Synthesis of 6-Substituted 1-oxoindanoyl Isoleucine Conjugates and Modeling Studies with the COI1-JAZ Co-Receptor Complex of Lima Bean

The conjugates of 6-substituted 1-oxoindanoyl carboxylic acids with L-isoleucine are mimics of the plant hormone (+)-7-iso-JA-L-Ile (3) that controls and regulates secondary metabolism and stress responses. In order to generate ligands that can be used as hormone-like compounds possessing different biological activities, an efficient and short synthesis of 6-bromo-1-oxoindane-4-carboxylic acid opens a general route to 6-Br-1-oxoindanoyl L-isoleucine conjugate (Br-In-L-Ile) (9a) as a key intermediate for several bioactive 6-halogen-In-L-Ile analogs (7a, 8a, 10a). The 6-ethynyl-In-L-Ile analog (11a) might be a valuable tool to localize macromolecular receptor molecules by click-chemistry. The activities of In-Ile derivatives were evaluated by assays inducing the release of volatile organic compounds (VOCs) in lima bean (Phaseolus lunatus). Each compound showed slightly different VOC induction patterns. To correlate such differences with structural features, modeling studies of In-Ile derivatives with COI-JAZa/b/c co-receptors of P. lunatus were performed. The modeling profits from the rigid backbone of the 1-oxoindanonoyl conjugates, which allows only well defined interactions with the receptor complex.