Oryzalexin F, a diterpene phytoalexin from UV-irradiated rice leaves

A new rice phytoalexin, oryzalexin F, was isolated from UV-irradiated rice leaves. Its structure was established as ent-isopimara-8(14),15-diene-3β,18-diol by spectroscopic methods. The ED50 value of oryzalexin F against spore germination of the blast fungus, Pyricularia oryzae, was 103 ppm. Oryzalexin F was also produced in blast fungus-infected or jasmonic acid-treated rice leaves.