Arachidonate 12-lipoxygenase, 12S-type (ALOX12) catalyses the conversion of leukotriene A4 (LTA4) into the lipoxins LXA4, which has its third hydroxyl positioned at C-6 and LXB4, which has it positioned at C-14 (Romano et al. 1993, Serhan & Sheppard 1990). One of the reaction intermediates of this process might be 5S,6S-epoxy-15S-hydroxy-7E,9E,11Z,13E-eicosatetraenoic acid (5,6-Ep-15S-HETE) (Puustinen et al. 1986). However, its generation from LTA4 is unclear but it can be hydrolysed to form the lipoxins.