[Seperation and structure elucidation of alkaloids from Chinese drug buzhaye, Folium Microcos].

From the chloroform extracts of the dried Folium Microcos, four compounds were isolated by using repeated column chromatography on silica gel and recrystallization and their structures were elucidated by physicochemical properties and UV, MS and NMR, separately. They are N-methyl-6alpha-(deca-1', 3', 5'-trienyl)-3beta-methoxy-2beta-methylpiperidine, 6-(deca-1', 3', 5'-trienyl)-3-methoxy-2-methylpiperidine, N-methyl-6-(deca-1', 3', 5'-trienyl)-2, 3-dimethylpiperidine and N-methyl-6-(deca-1', 3', 5'-trienyl)-2-methylpiperidine, named as micropiperidine A, micropiperidine B, micropiperidine C and micropiperidine D, respectively. The latter three are new compounds.

Screening of plant extracts for antiprotozoal and cytotoxic activities.

Methanolic and aqueous extracts derived from 43 plant species, selected either from ethnobotanical or chemotaxonomical data, were screened for their antiprotozoal activity against Leishmania donovani and Trypanosoma brucei brucei. The cytotoxic activity against KB cells was also determined. Eight extracts had IC50 values of less than 10 microg/ml against Leishmania donovani. The most active was Triclisia patens with an IC50 value of 1.5 microg/ml against Leishmania donovani. Annona purpurea and Alstonia macrophylla had IC50 values below 10 microg/ml against Trypanosoma brucei brucei. Annona purpurea was the most cytotoxic against KB cells.

St John's wort (Hypericum perforatum L.): a review of its chemistry, pharmacology and clinical properties.

The chemical composition of St. John's wort has been well-studied. Documented pharmacological activities, including antidepressant, antiviral, and antibacterial effects, provide supporting evidence for several of the traditional uses stated for St John's wort. Many pharmacological activities appear to be attributable to hypericin and to the flavonoid constituents; hypericin is also reported to be responsible for the photosensitive reactions that have been documented for St. John's wort. With regard to the antidepressant effects of St John's wort, hyperforin, rather than hypericin as originally thought, has emerged as one of the major constituents responsible for antidepressant activity. Further research is required to determine which other constituents contribute to the antidepressant effect. Evidence from randomised controlled trials has confirmed the efficacy of St John's wort extracts over placebo in the treatment of mild-to-moderately severe depression. Other randomised controlled studies have provided some evidence that St John's wort extracts are as effective as some standard antidepressants in mild-to-moderate depression. There is still a need for further trials to assess the efficacy of St John's wort extracts, compared with that of standard antidepressants, particularly newer antidepressant agents, such as the selective serotonin reuptake inhibitors (recent comparative studies with fluoxetine and sertraline have been conducted). Also, there is a need for further studies in well-defined groups of patients, in different types of depression, and conducted over longer periods in order to determine long-term safety. St John's wort does appear to have a more favourable short-term safety profile than do standard antidepressants, a factor that is likely to be important in patients continuing to take medication. Concerns have been raised over interactions between St John's wort and certain prescribed medicines (including warfarin, ciclosporin, theophylline, digoxin, HIV protease inhibitors, anticonvulsants, selective serotonin reuptake inhibitors, triptans, oral contraceptives); advice is that patients taking these medicines should stop taking St John's wort, generally after seeking professional advice as dose adjustment of conventional treatment may be necessary.

Phytochemistry and medicinal plants.

A truncated history of the contribution of plants to medicine is given with reference to some of the less well known ancestors of the Harborne family. Six of the top 20 prescriptions dispensed in 1996 were natural products and the clinical use of drugs such as artemisinin, etoposide and taxol has once more focussed attention on plants as sources of novel drug entities. High through-put robotic screens have been developed by industry and it is possible to carry out 50,000 tests per day in the search for compounds which have specificity of action against a key enzyme or a subset of receptors. Bioassay-guided fractionation of plant extracts linked to chromatographic separation techniques leads to the isolation of biologically active molecules whose chemical structures can readily be determined by modern spectroscopic methods. The role of academics in the search for new drugs is discussed by reference to some of our research into natural products with activity on the central nervous system, on pain receptors, the malaria parasite Plasmodium falciparum, the wound healing properties of the sap of species of Croton (Dragon's blood), and a traditional Chinese medicine used to treat eczema. Expertise in phytochemistry has been essential for this research and the strong lead shown by Professor Jeffrey Harborne is gratefully acknowledged.

