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June 2012 - November 2015
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Publications (142)
All learners have a contribution to make to the development of the Chemical Sciences, be that in novel ways to teach, and their perspectives and contexts, but also in research, both in chemical education and the wider Chemical Sciences. Through four case studies, this paper explores interactions with diverse groups and how this has altered perspect...
Algoa Bay, the largest crenulate bay on the southeastern coast of South Africa, is currently one of the most well-studied marine ecosystems in southern Africa. A plethora of endemic marine invertebrates inhabits the benthic reefs on the western edge of the Bay in close proximity to South Africa's sixth largest city. Over the past 25 years, South Af...
The selected acyclic halogenated monoterpenes derived from red macroalgae are investigated in terms of their isolation, their reactions with oxidants (ozone, OH radical) and the impacts of the first-generation oxidation products on the atmosphere. The yields of these monoterpenes from marine algae are small and highly variable (0.01-6.7%), the frac...
Unregulated chlorocarbons - here defined as dichloromethane (CH2Cl2), perchloroethene (C2Cl4), chloroform (CHCl3) and methyl chloride (CH3Cl) – are gases not regulated by the Montreal Protocol. While CH3Cl is the largest contributor of atmospheric chlorine, recent studies have shown that growth in emissions of the less abundant chlorocarbons could...
Benzene and toluene, emitted into the atmosphere from a number of common anthropogenic activities, pose a significant human health risk. The mole fractions of toluene and benzene were measured at two urban locations (Foreshore and Potsdam) in Cape Town and one background site at Cape Point, South Africa over the period of July-November 2017. The an...
Volatile organic halocarbons play a significant role in the biogeochemical cycling of halogens in the atmosphere. High frequency, in situ measurements of methyl iodide (CH3I), bromoform (CHBr3), dibromomethane (CH2Br2) and methyl bromide (CH3Br) were measured in the marine boundary layer at Cape Point, South Africa by an automated Absorption Desorp...
One hydrochlorofluorocarbon and two hydrofluorocarbons (HCFC-22, HFC-125 and HFC-152a) were measured in air samples at the Cape Point observatory (CPT), South Africa during 2017. These data represent the first such atmospheric measurements of these compounds from south western South Africa (SWSA). Baseline atmospheric growth rates were estimated to...
Marine sponges – in common with many other sessile marine invertebrates seemingly devoid of obvious physical forms of defence against predators, e.g. spines or shells – are the sources of a diverse array of organic chemical compounds known as marine natural products or secondary metabolites. Recent research has indicated that the production of natu...
South Africa’s Cape Point (CPT) trace gas observatory, operated by the South African Weather Service (SAWS), has been monitoring mole fractions (mol/vol) of ambient greenhouse gases (GHGs), e.g. carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and selected halocarbons (CFCs and CCl4) since the late 1970s. In addition, the Cape Point trace...
Extracts of 13 species of marine ascidian collected in Algoa Bay were analyzed by LC-ICP-MS/ESI-MS. This technique allows parallel analysis of the molecular species and the presence of certain elements. The LC-ICP-MS/ESI-MS technique was used to target iodinated metabolites in this study. Three ascidian species afforded the known 3,5-diiodo-4-metho...
Ambiguities and errors in the structural assignment of organic molecules hinder both drug discovery and total synthesis efforts. Newly described NMR experimental approaches can provide valuable structural details and a complementary means of structure verification. The caulamidines are trihalogenated alkaloids from a marine bryozoan with an unprece...
Due to the rise in multi-drug resistant pathogens and other diseases, there is renewed interest in marine sponge endosymbionts as a rich source of natural products (NPs). The South African marine environment is rich in marine biota that remains largely unexplored and may represent an important source for the discovery of novel NPs. We first investi...
The Latrunculiidae are a family of cold water sponges known for their production of bioactive pyrroloiminoquinone alkaloids. Previously it was shown that the bacterial community associated with a Tsitsikamma sponge species comprises unusual bacterial taxa and is dominated by a novel Betaproteobacterium. Here, we have characterized the bacterial com...
Recent developments in marine drug discovery from three South African marine invertebrates, the tube worm Cephalodiscus gilchristi, the ascidian Lissoclinum sp. and the sponge Topsentia pachastrelloides, are presented. Recent reports of the bioactivity and synthesis of the anti-cancer secondary metabolites cephalostatin and mandelalides (from C. gi...
