Acetylcholinesterase inhibitor from Anthocleista vogelii leaf extracts.

BACKGROUND: Anthocleista vogelii (Planch) is used in folk medicine in conditions related to inflammation and oxidative stress. This suggests that some of its constituents could possess ability to reduce oxidative damage to cells and ameliorate inflammatory conditions which are two prominent features in the brain of a person suffering from Alzheimer's disease. AIM OF STUDY: The leaf extracts were investigated for their bioactive constituents in our quest for novel compounds for the management of Alzheimer's disease. MATERIALS AND METHODS: Anthocleista vogelii crude leaf extract obtained from 80% methanol was successively partitioned with n-hexane, dichloromethane (DCM), ethyl acetate (EtOAc) and n-butanol. This gave four solvent fractions of the crude extract. These fractions and isolated compound were subjected to acetylcholinesterase (AChE) inhibitory activity test using the microplate assay method. The structure of the isolated compound was determined using spectroscopic methods (1D and 2D NMR, and MS). RESULTS: The results of the acetylcholinesterase inhibitory assay revealed that n-BuOH and ethyl acetate fractions had the best activity with IC50 of 564.58 and 727.63 µg/mL respectively. Activity directed fractionation of each of these fractions led to the isolation of the same compound identified as a C-glucosylflavone; isovitexin-7-O-methyl ether (swertisin). This rare C-glucosylflavone co-exist as two rotamers and exhibited duplication of NMR signals. It is reported from this plant for the first time. Swertisin displayed better acetylcholinesterase inhibitory activity with IC50 of 32.09 µg/mL than physostigmine (eserine) with IC50 of 56.09 µg/mL used as a standard. CONCLUSIONS: This study reports isolation and characterization of a rare C-glycosylflavone; isovitexin-7-O-methyl ether (swertisin). Isolated compound exhibited duplication of NMR signals and better acetylcholinesterase inhibitory activity than eserine used as a standard. The activity exhibited by this compound suggests that it could be useful in the management of Alzheimer's disease.

Isolation and characterization of antimicrobial compounds from Terminalia phanerophlebia Engl. & Diels leaf extracts.

ETHNOPHARMACOLOGICAL RELEVANCE: The emergence of drug resistant-tuberculosis and other pathogenic diseases over the past decades, constitutes a serious threat to human health worldwide. According to a 2012 report by the World Health Organization (WHO), South Africa, China, India and Russia are the countries with the highest prevalence of Multi-Drug Resistant tuberculosis (MDR-tuberculosis) as they represented 60% of the total. Several reports have documented antimycobacterial properties of Terminalia species but only a few species from this genus have been explored for their antimycobacterial constituents. The crude extracts of Terminalia phanerophlebia showed good antimicrobial activities in our previous study against two Mycobacterium as well as two other bacterial strains responsible for opportunistic infections related to respiratory ailments. This paper studies the isolation of compounds responsible for such activities and to isolate compounds responsible for antimicrobial activities from the crude extracts of Terminalia phanerophlebia leaves. MATERIALS AND METHODS: Terminalia phanerophlebia crude extracts obtained from 80% methanol was successively extracted with hexane, dichloromethane (DCM), ethyl acetate (EtOAc) and n-butanol. The fractions obtained and isolated compounds were tested for their antibacterial activities against Mycobacterium aurum, Mycobacterium tuberculosis, Staphylococcus aureus and Klebsiella pneumoniae. Bioguided fractionation of the EtOAc fraction afforded two bioactive compounds. Structure elucidation was carried out using NMR (1D and 2D) spectroscopic methods. RESULTS: EtOAc fraction exhibited highest antimicrobial activities and its fractionation afforded methyl gallate (methyl-3,4,5-trihydroxybenzoate) (1) and a phenylpropanoid glucoside, 1,6-di-O-coumaroyl glucopyranoside (2) These compounds are reported from Terminalia phanerophlebia for the first time. Both compounds showed good antimicrobial activity against all bacterial strains tested with minimum inhibitory concentration (MIC) values ranging from 63 to 250 µg/mL. Inhibition of Mycobacterium tuberculosis by 1,6-di-O-coumaroyl glucopyranoside (2) at a MIC value of 63 µg/mL was noteworthy, as this bacterial strain is reported to be the leading cause of tuberculosis worldwide. CONCLUSIONS: Good antimicrobial activities exhibited by the compounds isolated from Terminalia phanerophlebia authenticate the traditional use of this plant in treating tuberculosis and its related symptoms. Compound (2), 1,6-di-O-coumaroyl glucopyranoside could serve as a lead compound for tuberculosis drug discovery.

