11(R)-HETE is biosynthesized by 11(R)-LOs of the sea urchin, S. purpuratus, and the fresh water hydra, H. vulgaris. The biological activity of 11(R)-HETE relates to oocyte maturation and tentacle regeneration, respectively, in these two species. 11(R)-HETE is also produced when aspirin-treated recombinant COX-2 is incubated with arachidonic acid. Stereochemical assignment of the (R) enantiomer is based on comparison of chiral HPLC retention times to published results.