A novel analog of hepoxilin A 3 has been chemically synthesized in which the 11,12-epoxide group has been altered to a thiirano group. This has been accomplished through allylic rearrangement of unnatural (11 R,12R)-hepoxilin B 3 under Mitsunobu conditions, first into unnatural (11R,12R)-hepoxilin A 3 , followed by conversion of this compound with inversion of the epoxide centers into the thiirano-hepoxilin A 3 having the natural 11S,12S configuration. We also report herein evidence showing that thiirano-hepoxilin A 3 raises intracellular calcium concentrations in intact human neutrophils.