Both the S and R enantiomers of (E)-13-hydroxy-10-oxo-11-octadecenoic acid (1) and (E)-10-oxo-11-octadecen-13-olide (2) had similar IC50 values against P388 mouse leukemia cells; i.e. the stereochemistry of the asymmetric center of 1 and 2 had no influence on the cytotoxic activity. Bioassay results