New cyclopentenone fatty acids formed from linoleic and linolenic acids in potato

[1-¹⁴C]Linoleic acid was incubated with a whole homogenate preparation from potato stolons. The reaction product contained four major labeled compounds, i.e., the α-ketol 9-hydroxy-10-oxo-12(Z)-octadecenoic acid (59%), the epoxy alcohol 10(S),11(S)-epoxy-9(S)-hydroxy-12(Z)-octadecenoic acid (19%), the divinyl ether colneleic acid (3%), and a new cyclopentenone (13%). The structure of the last-mentioned compound was determined by chemical and spectral methods to be 2-oxo-5-pentyl-3-cyclopentene-1-octanoic acid (trivial name, 10-oxo-11-phytoenoic acid). Steric analysis demonstrated that the relative configuration of the two side chains attached to the five-membered ring was cis, and that the compound was a racemate comprising equal parts of the 9(R), 13(R) and 9(S), 13(S) enantiomers. Experiments in which specific trapping products of the two intermediates 9(S)-hydroperoxy-10(E), 12(Z)-octadecadienoic acid and 9(S), 10-epoxy-10, 12(Z)-octadecadienoic acid were isolated and characterized demonstrated the presence of 9-lipoxygenase and allene oxide synthase activities in the tissue preparation used. The allene oxide generated from linoleic acid by action of these enzymes was further converted into the cyclopentenone and α-ketol products by cyclization and hydrolysis, respectively. Incubation of [1-¹⁴C]linolenic acid with the preparation of potato stolons afforded 2-oxo-5-[2′(Z)-pentenyl]-3-cyclopentene-1-octanoic acid (trivial name, 10-oxo-11, 15(Z)-phytodienoic acid), i.e., an isomer of the jasmonate precursor 12-oxo-10, 15(Z)-phytodienoic acid. Quantitative determination of 10-oxo-11-phytoenoic acid in linoleic acid-supplied homogenates of different parts of the potato plant showed high levels in roots and stolons, lower levels in developing tubers, and no detectable levels in leaves.