The crude organic extracts of ascidian species collected from Algoa Bay, South Africa were analysed using liquid chromatography with parallel inductively coupled plasma mass spectrometry/electrospray mass spectrometry (LC-ICP-MS/ESI-MS). The data obtained was used to detect a number of brominated and iodinated tyramine and tyrosine derivatives with...
Over a decade ago Wright et al., proposed a putative antiplasmodial mechanism of action for marine isonitriles (1, and 3-6) and isothiocyanate (2) that involved interference in heme detoxification by Plasmodium falciparum thus inhibiting the growth of the parasite. In the current paper we describe the successful down scaling of Egan's β-hematin inh...
his chapter, covering the chemistry literature up until June 2013 and comprising 142 references, records the chemical structures of 130 bi-, bis-, and trisindole alkaloids isolated from a plethora of marine phyla including bacteria, algae, bryozoans, sponges, mollusks, hard corals, and ascidians. While the vast majority of bisindoles have been isol...
Two known isocopalane diterpene diacylglycerides 1 and 2 and one new isocopalane diterpene diacetate, (12S, 13R, 14S)-isocopalan-13-ol-12,14-diacetate, 3 were isolated from an unidentified sub-Antarctic nudibranch. The structure and stereochemistry of the new minor metabolite 3 was established from spectroscopic data and recourse to biosynthetic ar...
As part of an ongoing study to elucidate the SAR of bisindole alkaloid inhibitors against the evolutionary conserved MRSA pyruvate kinase (PK), we present here the synthesis and biological activity of six dihalogenated analogues of the naturally occurring sponge metabolite deoxytopsentin, including the naturally occurring dibromodeoxytopsentin. The...
The public health care crisis caused by the emergence of drug resistant bacterial strains, e.g., methicillin resistant Staphylococcus aureus (MRSA) has underlined the urgent need to accelerate the discovery of new chemical entities active against antibiotic resistant bacteria. We report here the synthesis of a series thiazole containing deoxytopsen...
The health care crisis caused by methicillin resistant Staphylococcus aureus (MRSA) is due in part to a lack of fundamental drug discovery research into new antibiotics with novel modes of action. Marine bis-indole alkaloids have proved to be effective in vitro antibacterials. We present the synthesis of thiazole containing analogues of the marine...
A detailed hydrographic and biological survey was carried out in the region of the South-West Indian Ridge during April 2004. Altimetry and hydrographic data have identified this region as an area of high flow variability. Hydrographic data revealed that here the Subantarctic Polar Front (SAF) and Antarctic Polar Front (APF) converge to form a high...
Oesophageal cancer is one of the most common causes of cancer-related deaths in South African black males. The limited efficacy of chemotherapeutic agents to treat this disease has prompted a search for potential new chemical entities with anticancer properties. We report here on the evidence for anti-oesophageal cancer activity in the methanolic e...
The known 3,6-dibromoindole (1), 6-bromo-3-chloroindole (2) and 6-bromo-2-oxindole
(3) were isolated from the marine ascidian (sea squirt) Distapliaskoogi collected from
Algoa Bay, South Africa. Standard spectroscopic techniques were used to elucidate the
structures of 1-3. All three compounds were found to be moderately cytotoxic to
metastatic MDA...
The SEAChange programme, instituted in 2007 under the auspices of the South African Network for Coastal and Oceanic Research (SANCOR), included four interdependent research themes, one of which was Marine Biotechnology. Marine biotechnology is a discipline that involves both basic and applied research, and is aimed at the commercial exploitation of...
The known 3,6-dibromoindole (1), 6-bromo-3-chloroindole (2) and 6-bromo-2-oxindole (3) were isolated from the marine ascidian (sea squirt) Distapia skoogi collected from Algoa Bay, South Africa. Standard spectroscopic techniques were used to elucidate the structures of 1-3. All three compounds were found to be moderately cytotoxic to metastatic MDA...
MRSA pyruvate kinase is an evolutionary conserved enzyme, responsible for catalysing the rate limiting final step in glycolysis. Sequence alignment and X-ray co-crystallography revealed amino acid sequence divergence from common human PK orthologs at the small interface, which is also the site of inhibitor binding. As part of an ongoing investigati...
Education institutions globally are increasingly expected to explore avenues for the implementation of service-learning into their curricula. A second-year undergraduate organic chemistry laboratory experiment, in which the undergraduate students make azo dyes, can provide a vehicle for a service-learning module in which university undergraduate st...
