasmin, with an apparent K m value of 0.55 mM. TvMAS1 mRNA accumulated with S-(methylthiomethyl)-L-cysteine and marasmin in various organs of T. violacea. Our findings suggest that TvMAS1 catalyzes the S-oxygenation reaction during the last step of marasmin biosynthesis in T. violacea.

Recent studies on chemical constituents of Ophiorrhiza plants.

Ophiorrhiza plants (Family Rubiaceae) are known to produce diverse monoterpenoid indole alkaloids including camptothecin with potent antitumor activity. This review contains a summary of recent chemical studies reported over the past 10 years regarding alkaloids (monoterpenoid indole and tetrahydroisoquinoline alkaloids, and cyclopeptide) in Ophiorrhiza plants. In addition, the alkaloid biosynthetic pathways based on their reported structures were proposed.

New otonecine-type pyrrolizidine alkaloid from Petasites japonicus.

One new otonecine-type pyrrolizidine alkaloid secopetasitenine (1), along with petasitenine (fukinotoxine, 2), neopetasitenine (3), and senkirkine (4), was isolated from the whole plant of Petasites japonicus. The structure of 1 was determined by spectroscopic analyses and chemical conversion from the known alkaloid petasitenine (2).

Kopsiyunnanines J1 and J2, new strychnos-type homo-monoterpenoid indole alkaloids from Kopsia arborea.

Two new indole alkaloids, kopsiyunnanines J1 and J2, were isolated from Yunnan Kopsia arborea, and their structures were determined by spectroscopic analyses. Kopsiyunnanines J1 and J2 are unprecedented Strychnos-type indole alkaloids having an additional C1 unit in the secologanin moiety of the molecule.

A flavonoid 3-O-glucoside:2"-O-glucosyltransferase responsible for terminal modification of pollen-specific flavonols in Arabidopsis thaliana.

Flavonol 3-O-diglucosides with a 1→2 inter-glycosidic linkage are representative pollen-specific flavonols that are widely distributed in plants, but their biosynthetic genes and physiological roles are not well understood. Flavonoid analysis of four Arabidopsis floral organs (pistils, stamens, petals and calyxes) and flowers of wild-type and male sterility 1 (ms1) mutants, which are defective in normal development of pollen and tapetum, showed that kaempferol/quercetin 3-O-ß-d-glucopyranosyl-(1→2)-ß-d-glucopyranosides accumulated in Arabidopsis pollen. Microarray data using wild-type and ms1 mutants, gene expression patterns in various organs, and phylogenetic analysis of UDP-glycosyltransferases (UGTs) suggest that UGT79B6 (At5g54010) is a key modification enzyme for determining pollen-specific flavonol structure. Kaempferol and quercetin 3-O-glucosyl-(1→2)-glucosides were absent from two independent ugt79b6 knockout mutants. Transgenic ugt79b6 mutant lines transformed with the genomic UGT79B6 gene had the same flavonoid profile as wild-type plants. Recombinant UGT79B6 protein converted kaempferol 3-O-glucoside to kaempferol 3-O-glucosyl-(1→2)-glucoside. UGT79B6 recognized 3-O-glucosylated/galactosylated anthocyanins/flavonols but not 3,5- or 3,7-diglycosylated flavonoids, and prefers UDP-glucose, indicating that UGT79B6 encodes flavonoid 3-O-glucoside:2″-O-glucosyltransferase. A UGT79B6-GUS fusion showed that UGT79B6 was localized in tapetum cells and microspores of developing anthers.

Orally active opioid µ/δ dual agonist MGM-16, a derivative of the indole alkaloid mitragynine, exhibits potent antiallodynic effect on neuropathic pain in mice.

