Identification of two chromone phytoalexins in the sweet pea, Lathyrus odoratus

A major phytoalexin isolated from the Helminthosporium Carbonum-inoculated leaflets and pods of Lathyrus odoratus has been identified by spectroscopic procedures as 5,7-dihydroxy-3-ethylchromone (lathodoratin). Small amounts of the corresponding 7-O-methyl ether (methyl-lathodoratin) are also formed by this plant. Both compounds similarly occur as phytoalexins in the closely related legume L. hirsutus but are absent from the other Lathyrus species examined. The unusual 3-substitution of the chromone nucleus appears to be essential for fungitoxicity since the synthetic isomer 5,7-dihydroxy-2-ethylchromone is apparently inactive.