ISOLATION AND CHARACTERIZATION OF CHEMICAL CONSTITUENTS FROM CHRYSOPHYLLUM ALBIDUM G. DON-HOLL. STEM-BARK EXTRACTS AND THEIR ANTIOXIDANT AND ANTIBACTERIAL PROPERTIES.

BACKGROUND: The plant, Chrysophyllum albidum is indigenous to Nigeria and its stem-bark has wide application in traditional medicine for the treatment of infections and oxidative stress related diseases. The aim of the study was to isolate the chemical constituents responsible for the antioxidant and antibacterial activity from the stem-bark of the plant in order to justify some of its ethnomedicinal uses. MATERIALS AND METHODS: Crude extract of stem-bark of Chrysophyllum albidum obtained from 80% ethanol was successively partitioned with ethyl acetate (EtOAc) and n-butanol. The solvent fractions and isolated compounds were tested for antioxidant property using 2-2-diphenyl-1-picrylhydrazyl. Antibacterial activities were also assessed by means of agar-diffusion and broth micro dilution methods. EtOAc fraction was repeatedly fractionated on column chromatography to afford four compounds and their chemical structures were established using NMR (1D and 2D) and MS. RESULTS: Chromatographic fractionation of EtOAc fraction with the highest antioxidant and antimicrobial activities afforded stigmasterol (1),: epicatechin (2),: epigallocatechin (3): and procyanidin B5 (4).: Procyanidin B5 isolated for the first time from genus Chrysophyllum demonstrated the highest antioxidant activity with IC50 values of 8.8 µM and 11.20 µM in DPPH and nitric oxide assays respectively and equally demonstrated the highest inhibitory activity against Escherichia coli (MIC 156.25 µg/mL), Staphylococcus aureus (MIC 156.25 µg/mL), Pseudomonas aeruginosa (MIC 625 µg/mL) and Bacillus subtilis (MIC 156.25 µg/mL). CONCLUSION: The antibacterial and antioxidant activities of epicatechin, epigallocatechin and procyanidin B5 isolated from Chrysophyllum albidum stem-bark validate the folkloric uses.

Toxicity and mutagenic activity of some selected Nigerian plants.

The toxicity and mutagenic potential of most African plants implicated in the management of cancer have not been investigated. The ethanolic extracts of selected Nigerian plants were subsequently studied using the brine shrimp lethality tests, inhibition of telomerase activity and induction of chromosomal aberrations in vivo in rat lymphocytes. Morinda lucida root bark, Nymphaea lotus whole plant and Garcinia kola root were active in the three test systems. Bryophyllum calycinum whole plant, Annona senegalensis root, Hymenocardia acida stem bark, Erythrophleum suaveolens leaves and Spondiathus preussii stem bark were toxic to brine shrimps and caused chromosomal damage in rat lymphocytes. Ficus exasperata leaves, Chrysophyllum albidum root bark and Hibiscus sabdariffa leaves were non-toxic to all the three test systems. Chenopodium ambrosioides whole plant was non-toxic to brine shrimps and rat lymphocyte chromosomes but showed inhibition in the conventional telomerase assay indicating a possible selectivity for human chromosomes. The result justified the use of the first eight plants and Chenopodium ambrosioides in the management of cancer in south west Nigeria although they appear to be non-selective and their mode of action may be different from plant to plant. All these plants except Chenopodium ambrosioides are also mutagenic and cytotoxic.

Hypoglycaemic constituents of Stachytarpheta cayennensis leaf.

The aqueous infusion (tea) of Stachytarpheta cayennensis leaves is used ethnomedically in Peru, Nigeria and other tropical countries for the management of diabetes. Oral administration (p. o.) of aqueous (125 mg/kg) and methanolic (2000 mg/kg) extracts of the leaves to alloxan-diabetic rats showed significant blood glucose reductions by 43 and 53%, respectively, at the end of a 4 hour period similar to the strong effect of glibenclamide (5 mg/kg, P. O.). The methanolic extract was successively partitioned into ethyl acetate, butanol and water fractions, and the same test showed that the butanol fraction (2000 mg/kg) had the highest (50%) hypoglycaemic activity at 4 hours after oral administration. It was also the most active fraction when tested in vitro [insulin release from an insulin secreting cell line (INS-1)] and was also active in normal rats and rats made hyperglycaemic by a glucose load. Its activity was comparable to that of glibenclamide (positive control) in these models. This active butanol fraction was subjected to chromatographic subfractionation; some subfractions reduced hyperglycaemia in alloxan-diabetic rats to 60 and 78% and induced insulin release from the INS-1 cells; other subfractions, however, gave hyperglycaemic activities IN VIVO and inhibition of insulin release from the INS-1 cells. Three major compounds of the butanol fraction were isolated and characterised as 6beta-hydroxyipolamide, ipolamide and isoverbascoside; they increased insulin secretion from INS-1 cells to 125, 128 and 127%, respectively, whereas glibenclamide increased insulin secretion to 157%. The results justify the ethnomedical use of the plant in the management of diabetes and suggest that the butanol fraction and some of its isolated constituents mediate their actions primarily by stimulating insulin release directly.

