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Chalcones and other constituents of Dorstenia prorepens and Dorstenia zenkeri

Abegaz, B.M.; Ngadjui, B.T.; Dongo, E.; Ngameni, B.; Nindi, M.N.; Bezabih, M. (Elsevier Science Ltd. www.elsevier.com/locate/phytochem, NaN, 2002)

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Abstract:

The twigs of Dorstenia prorepens furnished the digeranylated chalcone, 5,30-(3,7-dimethyl-2,6-octadienyl)-3,4, 20,40-tetrahydroxychalcone while Dorstenia zenkeri yielded the 30,40-(3-hydroxy-2,2-dimethyldihydropyrano)-4,20-dihydroxychalcone and a bichalcone. 4-Hydroxylonchocarpin was found in both plants. D. prorepens also yielded the known compounds: psoralen, bergapten, b-sitosterol and its D-glucopyranosyl derivative. D. zenkeri yielded p-hydroxybenzaldehyde, dorsmanin A, 4,20,40-trihydroxychalcone and 4,20,40-trihydroxy-30-prenylchalcone. Structures of the new compounds were established by UV, IR, MS and 2-D NMR analysis.

URI:

http://hdl.handle.net/10311/254

Files in this item: 2

Chalcones and other constituents.pdf (3.760Mb)

license.txt (1.998Kb)

Characterization and Compositional Studies of the Oils from Some Legume Cultivars, Phaseolus vulgaris, Grown in Southern Africa

Mabaleha, M.B.; Yeboah, S.O. (AOCS Press., NaN, 2004)

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Abstract:

Seed oils from six legume cultivars of Phaseolus vulgaris, grown in the Kingdom of Lesotho, were extracted and their physicochemical properties and FA compositions were determined in order to compare their dietary lipids with those in P. vulgaris cultivars grown in other parts of the world. The oil content of the beans was very low, ranging from 1.5 to 2.0% (w/w). The acid values ranged from 11.0 to 19.2 mg KOH/g, whereas a combination of the PV and the p-anisidine values in Holm’s equation gave oxidation values that ranged from 11.0 to 15.0. Thus, considerable enzymatic hydrolysis and oxidation had taken place in the beans during storage. Iodine values ranged from 80.5 to 92.3 (Wijs method), indicating moderate unsaturation in the oils. However, capillary GC analysis, supported by proton NMR analysis of the FAME, gave a total unsaturation range from 79.67 to 84.24%. The dominant FA were α-linolenic acid (36.47–48.81%) and linoleic acid (20.96–36.10%), with appreciable amounts of palmitic acid (14.33–18.23%). This FA composition pattern is quite similar to the FA distribution reported for low oil-bearing legume seeds. Thus, notwithstanding the different climatic and soil conditions, the general properties of lipids in the southern African legume cultivars were quite similar to those of lipids in P. vulgaris cultivars grown in other parts of the world. The high content of α-linolenic acid in the cultivars of P. vulgaris could very likely play a beneficial role in reducing the risk of coronary heart disease among the large populations consuming them in the southern African region.

URI:

http://hdl.handle.net/10311/303

Files in this item: 1

Characterization and compositional.pdf (3.533Mb)

Chemical constituents of Treculia acuminata and Treculia africana (Moraceae)

Metuno, R.; Ngandeu, F.; Tchinda, A.T.; Ngameni, B.; Kapche, G.D.W.F.; Djemgou, P.C.; Ngadjui, B.T.; Bezabih, M.; Abegaz, B.M. (Elsevier Ltd. www.elsevier.com/locate/biochemsyseco, NaN, 2007)

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Three species of the genus Treculia namely, Treculia acuminata Baill., Treculia africana Decne ex. TreÃ Â´cul and Treculia obovoidea N.E.Br. grow in the humid rain forest of southwest Cameroon. They are also widely distributed in tropical Africa. T. africana is commonly known as African bread fruit. These three species are commonly used in folk medicine against skin diseases and dental allergies (Berg et al., 1985). The twigs, stem and wood of T. acuminata and the leaves of T. africana, whose chemical constituents are reported herein, were collected from Kumba, Cameroon, in August 2004, and identified by Mr Victor Nana of the National Herbarium in Yaounde, Cameroon where voucher specimens (N 2921/Srf/CAM and 29053/SRF/Cam, respectively) are deposited.

