Charlene Marais

(S)- and (R)-Eriodictyol-6-C-ß-D-glucopyranoside, novel keys to the fermentation of rooibos (Aspalathus linearis)

The processed leaves and stems of Aspalathus linearis contain a new diastereomeric pair of the flavanones, (S)- and (R)-eriodictyol-6-C-beta-D-glucopyranoside, which is also formed via the oxidative cyclization of the dihydrochalcone, aspalathin, under conditions which mimic the fermentation process.

The occurrence of phenylpyruvic acid in woody plants: Biosynthetic significance

Abstract The leaves and stems of Aspalathus linearis, a member of the Fabaceae, contains (Z)-3-phenyl-2-β-D-glucopyranosyloxypropenoic acid, an enolic glucoside of phenylpyruvic acid which is of relevance to the shikimic acid pathway.

Occurrence of phenylpyruvic acid in woody plants: biosynthetic significance and synthesis of an enolic glucoside derivative

The leaves and stems of Aspalathus linearis, a member of the Fabaceae, contains (Z)-2-(β-D-glucopyranosyloxy)-3-phenylpropenoic acid 1, an enolic glucoside of phenylpyruvic acid, representing the first unequivocal evidence for the latters presence in woody plants. The synthesis of a derivative 2 of the natural product, and of related regiomeric and geometrical isomers 3,4 and 5, and the biosynthetic significance in relation to the shikimic acid pathway are discussed.

Catalytic epoxidation of stilbenes with non-peripherally alkyl substituted carbonyl ruthenium phthalocyanine complexes

A number of novel carbonyl(1,4,8,11,15,18,22,25-octaalkylphthalocyaninato)-ruthenium(II) complexes were prepared by metal insertion with Ru3(CO)12. The new compounds have been characterized by 1H NMR, 13C NMR, IR, UV-vis and mass spectroscopy. This study demonstrated that this type of complexes and specifically carbonyl(1,4,8,11,15,18,22,25-octahexylphthalo-cyaninato)ruthenium(II) and carbonyl[1,4,8,11,15,18,22,25-octa(2-cyclohexylethyl)phthalocyaninato]-ruthenium(II), exhibit high catalytic activity and stability in the epoxidation of stilbenes with 2,6-dichloropyridine N-oxide as oxidant.

Studies Towards the Stereoselective α-Hydroxylation of Flavanones. Biosynthetic Significance

The enolates of various propiophenones, chromanones, and also analogues of naturally occurring flavanones were stereoselectively hydroxylated at the α-position, by employing commercially available enantiopure oxaziridines, to afford the desired α-hydroxylated target molecules in good to exceptional stereoselectivities and in moderate to good chemical yields. A mechanistic rationale is presented to account for the stereoselectivities achieved. These in vitro results were tentatively related to the stereoselective biosynthesis of enantio-enriched dihydroflavonols while questions were raised about the authenticity of certain natural compounds.

Al(OTf)3 Catalysed Friedel-Crafts Michael Type Addition of Indoles to α,β-Unsaturated Ketones with PEG-200 as Recyclable Solvent

An Al(OTf)3 catalysed efficient Friedel–Crafts Michael type addition of indoles to α,β-unsaturated ketones using recyclable PEG-200 as an alternative reaction solvent is disclosed. The reaction under microwave irradiation is clean, leads to excellent yields in minutes and reduces the use of volatile organic compounds.

Non-peripherally alkyl substituted ruthenium phthalocyanines as catalysts in the epoxidation of alkenes

Non-peripherally alkyl substituted ruthenium phthalocyanines were demonstrated to be highly active epoxidation catalysts. It is compatible with pyridine N-oxides, and especially 2,6-dichloropyridine N-oxide. The catalytic activity towards a variety of alkenes was comparable to that published for other catalytic systems, but superior in the cases of 1,2-dihydronaphthalene and trans-stilbene. Linear substituents on the non-peripheral sites of the phthalocyanine were able to reduce aggregation and increase the solubility of the catalyst without compromising its activity by steric congestion as all substituted catalysts were more reactive than the unsubstituted phthalocyanine, whereas the bulky isopentyl and cyclohexyl substituted catalysts were less active than those with linear substituents. Although the epoxidation mechanism and the exact active intermediate is still ambigious, it likely involves the coordination of the N-oxide to ruthenium and subsequent transfer of the oxygen to the metal to form a high-valent oxo-ruthenium species. It is proposed that the alkene approaches this metal oxo moiety from the top and that oxygen transfer to the alkene is concerted with concomitant stereoretention.

Thermo-analytical determination of intermediates in the copper catalysed rearrangement of o-toluic acid to meta-cresol

The intermediates formed during the conversion of o-toluic acid 2 to m-cresol 1 in the presence of Cu(II) according to the Keading process, together with the temperatures at which crucial changes occur, have been investigated by means of X-ray diffractometry [which confirmed the formation of the paddlewheel copper complex tetrakis(μ2-2-methylbenzoato)bis(2-methylbenzoic acid)copper(II) 5 with two apical o-toluic acid ligands], differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), NMR spectroscopy, infrared spectrometry (IR) and Maldi-Tof mass spectrometry. The major chemical change observed at 164 °C might be ascribed to the dissociation of the apical o-toluic acid ligands from 5 to give tetrakis(μ2-2-methylbenzoato)copper(II) 6 accompanied by water loss. O–C bond formation between the carboxylate oxygens and ortho-carbons of the toluic acid moieties in adjacent paddlewheels of the stepped polymeric 6 is proposed to explain the formation of copper(I) 2-methyl-6-{[(2-methylphenyl)carbonyl]oxy}benzoate 8via intermediate 7 and initiates the decomposition observed by DSC at 236 °C. Decarboxylation of 8 at 249.5 °C gives 3-methylphenyl 2-methylbenzoate 4, which can be hydrolysed to o-toluic acid 2 and the target compound, m-cresol 1.