Antimicrobial and acetylcholinesterase inhibitory activities of Buddleja salviifolia (L.) Lam. leaf extracts and isolated compounds.

ETHNOPHARMACOLOGICAL RELEVANCE: Buddleja salviifolia leaves are used for the treatment of eye infections and neurodegenerative conditions by various tribes in South Africa. AIM OF STUDY: This study was designed to isolate the phenolic constituents from the leaf extracts of Buddleja salviifolia and evaluate their antimicrobial and acetylcholinesterase (AChE) activities. MATERIAL AND METHODS: Three phenolic compounds were isolated from the ethyl acetate fraction of a 20% aqueous methanol leaf extract of Buddleja salviifolia using Sephadex LH-20 and silica gel columns. Structure elucidation of the isolated compounds was carried out using spectroscopic techniques: mass spectrometry (ESI-TOF-MS) and NMR (1D and 2D). The extracts and isolated compounds were evaluated for antimicrobial and acetylcholinesterase activities using the microdilution technique. The bacteria used for the antimicrobial assays were Gram-positive Bacillus subtilis and Staphylococcus aureus and Gram-negative Escherichia coli and Klebsiella pneumoniae. RESULTS: The isolated compounds were characterized as: 4'-hydroxyphenyl ethyl vanillate (1) a new natural product, acteoside (2) and quercetin (3). The crude extract, fractions and the isolated compounds from the leaves of the plant exhibited a broad spectrum of antibacterial activity. The EtOAc fraction exhibited good activity against Bacillus subtilis and Staphylococcus aureus with MIC values ranging from 780.0 to 390.0 µg/mL. Isolated compound 2 exhibited good activity against Staphylococcus aureus with an MIC value of 62.5 µg/mL. The hexane and DCM fractions of leaves showed the best activity against Candida albicans with MIC and MFC values of 390.0 µg/mL. In the AChE inhibitory test, among the tested extracts, the hexane fraction was the most potent with an IC50 value of 107.4 µg/mL, whereas for the isolated compounds, it was compound (3) (quercetin) with an IC50 value of 66.8 µg/mL. CONCLUSIONS: Activities demonstrated by the extracts and isolated compounds support the ethnopharmacological use of Buddleja salviifolia against eye infections and neurodegenerative diseases.

Isolation and characterisation of novel antioxidant constituents of Croton zambesicus leaf extract.

A 1,1-diphenyl-2-picrylhydrazyl (DPPH)-activity-directed fractionation was used to target antioxidant constituents of the ethyl acetate fraction obtained from a 20% aqueous methanol crude extract of Croton zambesicus leaf. Repeated column chromatography of the fraction on silica gel and Sephadex LH-20 led to the isolation of a new natural product, identified as quercetin-3-O-ß-6″(p-coumaroyl) glucopyranoside-3'-methyl ether, helichrysoside-3'-methyl ether (1), along with kaempferol-3-O-ß-6″(p-coumaroyl) glucopyranoside, tiliroside (2) and apigenin-6-C-glucoside, isovitexin (3) as the antioxidant constituents. The structures of the isolated compounds were elucidated using spectroscopic techniques, namely NMR (1D and 2D) and mass spectrometry. Compounds 1 and 2 are reported from this species for the first time. In the qualitative antioxidant assay, the three isolated compounds instantly bleached the DPPH (0.2% MeOH) purple colour indicating antioxidant activity. In the quantitative antioxidant assay, all the isolated compounds demonstrated weak antioxidant activity compared to quercetin and rutin used as positive control antioxidant agents. The compounds displayed little to no cytotoxicity against Vero cells in an in vitro assay. The presence of these antioxidant compounds in the leaf extract of C. zambesicus could provide a rationale for the ethnomedicinal use of the plant in the management of oxidative-stress-related diseases in folk medicine.

Four pentacyclic triterpenoids with antifungal and antibacterial activity from Curtisia dentata (Burm.f) C.A. Sm. leaves.

