Browsing by Author "Crouch, Neil Robert."
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Item Bioprospecting the flora of southern Africa : optimising plant selections.(2005) Douwes, Errol.; Edwards, Trevor John.; Crouch, Neil Robert.Focused procedures which streamline and optimise plant prioritisation and selection in bioprospecting have the potential to save both time and resources. A variety of semiquantitative techniques were assessed for their ability to prioritise ethnomedicinal taxa in the Flora of Southern Africa (FSA) region. These techniques were subsequently expanded upon for application in plant selection for the Novel Drug Development Platform bioprospecting programme. Least squares regression analyses were used to test the hypothesis that ethnomedicinal plant use in southern Africa is strictly random, i.e. no order or family contains significantly more medicinal plants, than any other order or family. This hypothesis was falsified revealing several 'hot' plant orders. The distribution of southern African ethnomedicinal taxa was investigated, and revealed low ethnomedicinal plant usage in the Western Cape and Northern Cape. The historical settlement of Bantu tribes in the eastern regions of southern Africa was one explanation for this discrepancy. Growth forms of ethnomedicinal taxa in 'hot' orders (identified in the regression analysis) were analysed. The results indicated no clear preferences across orders, but rather a preference for particular growth forms in certain orders. With respect to distribution, endemism and Red Data List status of ethnomedicinal taxa, the Western Cape had the greatest proportion of endemics and Namibia had the highest proportion of Red Data Listed ethnomedicinal taxa. With respect to chemotaxonomy, the Asteraceae contained the highest proportion of terpenoids, the Rubiaceae the highest proportion of alkaloids and the Fabaceae the highest proportion of flavonoids. The predictive value of regression analyses was tested against an existing analysis of anti-malarials and the subsequent in vitro bioassays on Plasmodium falciparum. In particular, the ability of these analyses to identify plants with anti plasmodial IC50 values of [less than or equal to] 10 [micro]g/ml was assessed. Most species in 'hot' genera showed comparatively good antiplasmodial activities (IC50 [less than or equal to] 10 [micro]g/ml). Plant candidates were prioritised for screening anti-tuberculosis, anti-diabetes and immune-modulatory compounds, using a weighting system based on; their ethnomedicinal application, chemotaxonomic potential, frequency in ethnomedicinal trade, association with the relative disease, toxicity, Red Data status, indigenous or endemic status, and family selection in ethnomedicine (identified through regression analyses). Other taxa were short-listed due to their presence in biodiversity hotspots where few ethnomedicinal plant use records are documented, and still others were incorporated due to their taxonomic association with efficacious exotic allies. Statistical analyses of the weighting processes employed were not possible in the absence of screening results which are due only in December 2006. The legislation governing bioprospecting in South Africa is discussed and several recommendations are presented to minimise negative impacts on the industry.Item The chemical investigation of Ledebouria ovatifolia, Clivia caulescens and Haemanthus pauculifolius.(1999) Pohl, Tracy-Lee.; Mulholland, Dulcie Aca.; Crouch, Neil Robert.Ledebouria ovatifolia (Bak.) lessop, Clivia caulescens R.A.Dyer and Haemanthus pauculifolius Snijman & Van Wyk were the three species investigated in this work. Ledebouria ovatifolia belongs to the family Hyacinthaceae (Liliaceae sensu lato) and, to date, the chemical composition of this species has not been investigated. Members of this family are widely distributed, but are particularly well represented in Southern Africa. The Ledebouria genus was formerly classified as part of the Scilla genus from which a large number of naturally occurring oxygen heterocycles known as homoisoflavonoids have been isolated. In this work the bulbs of L. ovatifolia were investigated and two compounds were isolated. These were the homoisoflavonoid, 5,7-dihydroxy-3-(4'-hydroxybenzyl)-4-chromanone and the chalcone, 6',2'-dimethoxy-4,4'dihydroxychalcone, both of which are known naturally occurring compounds. Clivia caulescens and Haemanthus pauculifolius are both members of the Amaryllidaceae family. The plants of the Amaryllidaceae family form a large