Terpenoids from Guarea rhophalocarpa.

Four new terpenes including, two sandaracopimaradiene diterpenoids, ent-8(14),15-sandaracopimaradiene-2alpha,18-diol, and ent8(14),15-sandaracopimaradiene-2beta,18-diol, and two lanostane triterpenoids, 23-hydroxy-5alpha-lanosta 7,9(11),24-triene-3-one, and 5alpha-lanosta-7,9(11),24-triene-3alpha,23-diol, were isolated from the methanolic extract prepared from the leaves of G. rhopalocarpa together with the known steroid stigmasterol and the coumarin, scopoletin. The isolates showed weak antiprotozoal activity against Leishmania donovani promastigotes, and Trypanosoma brucei brucei blood stream trypomastigotes, and were devoid of interesting activity towards Plasmodium falciparum. The isolates did not show significant cytotoxic activity against KB cells.

Anti-leishmanial activity of neolignans from Virola species and synthetic analogues.

Surinamensin, a neolignan isolated from Virola surinamensis, 3,4,5-trimethoxy-8-[2',6'-dimethoxy-4'-(E)-propenylphenoxy]-phenylpropane, a neolignan isolated from Virola pavonis, and 25 of its synthetic analogues or correlated substances with ether linkages and their corresponding C-8 sulphur and nitrogen analogues, were tested for activity against Leishmania donovani amastigotes and promastigotes in vitro. Some were active against L. donovani promastigotes at 30 microM but inactive against intracellular amastigotes. The natural neolignan from V. pavonis was active against promastigotes at 100 microM. The highest selective activity was found in those compounds with sulphur bridges. The beta-ketosulfide (3,4-dimethoxy)-8-(4'-methylthiophenoxy)-propiophenone produced 42% inhibition of L. donovani amastigotes in the liver of BALB/c mice at 100 mg/kg given once daily for five consecutive days (P>0.05).

Antiplasmodial and antiamoebic activities of medicinal plants from Sierra Leone.

Crude ethanol extracts of 18 medicinal plants from Sierra Leone, West Africa were examined for antiplasmodial activity against Plasmodium falciparum, using an in vitro microtest. Eleven of these extracts were also screened for in vitro antiamoebic activity against Entamoeba histolytica. Only one plant extract, Triclisia patens (Menispermaceae) showed significant antiplasmodial activity (IC(50) = 8 microg/mL). None of the plant extracts was effective against Entamoeba histolytica.

Bioactive compounds from Celaenodendron mexicanum.

Bioactivity-directed fractionation of the CHCl3-MeOH extract of the leaves of Celaenodendron mexicanum by means of the brine shrimp lethality test and chromatographic techniques led to the isolation of three carboxylic acid triterpenes, the new tirucalla-type triterpene, 3 alpha-hydroxytirucalla-7,24Z-dien-26-oic acid, 3-oxotirucalla-7,24Z-dien-26-oic acid, and epi-oleanolic acid, and three biflavonoids amentoflavone, podocarpusflavone A, and podocarpusflavone B. Four non-active compounds friedelin, maytensifolin B, 3 beta-hydroxyfriedelan-16-one, and celaenodendrolide were also obtained. epi-Oleanolic acid was the most active against brine shrimps with LC50 value of 23.3 microM. In addition, all isolates were tested for in vitro antiprotozoal and cytotoxic activities. 3-Oxotirucalla-7,24Z-dien-26-oic acid and epi-oleanolic acid showed the highest activity against Leishmania donovani promastigotes with IC50 values of 13.7 and 18.8 microM, respectively. Only 3-oxotirucalla-7,24Z-dien-26-oic acid showed activity against Trypanosoma brucei brucei bloodstream forms with IC50 value of 16.8 microM.

Oxoaporphine alkaloids and quinones from Stephania dinklagei and evaluation of their antiprotozoal activities.

