Dennis K. Taylor

Artemisinin and a Series of Novel Endoperoxide Antimalarials Exert Early Effects on Digestive Vacuole Morphology

ABSTRACT Artermisinin and its derivatives are now the mainstays of antimalarial treatment; however, their mechanism of action is only poorly understood. We report on the synthesis of a novel series of epoxy-endoperoxides that can be prepared in high yields from simple starting materials. Endoperoxides that are disubstituted with alkyl or benzyl side chains show efficient inhibition of the growth of both chloroquine-sensitive and -resistant strains of Plasmodium falciparum. A trans-epoxide with respect to the peroxide linkage increases the activity compared to that of its cis-epoxy counterpart or the parent endoperoxide. The novel endoperoxides do not show a strong interaction with artemisinin. We have compared the mechanism of action of the novel endoperoxides with that of artemisinin. Electron microscopy reveals that the novel endoperoxides cause the early accumulation of endocytic vesicles, while artemisinin causes the disruption of the digestive vacuole membrane. At longer incubation times artemisinin causes extensive loss of organellar structures, while the novel endoperoxides cause myelin body formation as well as the accumulation of endocytic vesicles. An early event following endoperoxide treatment is the redistribution of the pH-sensitive probe LysoSensor Blue from the digestive vacuole to punctate structures. By contrast, neither artemisinin nor the novel endoperoxides caused alterations in the morphology of the endoplasmic reticulum nor showed antagonistic antimalarial activity when they were used with thapsigargin. Analysis of rhodamine 123 uptake by P. falciparum suggests that disruption of the mitochondrial membrane potential occurs as a downstream effect rather than as an initiator of parasite killing. The data suggest that the digestive vacuole is an important initial site of endoperoxide antimalarial activity.

Microwave-assistance provides very rapid and efficient extraction of grape seed polyphenols

A microwave assisted extraction (MAE) method has been developed for the extraction of polyphenols from grape seeds of Vitis vinifera cultivars Cabernet Sauvignon, Shiraz, Sauvignon Blanc and Chardonnay. An initial five-factor (ethanol concentration in the extraction solvent, liquid:solid ratio, time, power and temperature), five-level orthogonal experimental array was designed and three factors (ethanol concentration in the extraction solvent, liquid:solid ratio and time) plus their best levels were chosen to optimise the extraction using a central composite rotatable design (CCRD) experiment. This revealed, after the use of response surface methodology, that the optimal extraction conditions were ethanol concentration (47.2%), liquid:solid ratio (45.3:1) and time (4.6min). Total polyphenols were determined by application of the Folin-Ciocalteau method. Sequential application of the optimal conditions to one sample revealed that approximately 92% of the total polyphenols were extracted in the first instance. In comparison with other extraction methods, MAE provided comparable or better extraction, but was very much quicker. One key finding was that varying the applied power to the extraction was essentially irrelevant; inspection of the applied power profile during extraction revealed that the power was strictly modulated to maintain a constant temperature in the reaction cell.

Occurrence, sensory impact, formation, and fate of damascenone in grapes, wines, and other foods and beverages

Among plant-derived odorants, damascenone is one of the most ubiquitous, sometimes occurring as an apparent natural product but more commonly occurring in processed foodstuffs and beverages. It has been widely reported as a component of alcoholic beverages, particularly of wines made from the grape Vitis vinifera . Although damascenone has one of the lowest ortho- and retronasal detection thresholds of any odorant, its contribution to the sensory properties of most products remains poorly understood. Damascenone can be formed by acid-catalyzed hydrolyses of plant-derived apocarotenoids, in both aglycon and glycoconjugated forms. These reactions can account for the formation of damascenone in some, but not all, products. In wine, damascenone can also be subject to degradation processes, particularly by reaction with sulfur dioxide.

Hydroxycinnamic Acid Ethyl Esters as Precursors to Ethylphenols in Wine

A method for determining ethyl coumarate and ethyl ferulate in wine using GC-MS with deuterium-labeled analogues has been developed and used to measure the evolution of these two esters during the production of two commercial monovarietal red wines, cv. Grenache and Shiraz. During fermentation, the concentration of ethyl coumarate rose from low levels to 0.4 mg/L in Grenache and 1.6 mg/L in Shiraz wines. These concentrations then increased further during barrel aging to 1.4 and 3.6 mg/L, respectively. The concentration of ethyl ferulate was much lower, reaching a maximum of only 0.09 mg/L. Conversion of ethyl coumarate and ethyl ferulate to their corresponding ethylphenols was observed during fermentations of a synthetic medium with two strains of Dekkera bruxellensis (AWRI 1499 and AWRI 1608), while a third (strain AWRI 1613) produced no ethylphenols at all from these precursors. Strains AWRI 1499 and 1608 produced 4-ethylphenol from ethyl coumarate in 68% and 57% yields, respectively. The corresponding yields of 4-ethylguaiacol from ethyl ferulate were much lower, 7% and 3%. Monitoring of ethyl coumarate and ethyl ferulate concentration during the Dekkera fermentations showed that the selectivity for ethylphenol production according to yeast strain and the precursor was principally a result of variation in esterase activity. Consequently, ethyl coumarate can be considered to be a significant precursor to 4-ethylphenol in wines affected by these two strains of Brettanomyces/Dekkera yeast, while ethyl ferulate is not an important precursor to 4-ethylguaiacol.

