Cysteine adds to liquid hydroperoxide.

Cysteine reacts with linoleic acid hydroperoxide to yield several products, some of which were identified as fatty acid-cysteine adducts. The addition was catalyzed by ferric chloride (10(-5) M) by initiating free radical reactions. When isomerically pure 13-hydroperoxy-cis-9,trans-11-octadecadienoic acid and cysteine were reacted in 80% ethanol under N2, the major adducts were 9-S-cysteine-13-hydroxy-10-ethoxy-trans-11-octadecenoic acid (I) and 9-S-cysteine-10,13-dihydroxy-trans-11-octadecenoic acid (II). When the reaction included both isomers of the hydroperoxide (13- and 9-hydroperoxide) and air, an adduct of 9-oxononanoic acid and cysteine also was isolated. Additional experiments gave information about possible mechanisms of I and II formation.