Keenamide A, a bioactive cyclic peptide from the marine mollusk Pleurobranchus forskalii.

Keenamide A (1), a new cytotoxic cyclic hexapeptide, was isolated from the notaspidean mollusk Pleurobranchus forskalii. Its structure was determined by NMR spectral data interpretation and chiral amino acid analysis. Keenamide A (1) exhibited significant activity against the P-388, A-549, MEL-20, and HT-29 tumor cell lines, but was inactive when evaluated against the D6 and W2 Plasmodium falciparum malarial clones.