Structural Elucidation of Naturally Occurring 9, 12, 13-Trihydroxy Fatty Acids by a Synthetic Study1)

Our investigation on anti-rice blast fungus materials from the rice plant has already led to the isolation of various types of oxygenated unsaturated fatty acids, which play an essential role in the defense of the rice plant against this fungus. Among those isolated were 9,12,13-trihydroxy C-18 fatty acids. We have determined the relative stereochemistry of the trihydroxy acid by synthesizing the possible stereoisomers. This paper describes the details of our synthetic study, demonstrating the fatty acid to be 9S,12S,13S-trihydroxyoctadeca-10E,15Z-dienoic acid and its 15-dihydro analogue. The absolute configuration was determined by observing a positive Cotton effect in the CD spectrum of the benzoate derivative of the natural material.