Bioactivity-guided fractionation of Stephania dinklagei yielded six compounds including, two zwitterionic oxoaporphine alkaloids, N-methylliriodendronine, and 2-O,N-dimethylliriodendronine, two oxoaporphine alkaloids, liriodenine, and dicentrinone, one aporphine alkaloid, corydine, and one anthraquinone, aloe-emodin. Apart from corydine, the isolates have not been reported as constituents of S. dinklagei. N-Methylliriodendronine, and 2-O,N-dimethylliriodendronine are reported for the first time as natural products. All isolated compound were tested for antiprotozoal activity and cytotoxic activities in vitro. N-Methylliriodendronine was the most active against L. donovani amastigotes (IC50 = 36.1 microM). Liriodenine showed the highest activity against Leishmania donovani, and Plasmodium falciparum with IC50 values of 26.16 and 15 microM, respectively. Aloe-emodin was the only compound active (IC50 = 14 microM) against T. b. brucei.

Ethnomedicinally selected plants as sources of potential analgesic compounds: indication of in vitro biological activity in receptor binding assays.

A number of plant species used in traditional medicine for the relief of pain have been selected from the medicinal and scientific literature of China, South America, Asia and West Africa. Extracts were prepared and tested in three in vitro receptor radioligand binding assays to determine whether there was an indication of biological activity, in particular their selectivity to a single receptor implicated in the mediation of pain. The three neuropeptide receptors chosen were Bradykinin (BK II), expressed in Chinese hamster ovary cells (CHO), neurokinin 1 (NK 1) expressed in astrocytoma cells, and calcitonin gene related peptide (CGRP) which were all implicated in the mediation of acute pain in the mammaliancentral nervous system. The plant species chosen to investigate were Ageratum conyzoides, Barringtonia edulis, Croton tiglium, Ipomea pes-caprae, Panax ginseng, Physostigma venenosum, Sinomenium acutum, Solidago virgaurea, Symplocos leptophylla and Typhonium giganteum. The results showed that there was a strong indication of biological activity for some of the plants which are used ethnomedicinally to treat pain, in the three in vitro receptor binding assays used, and particular plant extracts exhibited selective action to a single receptor.

In vitro antiplasmodial, antiamoebic, and cytotoxic activities of some monomeric isoquinoline alkaloids.

Twenty-one alkaloids have been assessed for activities against Plasmodium falciparum (multidrug- resistant strain K1) in vitro; 18 of these are reported for the first time. Two protoberberine alkaloids, dehydrodiscretine and berberine, were found to have antiplasmodial IC(50) values less than 1 M, while seven alkaloids-allocrytopine, columbamine, dehydroocoteine, jatrorrhizine, norcorydine, thalifendine, and ushinsunine-had values between 1 and 10 M. These results are discussed in the context of structure-activity relationships. Compounds were also assessed for antiamoebic and cytotoxic activities, but none was significantly active except for berberine, which was moderately cytotoxic.

Plant polyphenols: biologically active compounds or non-selective binders to protein?

Twenty phenolic compounds, representatives of proanthocyanidins and gallic acid/hexahydroxyldiphenic acid esters of glucose, have been assessed for their ability to inhibit binding of specific radioligands to 16 receptors. The receptors utilized were alpha 1-, alpha 2- and beta-adrenoceptors, adenosine 1, dopamine 1 and 2, muscarinic, Ca2+ channel, sulphonylureas, 5HT1, 5HT1A, 5HT2, histamine 1, benzodiazepine, opiate and Na+/K/ATPase. These phenolic compounds failed to inhibit ligands binding to 10 of the receptors under the test conditions. The most susceptible receptors to phenolic binding were beta-adrenergic, 5HT1 and opiate. Some of the compounds tested showed selectivity for a single or for two receptors. The inhibition of binding of radioligands to receptors by the phenolic compounds cannot be explained solely in terms of phenolic-protein binding. The results indicate that the removal of tannins from plant extracts prior to screening for receptor activities may result in missing biologically active compounds with specificity of action.

Application of radioligand receptor binding assays in the search for CNS active principles from Chinese medicinal plants.

Extracts of Schefflera bodinieri and S. delavayi (Araliaceae), Celastrus angulatus and C. orbiculatus (Celastraceae), Clerodendrum mandarinorum and C. bungei (Verbenaceae), Periploca callophylla and P. forrestii (Asclepiadaceae), Alangium platanifolium (Alangiaceae) and Uncaria rhynchophylla (Rubiaceae) were assessed for CNS activity against 18 radioligand receptor binding assays. The receptors used were alpha 1-, alpha 2- and beta-adrenoceptors, 5HT-1, 5HT-1A, 5HT-2, opiate, adenosine-1, benzodiazepine, Ca+2 channel, sulphonylureas, dopamine-1, dopamine-2, muscarinic, histamine-1, Na+/K+ ATPase, GABAA and GABAB. The results indicate that these ligand-receptor binding assays are useful for understanding the mode of action of herbal medicines and for bioassay guided fractionation of plant active ingredients.