URI:

http://hdl.handle.net/10311/291

Files in this item: 1

Chemical constituents of Treculia.pdf (2.209Mb)

Cyclic voltammetric studies of tris(alkylisocyanide)-bis(triarylphosphine)cobalt(II) and tris-(alkylisocyanide)bis(triarylphosphine)cobalt(I) complexes exhibiting synthetic interconvertability

Ahmad, J.; Bothata-Nareetsile, F.; Becker, C.A.L. (NRC Research Press, http://www.nrcresearchpress.com/loi/cjc, NaN, 2003)

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Abstract:	Nine pairs of corresponding [CoI(CNR)3(PR3 ′ )2]X, [CoII(CNR)3(PR3 ′ )2]X2 complexes — where X = ClO4, BF4; CNR = CNCMe3, CNCHMe2, CNC6H11, CNCH2Ph; PR3′ = PPh3, P(C6H4Me-p)3, P(C6H4OMe-p)3 — have been studied using cyclic voltammetry in CH3CN solutions. All cycles are reversible, and E1/2 for the Co(I) complexes, initially oxidized, are within experimental error identical to E1/2 values for the corresponding Co(II) complexes, initially reduced. E1/2 values are strongly dependent on the triarylphosphine ligand, decreasing in the order PPh3 > > P(C6H4Me-p)3 > P(C6H4OMe-p)3, and weakly dependent on the alkylisocyanide ligand, decreasing in the order CNCH2Ph > CNCMe3 > CNC6H11 ≥ CNCHMe2. Solution ν(-N C) IR patterns reveal that the [CoI(CNR)3(PR3′)2]X complexes do not have regular trigonal bipyramidal coordination, their structure being determined by the particular CNR ligand, while the [CoII(CNR)3(PR3′)2]X2 complexes, specifically in CF3CH2OH, appear to have regular trigonal bipyramidal coordination.
Description:	Signs on the abstract may be different to the original document
URI:	http://hdl.handle.net/10311/1034

Files in this item: 1

Ahmad_CJC_2003.pdf (782.1Kb)

Deltamethrin in sediment samples of the Okavango Delta, Botswana

Daka, P.S.; Obuseng, V.C.; Torto, N.; Huntsman-Mapila, P. (Water SA Pretoria; Water Research Commission; http://www.wrc.org.za/, October NaN, 2006)

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Abstract:

Deltamethrin concentrations were determined in 35 sediment samples collected from three different habitats: channel, lagoon and pool sites from Xakanaxa in the Okavango Delta, NW Botswana. The samples were Soxhlet-extracted in acetone to extract deltamethrin residues and subsequently cleaned-up with silica gel 60. The final determination was carried out with a gas chromatograph equipped with an electron capture detector (GC-ECD). The sample work-up and determination gave deltamethrin recoveries of 54 to 97%, and detection limits of 0.004 mg/kg dw. The concentration of deltamethrin residues in the sediment samples collected from the three sprayed areas in the Okavango delta ranged between 0.013 and 0.291 mg/kg dw, with the highest concentrations observed in samples obtained from the pool sites. Analysis of samples for organic matter content showed percentage total organic carbon (% TOC) ranging between 0.19% and 8.21%, with samples collected from the pool having the highest total organic carbon. The concentrations of deltamethrin residues and the % TOC in sediment samples showed a similar trend with the highest levels recorded in the pool samples. These data confirmed that a simple method based on GC-ECD, after Soxhlet extraction, was robust enough to enable quantification of deltamethrin in the sediments, because comparable results were obtained with a more sophisticated system consisting of a GC coupled to a mass spectrometer with a time of flight (TOF) analyser.

