The natural phytotoxin coronatine, which is composed of two individual parts, coronafacic acid and coronamic acid, exhibits various promising biological activities similar to jasmonic acid, which is noe of the phytohormones. Interstingly, coronatine induces stomatal opening involving the swelling of guard cells in which jasmonic acid is not involved as an endogenous regulator. In order to apply the enantiodifferential approach for the identification of its target protein, we established syntheses of four stereoisomers of coronatine employing the exo-selectie Diels-Alder reaction as a key step. It will be advantageous to go through versatile intermediate for the preparation of various derivatives. Remarkable differences in a stomatal opening activity were observed between enantiomers of coronatine. This result strongly suggests that the stereostructure of coronatine is so important for its stomatal opening activity. In addition, structure-activity relationship studies suggested that coronatine operates as a molecular mimic of jasmonyl-L-isoleucine in plant guard celld. We also synthesized coronatine azide according to our synthetic strategy of coronatine, which possessed potent stomatal opening activity.
