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A synthetic and computational investigation of trishomocubane-amino acid derivatives.January 2003 (has links)
The class of polycyclic hydrocarbons including adamantane, pentacyclo [5.4.0.02
,6.
03,I0.05,9]undecane (PCU) and trishomocubane have proven to be an exciting investigation
for synthetic chemists. Many derivatives have been shown to possess excellent antiviral
and antibacterial properties, as well as potent anti-Parkinson agents. Some improve the
lipophilic nature of biologically active drugs, while others affect the three-dimensional
structure of peptides once incorporated as amino acid analogues.
This investigation focussed on deriving routes to improve yields of racemic 4-amino-(D3)trishomocubane-
4-carboxylic acid (tris-amino acid), the synthesis of enantiomerically pure
tris-amino acid, the incorporation of tris-amino acid into a short peptide, as well as the
simulation of the rearrangement of PCU to trishomocubane by using computational tools.
Research into developing a more efficient hydrolysis of trishomocubane-hydantoin (trishydantoin)
to yield racemic tris-amino acid, led to the development of two novel
compounds: the mono-Boc [Novel Compound 1, (NC1)] and bis-Boc [Novel Compound
2, (NC2)] protected hydantoin. Base hydrolysis of NC2 quantitatively yielded the racemic
tris-amino acid, which was a significant improvement on previously documented synthetic
routes.
The first attempt to produce enantiomerically pure tris-amino acid was through the
synthesis of diastereomeric derivatives of tris-hydantoin, chromatographic separation of the
diastereomers, followed by base hydrolysis of the hydantoin ring to produce
enantiomerically pure tris-amino acid. This research led to the development of two novel
N-protected tris-hydantoin derivatives (NC3 and NC4). Failure to chromatographically
separate the diastereomers resulted in the abandonment of this particular route.
The use of enzymes was, therefore, attempted to produce enantiomerically pure tris-amino
acid. A novel ester derivative of tris-amino acid (NC5) was synthesised, which was
followed by the application of Pig Liver Esterase (PLE). PLE is an enzyme which cleaves
ester functionalities. Some success was achieved but the extremely low yields of
enantiomerically pure tris-amino acid did not warrant this enzyme as a viable route for
production of the desired product.
Solid phase techniques were employed for the production of a tripeptide consisting of
alanine-glycine-tris-amino acid (ala-gly-tris). Some difficulty was encountered in
extending the amino acid sequence due to suspected Schiff base interaction between the
free amino group of tris-amino acid and the carbonyl functionality of glycine in the second
position.
A computational study, using ab initio methods, was performed on the rearrangement of the
PCU diol to 7-fluoro-11-hydroxy-trishomocubane. Two mechanisms (Proposed Mechanism
1 and Proposed Mechanism 2) were explored and both showed that the
stereochemistry of the hydroxyl groups has only a marginal influence on the transition state
energies of the various isomers. Both mechanisms were also indicated to occur through an
intramolecular SN2 mechanism. / Thesis (M.Sc.)-University of Natal, Durban, 2003.
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Extractives from marine organisms.Cele, Cyril M. January 2000 (has links)
The study involves the investigation of the chemical composition of some marine organisms. This entails collecting the organism, extracting compounds from it and separation, characterization and identification of these compounds. Marine chemistry has been ignored by many scientists in the past and it is for this reason that these organisms have been investigated, with the aim of discovering their chemistry and also finding new compounds which might be of value in our society. Such value may be the medicinal benefit and/or the understanding of some toxicological effect of some species. This study was conducted on Codium extricatum, Palythoa natalensis, Zoanthus sansibaricus and Zoanthus durbanensis all of which were collected from reefs situated at the southern part of Durban in KwaZulu-Natal (KZN). Carpobrotus edulis was another organism that was used in this work. The plant normally occurs on sand dunes. This, however, was collected from the terrestrial environment within the premises of University of Natal (Durban). Sterols, i.e., compound l, 2 and compound 4 were obtained from both the Codium and Zoanthus genera. Zoanthus also gave compounds which are derivatives of genetic material and these include inosine nucleoside, adenine nucleoside and guanine nucleoside. Zoanthus further gave a compound which is aromatic in nature i.e., compound 5 and this belongs to a class of compounds known as the tyramines. Cinnamic acid was found from Carpobrotus edulis. The structures of all compounds were elucidated by conducting a number of experiments using spectroscopic methods. These included nuclear magnetic resonance spectroscopy (n.m.r), mass and infrared spectroscopy. / Thesis (M.Sc.)-University of Natal, Durban, 2000.