group of over sixty genera, which are concentrated mainly in Southern Africa. Plants from this family have been extensively used in traditional medicines and many have pharmacological properties. The compounds responsible for most of these effects are a group of isoquinoline alkaloids, which are found almost exclusively in plants belonging to this family. The alkaloids isolated from plants belonging to this group are known to cause poisoning in low doses and can cause excessive salivation and diarrhoea. Higher doses of the active compounds can cause CNS depression and large enough doses can prove fatal. Although many of these alkaloids are harmful to man, some of the unique Amaryllidaceae alkaloids exhibit anti-tumour and anti-viral activities, and are thus potentially beneficial to man. The Clivia genus is endemic to South Africa and the most common species, C. miniata, is used by traditional healers to facilitate childbirth and as a snake bite remedy. In this chemical investigation both the bulbs and the leaves of C. caulescens were investigated. The ethanol extract of the bulbs yielded four alkaloids, hippeastrine, haemanthamine, lycorine and ll-(S)-hydroxyvittatine. The investigation of the leaf extract also yielded lycorine and hippeastrine as well as an additional alkaloid sternbergine. Haemanthus pauculifilius is a recently described member of the Haemanthus genus, which consists of 27 taxa that are restricted to Southern Africa and Namibia. In this chemical investigation the ethanol extract of the bulbs and leaves yielded the common triterpenoid sitosterol as well as two novel 5,11-methanomorphanthridine type alkaloids, montanine hydrochloride and manthidine.Item The chemical investigation of Ledebouria zebrina and Scilla natalensis.(2001) Moodley, Nivan.; Crouch, Neil Robert.; Mulholland, Dulcie Aca.Ledebouria zebrina and Scilla natalensis Planch were the two species investigated in this work. Ledebouria zebrina belongs to the Hyacinthaceae (Liliacea sensu lato) and to this date, the chemical composition of this species has not been investigated. Members of this family are found in southern Africa. The Ledebouria genus was formerly classified as part of the Scilla genus from which a large member of naturally occuring oxygen heterocycles known as homoisoflavanones have been isolated. In this work the bulbs of L. zebrina were investigated and five compounds were isolated. Three compounds were of the homoisoflavanone type while the remaining two belong to the eucosterol type triterpernoids. Scilla natalensis Planch also belongs to the Hyacinthaceae family. Previous chemical investigations of the bulbs of this plant yield two homoisoflavanones of the 3-benzyl-4- chromanone type. Members of this family are mostly found in the Eastern parts of the country, ranging from the Eastern Cape to Mpumalanga province including Lesotho and Swaziland. The bulbs of this plant were investigated and this yielded ten compounds. The structures of the isolated compounds were elucidated using spectroscopic methods.Item The chemical investigation of the Amaryllidaceae and Hyacinthaceae.(2004) Moodley, Nivan.; Mulholland, Dulcie Aca.; Crouch, Neil Robert.This work is an account of investigations into the chemistry of members of the Amaryllidaceae and Hyacinthaceae families. The plants of the family Amaryllidaceae are a large group comprising over sixty genera and more than a thousand species. They are widely distributed, but are found more richly in the tropics, with a particularly high density in South Africa, with smaller centers of diversity in Andean South America and the Mediterranean. Amaryllidaceae plants have been extensively used by local traditional healers and have been reported to have numerous pharmacological uses. The alkaloids isolated from this family are a group of isoquinoline alkaloids found exclusively in this family. Plants belonging to two Amaryllidaceae genera were investigated phytochemically, one from each of the sub-tribes Crinineae and Amaryllidineae were investigated phytochemically. Brunsvigia natalensis is used in local traditional medicine to "straighten bones of children", treat barrenness in women and ease childbirth. This is the first phytochemical investigation of Brunsvigia natalensis, and yielded two new alkaloids, a new ceramide type compound and a known flavanoid. A comparative phytochemical investigation was carried out on the bulbs and seeds of Crinum stuhlmanni, which resulted in a number of different alkaloids being isolated from the seeds and bulbs of this