David T. Coxon

Controlled synthesis of monohydroperoxides by α-tocopherol inhibited autoxidation of polyunsaturated lipids

Abstract α-Tocopherol influences product formation during the autoxidation of unsaturated lipids and, if present in sufficient quantity (5%; 0.1M), only cis,trans -conjugated diene monohydroperoxides are formed: the formation of trans,trans -isomers and secondary oxidation products (e.g. hydroperoxyepidioxides) is suppressed. At this high concentration α-tocopherol does not exert its recognised antioxidant effect but allows autoxidation to proceed smoothly and quite rapidly to produce good yields of monohydroperoxides. This property, coupled with preparative high performance liquid chromatography, has been utilised to prepare and isolate the isomeric monohydroperoxides of methyl arachidonate and 2-linoleoyl-1,3-dipalmitoylglycerol.

Abnormal metabolites produced by Daucus carota roots stored under conditions of stress

Abstract The formation of dihydroisocoumarins (I and II), the chromones (III and IV) and scopoletin (V) is induced in carrot roots by storage in the presence of low concentrations of ethylene and by inoculation with various fungi. There has been concern over possible toxic effects of dihydroisocoumarins and some preliminary toxicological data on (I), (II) and (IV) are included.

Cis-heptadeca-1,9-diene-4,6-diyne-3,8-diol, an antifungal polyacetylene from carrot root tissue

Abstract A compound isolated from root tissue extracts of Daucus carota L. showed antifungal activity towards Mycocentrospora acerina and Cladosporium cladosporioides . It was identified with the aid of u.v. and infrared spectroscopy, nuclear magnetic resonance and mass spectrometry as cis -heptadeca-1,9-diene-4,6-diyne-3,8-diol with the trivial name of falcarindiol. A concentration gradient in carrot roots varying from 93 μg/g fresh wt in periderm and pericyclic parenchyma to 2 μg/g in xylem parenchyma was demostrated. The ED 50 for inhibition of germination of chlamydospores of M. acerina was 31·8 μg/ml. The role of this compound in disease resistance is discussed.

Formation, isolation and structure determination of methyl linolenate diperoxides

Abstract Autoxidation of methyl linolenate gives rise to isomeric mono-hydroperoxides by reaction with one mole of oxygen but further reaction with a second mole of oxygen readily occurs to produce an isomeric mixture of diperoxides. Autoxidation of individual pure methyl hydroperoxylinolenate isomers has been used as a method of obtaining less complex diperoxide mixtures which can be separated into their pure components by preparative high-pressure liquid chromatography (HPLC). The major diperoxide isomers arising from the autoxidation of pure 9R- and 13S- hydroperoxides of methyl linolenate have been isolated and characterised as isomeric epidioxyhydroperoxides of methyl linolenate. These same compounds have been identified as components of the more complex mixture of diperoxides produced during methyl linolenate autoxidation. The structures of the isolated diperoxides have been determined by physico-chemical methods and a mechanism for their formation is proposed.

Antifungal phenanthrenes in yam tubers

Abstract An extract from the peel of yams ( Dioscorea rotundata ) showed anti-fungal activity towards both Cladosporium cladoporioides and a variety of ya

Wyerone epoxide as a phytoalexin in Vicia faba and its metabolism by Botrytis cinerea and B. fabae in vitro

Abstract Wyerone epoxide was identified as a third acetylenic phytoalex in Vicia faba . The epoxide accumulated in limited lesions formed by both Botrytis cinerea and B. fabae . Products of the metabolism of wyerone epoxide by B. cinerea and B. fabae were identified as wyerol epoxide and dihydrodihydroxywyerol respectively. The metabolites were less antifungal than wyerone epoxide.

IDENTIFICATION OF THREE HYDROXYFLAVAN PHYTOALEXINS FROM DAFFODIL BULBS

Abstract Three phytoalexins were isolated from daffodil bulb scales inoculated with Botrytis cinerea and identified as 7-hydroxyflavan, 7,4′-dihydroxyflavan and 7,4′-dihydroxy-8-methylflavan. The structures of the phytoalexins were confirmed by total synthesis.

Conversion of wyerone to wyerol by Botrytis cinerea and B. fabae in vitro

Abstract The phytoalexin wyerone was induced to accumulate in cotyledons of Vicia faba infected with Botrytis cinerea or B. fabae . The acetylenic keto ester, wyerone, was converted to the less antifungal corresponding hydroxy ester, wyerol, by both species of Botrytis in vitro .

Oxidative reactions of unsaturated lipids

Abstract Monohydroperoxides, which are the products of free radical autoxidation of unsaturated fatty acids, can under go further free radical chain reactions initiated by abstraction of hydrogen to reform peroxy radicals. In the autoxidation of methyl linolenate, the peroxy radicals corresponding to ‘inner’ hydroperoxides may cyclise and, after further oxygenation, yield diperoxides. The mixtures of the two peroxidic species, monohydroperoxides and diperoxides, obtained from linolenate can be identified and determined chromatographically. Mechanistic studies showed that the oxygenation of pentadienyl radicals to form peroxy radicals—an important propagation step in autoxidation—is reversible. H-donors can be used to control the relative rates of the forward and reverse reactions and so determine the relative proportions of different peroxidic species formed. α-Tocopherol was shown to be an effective H-donor and drastically altered the distribution of products formed in linolenate autoxidation. Such control of peroxide formation may be a factor determining the manifestations that are specific to the oxidative deterioration of a food product.

Agropine, a new amino acid derivative from crown gall tumours

Abstract Agropine, an unusual compound produced in plant tumours was shown by mass spectrometry and proton and carbon-13 nmr spectroscopy to be a bicyclic derivative of glutamic acid and a hexitol sugar.