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Extractives from the amaryllidacea and the fabaceae.Koorbanally, Neil Anthony. January 1999 (has links)
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. / Thesis (M.Sc.)-University of Natal, Durban, 1999.
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The chemical investigation of four medicinal plants.Langlois, Angela. January 2000 (has links)
This thesis describes a phytochemical investigation of four medicinal plants, namely, Agave attenuata (Agavaceae), Balanites maughamii (Balanitaceae), Astrotrichilia parvifolia (Meliaceae) and Combretum fragrans (Combretaceae). Investigations of A. attenuata and B. maughamii were undertaken as biological studies have shown that these plants possess anti-bilharzial properties. Schistosomiasis is an important public health issue in South Africa and attempts to deal with infected rural communities have forced scientists to focus their attention on snail control using plant molluscicides. A. attenuata yielded two glycosides, timosaponin A III (compound I) and 5?-pregn-16-en-20one- 3?-O-tetrasaccharide (compound II), while a coumarin, scopoletin (compound III) and a sterol, stigmasterol (compound IV) were isolated from B. maughamii A dammarane, shoreic acid (compound V) was isolated from A. parvifolia, this formed part of an ongoing investigation into the Meliaceae of Madagascar. Plants of the family Combretaceae are widespread in Africa and are used by traditional healers for a wide range of illnesses. The leaves and bark are used abundantly, however, the winged fruits are never eaten as they are highly toxic to animals and humans. The leaf surface is covered with epidermal scale-like trichomes through which acidic triterpenoid mixtures are secreted. Six lupane-type triterpenoids were isolated from C. jragrans, namely, lupeol (compound VI), lupenone (compound VII), lupeol 3?- docosanoate (compound VIII), lupeol 3?-eicosanoate (compound IX) hennadiol (compound X) and 30hydroxylupenone (compound XI). All the above compounds were isolated by column chromatography and the structures were elucidated by means of NMR spectroscopy, mass spectrometry and infra red spectroscopy. / Thesis (M.Sc.)-University of Natal, Durban, 2000.
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Capillary electrophoresis and related techniques for the analysis of fresh water algal toxins.John, Wilson. January 1997 (has links)
As cyanobacteria (also known as blue green algae) produce a range of cyclic peptides which
are highly toxic, capillary electrophoresis and associated techniques have been investigated
to assess their applicability for toxin monitoring in the water bodies of kwaZulu Natal,
South Africa. Capillary electrophoresis (CE) is a technique in which charged molecules can
be efficiently separated in a buffer solution within a capillary tube under the influence of a
strong electric field. Two CE modes, namely capillary zone electrophoresis (CZE) and
micellar electrokinetic capillary chromatography (MECC) were initially evaluated using a
laboratory-built CE instrument. The former mode lacked selectivity due to the similar
charge to size ratio of the algal toxins. However, with the latter mode, incorporation of a
surfactant (sodium dodecyl sulphate) into the buffer, produced sufficient resolution between
components. Parameters including surfactant concentration, buffer ionic strength, buffer
pH and operating voltage were systematically optimized to separate the four algal toxins
under investigation (microcystin YR, microcystin LR, microcystin RR and nodularin). The
optimum separation conditions were: 30 mM borax, 9 mM sodium dodecyl sulphate, pH
9.18, 30 kV applied voltage, 10 s hydrodynamic injection, 70 cm x 50 Ilm Ld. bare fused
silica capillary (LEFF 40 cm) and UV detection at 238 nm. Under these conditions, typical
detection limits were in the low ng/IlL range (14.13 ng/IlL for microcystin LR to 29.85
ng/ILL for nodularin).
The MECC method was evaluated in terms of migration time precision, efficiency and
resolution, peak area and normalised peak area precision. Standard deviation values for
retention times acquired using replicate electrokinetic injections ranged from 0.018 to 0.054
and 0.069 to 0.148 for hydrodynamic injections. Normalised peak area precision for
replicate hydrodynamic injections were in the range 84 to 97 % RSD, while improved %
RSD values of 11.5 to 18.7 were achieved for electrokinetic injections. Due to poor
precision resulting from the lack of automation on the laboratory built CE system, poor
correlation between increasing concentration and a corresponding change in normalised peak
areas were achieved. The MECC method developed was applied to the analysis of an algal
scum extract to illustrate the technique. A general problem with CE is that it suffers from poor detection sensitivity. Hence in this
study, alternative injection modes, sample concentration strategies and alternative detection
techniques were investigated in an attempt to improve detection limits for algal toxins.