(E)-Methyl 2-((2S,3S,7aS,12bS)-3-ethyl-7a-hydroxy-8-methoxy-1,2,3,4,6,7,7a,12b-octahydroindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate (7-hydroxymitragynine), a main active constituent of the traditional herbal medicine Mitragyna speciosa, is an indole alkaloid that is structurally different from morphine. 7-Hydroxymitragynine induces a potent antinociceptive effect on mouse acute pain through µ-opioid receptors. In this study, we developed dual-acting µ- and δ-opioid agonists MGM-15 and MGM-16 from 7-hydroxymitragynine for the treatment of acute and chronic pain. MGM-16 showed a higher potency than that of 7-hydroxymitragynine and MGM-15 in in vitro and in vivo assays. MGM-16 exhibited a high affinity for µ- and δ-opioid receptors, with K(i) values of 2.1 and 7.0 nM, respectively. MGM-16 showed µ- and δ-opioid full agonistic effects in a guanosine 5'-O-(3-[(35)S]thiotriphosphate) binding assay and in a functional test using electrically elicited guinea pig ileum and mouse vas deferens contractions. Systemic administration of MGM-16 produced antinociceptive effects in a mouse acute pain model and antiallodynic effects in a chronic pain model. The antinociceptive effect of MGM-16 was approximately 240 times more potent than that of morphine in a mouse tail-flick test, and its antiallodynic effect was approximately 100 times more potent than that of gabapentin in partial sciatic nerve-ligated mice, especially with oral administration. The antinociceptive effect of MGM-16 was completely and partially blocked by the µ-selective antagonist ß-funaltrexamine hydrochloride (ß-FNA) and by the δ-selective antagonist naltrindole, respectively, in a tail-flick test. The antiallodynic effect of MGM-16 was completely blocked by ß-FNA and naltrindole in a neuropathic pain model. These findings suggest that MGM-16 could become a class of a compound with potential therapeutic utility for treating neuropathic pain.

Two new alkaloids from Crinum asiaticum var. sinicum.

Two new alkaloids (1, 2) were isolated from the whole plants of Crinum asiaticum var. sinicum together with seven known alkaloids. The structures of the new alkaloids were elucidated by spectroscopic analyses and chemical conversions from known alkaloids. New alkaloid 1 was isolated for the first time as a natural product, although it has been prepared as a synthetic product.

Discovery of indole alkaloids with cannabinoid CB1 receptor antagonistic activity.

Three indole alkaloids, voacamine (1), 3,6-oxidovoacangine (2), and a new alkaloid, 5-hydroxy-3,6-oxidovoacangine (3), isolated from Voacanga africana were found to exhibit potent cannabinoid CB1 receptor antagonistic activity. This is the first example of CB1 antagonists derived from natural alkaloids.

Bioactive metabolites of Diaporthe sp. P133, an endophytic fungus isolated from Pandanus amaryllifolius.

Two new benzopyranones, diaportheone A (1) and B (2), were obtained via bioassay-guided isolation of the secondary metabolites from the endophytic fungus Diaporthe sp. P133 isolated from Pandanus amaryllifolius leaves. Their structures were determined from spectral analysis including mass spectrometry, 1D and 2D nuclear magnetic resonance. Both 1 and 2 inhibited the growth of the virulent strain of Mycobacterium tuberculosis H(37)Rv with minimum inhibitory concentrations of 100.9 and 3.5 µM, respectively.

Inhibitory effect of Iboga-type indole alkaloids on capsaicin-induced contraction in isolated mouse rectum.

Voacanga africana (Apocynaceae) is used as an anti-diarrheal medicine in West Africa. In the present study, we investigated the effect of an extract of V. africana and its constituents on smooth muscle contraction induced by capsaicin in mouse rectum, where transient receptor potential vanilloid type 1 (TRPV1)-immunoreactive fibers are abundant. Methanol and alkaloid extracts of the root bark of V. africana were found to inhibit capsaicin-induced contraction in a dose-dependent manner (30-300 µg/ml). Major constituents isolated from the alkaloid extract were then studied for their effects on the capsaicin-induced contraction. The main active constituents were found to be Iboga-type alkaloids, including voacangine (1), 3-oxovoacangine (2), voacristine (3), and (7α)-voacangine hydroxyindolenine (4). The voacangine concentration dependently (3-100 µM) inhibited the capsaicin-induced contraction. The capsaicin-induced contraction was almost completely inhibited by the TRPV1 antagonist, N-(4-tertiarybutylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide (BCTC). On the other hand, the Iboga-type alkaloids did not inhibit the contractions induced by 3 µM acetylcholine and 300 µM nicotine. These results suggest that Iboga-type alkaloids isolated from V. africana inhibit capsaicin-induced contraction in the mouse rectum, possibly via the inhibition of a TRPV1-mediated pathway. This inhibition may be involved in the anti-diarrheal effect of V. africana.

