Adrienne L. Davis

1H and 13C NMR Assignments of Some Green Tea Polyphenols

Complete and unequivocal 1H and 13C NMR assignments for a range of green tea polyphenols [epiafzelechin, catechin, epicatechin, gallocatechin, epigallocatechin, catechin‐3‐O‐gallate, epicatechin‐3‐O‐gallate, gallocatechin‐3‐O‐gallate, epigallocatechin‐3‐O‐gallate and epigallocatechin‐3‐O‐(3′‐O‐methyl)‐gallate] in acetone‐d6 solvent have been achieved using the 2D proton–carbon correlation experiments HMQC and HMBC and also 1D NOE difference spectroscopy.

Homologation and functionalization of carbon monoxide by a recyclable uranium complex

Carbon monoxide (CO) is in principle an excellent resource from which to produce industrial hydrocarbon feedstocks as alternatives to crude oil; however, CO has proven remarkably resistant to selective homologation, and the few complexes that can effect this transformation cannot be recycled because liberation of the homologated product destroys the complexes or they are substitutionally inert. Here, we show that under mild conditions a simple triamidoamine uranium(III) complex can reductively homologate CO and be recycled for reuse. Following treatment with organosilyl halides, bis(organosiloxy)acetylenes, which readily convert to furanones, are produced, and this was confirmed by the use of isotopically 13C-labeled CO. The precursor to the triamido uranium(III) complex is formed concomitantly. These findings establish that, under appropriate conditions, uranium(III) can mediate a complete synthetic cycle for the homologation of CO to higher derivatives. This work may prove useful in spurring wider efforts in CO homologation, and the simplicity of this system suggests that catalytic CO functionalization may soon be within reach.

Analysis of conjugated linoleic acid isomers by 13C NMR spectroscopy

Abstract The conjugated linoleic acids (CLAs), octadeca-10E,12Z-dienoic and octadeca-11Z, 13E-dienoic acids, have been identified by 2D NMR spectroscopy in simple fatty acid mixtures. Unequivocal assignments for reporter resonances in the 13C NMR spectra of these molecules are given. NMR assignments for the olefinic carbons of octadeca-8E,10Z-dienoic acid have also been obtained, along with full 13C assignments for the octadeca-9,11-dienoic acids (ZE, ZZ and EE isomers). These data have been used to interpret the 13C NMR spectrum of a complex CLA mixture, allowing the olefinic carbon chemical shifts of all isomers of 7,9 to 11,13 CLAs to be deduced. A method for the quantification of these compounds by 13C NMR is described, demonstrating the utility of 13C NMR spectroscopy in the analysis of complex CLA mixtures.

A polyphenolic pigment from black tea

A yellow polyphenolic compound has been isolated from black tea (fermented leaves of Camellia sinensis) and its structure characterized using a number of spectroscopic techniques. This compound, theacitrin A, represents a new class of polyphenolic pigments in black tea.

A New Type of Tea Pigment—From the Chemical Oxidation of Epicatechin Gallate and Isolated from Tea

( - )-Epicatechin-3-O-gallate (ECG), one of the major green tea poly-phenols, was oxidised chemically using potassium ferricyanide. The major oxidation product, termed theaflavate A, which gave a sharp peak on HPLC analysis, was separated and purified by a combination of chromatography on Sephadex LH-20 and a semi-preparative HPLC method. This compound was characterised by NMR spectroscopy (1H, 13C, HMQC, HMBC and ROESY) and mass spectrometry (Electrospray method) and was found to have a novel benzotropolone skeleton formed between the B-ring of one ECG molecule and the galloyl ester group of another. Compounds containing this type of benzotropolone link were also found to be present in black tea. This benzotropolone link is of great interest, since it shows that the galloyl ester groups of flavan-3-ols participate in oxidative condensation reactions. This illustrates the complexity of theaflavin-type compounds in black tea and provides an additional reaction pathway for the formation of thearubigins which has not been previously considered.

Synthesis of 19-substituted geldanamycins with altered conformations and their binding to heat shock protein Hsp90

The benzoquinone ansamycin geldanamycin and its derivatives are inhibitors of heat shock protein Hsp90, an emerging target for novel therapeutic agents both in cancer and in neurodegeneration. However, the toxicity of these compounds to normal cells has been ascribed to reaction with thiol nucleophiles at the quinone 19-position. We reasoned that blocking this position would ameliorate toxicity, and that it might also enforce a favourable conformational switch of the trans-amide group into the cis-form required for protein binding. Here, we report an efficient synthesis of such 19-substituted compounds and realization of our hypotheses. Protein crystallography established that the new compounds bind to Hsp90 with, as expected, a cis-amide conformation. Studies on Hsp90 inhibition in cells demonstrated the molecular signature of Hsp90 inhibitors: decreases in client proteins with compensatory increases in other heat shock proteins in both human breast cancer and dopaminergic neural cells, demonstrating their potential for use in the therapy of cancer or neurodegenerative diseases.