URI:

http://hdl.handle.net/10311/140

Files in this item: 2

dakaetal.pdf (463.1Kb)

license.txt (1.998Kb)

Dinklagins A, B and C: three prenylated flavonoids and other constituents from the twigs of Dorstenia dinklagei

Ngadjui, B.; Dongo, E.; Abegaz, B.; Fotso, S.; Tamboue, H. (Elsevier Science Ltd. www.elsevier.com/locate/phytochem, NaN, 2002)

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Abstract:

Three prenylated flavonoids, dinklagins A, B and C identified, respectively, as ( )-6-(3,3-dimethylallyl)-7-hydroxy-6000, 6000-dimethylchromeno-( 40,30,2000,3000)-flavanone, (+)-5,40,500x-trihydroxy-600,600-dimethylchromano-(7,6,200,300)-flavone and (+)6-(2x-hydroxy- 3-methyl-3-butenyl)-5,7,40-trihydroxyflavone were isolated from the twigs of Dorstenia dinklagei together with the known 6-prenylapigenin, 4-hydroxylonchocarpin, stipulin and 5,40-dihydroxy-600,600-dimethylchromano-(7,6,200,300)-flavone. Their structures were determined on the basis of spectral data and by comparison with data reported in the literature and with authentic specimens for known compounds.

URI:

http://hdl.handle.net/10311/262

Files in this item: 2

Dinklagins A, B and C three prenylated.pdf (3.292Mb)

license.txt (1.998Kb)

Diprenylated chalcones and other constituents from the twigs of Dorstenia barteri var. subtriangularis

Ngameni, B.; Ngadjui, B.; Folefoc, G.; Watchueng, J.; Abegaz, B. (Elsevier Ltd; www.elsevier.com/locate/phytochem, NaN, 2003)

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Abstract:

The twigs of Dorstenia barteri var. subtriangularis yielded three diprenylated chalcones: ( )-3-(3,3-dimethylallyl)-50-(2-hydroxy-3- methylbut-3-enyl)-4,20,40-trihydroxychalcone, (+)-3-(3,3-dimethylallyl)-40,50-[2000-(1-hydroxy-1-methylethyl)-dihydrofurano]-4,20- dihydroxychalcone and 3,4-(600,600-dimethyldihydropyrano)-40,50-[2000,-(1-hydroxy-1-methylethyl)-dihydrofurano]-20-hydroxychalcone for which the names bartericins A, B and C, respectively, are proposed. Stipulin, b-sitosterol and its 3-b-D-glucopyranosyl derivative were also isolated. The structures of these secondary metabolites were determined on the basis of spectroscopic analysis, especially, NMR spectra in conjunction with 2D experiments, COSY, HMQC and HMBC. The structural relationship of bartericins B and C was further established by the chemical cyclization of one to the other.

URI:

http://hdl.handle.net/10311/258

Files in this item: 2

Diprenylated chalcones and other.pdf (3.479Mb)

license.txt (1.998Kb)

Diterpenoids from the stem bark of Croton zambesicus

Ngadjui, B.T.; Abegaz, B.M.; Keumedjio, F.; Folefoc, G.N.; Kapchec, G.W.F. (Elsevier Science Ltd. www.elsevier.com/locate/phytochem, NaN, 2002)

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Abstract:

Three clerodane diterpenoids, crotozambefurans A, B and C were isolated from the stem bark of Croton zambesicus together with the known clerodane crotocorylifuran and two trachylobanes: 7b-acetoxytrachyloban-18-oic acid and trachyloban-7b, 18-diol. Betulinol, lupeol, sitosterol and its 3b-glucopyranosyl derivative were also obtained. The structures of crotozambefurans A, B and C were determined, respectively, as: 15,16-epoxy-1,3,13(16),14-clerodatetraen-20,12-olide-18,19-dioic acid dimethylester, 15,16-epoxy- 1,3,13(16),14-clerodatetraen-18,19,20-trioic acid trimethylester and 15,16-epoxy-3,13(16),14-clerodatrien-19,1a:20,12-diolide-18-oic acid methylester, using spectroscopic analysis, especially, NMR spectra in conjunction with 2D experiments, COSY, HSQC, HMBC and TOCSY.

URI:

http://hdl.handle.net/10311/251

Files in this item: 2

Diterpenoids from the stem bark.pdf (2.493Mb)

license.txt (1.998Kb)

An efficient synthesis of flavans from salicylaldehyde and acetophenone derivatives

Mazimba, O.; Masesane, I.B.; Majinda, R.R. (Elsevier Science Ltd, http://www.elsevier.com/locate/tetlet, NaN, 2011)

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An efficient total synthesis of flavans from the reactions of salicylaldehyde and acetophenone derivatives is reported. The synthesis involves preparation of chalcones through an aldol reaction followed by reduction of both the double bond and the ketone using NaBH4 and an acetic acid mediated cyclization. Methoxy groups on the aromatic rings did not affect significantly the yields of the procedure.