Two new aspidosperma indole alkaloids from Yunnan Kopsia arborea.

Two new indole alkaloids, kopsiyunnanines G (1) and H (2), possessing the Aspidosperma skeleton were isolated from the aerial part of Yunnan Kopsia arborea BLUME (Apocynaceae). Their structures and stereochemistry were elucidated by means of MS and 2D NMR analyses.

Amides, triterpene and flavonoids from the leaves of Melastoma malabathricum L.

Successive extraction of the dried leaves of Melastoma malabathricum, followed by purification using repeated chromatographic techniques, yielded six compounds, including two amides, auranamide and patriscabratine, a triterpene, alpha-amyrin, and three flavonoids, quercitrin, quercetin and kaempferol-3-O-(2'',6''-di-O-p-trans-coumaroyl)-beta-glucoside. Their structures were elucidated by spectroscopic means and also by direct comparison of their spectroscopic data with respective published data. These three phenolic constituents were found to be active as free radical scavengers, with quercetin being the strongest radical scavenger, having an IC(50) value of 0.69 microM in the UV method. Quercitrin and kaempferol-3-O-(2'',6''-di-O-p-trans-coumaroyl)-beta-glucoside showed moderate radical scavenging, with IC(50) values of 74.1 and 108.8 microM, respectively.

Kopsiyunnanines F and isocondylocarpines: new tubotaiwine-type alkaloids from Yunnan Kopsia arborea.

Five new alkaloids, including three 19,20-epoxytubotaiwine stereoisomers, viz. kopsiyunnanines F1 (1), F2 (2), and F3 (3), (Z)-isocondylocarpine (4), and (Z)-isocondylocarpine N-oxide (5), along with five known tubotaiwine-type indole alkaloids were isolated from the aerial part of Yunnan Kopsia arborea Blume (Apocynaceae). Their structures including absolute configurations were elucidated by spectroscopic and chemical means.

Rhazinilam and quebrachamine derivatives from Yunnan Kopsia arborea.

Three new rhazinilam-derived alkaloids, kopsiyunnanines C1, C2, and C3, and a new quebrachamine-type alkaloid, kopsiyunnanine D, which possess an unusual methoxymethyl or ethoxymethyl function, were isolated from the aerial parts of Yunnan Kopsia arborea. This is the first report of the presence of these functions in natural alkaloids. The structures and absolute configurations of the alkaloids were determined by spectroscopic methods and confirmed by semisynthesis.

MGM-9 [(E)-methyl 2-(3-ethyl-7a,12a-(epoxyethanoxy)-9-fluoro-1,2,3,4,6,7,12,12b-octahydro-8-methoxyindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate], a derivative of the indole alkaloid mitragynine: a novel dual-acting mu- and kappa-opioid agonist with potent antinociceptive and weak rewarding effects in mice.

