76. 紫外線照射イネ葉からの新奇ジテルペン化合物ent-10-oxodepressinの単離(口頭発表,植物化学調節学会第46回大会)

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Phytoalexins (PAs) are low-molecular-weight, antimicrobial compounds accumulated in plants after exposure to pathogen. Four-teen diterpenoid PAs have identified from rice (Oryza sativa L.): momilactones A and B, oryzalexins A-F and S, phytocassanes A-F. In the rice plant, the biosynthesis of PAs can be induced not only by invasion of rice blast fungus, Magnaporthe oryzae, but also by exposure to UV-irradiation. In this study, we tried to identify novel PAs, biosynthetic intermediates, or metabolites of PA from UV-irradiated rice leaves. A 70% methanol extract of UV-irradiated rice leaves (400 g) was separated by silica gel chromatography and ODS preparative HPLC to obtain a purified compound (2.1 mg, designed as PA-300) which showed a possible molecular ion at m/z 300 in GC/MS analysis. HRMS indicated a molecular formula of C_<20>H_<28>O_2. Its structure was determined by NMR spectroscopic methods. PA-300 has a casbane skeleton which has never reported from rice plants. The ^1H and ^<13>C NMR spectra of PA-300 were identical to those of 10-oxodepressin (1), a diterpenoid derived from soft coral Sinularia depressa. The [α]_D value of 1 was negative, while that of PA-300 was positive. Therefore, PA-300 was established as ent-10-oxodepressin (2). Compound 2 inhibited spore germination of rice blast fungus (IC_<50> value, 31 ppm). Compound 2 was also produced in jasmonic acid- and CuCl_2 -treated rice leaves.
2011-10-03