A new isoflavan phytoalexin from leaflets of Lotus hispidus

A new isoflavonoid phytoalexin isolated from the fungus-inoculated leaflets of Lotus hispidus (hairy birdsfoot trefoil) has been identified as 5,4′-dimethoxy-7,2′-dihydroxyisoflavan (5-methoxyvestitol). Three known isoflavans (demethylvestitol, vestitol and sativan) are also produced by L. hispidus. The synthesis of 5-, 6- and 8-methoxyvestitol is described. Preparation of the pterocarpan analogues of 6- and 8-methoxyvestitol has allowed the structures of two additional legume phytoalexins to be unequivocally confirmed.     

Isolation of a new isoflavan phytoalexin from two Lotus species

A phytoalexin isolated from the fungus-inoculated leaflets of Lotus angustissimus and L. edulis has been characterised as 5,7-dimethoxy-2′,4′-dihydroxyisoflavan (lotisoflavan). The total synthesis of lotisoflavan is described.     

Isoflavan phytoalexins from Anthyllis,lotus and Tetragonolobus

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.     

Isopterofuran,a new 2-arylbenzofuran phytoalexin from Coronilla emerus

Two 2-arylbenzofuran phytoalexins isolated from the fungus-inoculated leaflets of Coronilla emerus (scorpion senna) have been identified as 6-demethylvignafuran and the previously unreported 2-(4-hydroxy-2,3-dimethoxyphenyl)-6-hydroxybenzofuran (isopterofuran). The synthesis of isopterofuran is described.     

New pterocarpan phytoalexins from Lathyrus nissolia

In addition to 3-hydroxy-9-methoxypterocarpan (medicarpin), the fungus-inoculated phyllodes of Lathyrus nissolia produce two previously unreported isoflavonoid phytoalexins. These compounds have been identified as 3,9-dihydroxy-10- methoxypterocarpan (nissolin) and 3-hydroxy-9,10-dimethoxypterocarpan (methyl-nissolin).     

Isoflavonoid phytoalexins of the genus Medicago

Detached leaves of 25 annual and perennial Medicago species have been inoculated with the fungus, Helminthosporium carbonum, and examined for subsequent production of isoflavonoid phytoalexins. Hydroxylated pterocarpan (medicarpin) and isoflavan (vestitol, sativan and isosativan) phytoalexins were obtained from most of the species investigated. Although large quantities of two flavonoid derivatives, isoliquiritigenin and liquiritigenin, were isolated from leaves of M. lupulina, this species was apparently unable to produce isoflavonoid compounds. Traces of 7-hydroxy-2′,4′-dimethoxyisoflavanone (a substance not previously recorded in the tribe Trifolieae) were obtained (together with medicarpin, vestitol and sativan) from M. sativa cv Du Puits. Some taxonomic aspects of phytoalexin induction are discussed with reference to the generic location of certain controversial Medicago species including M. (Trigonella) radiata.     

Isoflavonoid and stilbene phytoalexins of the genus Trifolium

The fungus-inoculated leaflets of 55 Trifolium species have been examined for the presence of isoflavonoid and non-flavonoid phytoalexins. Isoflavonoid derivatives belonging to the pterocarpan (medicarpin, maackiain and 4-methoxymaackiain) and isoflavan (vestitol, isovestitol, sativan, isosativan and arvensan) classes were isolated from 50 species whilst T. campestre and T. dubium accumulated the trihydroxy stilbene, transresveratrol. Three other species (T. badium, T. scutatum and T. spadiceum) apparently did not produce phytoalexins in response to fungal inoculation. The distribution and biosynthetic relationship of Trifolium phytoalexins is discussed and the genus compared with others belonging to the Trifolieae and related tribes.     

Insect feeding deterrent activity of phytoalexin isoflavonoids

When incorporated into an agar-cellulose medium containing feeding stimulants, phytoalexin isoflavonoids from several legumes show feeding deterrent activity against larvae of the insect Costelytra zealandica and Heteronychus arator. The levels at which these compounds deter feeding are of the same order of magnitude as those at which they reduce fungal growth. The most active compound tested was phaseollin. These results suggest that phytoalexin isoflavonoids show a dual acitvity against insects and fungi.     

