Variabilin,a 6a-hydroxypterocarpan from Dalbergia variabilis

Bark and wood of the creeper Dalbergia variabilis contain the previously described friedelin, O-acetyl-oleanolic acid, formononetin, 8-O-methylretusin, (+)-vestitol, (±)-mucronulatol, (+)- and (±)-medicarpin, besides (+)-variabilin [(6aR,11aR)-6a-hydroxy-3,9-dimethoxypterocarpan]. This structure was confirmed by the conversion of (+)-variabilin into di-O-methylcoumestrol.     

Mucronulatol,mucroquinone and mucronucarpan,isoflavonoids from Machaerium mucronulatum and M. villosum

Additionally to the cinnamylphenols described in a previous paper, wood samples of Machaerium mucronulatum and M. villosum contain isoflavones, besides (?)-duartin, (?)- and (±)-mucronulatol [(3S)- and rac-7,3′-dihydroxy-2′,4′-dimethoxyisoflavan], (?)-mucroquinone [(3S)-2-methoxy-5-(7-hydroxy-8-methoxychroman-3-yl)-1,4-benzoquinone] and (+)-mucronucarpan [(6aS,11aS)-2,10-dihydroxy-3,9-dimethoxypterocarpan]. The constitutions of mucronulatol, mucroquinone and mucronucarpan were deduced by spectra and degradations, and confirmed by syntheses.     

Absolute configurations of isoflavans

The absolute configurations of isoflavans and isoflavanquinones isolated from Cyclolobium, Dalbergia and Machaerium species were established by comparison of their ORD curves with that of (3S)-5,7,3′,4′-tetra-methoxyisoflavan and (3S)-7,4′-dimethoxyisoflavan-2′,5′-quinone, respectively. The assignments were checked by the ozonolysis of the isoflavan (?)-duartin to (R)-paraconic acid and the oxidation of isoflavans to isoflavanquinones. The PMR spectra of the dihydropyran ring of the isoflavans are discussed in terms of the preferred conformation of this ring.     

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.     

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.).     

Duartin,an isoflavan from Machaerium opacum

The heartwood of Machaerium opacum contains 2,3-dimethoxyphenol, the stilbenes pinosylvin monomethyl ether and dimethyl ether, and the isoflavans (?)-duartin and (?)-mucronulatol. The structure of (3S)-7,3′-dihydroxy-8,2′,4′-trimethoxyisoflavan was deduced for duartin and the constitution confirmed by synthesis of the racemate.     

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.     

Isoflavonoids from Cyclolobium species

(3R)-Claussequinone (7-hydroxy-4′-methoxyisoflavanquinone is the principal constituent of Cyclolobium clausseni Benth. and C. vecchii A.