Naphthoquinones have been found to have a wide range of biological activities, including cytotoxicity to cancer cells. The secondary metabolites lapachol, α- and β-lapachone and a series of 25 related synthetic 1,4-naphthoquinones were screened against the oesophageal cancer cell line (WHCO1). Most of the compounds exhibited enhanced cytotoxicity (...
Background: Sponges belonging to family Latrunculiidae are known for their production of the
biologically active pyrroloiminoquinones. Pyrroloiminoquinones are potent DNA intercalators that
cleave the DNA or inhibit topoisomerase II and they have potential for anti-cancer and anti-malarial
drug development. Marine sponges are associated with divers...
The CH(2)Cl(2)-MeOH extract of a South African tunicate described as the new Synoicum globosum Parker-Nance sp. nov. (Ascidiacea, Aplousobranchia) was subjected to (1)H NMR-guided fractionation. This resulted in the identification of new 3″-bromorubrolide F (1), 3'-bromorubrolide E (2), 3'-bromorubrolide F (3), and 3',3″-dibromorubrolide E (4) and...
Mandelalides A-D are variously glycosylated, unusual polyketide macrolides isolated from a new species of Lissoclinum ascidian collected from South Africa, Algoa Bay near Port Elizabeth and the surrounding Nelson Mandela Metropole. Their planar structures were elucidated on submilligram samples by comprehensive analysis of 1D and 2D NMR data, suppo...
Natural products isolated from marine invertebrate fauna and their associated microbial communities are globally recognized as potentially rich sources of new pharmaceuticals, especially anti-cancer agents. With the exception of southern Africa, Africa’s marine biodiversity is generally poorly described especially from marine biota found in the mor...
Covering: 1972 to 2011. This review covers the literature of prenylated quinone, hydroquinone and naphthoquinone marine natural products with reported cytotoxic and/or antioxidant properties. The structures, biological activity and, where applicable, the syntheses of 159 cytotoxic/antioxidant compounds, isolated from various marine organisms, are p...
Tsitsikamma favus is a latrunculid sponge endemic to the coast of South Africa that produces unique pyrroloiminoquinones known as tsitsikammamines. Wakayin and makaluvamine A are structurally similar to the tsitsikammamines and are the only pyrroloiminoquinones isolated from a source other than Porifera (namely a Fijian ascidian Clavelina sp. and a...
Three new polypropionate metabolites, 6Z,8E-Δ(8)-siphonarienfuranone (1), 6E,8E-Δ(8)-siphonarienfuranone (2), and 6E,8E-3-hydroxy-4,6,8,10,12-pentamethylpentadeca-6,8-dien-5-one (3), and the known polypropionate siphonarienfuranone (4) were isolated from the intertidal South African marine mollusk Siphonaria oculus. Evidence is presented to suggest...
Novel classes of antimicrobials are needed to address the emergence of multidrug-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA). We have recently identified pyruvate kinase (PK) as a potential novel drug target based upon it being an essential hub in the MRSA interactome (Cherkasov, A., Hsing, M., Zoraghi, R., Foster,...
We report an improved procedure for the synthesis of phenyl glyoxal and a series of para-substituted aryl glyoxals by microwave-assisted selenium dioxide oxidation. The reaction time has been reduced from several hours to three minutes for activated aryl methyl ketone substrates and 18min for deactivated substrates, with all reactions affording qua...
Novel classes of antimicrobials are needed to address the emergence of multidrug-resistant bacteria such as methicillin-resistant
Staphylococcus aureus (MRSA). We have recently identified pyruvate kinase (PK) as a potential novel drug target based upon
it being an essential hub in the MRSA interactome (1,2). Screening of an extract library of marin...
Leonotis leonurus L. (Lamiaceae) is used as a traditional medicine for a variety of ailments in South Africa. The diterpene marrubiin is the major product constituent in specimens of this plant occurring in South Africa.
Marrubiin isolated from South African specimens of L. leonurus in addition to an organic extract of L. leonurus were tested in vi...
A variety of 8β,13β-dihydroxypodocarpane derivatives (V) (8 examples) are synthesized starting from naturally occurring diterpene (+)-manod.