plant. The southern African Hyacinthaceae is a large and chemically morphologically diverse group of plants. This family comprises approximately sixty-seven genera and nine hundred species worldwide, of which twenty-seven genera and three hundred and sixty - eight species are found locally. There are five sub-families of which three occur in southern Africa. The chemical constituents of this family can be divided into four classes, namely homoisoflavanones, steroidal compounds, bufadienolides and miscellaneous compounds. These plants are used in local traditional medicine for treating ailments such as hangovers, rheumatic fever, sprains and even cancer. The phytochemistry of three Hyacinthaceae plants was studied. The phytochemical investigation of Drimia macrocentra and Urginea riparia yielded a novel bufadienolide glycoside. These glycosides are quite unusual with the glycone attached to the aglycone at C-2 and C-3 and this has only been reported only once before in this family. The phytochemical investigation of Ledebouria revoluta yielded a number of homoisoflavanones. These homoisoflavanones have been shown to have anti-inflammatory activity and all of the compounds isolated in this work have been screened for this activity. Structural elucidation was carried out using spectroscopic methods such as NMR, MS, UV and IR.Item Effect of auxin on 6-(benzylamino)purine metabolism in suspension cultures.(1993) Crouch, Neil Robert.; Van Staden, Johannes.A review of the literature indicated that the purine cytokinin 6-(benzylamino)purine (SA) may be converted to a wide range of metabolites. Although the functional significance of these metabolites remains obscure, cytokinin physiologists have essentially classed them as either active or inactive. Inactivation of cytokinins is considered to proceed via catabolic oxidation (side-chain cleavage), or N-conjugation with glucose or alanine moieties. The literature survey was hampered by the confusing array of synonyms which have been coined for cytokinin metabolites. Accordingly, a working system of (semi-systematic) abbreviations was devised which accommodated all groups and classes of purine cytokinins. Prior to commencing metabolic interactive studies, it was necessary to resolve the contentious issue associated with the successful extraction of cytokinin nucleotides. Five-week-old soybean callus was fed [8[-14]C]BA and subsequently extracted using four widely used cytokin in extraction techniques. Techniques compared were a modified Bieleski method, 80% ethanol with tissue homogenisation, 80% ethanol without homogenisation, and boiling ethanol. All four procedures produced similar results, showing that all metabolites of SA, including the nucleotide, were adequately extracted. It was concluded that the extraction of nucleotides with Bieleski solvents did not warrant the inconvenience. Auxins have been shown to interact with cytokinins in the regulation of many physiological processes, although little is known of the mechanisms of interaction which proceed at the metabolic level. Previous investigators have shown that auxin promoted cytokinin degradation through catabolic oxidation, Shoot-apex and seed derived cell suspensions of Dianthus zevheri subsp. natalensis were incubated with [8[-14] C]BA for between 30 minutes and 48 hours in the presence of both low (2 mg l-1) and high (4 mg 1¯¹) levels of exogenously supplied 2,4-dichlorophenoxyacetic acid (2,4-D), In both systems, the auxin 2,4-D was shown to promote SA inactivation through 7-glucosylation (N-conjugation). This observation represents the first report of auxin-promoted cytokinin N-conjugate formation. The auxin effect on metabolism was transient in the case of shoot-apex, but not in seed-derived systems over a 48 hour period. Formation of the 7-glucoside of SA was dose-dependent in apex-derived cultures. Further studies were undertaken with indole-3-acetic acid (lAA) and α-naphthaleneacetic acid (NAA). It was found that auxin-promoted 7-glucosylation of SA was only minimally effected by these two auxins. In comparable studies with soybean suspension cultures (Glycine max cv. Acme), 2,4-D-promoted catabolic oxidation was observed between 18 and 48 hours, following application of phytohormones. The main catabolite was tentatively identified as adenosine-5'-monophosphate (AMP), based on chromatographic characteristics. Carrot (Daucus carota) cell suspensions similarly supplied with 2,4-D and SA maintained a large active cytokinin pool. Neither substantial oxidative nor Nconjugative processes were observed. Instead, there was a transient effect by 2,4- D on the relative formation of the riboside and the 7- and 9-glucosides of SA. The effect of auxin on the metabolism of SA thus varied with the species and system investigated. Generally, auxin promoted (rather than inhibited), the formation of inactivated metabolites and catabolites of SA, possibly by the induction of relevant enzyme systems. Transient auxin effects on the metabolism of SA are discussed in relation to the role of the auxin/cytokinin balance in the induction of developmental processes.Item Extractives from the amaryllidacea and the fabaceae.