Flavonoids and isoflavonoids with antifungal properties from Platymiscium yucatanum heartwood

Platymiscium yucatanum is a tropical wood highly resistant to the fungi Lenzites trabea and Coriolus versicolor. In order to determine the reason for this property, heartwood extracts and isolated compounds were tested in vitro against these fungi. The methylene chloride extract completely inhibited (5 mg/ml) the mycellium growth of both fungi. Chromatographic separation of the extract afforded several flavonoids and isoflavonoids, among them the novel 4,2',5'-trihydroxy-chalcone, isoliquiritigenin (4,2',4'-trihydroxychalcone), (+)-liquiriti-genin, (+)-medicarpin, and homopterocarpin. The coumarin aesculetin dimethyl ether was also isolated. Antifungal activity of five of the isolated compounds were measured at 0.25 mg/ml. (+)-Medicarpin and the two chalcones inhibited the growth of both fungi. Aesculetin dimethyl ether and (+)-liquiritigenin were only active against C. versicolor. (+)-Medicarpin was the most active of the compounds tested and had greater activity than phenol against C. versicolor. The results suggest that the various compounds present all contributions in some degree to the heartwood durability, but not all compounds are equally effective.