URI:

http://hdl.handle.net/10311/1027

Files in this item: 1

Mazimba_TL_2011.pdf (204.0Kb)

Electrospray Liquid Chromatography–Mass Spectrometry of the Leaf Extract of Rhamnus prinoides

Nindi, M.M.; Kgarebe, B.V.; Wolfender, J.L.; Abegaz, B.M. (John Wiley & Sons, Ltd., NaN, 1999)

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Abstract:

Three naphthalenic derivatives, four flavonoids and two of the four anthraquinones previously isolated from the leaves of Rhamnus prinoides were successfully ionised under electrospray ionisation conditions. These compounds were subsequently detected in the leaf extract of the plant using electrospray liquid chromatography–mass spectrometry (LC–ESI–MS). The potential of LC–ESI–MS for screening a leaf extract, with the focus on the suitability of the method for assaying the bitter principle, geshoidin, of this commercially important plant, is presented.

URI:

http://hdl.handle.net/10311/290

Files in this item: 1

Electrospray Liquid.pdf (1.464Mb)

Epoxylignans from the seeds of Centaurea cyanus (Asteraceae)

Shoeb, M.; Jaspars, M.; MacManus, S.M.; Majinda, R.R.T.; Sarker, S.D. (Elsevier Ltd. www.elsevier.com/locate/biochemsyseco, NaN, 2004)

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A study focusing on Centaurea cyanus L. (family: Asteraceae alt. Compositae), otherwise known as "cornflower" or "bachelor's button. The seed is purchased from B & T World Seeds sarl, Pauguignan, 34210 Olonzac, France and the voucher specimen (PHSH0002) kept in the Plant and Soil Science Department, University of Aberdeen, UK for testing. The result shows the occurrence of epoxylignans, berchemol (1) and lariciresinol 4-O-b-d-glucopyranoside (2) in the seeds of C. cyanus.

URI:

http://hdl.handle.net/10311/300

Files in this item: 1

epoxylignans from the seeds.pdf (1.594Mb)

Evaluation of methods for the isolation, detection and quantification of cyanobacterial hepatotoxins

Msagati, T A M; Siame, B A; Shushu, D D (Elsevier Ltd. www.elsevier.com/locate/aquatox, NaN, 2006)

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Abstract:

Cyanobacterial hepatotoxins such as microcystins and nodularins have been responsible for the poisoning of both animals and humans who ingest or come into contact with toxic blooms. They are extremely stable in water due to their stable chemical structure and can tolerate radical changes in water chemistry, including pH and salinity. Different methods for the extraction and detection of these compounds have been reported. Extraction methods utilizing both aqueous and organic solvent systems have been reported. The detection methods ranging from immunological or biochemical assays such as enzyme linked immunosorbent assays (ELISA) and enzyme activity assays, to chemicals methods such as high performance liquid chromatography (HPLC) and more sophisticated liquid chromatography–mass spectrometry (LC–MS) have been documented as well. We review some important aspects of cyanobacterial hepatotoxins and methods of analysis for these toxins.

URI:

http://hdl.handle.net/10311/314

Files in this item: 1

Evaluation of methods for the.pdf (12.27Mb)

Evaluation of methods for the isolation, detection and quantification of cyanobacterial hepatotoxins

Msagati, T.A.M.; Siame, B.A.; Shushu, D.D. (Elsevier Ltd. http://www.elsevier.com/wps/find/journaldescription.cws_home/505509/description#description, NaN, 2006)

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Abstract:

Cyanobacterial hepatotoxins such as microcystins and nodularins have been responsible for the poisoning of both animals and humans who ingest or come into contact with toxic blooms. They are extremely stable in water due to their stable chemical structure and can tolerate radical changes in water chemistry, including pH and salinity. Different methods for the extraction and detection of these compounds have been reported. Extraction methods utilizing both aqueous and organic solvent systems have been reported. The detection methods ranging from immunological or biochemical assays such as enzyme linked immunosorbent assays (ELISA) and enzyme activity assays, to chemicals methods such as high performance liquid chromatography (HPLC) and more sophisticated liquid chromatographyÃ Â¢ mass spectrometry (LC-MS) have been documented as well. We review some important aspects of cyanobacterial hepatotoxins and methods of analysis for these toxins.

