Susan L Bonnet

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A novel and efficient method for the oxidative condensation of tetra-O-methyl-3-oxocatechin 4 with tetra-O-methylcatechin is described. Treatment of a solution of 3 (2 equiv) and 4 (1 equiv) with silver tetrafluoroborate readily affords the phenolic per-O-methyl ethers of 3-oxocatechin(4-8)-catechin 18 and 19. Subsequent metal hydride reduction provides(More)
Wattle (Acacia mearnsii) bark extract is an important renewable industrial source of natural polymers for leather tanning and adhesive manufacturing. The wattle bark proanthocyanidin oligomers have 5-deoxy extender units that render the interflavanyl bonds resistant to acid catalysed hydrolysis and their composition cannot be determined via conventional(More)
Z-2-(β-d-glucopyranosyloxy)-3-phenylpropenoic acid (PPAG), a compound postulated to contribute to the taste and mouthfeel of fermented rooibos tea (Aspalathus linearis), was isolated from unfermented rooibos plant material. Its structure was unequivocally confirmed by LC-MS, -MS(2), FT-IR and NMR of the underivatised natural product, and optical rotation(More)
Aspalathin (1), a dihydrochalcone C-glucoside, exhibits powerful plasma sugar-lowering properties and thus potentially could be used to treat diabetes. Small quantities occur in rooibos tea, manufactured via fermentation of the leaves of Aspalathus linearis, hence necessitating the need for an efficient and concise synthesis. Efforts to synthesize(More)
Flavonoids and their photochemical transformations play an important role in biological processes in nature. Synthetic photochemistry allows access to molecules that cannot be obtained via more conventional methods. This review covers all published synthetic photochemical transformations of the different classes of flavonoids. It is first comprehensive(More)
The benzophenone, iriflophenone-3-C-glucoside, was isolated from Cyclopia genistoides using a combination of fluid-fluid extraction, high performance counter-current chromatography (HPCCC) and semi-preparative high performance liquid chromatography (HPLC). The microplate oxygen radical absorbance capacity (ORAC) assay, with fluorescein as probe, was adapted(More)
Solid state ¹³C-NMR spectra of pure tannin powders from four different sources--mimosa, quebracho, chestnut and tara--are readily distinguishable from each other, both in pure commercial powder form, and in leather which they have been used to tan. Groups of signals indicative of the source, and type (condensed vs. hydrolyzable) of tannin used in the(More)
Two new compounds a flavanolignan (1), and an alkane (2) along with four known compounds including two fatty acid esters (3-4) and two isocoumarins (5-6) were isolated from the methanolic extract of the stem bark of Newtonia griffoniana. Their structures were elucidated using spectroscopic methods including extensive 1-D and 2-D NMR experiments.
Proanthocyanidins (PACs) are natural plant-derived polymers used in leather tanning, wood adhesives, water purification, and mud additives for oil drilling. Quebracho (Schinopsis lorentzii and Schinopsis balansae) heartwood and mimosa (Acacia mearnsii) bark extracts are the major industrial sources of PACs. These commercial extracts are often sulfited via(More)
The oligosaccharides present in the milk of an African elephant (Loxodonta africana africana), collected 4 days post partum, were separated by size exclusion-, anion exchange- and high-performance liquid chromatography (HPLC) before characterisation by (1)H NMR spectroscopy. Neutral and acidic oligosaccharides were identified. Neutral oligosaccharides(More)