Isoneorautenol and Other Pterocarpan Phytoalexins from Calopogonium mucunoides

Following inoculation with the fungus Helm inthosporium carbonum, excised leaflets of the tropical papilionate legume C alopogonium mucunoides have been found to produce isoneorautenol, a new dimethylpyrano-substituted isoflavonoid (pterocarpan) phytoalexin. This compound accumulates together with demethylmedicarpin, neodunol, tuberosin, sophorapterocarpan A , and a sixth highly antifungal isoflavonoid (calopocarpin) characterised as 3,9dihydroxy-2-(3,3-dimethylallyl)pterocarpan. Chromatographic and spectroscopic examination of ‘hom oedudiol’ (a pterocarpan from Neorautanenia edulis roots previously considered to possess the structure now assigned to calopocarpin) has shown that in reality this substance is identical with sophorapterocarpan A . The systematic relationship o f Calopogonium to other genera within the legume tribe Phaseoleae is briefly discussed.