(±)5(6)-DiHET lactone is a 1,5 cyclic ester derived from (±)5(6)-DiHET , which, in turn, is a potential derivative of epoxidation of arachidonic acid at the α-5 double bond. (±)4(5)-DiHDPA lactone is a derivative of docosahexaenoic acid that is analogous to (±)5(6)-DiHET lactone. It is the 1,4 cyclic ester derived from (±)4(5)-DiHDPA, which is produced by epoxidation of DHA at the α-4 double bond. Its biological activity is unknown.