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.     

Isoflavonoid phytoalexins from fungus-inoculated leaves of Apios tuberosa

A new phytoalexin (apiocarpin) isolated from the fungus-inoculated leaflets of Apios tuberosa has been identified by chemical and spectroscopic pro     

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.     

Phytoalexin induction and its chemosystematic significance in the genus Trigonella

Using the drop-diffusate technique, a number of isoflavonoid phytoalexins have been obtained from the excised, fungus-inoculated leaflets of 41 species belonging to the legume genus Trigonella. Leaf diffusates variously contained pterocarpan (medicarpin and maackiain) and isoflavan (vestitol and sativan) derivatives previously associated with genera closely allied to Trigonella. In diffusates from T. calliceras, medicarpin was accompanied by a phytoalexin (designated TC-1) provisionally identified as a new hydroxylated pterocarpan. Most of the Trigonella species were also examined for their ability to release coumarin upon tissue maceration. The combined phytoalexin/coumarin data suggest that three major intrageneric chemical divisions occur in Trigonella; two of these apparently link the genus to Medicado/Factorovskya and Melilotus respectively, whilst the third provides some evidence for a connection with Trifolium. The taxonomic aspects of these findings are discussed in the light of earlier morphological studies which provided evidence for a distinct floral dichotomy amongst Trigonella species.     

Astraciceran: a new isoflavan phytoalexin from Astragalus cicer

A new phytoalexin isolated from the fungus-inoculated leaflets of Astragalus cicer has been identified as 7-hydroxy-2′-methoxy-4′,5′-methylenedioxyisoflavan (astraciceran). The synthesis of astraciceran and its 3′,4′-methylenedioxy analogue 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).     

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.     

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.).     

Phytoalexin production by Ononis species

Following exposure to short wavelength (254 nm) ultra-violet light, the detached leaflets of Passaea (Ononis) ornithopodioides and 31 species and subspecies of Ononis have been found to accumulate substantial quantities of the isoflavonoid (pterocarpan) phytoalexin, medicarpin. Apart from P. (Ononis) ornithopodioides, O. cristata, O. fruticosa, O. pubescens and O. rotundifolia, leaf tissues of all the species investigated similarly contained small amounts of the related fungitoxic pterocarpan, maackiain. Isoflavan phytoalexins common in genera such as Medicago and Trifolium (tribe Trifolieae) were absent from both Ononis and Passaea. The phytoalexin data suggest that Passaea should probably be combined with Ononis and, in conjunction with information on constitutive isoflavonoids, that Ononis itself should be assigned to the Trifolieae rather than to the distinct tribe Ononideae. Chemical evidence for and against an especially close taxonomic association between Ononis and Cicer (tribe Cicereae) is also briefly discussed.     

Two novel stilbene phytoalexins from Arachis hypogaea

Three phytoalexins were isolated from groundnut seeds which had been sliced and incubated for 48 hr at 252. Two were novel isoprenylated stilbene der     

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     

Metabolism of the phytoalexins medicarpin and maackiain by Fusarium solani

Non-inhibitory concentrations of the pterocarpan phytoalexin medicarpin were completely metabolized by isolates of Fusarium solani f. sp. pisi, f. sp. cucurbitae, f. sp. phaseoli and two other F. solani isolates genetically related to f. sp. pisi during 24 hr of growth in liquid medium. The major metabolic products accumulated without significant further degradation. Medicarpin was modified at one of three adjacent carbon atoms to form either an isoflavanone derivative, a 1a-hydroxydienone derivative or 6a-hydroxymedicarpin. Whereas each isolate degraded medicarpin to one or more metabolises, the isolates varied as to which metabolise they produced. Maackiain, another pterocarpan phytoalexin, was also metabolized by all the isolates to products analogous to those formed from medicarpin. The ability to metabolize medicarpin and maackiain was not always associated with the ability to metabolize pisatin and phaseollin, two other pterocarpan phytoalexins that were degraded by several of the isolates. Tolerance of medicarpin and maackiain was similarly not always associated with tolerance to pisatin.     

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.     

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.     

Identification of 1 a-hydroxy phaseollone,a phaseollin metabolite produced by Fusarium solani

A structure for the phaseollin metabolite of Fusarium solani f. sp phaseoli has been proposed and assigned the name 1 a-hydroxyphaseollone.     

Biosynthesis of pterocarpan phytoalexins in Trifolium pratense

Feeding experiments have demonstrated that 7,2′-dihydroxy-4′-methoxy-isoflavone-[¹⁴C-Me] and -isoflavanone-[¹⁴C-Me] are extremely efficient precursors of the phytoalexin demethylhomopterocarpin in Cu²⁺-treated red clover seedlings. Neither of these compounds, nor demethylhomopterocarpin-[¹⁴C-Me], was incorporated into a second pterocarpan phytoalexin, maackiain. 3-Hydroxy-9-methoxypterocarp-6a-ene-[¹⁴C-Me] was a poor precursor of both pterocarpans. A biosynthetic pathway to demethylhomopterocarpin via 2′-hydroxylation of formononetin (7-hydroxy-4′-methoxyisoflavone) and subsequent reduction to the isoflavanone is proposed. The conversion of this isoflavanone into the pterocarpan may involve the corresponding isoflavanol and a carbonium ion intermediate. The branch-point to maackiain is probably at the formononetin stage. The presence of two coumestans, 9-O-methylcoumestrol and medicagol, previously unreported in red clover, is demonstrated. Biosynthetic implications are discussed.     

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.     

Two novel stilbene-2-carboxylic acid phytoalexins from Cajanus cajan

Three phytoalexins were isolated from leaves of pigeon pea which had been challenged with Botrytis cinerea. One was identified as pinostrobin chalc     

Isoflavonoids of Mildbraedeodendron excelsa

The heartwood of Mildbraedeodendron excelsa has yielded five isoflavones and an ( ± )-isoflavanone. The structure of 7,4′-dihydroxy-6-methoxyisoflavone (glycetein) was confirmed by synthesis.     

Occurrence of phytoalexins and phenolic compounds in endomycorrhizal interactions,and their potential role in biological control

This paper will review work mainly done during the last twenty years on the involvement of phytoalexin and phenolic compounds in mycorrhizal interactions. It has been observed that phytoalexins and associated molecules accumulate in roots after mycorrhizal infection, but less intensively and more slowly than in pathogenic interactions. Following mycorrhizal infection, enzymes of phenylpropanoid metabolism have been shown to be activated differentially. Some flavonoids and isoflavonoids have been reported to stimulate in vitro germination of mycorrhizal fungi or in vitro mycorrhizal infection, but their biological significance in signalling between the two symbiotic partners, and in biocontrol of plant disease by arbuscular mycorrhizal fungi, have not yet been elucidated.