Using optimized electrokinetic injection conditions, detection limits were five to ten times
better than those obtained with hydrodynamic injections. On-line sample concentration
methods were partially successful. Field amplified back and forth MECC in which analyte
injected in the entire column volume and subsequently focused in a narrow band by
manipulating the electric field, resulted in an enormous sensitivity enhancement that ranged
from 197 times for microcystin RR to 777 times for microcystin YR when compared to
hydrodynamic injections. Field amplified sample stacking (FASI) was ineffective for toxin
preconcentration, while electro-extraction produced detection limits ranging from 0.27
ng/J.tL for microcystin YR to 1.08 ng/J.tL for microcystin RR. Solid phase extraction, in
which analytes are first trapped and concentrated on HPLC material in a cartridge and then
eluted in a more concentrated form for injection, was found to be practical only in the offline
mode. A concentration detection limit of less than 0.002 ng/J.tL was obtained.
Attempts with on-line solid phase extraction failed due to problems associated with coupling
the cartridge with the separation capillary. Finally, laser induced fluorescence (LIF)
detection was investigated as an alternative to UV detection. Unfortunately, the algal toxins
were not amenable to LIF detection because tagging with the fluorescent moiety, fluorescein
isothiocyanate (FITC), was prevented by the stereochemistry of these cyclic peptides.
A comparative study between HPLC and MECC revealed that the former displayed poor
efficiency peaks and long analysis times for toxin analysis. However HPLC was superior in
terms of retention time precision (0.12 to 0.64 % RSD) and area precision (1.78 to 2.86 %
RSD). Mass detection limits for MECC (0.0142 to 0.0603 ng) were far superior to those
achieved by HPLC (0.55 to 1.025 ng). In addition to HPLC and MECC, a preliminary
investigation of micro-high performance liquid chromatography (J.tHPLC) and capillary
electrochromatography (CEC) for the analysis of algal toxins was made using 50 J.tm Ld.
capillary columns packed in-house, with reverse phase HPLC packing material. / Thesis (M.Sc.)-University of Natal, 1997.
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Soya protein isolate production by various methods.Sunley, Nigel Crispin. January 1995 (has links)
The concentrated protein fractions of soyabeans, known as soya protein isolate, was produced
by three different methods from the same raw material namely defatted soya flakes.
Extraction of the soluble fraction of the raw material is common to all three methods. A
study was therefore undertaken to optimise the extraction process conditions in terms of time,
temperature, pH, extraction time, extraction volume and raw material particle size, thereby
maximising yields of soluble material.
The three different methods, namely isoelectric precipitation, ultrafiltration and swollen gel
technology were then used to separate the soluble and non-soluble protein fractions. Both the
isoelectric and ultrafiltration methods gave good yields of finished product, with the
ultrafiltration process giving the better overall yield, but the swollen gel method gave
disappointing results and was not feasible in practice.
Functional properties of the products from the isoelectric and ultrafiltration methods were
compared and found to be broadly similar although different in certain respects from those
of commercial soya isolates.
Levels of the anti-nutritional factors trypsin inhibitor and phytate in products from the three
processes were determined and the substantial differences observed in trypsin inhibitor levels
were further investigated. Determination of lysinoalanine levels was also attempted but the
results obtained were unsatisfactory. Amino acid composition and polyacrylamide gel
electrophoresis were used to compare the chemical composition of products from the three
processes. The comparative economics of the isoelectric and ultrafiltration processes for large
scale production of soya protein isolates were evaluated, taking into account the comparative
efficiencies of the two processes as determined during the study. It was established that,
while the isoelectric process initially appears more economical, it may be possible to modify
the ultrafiltration process in such a manner as to make it more economical than the isoelectric
process. Overall figures however indicate that the manufacture of soya protein isolate in
South Africa is not currently a viable economic proposition, due to high raw material costs. / Thesis (M.Sc.)-University of Natal, 1995.
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A chemical investigation of a KwaZulu-Natal medicinal plant, Momordica foetida Schum. & Sond.Sewram, Vikash. January 1994 (has links)
Momordica foetida Schum. & Sond. (Cucurbitaceae), locally known as
iNtshungu, is widely used by the Zulu people of Natal-KwaZulu for the
treatment of a variety of ailments.
The dried leaves leaves and stems of this plant was subjected to soxhlet
extraction by refluxing with hexane, chloroform and methanol successively.
Thin layer chromatography of the chloroform extract of the leaves revealed a
multiplicity of compounds. The chloroform extract was further partitioned with
sodium hydroxide resulting in an organic and aqueous phase. The organic
phase, containing extract A, afforded two compounds, viz. compounds 1 and 2.