Mitragynine is a major indole alkaloid isolated from the Thai medicinal plant Mitragyna speciosa that has opium-like properties, although its chemical structure is quite different from that of morphine. We attempted to develop novel analgesics derived from mitragynine, and thus synthesized the ethylene glycol-bridged and C10-fluorinated derivative of mitragynine, MGM-9 [(E)-methyl 2-(3-ethyl-7a,12a-(epoxyethanoxy)-9-fluoro-1,2,3,4,6,7,12,12b-octahydro-8-methoxyindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate]. We hypothesized that a dual-acting mu- and kappa-opioid agonist could produce potent antinociceptive effects with fewer rewarding effects compared with mu agonists. In this study, MGM-9 exhibited high affinity for mu- and kappa-opioid receptors with Ki values of 7.3 and 18 nM, respectively. MGM-9 showed a potent opioid agonistic effect, and its effects were meditated by mu- and kappa-opioid receptor mechanisms in in vitro assays. Subcutaneous and oral administration of MGM-9 produced potent antinociceptive effects in mouse tail-flick, hot-plate, and writhing tests. When administered orally, the antinociceptive effect of MGM-9 was seven to 22 times more potent than that of morphine. The antinociceptive effects of MGM-9 were mediated by both mu- and kappa-opioid receptors. Subcutaneous administration of MGM-9 twice daily for 5 days led to antinociceptive tolerance. In the gastrointestinal transit study, MGM-9 inhibited gastrointestinal transit, but its effect was weaker than that of morphine at equi-antinociceptive doses. Furthermore, MGM-9 induced less hyperlocomotion and fewer rewarding effects than morphine. The rewarding effect of MGM-9 was blocked by a mu antagonist and enhanced by a kappa antagonist. Taken together, the results suggest that MGM-9 is a promising novel analgesic that has a stronger antinociceptive effect and weaker adverse effects than morphine.

A new prenylated dihydrochalcone from the leaves of Artocarpus lowii.

A new prenylated dihydrochalcone, 2',4'-dihydroxy-4-methoxy-3'-prenyldihydrochalcone (1), along with two known compounds, 2',4',4-trihydroxy-3'-prenylchalcone (2) and 2',4-dihydroxy-3',4'-(2,2-dimethylchromene)chalcone (3) were isolated from the leaves of Artocarpus lowii. The structures of 1-3 were elucidated by spectroscopic methods and by comparison with data reported in the literature. Compounds 1-3 showed strong free radical scavenging activity towards 2,2-diphenyl-1-picrylhydrazyl (DPPH) measured by electron spin resonance (ESR) spectrometry.

Antitubercular triterpenes and phytosterols from Pandanus tectorius Soland. var. laevis.

Bioassay-guided chromatographic purification of the antitubercular chloroform extract of Pandanus tectorius Soland. var. laevis leaves afforded a new tirucallane-type triterpene, 24,24-dimethyl-5 beta-tirucall-9(11),25-dien-3-one (1), squalene and a mixture of the phytosterols stigmasterol and beta-sitosterol. Microplate Alamar Blue Assay (MABA) showed that 1 inhibited the growth of Mycobacterium tuberculosis H(37)Rv with a MIC of 64 microg/mL, while squalene and the sterol mixture have MICs of 100 and 128 microg/mL, respectively.

Flavonols from Bauhinia malabarica.

Bauhinia malabarica Roxb. has been used in Thai traditional medicine for wound healing, as a diuretic, to fight dysentery and as an emmenagogue. Seven flavonols, including 6,8-di-C-methylkaempferol 3-methyl ether, kaempferol, afzelin, quercetin, isoquercitrin, quercitrin, and hyperoside were isolated from the methanol extract of leaves.

First total synthesis of trimeric indole alkaloid, psychotrimine.

The first total synthesis of (+/-)-psychotrimine, a novel trimeric indole alkaloid isolated from Psychotria rostrata, was achieved. In the total synthesis, the copper-mediated intramolecular and intermolecular aminations of halobenzenes, which respectively contributed to the construction of a pyrrolidinoindoline core and the installation of a third tryptamine unit, were used as key steps.

Design, synthesis, and biological evaluation of tricyclic heterocycle-tetraamine conjugates as potent NMDA channel blockers.

We have developed a new class of N-methyl-d-aspartate (NMDA) channel blockers having a conjugate structure that consists of a nitrogenous heterocyclic head and a tetraamine tail. Among them, dihydrodibenzazepine-homospermine conjugate (8) exhibited potent antagonistic activity at NR1/NR2A or NR1/NR2B NMDA subtype receptors compared with the lead compound, AQ343 (1), or memantine, as well as weak cytotoxicity. Its superior biological profiles compared with known compounds point to its potential use as therapeutic agents for neurological disorders.