Chemical and biological investigation of the root bark of Clerodendrum mandarinorum.

A 70% EtOH extract of Clerodendrum mandarinorum root bark was assessed for CNS activity against 18 radioligand receptor binding assays. The results showed that the extract was able to bind to opiate, adenosine-1, alpha 2-adrenergic, 5HT-1, 5HT-2, dopamine-2, histamine-1, GABA(A), and GABA(B) receptors. Fourteen compounds were isolated and identified by El-MS, 1H-NMR and 13C-NMR spectra as known triterpenoids (friedelanone, lupeol, betulinic acid), steroids (24S-stigmata-5,25-dien-3 beta-ol,22E,24S-stigmata-5,22,25-trien-3 beta-ol), flavonoids (cirsimaritin, cirsimaritin-4'-glucoside, quercetin-3-methyl ether), tetra-hydro-alpha-pyrone and saccharides (sucrose, alpha-D- and beta-D-glucopyranose, ethyl-alpha-D-glucopyranoside, 2-ethyl-beta-D-fructofuranoside). The isolated compounds were assessed for activity by the radioligand receptor binding assays. Betulinic acid and ethyl-alpha-D-glucopyranoside showed weak activities against sulphonylureas (IC50 = 7.5 microM) and muscarinic receptors (IC50 = 5.5 microM), respectively. Cirsimaritin-4'-glucoside was weakly active in the adenosine-1 binding assay (IC50 = 3.0 microM), whereas seven structurally related flavonoids, not isolated from C.mandarinorum, were inactive.

Anthranilate synthase in microorganisms and plants.

The enzymology of anthranilate synthase (EC 5.4.99.6) in microorganisms and plants is reviewed. Aminoacid sequences of the enzyme subunits in different species are compared, and the mechanism of reaction is discussed.

A matter of some sensitivity.

The development of sensitive chromatographic and spectroscopic techniques for the isolation and structure determination of natural products has greatly facilitated phytochemical investigations. Chemical investigations of herbarium material have resulted in the isolation of indole, quinoline and isoquinoline alkaloids from a wide number of plants. Examples of novel natural products from higher plants are given and include alkaloids, terpenoids, phenolics and quinones. Some plants investigated have not yielded the types of constituents which would have been predicted from them. Plant tissue cultures provide alternative sources of biologically active compounds and examples investigated include Cinchona, Ailanthus, Brucea and Artemisia for antiprotozoal compounds and Datura for tropane alkaloids. Biological tests are useful for bioassay-guided fractionation of plant extracts and examples of the isolation of a series of natural products with antiprotozoal and cytotoxic activities are given. Chemical and biological investigations into the traditional medicine Dragon's blood (Croton lechleri) from S. America and a Chinese prescription for the treatment of atopic eczema are described. The use of radio-ligand binding assays for the detection of a wide range of biological activities is discussed. Sensitivity of chemical and biological techniques has greatly improved prospects for finding new drug entities from plants and for investigating traditional medicines. Basic phytochemical investigations should continue to be encouraged especially in view of the rapid loss of plant species.

Bio-active compounds from Psychotria camponutans.

A new benzoquinone (1-hydroxybenzoisochromanquinone) and benz [g]isoquinoline-5, 10-dione have been isolated from the woody parts of Psychotria camponutans, as a result of bioactivity-guided fractionation. The compounds were characterized by UV, IR, EI-mass, 1H-, and 13C-NMR, and HETCOR NMR spectroscopy. Both compounds, together with acetylbenzoisochromanquinone, showed in vitro strong activity against brine shrimp, KB cells, and chloroquine-resistant P. falciparum.

Bioactive anthraquinone glycosides from Picramnia antidesma spp. fessonia.

A bioactivity guided fractionation, using KB cells and brine shrimp assays, of the methanolic extract from the leaves of Picramnia antidesma yielded two known anthraquinones, aloe-emodin and aloe-emodin anthrone, and three new aloe-emodin C-glycosides, named picramnioside A, picramnioside B and picramnioside C. Structures were established by spectroscopic methods (UV, IR, mass spectrometry, 1H and 13C and 2D NMR including COSY 45, HMQC, HMBC and ROESY). CD was used to establish the absolute configuration of the picramniosides.