A model oxidation system to study oxidised phenolic compounds present in black tea

Abstract A model oxidation system was developed and optimised in order to provide a relevant tool to study oxidation products generated during the manufacture of black tea. The system utilised endogenous tea enzymes prepared by removing the phenolic compounds and caffeine from unprocessed tea leaves in such a way that the polyphenoloxidase (PPO) and peroxidase (POD) activities remained unaffected. This immobilised enzyme system was then used to oxidise the flavan-3-ols obtained from an ethyl acetate extract of green tea. The disappearance of the flavan-3-ols and the appearance of the different theaflavins were monitored by HPLC-UV. The theaflavin species detected were shown to be similar to those already described in black tea. The 1 H NMR spectra of more oxidised compounds produced by the model system were compared with those observed in black tea. The 1 H NMR spectra of the products generated by the model system and of the black tea extract were similar, suggesting that the washed leaf, heterogeneous catalysis system can successfully simulate the molecular changes that occur during tea production.

Black Tea Dimeric and Oligomeric Pigments—Structures and Formation

Many of us consume tea daily, but it is surprizing how few know where it comes from or how it is made. Tea comes from the tea plant the botanical name for which is Camellia sinensis (L.) O. Kuntze.1 This is a white-flowered evergreen indigenous to the rainforests of Assam, Northwest Burma and South West China, but now cultivated in over 30 countries around the world in places as far apart as Argentina, China, Papua New Guinea, and Turkey. However, since most tea leaves are plucked by hand, the largest plantations are most often found in countries with low manual labor costs. Two main varieties of tea are cultivated; Camellia sinensis var sinensis and C. sinensis var assamica. There is some controversy as to whether these are varieties or two distinct species.1 C. sinensis var. sinensis L, is grown mainly in China and Japan; it is a slow-growing bush, has small narrow leaves and is used for green tea manufacture. The second variety Camellia sinensis var. assamica is grown primarily in India and Africa, is fast growing, has a treelike habit, large broad leaves, and is the source material for black tea. In its cultivated state, it is pruned to approximately 3 feet for ease of harvesting the young shoots (flush), from which the tea is manufactured. This process (plucking) is carried out every 7–14 days during the growing season.

Investigations by HPLC-electrospray mass spectrometry and NMR spectroscopy into the isomerisation of salinomycin

HPLC-MS studies have indicated that certain polyether ionophore veterinary drugs are prone to degradation when stored as water-methanol solutions at ambient temperature. Salinomycin and narasin were particularly susceptible, disappearing completely within weeks to produce more polar species, which were identified as isomers of the original compounds. Lasalocid appeared to be stable under such conditions. Structural elucidation of the principal ultimate salinomycin isomerisation product was achieved by 2D NMR spectroscopy. This indicated that the isomerisation process consists of the opening of the spiro rings in the salinomycin structure with the concomitant formation of a furan moiety. The MS data indicated that the isomers retain the ability to complex alkali metal ions and may therefore retain their pharmacological activity. These discoveries may have implications both for the development of legislation covering acceptable levels of polyether ionophore residues in foodstuffs and also for analytical protocols designed to detect them.

The influence of domain segregation in ionic liquids upon controlled polymerisation mechanisms: RAFT polymerisation

Recent evidence has suggested that the solvent environment in ionic liquids is dynamic and composed of polar and non-polar domains governed by the summation of weak interactions and self-assembly. Consequently, the effect of a nano-structured solvent environment on chemistries conducted in ionic liquids is coming under increased scrutiny. In this work we investigate how the domain-like structure of ionic liquids affects the kinetics and products of the reversible addition fragmentation chain transfer (RAFT) controlled free radical polymerisation (FRP) of methyl methacrylate in a number of room temperature ionic liquids. By utilising rotating frame Overhauser effect spectroscopy (ROESY) to probe the solvation environment of the 2-cyano prop-2-yl dithiobenzoate (CPDB) RAFT agent, we show that in almost all cases preferential partitioning of the dithiobenzoate-moiety of the RAFT agent into the ionic domain of the ionic liquid occurs.