The basic aqueous fraction was neutralised and re-extracted with chloroform to
give extract B, affording five compounds, viz. compounds 3,4,5,6 and 7.
Structural elucidation was accomplished by techniques such as IH and 13C NMR
spectroscopy, HETCOR, COSY, FTIR and High Resolution Mass
Spectrometry.
Compounds 1 and 2 were identified as cucurbitane triterpenoids known as
momordicines which had been previously discovered in the related species of
this plant, Momordica charantia L. The remaining five compounds were
identified as novel compounds, although natural derivatives of compounds 6
and 7 had been isolated previously from Momordica charantia L. Compounds
3-7 were each isolated as an epimeric mixture but it was possible to select the
resonances corresponding to the major epimer. These five epimers were
respectively identified as 5, 19-epoxy-19(R)-hydroxy-25-methoxy-5β-
cucurbita-6,23-diene-3β-ol [102], 5,19-epoxy-19(R),25-dihydroxy-5β-cucurbita-
6,23-diene-3β-ol [103], 5,19-epoxy-19(R)-methoxy-25-hydroxy-5β-cucrbita-
6,23-diene-3β-ol [104], 5,19-epoxy-25-methoxy-5β-cucurbita-6,23diene-
3β-ol [105] and 5,19-epoxy-19(R),25-dimethoxy-5β-cucurbita-6,23diene-
3β-ol [106].
Appropriate reactions were performed, where possible, on the compounds
isolated in order to confirm their identity. / Thesis (M.Sc.)-University of Natal, Durban, 1994.
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Characterisation of SAPPI SAICCOR pulp mill's effluent.Moodley, Brenda. January 2001 (has links)
SAPPI SAJCCOR, whose factory is situated south of Durban, South Africa, is one of the
few paper and pulp mills that uses the acid sulphite process with calcium and magnesium
bases to produce a high-grade cellulose pulp. Four streams of effluent, namely, the
calcium - spent liquor stream, the magnesium condensate stream and two streams from
the bleaching effluent are produced during this sulphite pulping process and they contain
a variety of organic compounds extracted from the wood. Characterisation of the effluent
was based on isolation using column chromatography and identification using NMR
techniques.
A range of constituents, such as lignans and lignin - type precursors, a trilerpenoid and
fatty acids were isolated and identified. X-ray diffraction was used to identify an
inorganic residue obtained from the calcium - spent liquor stream and gas
chromatography/mass spectrometry was used to identify a wax residue. which builds up
in the process. In addition to this, the carbohydrate content of the four streams of effluent
was detennined using UV/visiblc spectroscopy. / Thesis (M.Sc.)-University of Natal, Durban, 2001.
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Amino-, amido- and oxy-bipyridyl complexes of copper, ruthenium, molybdenum and rhodium.Bernardis, Francesco Luigi. January 1996 (has links)
The work described in this thesis concerns the synthesis and study of the coordination behaviour
of the 6-anilino-2,2'-bipyridyl (Habipy), 6-N-methylanilino-2,2'-bipyridyl (mabipy), 6-piperidyl2,2'.-
bipyridyl (pipbipy) and 2,2'-bipyridin-6-one (Hobipy) ligands.
Chapter one reviews the coordination chemistry of the 2-aminopyridyl (Rap), 2-hydroxypyridyl
(Hhp) and the 2-(2-pyridyl)-I,8-naphthyridine (pynp) ligands. These ligands are closely related
to Habipy, mabipy, pipbipy and Hobipy in that they share a common NCN or NCO fragment.
Thus the review of their coordination behaviour provides insight into the expected coordination
of the Habipy, mabipy, pipbipy and Hobipy ligands.
The synthesis and characteristaion of the novel Habipy, mabipy and pipbipy ligands are reported
in Chapter two. X-ray crystal structure determinations of mabipy and pipbipy reveal that the
geometry about the exocyclic nitrogen atom in both ligands is nearly planer, suggesting substantial
overlap of the nitrogen lone pair orbital with the 1t electron system of the bipyridyl rings. In both
mabipy and pipbipy the N3-C 10 bond lengths are shorter then normal N-C single bonds.
In Chapter three -the synthesis and characterisation of copper(I) complexes containing mabipy,
pipbipy and Habipy, and a copper(II) complex containing mabipy are reported. The copper(I)
complexes have the general formula [Cu(l12-L)2r, where L= mabipy 1, pipbipy 2 or Habipy 3. The
structures of complexes 1 and 2 are determined by X-ray crystallography. In complexes 1- 3 the
bipyridyl fragments of mabipy, pipbipy and Habipy chelate while the exocyclic nitrogen atoms
remain free. The crystal structures of 1 and 2 reveal that the exocyclic nitrogens have a planar
geometry as was the case in the uncoordinated ligand. The crystal structure of [Cu(1l2-mabipY)2f+
(4) is determined by X-ray crystallography and is very similar to that of the copper(I) species.