ETHNOPHARMACOLOGICAL RELEVANCE: Curtisia dentata is used in southern Africa to treat various diseases of bacterial and fungal origin in humans and animals to such a degree that the species is vulnerable and declining [Dold, A.R., Cocks, M.L., 2001. Traditional veterinary medicine in the Alice district of the Eastern Cape Province, South Africa. South African Journal of Science 97, 375-379]. Preliminary studies indicated good activity against Candida albicans. AIM OF THE STUDY: The phytochemistry and antimicrobial activity of this plant species has not been extensively investigated, and a closer examination of the compounds responsible for antimicrobial activity was warranted. MATERIALS AND METHODS: Broth microdilution assay and bioautography were used to evaluate antibacterial and antifungal activity in Curtisia dentata leaf extracts and fractions. Bioassay-directed fractionation using column chromatography yielded four compounds characterised by spectroscopic methods. RESULTS: Lupeol (1), betulinic acid (2), ursolic acid (3) and 2alpha-hydroxyursolic acid (4) were isolated from Curtisia dentata leaves. Betulinic acid, ursolic acid and 2alpha-hydroxyursolic acid appreciably inhibited fungal growth with MIC values ranging from 8 to 63mug/mL. CONCLUSIONS: The isolation of four antibacterial and antifungal triterpenoids is reported for the first time from Curtisia dentata. This study provides information on the antimicrobial compounds of this species, as well as a preliminary rationale for the use in traditional South African medicine.

Antioxidant activity and cytotoxicity study of the flavonol glycosides from Bauhinia galpinii.

The antioxidant activity of the crude extract and solvent fractions obtained from the leaves of Bauhinia galpinii was evaluated in terms of capacity to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals. The crude extract and the more polar solvent fractions (ethyl acetate and butanol) showed considerable antioxidant activity. The antioxidant potential of the extracts, expressed as EC50, ranged between 28.85 +/- 1.28 microg mL(-1)and 118.16 +/- 6.41 microg mL(-1). L-Ascorbic acid was used as a standard (EC50 = 19.79 +/- 0.14 microM). Bioassay guided fractionation of the two active solvent fractions led to the isolation of three flavonoid glycosides, identified as: quercetin-3-O-galactopyranoside (1), myricetin-3-O-galactopyranoside (2), and 2''-O-rhamnosylvitexin (3). These compounds are reported for the first time from this species. The structures of the compounds were determined on the basis of spectral studies (1H NMR, 13C NMR and MS). Their antioxidant potential was evaluated using a DPPH spectrophotometric assay. Compound 2 had higher and 3 had lower antioxidant activity than L-ascorbic acid. No cytotoxic effects were displayed by compounds 1 and 3, but compound 2 was cytotoxic to Vero cells (LC50 = 74.68 microg mL(-1)) and bovine dermis cells (LC50 = 30.69 microg mL(-1)).

Potential of neuroprotective antioxidant-based therapeutics from Peltophorum africanum Sond. (Fabaceae).

There is ample scientific and empirical evidence supporting the use of plant-derived antioxidants for the control of neurodegenerative disorders. Antioxidants may have neuroprotective (preventing apoptosis) and neuroregenerative roles, by reducing or reversing cellular damage and by slowing progression of neuronal cell loss. Although demand for phytotherapeutic agents is growing, there is need for their scientific validation before plant-derived extracts gain wider acceptance and use. We have evaluated antioxidant potential of Peltophorum africanum (weeping wattle), a plant widespread in the tropics and traditionally used, inter alia, for the relief of acute and chronic pain, anxiety and depression. The dried leaves, bark and root of P. africanum were extracted with acetone. Thin layer chromatograms were sprayed with 0.2% 2,2-diphenyl-1-picryl hydrazyl (DPPH) in methanol for screening for antioxidants. Quantification of antioxidant activity was assessed against 6-hydroxy-2, 5,7,8-tetramethylchromane-2-carboxylic acid (Trolox) and L-ascorbic acid (both standard antioxidants), using two free radicals, 2,2'-azinobis (3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) and DPPH, respectively. Results of our study show that the bark and root extracts had higher antioxidant activity than L-ascorbic acid and Trolox, a synthetic vitamin-E analogue. The respective TEAC (Trolox Equivalent Antioxidant Capacity) values for the bark and root extracts, and Trolox were 1.08, 1.28 and 1.0. EC(50) values for L-ascorbic acid (5.04 microg/mL) was more active than the leaf 6.54 (microg/mL), but much less active than the bark (4.37 microg/mL) and root (3.82 microg/mL) extracts. Continued work on P. africanum, and other plants rich in antioxidants, may avail neuroscientists with potent neuroprotective antioxidant therapeutics.