Polyunsaturated fatty acids such as linolenic and linoleic acids are susceptible to formation of hydroperoxides upon contact with oxygen in air. Hydroperoxides are highly reactive functional groups since they contain an oxidant (O-O bond) adjacent to a reductant (C-H bonds). When flanked by olefins, the hydroperoxides can be induced to rearrange to give the hemiacetal. It is this reaction that is catalyzed by hydroperoxide lyases. The resulting aldehydes are notable as fragrances, green leaf volatiles, and antifeedants.
An illustrative transformation involving a hydroperoxide lyase. Here cis-3-hexenal is generated by conversion of linolenic acid to the hydroperoxide by the action of a lipoxygenase followed by the lyase-induced formation of the hemiacetal.
^Grechkin AN, Brühlmann F, Mukhtarova LS, Gogolev YV, Hamberg M (2006). "Hydroperoxide lyases (CYP74C and CYP74B) catalyze the homolytic isomerization of fatty acid hydroperoxides into hemiacetals". Biochimica et Biophysica Acta. 1761 (12): 1419–28. doi:10.1016/j.bbalip.2006.09.002. PMID17049304.