Isolation and Structure Determination of cis-OPDA-α-Monoglyceride from Arabidopsis thaliana

Abstract

cis-12-oxo-Phytodieneoic acid-α-monoglyceride (1) was isolated from Arabidopsis thaliana. The chemical structure of 1 was elucidated based on exhaustive 1D and 2D NMR spectroscopic measurements and supported by FDMS and HRFDMS data. The absolute configuration of the cis-OPDA moiety in 1 was determined by comparison of 1 H NMR spectra and ECD measurements. With respect to the absolute configuration of the β-position of the glycerol backbone, the 2:3 ratio of (S) to (R) was determined by making ester-bonded derivatives with (R)-(+)-α-methoxy-α-trifluoromethylphenylacetyl chloride and comparing 1 H NMR spectra. Wounding stress did not increase endogenous levels of 1, and it was revealed 1 had an inhibitory effect of A. thaliana post germination growth. Notably, the endogenous amount of 1 was higher than the amounts of (+)-7-iso-jasmonic acid and (+)-cis-OPDA in intact plants. 1 also showed antimicrobial activity against Gram-positive bacteria, but jasmonic acid did not. It was also found that α-linolenic acid-α-monoglyceride was converted into 1 in the A. thaliana plant, which implied α-linolenic acid-α-monoglyceride was a biosynthetic intermediate of 1.O xylipin is the general term for structurally diverse plant metabolites produced through oxidation steps of unsaturated fatty acids, including aldehydes, divinyl ethers, oxo, keto, hydroxy, and hydroperoxy derivatives. These molecules play a pivotal role in plants because they are essential for developmental processes and defense. 1 Among oxylipins, jasmonates are representative examples. The compounds are biosynthesized using (+)-cis-12-oxo-phytodienoic acid ((+)-cis-OPDA) or (+)-dinor-cis-OPDA as common intermediates, in which (+)-7-iso-jasmonic acid ((+)-7-iso-JA) is a representative biologically active compound that is easily epimerized into (−)-JA during the process of isolation. 2 α-Linolenic acid (α-LA) and (13Z, 10Z, 7Z)-hexadeca-13,10,7-trienoic acid (HA) released by the lipase enzyme are oxygenated by 13-and 11-lipoxygenase (13-/11-LOX) enzymes, respectively, to afford 13-and 11-hydroperoxide intermediates, which are then catabolized through coupled dehydration−cyclization reactions catalyzed by allene oxide synthase (AOS) and allene oxide cyclase (AOC) enzymes to give cyclopentenones, (+)-cis-OPDA and (+)-dinor-cis-OPDA.