Kulolide, a cyclic depsipeptide, was isolated from a cephalaspidean mollusk, Philinopsis speciosa Pease, 1860. Kulolide is made up of five amino acid residues, one each of L-Ala, L-Pro, and N-Me-D-Val and two of L-Val, and two carboxylic acids, L-3-phenyllactic acid and the unprecedented (R)-3-hydroxy-2, 2-dimethyl-7-octynoic acid. The kulolide structure was elucidated by spectral techniques and hydrolytic reactions. Kulolide is active against L-1210 leukemia cells and P388 murine leukemia cells at IC50 values of 0.7 and 2.1 mu g/mL, respectively. Kulolide caused morphological change against rat 3Y1 fibroblast cells at the concentration of 50 mu M.