(1999) Koorbanally, Neil Anthony.; Mulholland, Dulcie Aca.; Crouch, Neil Robert.This work is an account of investigations into the chemistry of one of the members of the Amaryllidacae family, Ammocharis coranica, and one of the members of the Fabaceae family, Sophora velutina. Chapter one is an account of the extractives from the bulbs of Ammocharis coranica. In all, twelve compounds, eight alkaloids and four cycloartane compounds have been isolated of which one alkaloid and one cycloartane compound have not been described previously. Plants belonging to the Amaryllidacae family have been used by traditional healers, especially in Africa, to treat a range of illnesses and diseases. The alkaloids isolated from these plants have been shown to exhibit responses to muscle stimulant, antiviral, antifungal, antiyeast, antimalarial, cytotoxic and antitumoural activities. Ammocharis coranica is used by the Zulu tribe in South Africa to treat any illness believed to be caused by witchcraft. Alkaloids from the three most common types among the isoquinoline group were found in this species. These are lycorine, 1-O-acetyllycorine, hippadine, acetylcaranine, and the novel 1-O- acetyl-9-norpluviine from the lycorine type, 6-α-hydroxypowelline from the crinine type and hamayne and crinamine from the haemanthamine type. Cycloartane compounds have not been reported previously from the Amaryllidaceae family. All four cycloartane compounds had a common side chain, containing an olefinic methylene group at position 24, but differed in their substituents at positions 3 and 4. These compounds were found to be 24-methylenecycloartan-3β-ol, cycloeucalenol, cycloeucalenone and the novel compound 4-methylenepollinastanone. Chapter two is an account of the extractives from the seeds of Sophora velutina. The seeds of other Sophora species have been used in traditional ceremonies by the Indians of the Southwest United States and adjacent Mexico because of their hallucinogenic activity. The seeds of Sophora velutina subsp. zimbabweensis found in Zimbabwe are suspected to have historically been used by the natives for their hallucinogenic properties. These plants have been known to contain several quinolizidine alkaloids, flavonoids and isoflavonoids. One alkaloid, N-methylcytisine and two isoflavones, pseudobaptigenin and calycosin, as well as the common phytosterol, β-sitosterol were isolated from the seeds of this species. N-methylcytisine is a common quinolizidine alkaloid, isolated previously from several Sophora species and pseudobaptigenin and calycosin are well known isoflavones, isolated previously from several species in the Fabaceae.Item Extractives from the Amaryllidaceae : Brunsvigia radulosa and Cyrtanthus breviflorus.(2001) Chetty, Jonathan.; Crouch, Neil Robert.No abstract available.Item Extractives of three southern African medicinal plants.(1998) Page, Bronwen Ann.; Mulholland, Dulcie Aca.; Crouch, Neil Robert.In this investigation the chemistry of three southern African plants used for medicinal purposes was investigated. The plants were Dioscorea dregeana, Avonia rhodesica and Equisetum ramossisimum. Extracts of all three of these plants have been found to be active on the central nervous system. The structures of the compounds isolated were determined by using 1H and 13C n.m.r., i.f., UV-VIS, - mass spectroscopy and chemical methods. D. dregeana yielded two alkaloids and three aromatic compounds. A. rhodesica contained a large amount of wax which was analysed by GC-MS and its distribution and physical nature on the surface of the leaves was determined by SEM (scanning electron microscopy). This plant also contained two sterols. Equisetum ramossisimum extracts contained a carotenoid and several porphyrins, as well as large amounts of silica. A DTSA X-ray microanalysis system (which was a component of the scanning electron microscope) was used to determine the distribution of silica in the stem.