Novel Allene Oxide Synthase Products Formed via Favorskii‐Type Rearrangement: Mechanistic Implications for 12‐Oxo‐10,15‐phytodienoic Acid Biosynthesis

The allene oxide synthase (AOS) pathway is widespread in plants. Its products, such as cyclopentenone 12‐oxo‐10,15‐phytodienoic acid (12‐oxo‐PDA) and related jasmonates, play important biological roles in plants. We found that 12‐oxo‐PDA in some plant tissues co‐occur with an unknown minor oxylipin 1. In vitro incubations of AOSs with α‐linolenic acid 13(S)‐hydroperoxide reliably afforded 1 along with 12‐oxo‐PDA and α‐ketol. A similar oxylipin 3 was formed during the AOS conversions of γ‐linolenic acid 9(S)‐hydroperoxide. Linoleic acid hydroperoxides formed neither products similar to 1 and 3 nor cyclopentenones. Oxylipins 1 and 3 were purified and identified as the products of Favorskii‐type rearrangement, (2′Z,4Z)‐2‐(2′‐pentenyl)‐4‐tridecene‐1,13‐dioic acid and (2′Z,4Z)‐2‐(2′‐octenyl)‐4‐decene‐1,10‐dioic acid, respectively. Detection of Favorskii products 1 and 3 demonstrates that cyclopropanones are short‐lived AOS products along with allene oxides. The observed parallels between the Favorskii product 1 and 12‐oxo‐PDA formation suggests that cyclopropanone is either a byproduct or a precursor of 12‐oxo‐PDA.

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