Studies on the anti-inflammatory and toxic effects of the stem bark of Khaya ivorensis (Meliaceae) on rats.

Khaya ivorensis A. Chev. (Meliaceae) is a common feature in anti-malarial recipe prescribed by African traditional medical practitioners. Investigations have proved that Khaya species possesses some level of anti-plasmodial activity. Anti-inflammatory and toxicity studies were carried out on this plant using the Ugo Basile model 7140 and routine toxicity study methods, respectively, on adult wistar rats. The brain, spleen, heart, liver and kidneys were examined for dismorphological features, following oral administration of the ethanolic extract of K. ivorensis at the daily dose levels of 1000, 500 or 125 mg/kg for 7, 14 and 7 days after cessation of drug administration. The study showed that tissue toxicity, especially neurotoxicity was dose dependent, similarly the anti-inflammatory effect. The toxicity appeared to be reversible at lower doses. The wide margin between the therapeutic and toxic dosages makes the extract a possible safe drug in the management of malaria.

Prieurianoside, a protolimonoid glucoside from the leaves of Trichilia prieuriana.

The ubiquitous glycolipid 1,2-dilinolenoyl-3-galactopyranosylglycerol and a new protolimonoid glucoside, named prieurianoside, were isolated from the leaves of Trichilia prieuriana. The structure of the latter was established, by spectroscopic techniques, as 12beta,21-diacetoxy-29-beta-D-glucopyranosyloxy-23zeta -hydroxytirucalla-7,24-dien-3-one.

Rubiginoside, a farnesyl glycoside from Lepisanthes rubiginosa.

Chemical investigation of the methanolic fraction of Lepisanthes rubiginosa bark has led to the isolation and characterisation of a new tetrasaccharide derivative of farnesol named rubiginoside along with known triterpenoid saponins.

Antifungal properties of yam (Dioscorea alata) peel extract.

The extraction of natural antifungal compounds from the peels of yam (Dioscorea alata) and the effect of these compounds on both the vegetative and reproductive structures of some yam not pathogens were studied. Four prominent antifungal components were obtained; one of the components was fully characterized and identified as beta-sitosterol. The antifungal activity of the compounds toward the germination of spores of two yam pathogens showed an inhibition of less than 57% at a concentration of 50 mg/L while inhibition on the elongation of germ-tubes of Fusarium moniliforme was as high as 82% at the same concentration. However, the ED50 for inhibition of germ-tube elongation in the yam compounds for the same organism was below 32 mg/L. The role of the yam compounds at high concentrations in disease resistance is discussed.

Brominated beta-carbolines from the marine tunicate Eudistoma album.

Chemical investigation of the cytotoxic EtOH extract of the marine tunicate Eudistoma album led to the isolation of three brominated beta-carbolines which were characterized by their spectral data. Two of them, eudistomin E, which is already known for its potent antiviral activity, and the novel compound eudistalbin A [1], were shown to possess cytotoxic activity (ED50 less than 5.0 ng and 3.2 micrograms/ml respectively) in vitro against the growth of KB human buccal carcinoma cells. The third compound, eudistalbin B [2], is a new inactive natural product.

Effect of Zanthoxylum xanthoxyloides and some substituted benzoic acids on glucose-6-phosphate and 6-phosphogluconate dehydrogenases in Hbss red blood cells.

The ether fraction of the aqueous extract of the roots of Zanthoxylum xanthoxyloides (antisickling fraction), vanillic acid, parahydroxybenzoic acid and paraflurobenzoic acid possess antisickling inhibitory activity at low concentrations. Paraflurobenzoic acid was the most active. When the activities of NADP+-linked glucose-6-phosphate and 6-phosphogluconate dehydrogenases in washed Hbss blood specimens treated with these agents (6 mg/ml for antisickling fraction and 6 micrograms/ml for the acids) were compared with controls in vitro, there were no significant differences in either normal or sickled states. The media were devoid of enzyme activity. These agents neither affect the activities of these enzymes while exhibiting antisickling activity nor disrupt the cell membrane to the extent of causing leakage to the media.

The effect of beta-sitosterol on spore germination and germ-tube elongation of Aspergillus niger and Botryodiplodia theobromae.

The effect of beta-sitosterol on spore germination and prevention of elongation of germ-tube of Aspergillus niger and Botryodiplodia theobromae was studied. The antifungal activity of the compound showed a percentage inhibition, of the fungal spore germination, of about 40% at a concentration of 50 micrograms/ml while inhibition on the elongation of germ-tubes was as high as 65% at the same concentration. The ED50 for inhibition of germ-tube elongation in A. niger was about 31 micrograms/ml. The role of the compound in disease resistance is discussed.