Coordination of the mabipy ligand in 4 is the same as that in 1 and the exocyclic nitrogen in 4 is
also planar. The redox couple 4/1 is shown to be electrochemically reversible with EV2= 0.45 V.
In Chapter four the synthesis and chararcterisation of dinuclear complexes containing the Ru2
2+,
Ru/+, Mo24+and ~4+ cores are reported in which the abipy ligand bridges two metal centres.
The complexes [Rulll-L)lCO)4], where L= abipy 5 or obipy 6, were synthesised by the r~action
of the free ligands with [{RuiCO)102CCH3)2}n] in toluene. The structures of5 and 6 are
determined by X-ray crystallography and show the ligands bridging the Ru(I) atoms in a head to
tail fashion and occupy mutually cis positions about the octahedral Ru(I) atoms. The Ru-Ru
separations in 5 and 6 are 2.668(1) and 2.671(1) A respectively. The reaction of Habipy with
[Rui02CCH3)4CI]n was found to afford the mixed valence species [Ruill-abipy)(02CCH3)3CI]
(7), the structure of which is determined by X-ray diffraction methods. The structure of7 reveals
one abipy ligand bridging the two ruthenium atoms as in 5. The Ru-Ru separation in 7 is 2.294(2)
A. The reaction of [Moi02CCH3)4] with habipy in methanol affords (Moill-abipy)(02CCH3)3]
(8). The structure of 8 is determined by X-ray diffraction methods and reveals one abipy ligand
bridging two quadruply bonded molybdenum atoms which have a Mo-Mo separation of 2.094(2)
A. The [Rhlll~abipy)(02CCH3)iH20)] (9) is formed from the reaction of [Rh i02CCH3)4] with
Habipy in methanol. The structure of [Rh2(Il-abipy)(02CCH3)iNCPh)] is determined by X-ray
diffraction methods and shows the abipy ligand bridging two Rh(II) atoms which are separated
by 2.399(1) A. This chapter is concluded with a discussion of the possiblity of substitution of
more than one acetate ligand by the abipy ligand in terms of 'hard' and' soft' acid-base theory and
synthetic methods. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.
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Isolation and characterisation of secondary metabolites of two asteraceae species, Artemisia afra and Elytropappus rhinocerotis.Gakuba, Emmanuel. January 2009 (has links)
In this study two medicinal plant species, namely Artemisia afra Jacq. ex. Willd and Elytropappus rhinocerotis Less. (L.f) (= Dicerotamnus rhinocerotis Koekemoer), both belonging to the family Asteraceae, have been investigated and different compounds isolated and characterised. Both species are important plants used in traditional medicine in general in Africa and particularly in South Africa. A. afra, commonly called "African wormwood" is one of 400 species belonging to the genus Artemisia and it is the only one indigenous to Africa. E. rhinocerotis is one of eight Elytropappus species which are all restricted to the Cape floristic region. The aim of this study was to investigate the phytochemistry of these species. In total fifteen compounds were isolated and characterised. From the E. rhinocerotis extract, four known compounds, labdanolic acid, methyl labdanolate, 6, 7- dimethoxycoumarin and a sesquiterpene viridiflorol were isolated. These compounds were not previously reported from E. rhinocerotis. Two different chemotypes of A. afra were studied and eleven compounds were isolated. These compounds include sesquiterpenes such as taurin, artesin, maritimin, artemin, norsantolinifolide, santolinifolide A, and reynosin, a flavonoid, 5- hydroxy-7,4-dimethoxyflavone, a coumarin called scopoletin or 7-hydroxy-6- methoxycoumarin and other aromatic compounds such as p-hydroxyacetophenone, and 2,4-dihydroxy-6-methoxyacetophenone. Except for taurin, scopoletin and 5-hydroxy-7, 4- dimethoxyflavone , none of these other compounds has been reported previously from A. afra. This study has shown that A. afra contains a large number of sesquiterpenoids, mostly from the eudesmane-type. Structural elucidation of different compounds was performed using mainly NMR spectroscopy. Other methods used for identification include LC-MS and infrared spectroscopy. The major compound, labdanolic acid, is known to selectively inhibit cyclooxygenase-2, an enzyme associated with inflammation. The presence of labdanolic acid in the plant may account for its traditional use as an anti-inflammatory. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.
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