Formation of 12‐[18O]Oxo‐cis‐10,cis‐15‐phytodienoic acid from 13‐[18O]hydroperoxylinolenic acid by hydroperoxide cyclase

Abstract
13-[18O] Hydroperoxylinolenic acid was permitted to react with an extract of flaxseed acetone powder containing hydroperoxide cyclase activity. The resulting product, 12-oxo-cis-10,cis-15-phytodienoic acid (12-oxo-PDA), contained18O in the carbonyl oxygen at carbon 12, suggesting that an epoxide was an intermediate in the hyderoperoxide cyclase reaction. A substrate specificity study showed that acis double bond β,γ to the conjugated hydroperoxide group was essential for the substrate to be converted to a cyclic product by hydroperoxide cyclase.