Koshikamide A2 (2) was isolated as a cytotoxic metabolite from a marine sponge of Theonella sp. Its structure was elucidated to be a linear undecapeptide by spectroscopic and chemical methods, together with enzymatic conversion to known koshikamide A1 (1). The new peptide moderately inhibited the growth of P388 murine leukemia cells.