Identification of a second antifungal isoflavan from diseased Phaseolus vulgaris tissue

A second antifungal isoflavan has been isolated from diseased bean hypocotyls and identified as 2′-methoxyphascollinisoflavan.     

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

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.     

An isoflavan phytoalexin from leaves of Glycyrrhiza glabra

An isoflavonoid phytoalexin isolated from the leaves of Glycyrrhiza glabra has been characterised as 7,2′-dihydroxy-3′,4′-dimethoxyisoflavan     

Tephrocarpin,a pterocarpan phytoalexin from Tephrosia bidwilli and a structure proposal for acanthocarpan

The isoflavonoids (-)-6aR; 11aR-maackiain, (-)-6aS; 11aS-pisatin and (-)-6aR; 11aR-4-methoxy- maackiain have been isolated as p     

A 2-arylbenzofuran phytoalexin from cowpea (Vigna unguiculata)

2-(2′-methoxy-4′-hydroxyphenyl)-6-methoxybenzofuran (vignafuran) has been identified as the major phytoalexin from cowpea leaves infected with Colletotrichum lindemuthianum.     

6-Demethylvignafuran as a phytoalexin of Tetragonolobus maritimus

A phytoalexin isolated from the fungus-inoculated leaves of Tetragonolobus maritimus has been identified as 6-demethylvignafuran (2-[4-hydroxy-2-methoxyphenyl]-6-hydroxybenzofuran). The synthesis of 6-demethyl-vignafuran and two isomeric benzofurans is described. The presence of 3,9-dihydroxypterocarp-6a-ene in T. maritimus is also reported.     

Induction and identification of sativan and vestitol as two phytoalexins from Lotus corniculatus

Two phytoalexins, (-)-sativan, previously named sativin, [(-)-7-hydroxy-2′,4′-dimethoxyisoflavan], and (-)-vestitol, [(-)-7,2′-dihydroxy-4′-methoxyisoflavan], were induced by a spore suspension of Helminthosporium turcicum Pass. to accumulate in leaves of birdsfoot trefoil (Lotus corniculatus L.).     

A new isoflavone phytoalexin from fungus-inoculated stems of Glycine wightii

6-Isopentenylgenistein 1 (wighteone) has been isolated as a phytoalexin from the fungus-inoculated or CuCl₂-treated stems of Glycine wightii. Plants treated with aqueous CuCl₂, but not those inoculated with the fungus, also accumulated genistein (2) and its 2′-hydroxy derivative (3).     

New stilbene phytoalexins from American cultivars of Arachis hypogaea

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

Dihydrowyerone derivatives as components of the furanoacetylenic phytoalexin response of tissues of Vicia faba

Changes in concentrations of 7 wyerone derivatives in bean tissues undergoing resistant reactions to Botrytis cinerea or B. fabae and in cotyledons in response to mercuric chloride have been examined using high performance liquid chromatography. The proportion of derivatives occurring in their saturated (dihydro) forms varied between cotyledon, leaf and pod tissues and with time after inoculation. Unsaturated derivatives were always present in greater concentrations than their dihydro analogues.     

New isoflavonoid glycosides from Dalbergia paniculata

The methanolic extract of the bark of Dalbergia paniculata has yielded three new isoflavonoid glycosides whose structures have been determined. They are 8-C-glucosylprunetin and biochanin-A and formononetin 7-rutinosides.     

Identification of pterostilbene as a phytoalexin from Vitis vinifera leaves

An inducible antifungal compound in grapevine leaves (Vitis vinifera L., cv Cabernet-Sauvignon) has been identified as trans-pterostilbene (3,5-dimethoxy-4′-hydroxy stilbene). It is only a minor component of the phytoalexin response of V. vinifera but its antifungal activity is relatively high by comparison with resveratrol and the viniferins, stress metabolites which have been identified previously in grapevine. Methods for the quantitative analysis of pterostilbene, resveratrol, ε- and α-viniferins by HPLC are described.