Plasmodium falciparum heat shock protein 70 (PfHsp70-1) is thought to play an essential role in parasite survival and virulence in the human host, making it a potential antimalarial drug target. A malate dehydrogenase based aggregation suppression assay was adapted for the screening of small molecule modulators of Hsp70. A number of small molecules...
8β,13β-Dihydroxypodocarpane and eight C-13 substituted derivatives were prepared from the precursor 8bhydroxy-13-podocarpanone synthesised from the naturally occurring diterpene (+)-manool. The synthetic compounds exhibited a range of anti-plasmodial activities (IC50 1-29 μM) and only induced minimal haemolysis of erythrocytes at concentrations 50...
8β,13β-Dihydroxypodocarpane and eight C-13 substituted derivatives were prepared from the precursor 8 b hydroxy-13-podocarpanone synthesised from the naturally occurring diterpene (+)-manool. The synthetic compounds exhibited a range of anti-plasmodial activities (IC50 1–29 μM) and only induced minimal haemolysis of erythrocytes at concentrations 5...
Given the emphasis in Higher Education on community engagement in South Africa and the importance of international collaboration, we discuss a joint approach to chemistry outreach in two countries on two continents with widely differing target school audiences. We describe the history of the partnership between the chemistry departments at Rhodes U...
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Investigations of four different sponge populations of Latrunculia species collected in New Zealand waters has led to the characterization of a new diastereomer of discorhabdin H, named discorhabdin H(2), confirmation of the structure of discorhabdin K ((+)-7), and presentation of a new diastereomer, discorhabdin K(2) ((-)-8). In each case the stru...
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
A majority of chemistry graduates seek employment in a rapidly changing chemical industry. Our attempts to provide the graduates with skills in entrepreneurship and the ability to understand and communicate with their chemical engineering colleagues, in addition to their fundamental knowledge of chemistry, are described. This is done at second-year...
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
South African organic chemistry is deeply rooted in a rich history of natural product chemistry research with the secondary metabolites emanating from South Africa's unique floral kingdoms dominating this research for nearly a century. However, South Africa's terrestrial biodiversity is exceeded by an even greater diversity of marine flora and faun...
![Figure 1 Competition with total [ 3 H]-diprenorphine (2 nM) binding by...](profile/Michael-Davies-Coleman/publication/288132136/figure/fig1/AS:669964977582082@1536743506164/Competition-with-total-3-H-diprenorphine-2-nM-binding-by-phorbol-esters-PE-1-4_Q320.jpg)
Two known phorbol esters,12-deoxyphorbol-13-isobutyrate-20-acetate (1) and 12-deoxyphorbol-13-(2-methylbutyrate)-20-acetate (2), and two new phorbol esters, 12-deoxyphorbol-13-isobutyrate-16-angelate-20-acetate (3) and 12-deoxyphorbol-13-(2-methylbutyrate)-16-angelate-20-acetate (4), were isolated from the endemic South African plant Euphorbia both...
An apparently routine metal-halogen exchange (MHE) reaction gave variable low yields under typical conditions. (13)C and C (7)Li NMR studies suggested a diversity of organolithiums were formed in the MHE reaction leading to a plethora of products on subsequent electrophilic aromatic substitution with geranyl bromide. A reversal of reagent addition...
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Cynodon dactylon (Bermuda grass) has been observed to grow sporadically on the surface of coal dumps in the Witbank coal mining area of South Africa. Root zone investigation indicated that a number of fungal species may be actively involved in the biodegradation of hard coal, thus enabling the survival of the plant, through mutualistic interaction,...
Clionamines A-D (1- 4), new aminosteroids that modulate autophagy, have been isolated from South African specimens of the sponge Cliona celata. Clionamine D (4) has an unprecedented spiro bislactone side chain.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Pelargonium sidoides DC. (Geraniaceae) root extracts are used locally and globally as herbal medicines. Subsequently, high levels of wild root harvest in the years preceding this study, to supply international demand for raw materials, prompted this investigation of the prospects for sustainable root harvest through wild collection and greenhouse c...
A reinvestigation of extracts of the endemic South African intertidal limpet Trimusculus costatus yielded the known labdane diterpenes 6beta,7alpha-diacetoxylabda-8,13 E-dien-15-ol ( 1) and 2alpha,6beta,7alpha-triacetoxylabda-8,13 E-dien-15-ol ( 2) and three new metabolites, 6beta,7alpha,15-triacetoxylabda-8,13 E-diene ( 3), 3alpha,11-dihydroxy-9,1...