URI:

http://hdl.handle.net/10311/218

Files in this item: 2

Evaluation of m ... bacterial hepatotoxins.pdf (5.652Mb)

license.txt (1.998Kb)

Examination of Blepharis aspera as a possible Cu–Ni indicator plant

Nkoanea, B.B.M.; Wibetoe, G.; Lund, W.; Abegaz, B. (South African Journal of Science, NaN, 2007)

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Abstract:

BLEPHARIS ASPERA WAS COLLECTED FROM A copper–nickel mineralized area in Botswana and examined as a possible Cu–Ni indicator plant for biogeochemical prospecting. Different plant parts and the host soils were analysed using ultrasonic slurry sampling electrothermal atomic absorption spectrometry. All plant parts accumulated Cu and Ni in above-normal amounts, although not in hyperaccumulator concentrations. The leaf to soil Cu concentration ratio varied little with metal concentration in the soil. We propose Blepharis aspera as a Cu indicator plant.

URI:

http://hdl.handle.net/10311/282

Files in this item: 1

Examination of Blepharis.pdf (1.160Mb)

Fire and its influence on microbial community structure and soil biochemical properties in the Okavango Delta, Botswana

Mubyana-John, T.; Wutor, V.C.; Yeboah, S.O.; Ringrose, S. (Academic Journals. http://www.academicjournals.org/SRE, NaN, 2007)

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The influence of wild fires on microbial community structure, soil organic matter, sulphur oxidising and nitrifying microbial populations in the floodplains of the Okavango Delta of Botswana was assessed. Microbial community structure was assessed by phospholipids ester-linked fatty acids (PLFA) quantification while microbial sulphur oxidisers were assessed by Most Probable Number (MPN). Community structure assessment showed that burning shifted the microbial community structure from single cellular bacteria being the dominant groups to filamentous fungi and actinomycetes being the most dominant groups. Generally burning increased the fungal component (18:2 w6) matrix from 3.40 to 8.35 while the actinomycetes and sulphur reducing bacterial (10 Me 16:0) component also increased from 1.02 to 1.70 mostly in the floodplains. Generally, the organic matter content declined with burning. However, the influence of burning on soil pH was non conclusive. Soil microbial biomass carbon increased slightly after the fire. The number of heterotrophic and nitrite-oxidizing and sulphur reducing bacteria increased. Overall, these results indicate that burning significantly alters the microbial community structure as large above ground losses of nutrients during and after burning often results in low quantities of nutrients released into the soil.

URI:

http://hdl.handle.net/10311/349

Files in this item: 1

Fire and.pdf (2.461Mb)

The first 60-O-sulfated phenylanthraquinones: isolation from Bulbine frutescens, structural elucidation, enantiomeric purity, and partial synthesis

Mutanyatta, J.; Bezabih, M.; Abegaz, B.; Dreyer, M.; Brun, R.; Kocher, N.; Bringmann, G (Elsevier Ltd.http://www.elsevier.com/wps/find/journaldescription.cws_home/942/description#description, NaN, 2005)

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Abstract:

From the roots of Bulbine frutescens, the first sulfated phenylanthraquinones were isolated, together with their known sulfate-free analogs. Their structures were elucidated by spectroscopic and chiroptical methods, by acid hydrolysis or by partial synthesis. The new compounds have the usual stereo-orientation at the biaryl axis (i.e., with the acetyl portion above the anthraquinone plane) except for sodium ent-knipholone 60-O-sulfate (and thus, also its hydrolysis product, ent-knipholone), which exhibit an opposite axial configuration. We also describe the first stereoanalysis of natural phenylanthraquinones, some of which were found to be not enantiomerically pure, some even nearracemic. We furthermore, report on the first X-ray structure analysis of a phenylanthraquinone, viz. 40-O-demethylknipholone.

URI:

http://hdl.handle.net/10311/246

Files in this item: 2

license.txt (1.998Kb)

The first 6-0-O-sulfated phenylanthraquinones.pdf (6.446Mb)

A fluorescence spectroscopic study of a coagulating protein extracted from Moringa oleifera seeds

Kwaambwa, H.M.; Maikorera, R. (Elsevier B.V. www.elsevier.com/locate/colsurfb, NaN, 2007)

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The fluorescence studies of coagulating protein extracted from Moringa oleifera seeds have been studied using steady-state intrinsic fluorescence. The fluorescence spectra are dominated by tryptophan emission and the emission peak maximum ( max = 343±2 nm) indicated that the tryptophan residue is not located in the hydrophobic core of the protein. Changes in solution pH affected the protein conformation as indicated by changes in the tryptophan fluorescence above pH 9 whereas the ionic strength had minimal effect. The exposure and environments of the tryptophan residue were determined using collisional quenchers.