1,2,3-Triazolyl amino acids as AMPA receptor ligands

The central nervous system glutamate receptors are an important target for drug discovery. Herein we report initial investigations into the synthesis and glutamate receptor activity of 1,2,3-triazolyl amino acids. Two compounds were found to be selective AMPA receptor ligands, which warrant further investigation.

Evolution and Occurrence of 1,8-Cineole (Eucalyptol) in Australian Wine

A new method has been developed for the quantitation of 1,8-cineole in red and white wines using headspace solid-phase microextraction (SPME) combined with stable isotope dilution analysis (SIDA) and gas chromatography-mass spectrometry (GC-MS). An extensive survey of Australian wines (44 white and 146 red) highlighted that only red wines contained significant amounts of 1,8-cineole (up to 20 μg/L). Hydrolytic studies with limonene and α-terpineol, putative precursors to 1,8-cineole, showed a very low conversion into 1,8-cineole (< 0.6%) over a 2 year period, which does not account for the difference between white and red wines. 1,8-Cineole was chemically stable in model wine solution over 2 years, and absorption from a Shiraz wine by bottle closures was most evident for a synthetic closure only (14% absorption after 1 year). Two commercial ferments at two different locations were monitored daily to investigate the evolution of 1,8-cineole throughout fermentation. Both ferments showed daily increases in 1,8-cineole concentration while in contact with grape solids, but this accumulation ceased immediately after pressing. This observation is consistent with the extraction of 1,8-cineole into the ferment from the solid portions of the grape berries.

Production of the Pepper Aroma Compound, (−)-Rotundone, by Aerial Oxidation of α-Guaiene

The aroma link between pepper and wine has recently been elucidated to be due to the important aroma compound rotundone. To date, rotundone is the only known impact odorant with a peppery aroma. Although the concentration found in products of natural origin is small, the odor detection threshold is among the lowest of any natural product yet discovered. We report herein the identification of the first known precursor to rotundone, namely, α-guaiene, and that one mechanism of transformation is simple aerial oxidation.

A one-pot synthesis of thiophene and pyrrole derivatives from readily accessible 3,5-dihydro-1,2-dioxines

Abstract A one-pot synthesis of 2,5-disubstituted thiophene, 1,2,5-tri- and 2,5-disubstituted pyrrole derivatives from readily available 3,5-dihydro-1,2-dioxines is described. The reaction proceeds by an initial Kornblum–de la Mare rearrangement of the 3,5-dihydro-1,2-dioxine to its isomeric 1,4-diketone followed by condensation of the in situ 1,4-diketone with sulfur, ammonia or a primary amine.

Rapid Method for Proline Determination in Grape Juice and Wine

Proline is typically the most abundant amino acid present in grape juice and wine. The amount present is influenced by viticultural and winemaking factors and can be of diagnostic importance. A method for rapid routine quantitation of proline would therefore be of benefit for wine researchers and the industry in general. Colorimetric determination utilizing isatin as a derivatizing agent has previously been applied to plant extracts, biological fluids, and protein hydrolysates. In the current study, this method has been successfully adapted to grape juice and wine and proved to be sensitive to milligram per liter amounts of proline. At sugar concentrations above 60 g/L, interference from the isatin-proline reaction was observed, such that proline concentrations were considerably underestimated in grape juice and dessert wine. However, the method was robust for the analysis of fermentation samples and table wines. Results were within ±10% agreement with data generated from typical HPLC-based analyses. The isatin method is therefore considered suitable for the routine analysis required to support research into the utilization or release of proline by yeast during fermentation.

Expeditious synthesis of dihydronaphthofurans utilising 1,2-dioxines and stabilised phosphorus ylides

Abstract A new practical synthesis of functionalised 1,2-dihydronaphtho[2,1-b]furans from substituted 2,4a-dihydronaphtho[2,1-c][1,2]dioxines and stabilised phosphorus ylides is described. Functionalised γ-hydroxy enones and their isomeric hemiacetals are key intermediates.