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Two isomeric labdane aldehyde metabolites (1 and 2), first isolated from the skin of the Notaspidean nudibranch Pleurobranchaea meckelii, were synthesized in six steps from manool in 19 and 6% overall isolated yields, respectively.
The syntheses of four 2-substituted 1,4 naphthoquinones, related to the marine natural product 2-deoxylapachol, are reported. All four synthetic compounds were cytotoxic to WHCO1 oesophageal cancer cells.
Marine invertebrates, algae, and microorganisms are prolific producers of novel secondary metabolites. Some of these secondary metabolites have the potential to be developed as chemotherapeutic agents for the treatment of a wide variety of diseases, including cancer. We describe here the mechanism leading to apoptosis of esophageal cancer cell line...
The known 17-norisopimar-15-ene-8beta,13beta-diol (5) and five new semisynthetic norditerpenoids, ethyl 17-norabiet-13(15)-E-en-8beta-ol-16-oate (6), ethyl 17-norabiet-13(15)-Z-en-8beta-ol-16-oate (7), 17-norpimaran-13alpha-ethoxy-8,16-olactone (8), 17-norisopimarane-8beta,15-diol (9), and 17-norarabiet-13(15)-ene-8beta,16-diol (10), were prepared...
The coastline of southern Africa is divided into three bio-geographical zones, with each zone sustaining a unique diversity of marine fauna and flor Associated with this marine biodiversity are relatively high levels of species endemism, often a useful pre-requisite for the discovery of novel, bioactive ma natural products. This review is the first...
Two triprenylated toluquinone and toluhydroquinone marine fungal metabolites, 5-methyl-2-[(2′E,6′E)-3′,7′,11′-trimethyl-2′,6′,10′-dodecatrienyl]-2,5-cyclohexadiene-1,4-dione and 5-methyl-2-[(2′E,6′E)-3,7,11-trimethyl-2′,6′,10′-dodecatrienyl]-1,4-benzenediol, were synthesized in four and five steps, respectively, from 2-methyl-1,4-benzoquinone. The...
Despite their perceived inaccessibility, the marine intertidal and benthic environments of Antarctica, southern Africa and
South America have continued to provide marine natural products for chemists with unique opportunities to study the secondary
metabolite constituents and chemical ecology of a diverse array of marine gastropod molluscs. This re...
Three novel tetraprenylated alkaloids, malonganenones A-C (1-3), were isolated from the gorgonian Leptogorgia gilchristi collected near Ponto Malongane, Mozambique. Compound 1 is the first 3,7-disubstituted hypoxanthine to be discovered from a marine source, while 2 and 3 represent the first formamides to be isolated from gorgonians. The unexpected...
This review presents the structure, biological activity and, where applicable, references to the syntheses of 154 spongian and rearranged spongian diterpenoids isolated from marine sponges of the orders Dictyoceratida and Dendroceratida. There have been no studies of the biosynthesis of either spongian diterpenoids or their rearranged derivatives r...
Despite their perceived inaccessibility, the marine intertidal and benthic environments of Antarctica, southern Africa and South America have continued to provide marine natural products for chemists with unique opportunities to study the secondary metabolite constituents and chemical ecology of a diverse array of marine gastropod molluscs. This re...
The electrochemical properties of 14 structurally related pyrroloquinoline metabolites (compounds 1-14) isolated from marine sponges were studied in pH-varied experiments using cyclic and square wave voltammetry. In general both substitution patterns and pH were observed to influence the reduction potentials of these molecules.
The subtidal whelk Burnupena papyracea co-occurs with a voracious predator, the rock lobster Jasus lalandii, in situations where other potential prey are largely eliminated. The survival of B. papyracea has been ascribed to a symbiotic bryozoan, Alcyonidium nodosum, which characteristically encrusts the shells of this mollusc and deters feeding by...
Squamous cell esophageal cancer presents a significant health burden in many developing countries around the world. In South Africa, this disease is one of the most common causes of cancer-related deaths in black males. Because this cancer is only modestly responsive to available chemotherapeutic agents, there is a need to develop more effective th...
Marine invertebrates, algae and microorganisms produce a plethora of structurally unique and biologically active secondary metabolites. The ecological roles of these natural products, although not completely understood, range from chemical defence against predation to intra-specific cues for larval settlement. Surprisingly, a number of these metabo...