John L. Ingham

3,5,4′-trihydroxystilbene as a phytoalexin from groundnuts (Arachis hypogaea)

Abstract Cis and trans -resveratrol (3,5,4′-trihydroxystilbene) have been isolated from the infected hypocotyls of Arachis hypogaea and implicated as phytoalexins.

Phytoalexins and other natural products as factors in plant disease resistance

ConclusionIn recent years studies of plant disease resistance have concentrated on active resistance rather than on those mechanisms which rely on structural barriers such as the cuticle. This change has led to the detection and isolation of several post-infectional antifungal compounds, known collectively as phytoalexins, and to their implication as major factors in the disease resistance of several plant species. These substances were first discussed by Müller & Börger (1940) although it is only during the last decade that concerted attempts have been made by plant pathologists and biochemists to support or refute their hypothesis.As a result of this research numerous reports in the literature are concerned with production of phytoalexins or phytoalexin-like substances by diseased plants, and of these the phytoalexins from the Leguminosae constitute one of the more important groups. However, even in this extremely large Family only a few species have been studied in detail, and as a result there is great scope for the extensive screening of many more genera in order to detect antifungal metabolites of both pre- and post-infectional origin, research which would be of considerable value to chemotaxonomy as well as plant pathology. With the advanced analytical techniques now available it should also be possible to characterise many of the phytoalexin-like compounds produced by members of other plant Families in order to compare and contrast their structures with those of known antifungal metabolites.The detection and characterisation of phytoalexins and other related natural products, the elucidation of their biosynthetic pathways and where appropriate their antifungal mechanisms, and the development of these substances or synthetic analogues for use in crop protection provides a new and exciting field of plant pathology which without doubt will be greatly expanded in the years that lie ahead.

Fungitoxic dihydrofuranoisoflavones and related compounds in white lupin, Lupinus albus☆

Abstract Chromatographic investigation of a methanolic extract of white lupin roots has revealed the presence of six new dihydrofuranoisoflavones (lupinisoflavones A-F). Three monoprenylated (3,3-dimethylallyl-substituted) isoflavones (wighteone, luteone and licoisoflavone A), two diprenylated isoflavones [6,3′-di(3,3-dimethylallyl)genistein (lupalbigenin) and 6,3′-di(3,3-dimethylallyl)-2′-hydroxygenistein (2′-hydroxylupalbigenin)] and two pyranoisoflavones (parvisoflavone B and licoisoflavone B) have also been isolated from the same source. In addition to genistein, leaf extracts of L. italbus contain 3′-O-methylorobol which is presumed to be the precursor of lupisoflavone [5,7,4′-trihydroxy-3′-methoxy-6-(3,3-dimethylallyl)isoflavone]. Probable biogenetic relationships between the prenylated, and dihydrofurano-and pyrano-substituted isoflavones in roots and leaves of L. albus are briefly discussed.

The isopentenyl isoflavone luteone as a pre-infectional antifungal agent in the genus Lupinus

Abstract The prenylated isoflavone luteone has been isolated from healthy leaves of Lupinus albus and 11 other lupin species. Evidence is presented that this compound occurs as a leaf surface constituent. In vitro tests indicate that luteone and a second unidentified isoflavone frorn L. albus possess antifungal activity sufficient to support their proposed role as pre-infectional resistance factors. No evidence was obtained to suggest that phytoalexins were produced by the fungus-infected leaves of L. albus .

Fungal modification of pterocarpan phytoalexins from Melilotus alba and Trifolium pratense

Abstract Medicarpin (3-hydroxy-9-methoxypterocarpan), an isoflavonoid phytoalexin characteristic of sweetclover (Melilotus alba), is metabolised by three fungi, Botrytis cinerea, Colletotrichum lindemuthianum (race β) and C. coffeanum (isolates CCA and CCP) to afford products with decreased antifungal activity. Peterocarpan phytoalexins from red clover (Trifolium pratense) are similarly modified. A fourth organism, Helminthosporium carbonum apparently lacks this ability. Fungal-mediated tranformation principally involves hydroxylation, methylation and demethylation although ring fission has also been noted.

Seventeen isoflavonoids from Lupinus albus roots

Abstract A further investigation of the methanol extractives from white lupin (cv. Kievskij Mutant) roots has revealed a new coumaronochromone (lupinalbin F) and 13 new isoflavones. The latter compounds have been identified as four dihydrofurano-isoflavones (lupinisoflavones G-J), three dihydrohydroxypyrano-isoflavones (lupinisolones A-C), three 2-hydroxy-3-methyl-3-butenyl-substituted isoflavones (lupinisols A-C), two pyrano-isoflavones (isoderrone and isochandalone), and a diprenyl-isoflavone (2′-hydroxyisolupalbigenin). The structures of all 14 isoflavonoids were principally deduced by spectroscopic comparison (MS, UV and 1H NMR) with structurally similar compounds previously isolated from L. albus or obtained as fungal metabolites of prenylated isoflavones. Chemical transformation and/or the Gibbs test response was used to provide supporting structural evidence in some cases. The known isoflavones chandalone, angustone B and angustone C were also isolated from L. albus roots.

Inducibly-formed isoflavonoids from leaves of soybean

Abstract Isoformononetin, glyceollins I, II and 2-isopentenyl-3,6a,9-trihydroxypterocarpan (glyceocarpin) accumulated in soybean ( Glycine max ) leaves after treatment with aqueous sodium iodoacetate or a cell suspension of the bacterium, Pseudomonas pisi . These compounds were also accompanied by two previously unreported pterocarpans, glyceofuran its 9- O -methyl derivative. Glyceocarpin is described for the first time as a plant product.

Identification of the Erythrina phytoalexin cristacarpin and a note on the chirality of other 6a-hydroxypterocarpans

Abstract Cristacarpin, a new phytoalexin from Erythrina crista-galli is assigned the structure (−)-3,6a-dihydroxy-9-methoxy-10-γ,γ-dimethylallyl- cis -pterocarpan. It is accompanied by the known phytoalexins phaseollidin and demethylmedicarpin in this plant. Cristacarpin, phaseollidin and demethylmedicarpin were also obtained from E. sandwicensis and (together with isomedicarpin) from the related legume, Psophocarpus tetragonolobus . A compilation of selected optical rotation, NMR and conformational data for all known 6a-hydroxypterocarpans is presented and it is concluded that the previously assigned chiralities of neobanol, glyceollins I–IV and 3,6a,9-trihydroxypterocarpan should be reversed. Chirality assignments are made for a number of previously unassigned compounds.

New stilbene phytoalexins from American cultivars of Arachis hypogaea

Abstract Two phytoalexins from American varieties of Arachis have been characterized as the cis - and trans -isomers of 3,5,4′-trihydroxy-4-isopentenylstilbene.

Isoflavan phytoalexins from Anthyllis, lotus and Tetragonolobus

Abstract Two previously unreported phytoalexins, 7,4′dihydroxy-2′-methoxy- and 7,2′,4′-trihydroxyisoflavan, have been isolated from the fungus-inoculated leaves of Anthyllis vulneraria and 5 Tetragonolobus species. Examination of Lotus corniculatus revealed the co-occurrence of the latter with the known isoflavans, vestitol and sativan. Only 7,2′4′-trihydroxyisoflavan and vestitol were produced by the closely related L. uliginosus.