URI:

http://hdl.handle.net/10311/323

Files in this item: 1

Fluorescence spectroscopic study of a.pdf (4.565Mb)

The Free-Radical Copolymerization of Difurylmethane with Maleic anhydride

Ddamba, W.A.A.; Ngila, J.C.; Mokoena, T.T.; Motlhagodi, K. (South African Journal of Chemistry. <http://ejour.sabinet.co.za/images/ejour/chem/chem_v55_a1.pdf>., NaN, 2002)

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The copolymerization of difurylmethane with maleic anhydride in the presence of azobisisobutyronitrile as an initiator has been investigated at 65 °C, 72 °C and 85 °C in different solvents. Reaction feeds containing 85 mol % and higher of difurylmethane yielded a soluble alternating copolymer in which the furan residue entrained in the polymer chain formed 2,5 linkages and had 3,4 unsaturation. The 1:1 difurylmethane– maleic anhydride adduct was readily prepared, and at the above temperatures and in the presence of the radical initiator partially underwent retro-Diels–Alder reaction. Copolymerization of the difurylmethane and maleic anhydride thus formed yielded the unsaturated alternating copolymer. Copolymers prepared from reaction feeds with proportions of difurylmethane lower than 85 mol % had higher cross-link density and exhibited higher thermodecomposition temperatures.

URI:

http://hdl.handle.net/10311/305

Files in this item: 1

Free radical.pdf (2.417Mb)

From nature, through chemical synthesis, toward use in agriculture: Oryzoxymycin case study

Bwire, R N; Majinda, R R; Masesane, I B; Steel, P G (International Union of Pure and Applied Chemistry. http://stage.iupac.org/publications/pac/, NaN, 2009)

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Abstract:

The Diels–Alder adducts of ethyl (E)-3-nitroacrylate and furan provided a common and versatile template for the stereocontrolled synthesis of an isomer of the natural product oryzoxymycin and polyhydroxylated cyclohexyl β-amino acid derivatives. The strategy for the synthesis of the polyhydroxylated cyclic β-amino acid derivatives involved base-induced fragmentation of the oxanorbornene skeleton and face selective oxidation reactions. A Pd-catalyzed transfer hydrogenation reaction in the presence of organic acids is also described. This reaction is amenable to being enantioselective through use of optical pure chiral organic acids.

URI:

http://hdl.handle.net/10311/301

Files in this item: 1

From nature.pdf (2.826Mb)

Gaboroquinones A and B and 4'-O-demethylknipholone-4'-O-β-D-glucopyranoside, phenylanthraquinones from the roots of Bulbine frutescens

Abegaz, B.M.; Bezabih, M.; Msuta, T.; Brun, R.; Menche, D.; Muhlbacher, J.; Bringmann, G. (American Chemical Society. http://pubs.acs.org/jnp/, NaN, 2002)

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Abstract:

The novel phenylanthraquinones 4'-O-demethylknipholone-4'-O-β-D-glucopyranoside (2) and gaboroquinones A (3) and B (4) were isolated from the African medicinal plant Bulbine frutescens. Biaryl 2 represents the first phenylanthraquinone glucoside, while 3 and 4 are the first side-chain-hydroxylated phenylanthraquinones. Their constitutions were determined by spectroscopic analysis, in particular by HMBC, HMQC, and ROESY NMR investigations, and by chemical transformations. The axial configurations were elucidated chemically, by deglucosylation of 2 and by side-chain deoxygenation of 3 and 4 to give the known phenylanthraquinones 4'-O-demethylknipholone (5), isoknipholone (6), and knipholone (1), respectively, and chiroptically, by CD investigations. Compounds 2, 3, and 4 showed moderate to good antiplasmodial and antitrypanosomal activities in vitro.

URI:

http://hdl.handle.net/10311/346

Files in this item: 1

Gaboroquinones.pdf (407.3Kb)

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