Insight into the chemistry of cycloaddition between α-ketol oxylipin and epinephrine: isolation and structure elucidation of a new reaction product

Abstract The α-ketol oxylipin (12 Z ,15 Z )-9-hydroxy-10-oxooctadeca-12,15-dienoic acid ( 1 ) reacts with epinephrine ( 2 ) to afford unique cycloadducts, KE1 ( 3 ) and KE2 ( 4 ), both of which strongly induce flowering in Lemna paucicostata . Here we isolate compound 5 from the reaction mixture and identify it as a Michael-type adduct of 1 with adrenochrome ( 6 ), an oxidized form of 2 . Compound 5 was gradually converted into KEs in aqueous solution, suggesting that the compound is an intermediate of KEs. From these results, we newly propose the reaction mechanism of the cycloaddition between 1 and 2 .