Synthesis of the amino acid conjugates of epi-jasmonic acid.

The TES ether of the C6-hydroxy derivative of naturally occurring epi-jasmonic acid (epi-JA) was designed as epimerization-free equivalent of epi-JA. The TES ether was synthesized from (1R,4S)-4-hydroxycyclopent-2-enyl acetate in 13 steps. The acid part of the ether was activated with ClCO2Bui and subjected to condensation with L-amino acid at room temperature for 48 h. The TES group in the condensation product was removed in HCO2H (0°C, 30 min) and the resulting hydroxyl group was oxidized with Jones reagent (acetone, 0°C, 30 min) to furnish the amino acid conjugate of epi-JA. The amino acids examined are L-isoleucine, L-leucine, L-alanine, L-valine, and D-allo-isoleucine, which afforded the conjugates in 48-68% yields with 89-96% diastereomeric purity over the trans isomers. Similarly, the possible three stereoisomers of epi-JA were condensed with L-isoleucine successfully, producing the corresponding stereoisomers in good yields.