Pleurobranchus forskalii

Keenamide A is another novel cytotoxic cyclic hexapeptide isolated from a marine mollusk (Pleurobranchus forskalii Fig. 5.2 Wesson and Hamann, 1996). Keenamide A exhibited significant activity against the P-388, A-549, MEL-20, and HT-29 tumor cell lines. New classes of anticancer drug candidates isolated from marine organisms have been shown to possess powerful cytotoxic activity against multiple tumor types. 

FIGURE S.2 Structure of the cyclic peptide keenamide A derived from the notaspidean mollusk Pleurobranchus forskalii. 

Wesson, K. J. and Hamann, M. T. (1996). Keenamide A, a bioactive cyclic peptide from the marine mollusk Pleurobranchus forskalii. J. Nat. Prod. 59,629-631. 

Keenamide A (211) is a thiazoline-containing cytotoxic, cyclic hexapeptide that was isolated from the mollusc Pleurobranchus forskalii, which is known to feed on ascidians [217]. 

Fu X, Palomar AJ, Hong EP, Schmitz FJ, Valeriote FA (2004) Cytotoxic Lissoclimide-Type Diterpenes from the Molluscs Pleurobranchus albiguttatus and Pleurobranchus forskalii. J Nat Prod 67 1415... 

Schmitz and co-workers173 reported the isolation and structural characterization of several cytotoxic lissoclimide-type diterpenes from the mollusks Pleurobranchus albiguttatus and Pleurobranchus forskalii. 

Mollamide C differs from keenamide A, which was isolated from the mollusk Pleurobranchus forskalii (see Chapter 23), only by the replacement of a thiazoline by a thiazole. 

Fu, X., Palomar, A.J., Hong, E.P., Schmitz, F.J., and Valeriote, F.A. (2004) Cytotoxic lissoclimide-type diterpenes from the molluscs Pleurobranchus albiguttatus and Pleurobranchus forskalii. J. Nat. Prod., 67,1415-1418. 

Chemical data on the family Pleurobranchidae are still very fragmentary. The species Pleurobranchus forskalii (Indonesia) and P. membranaceus (Italy), respectively, yielded keenamide a moderately cytotoxic cyclic peptide (Wesson and Hamann, 1996) and three new polypropionates (membrenones), which permeate the mantle of the mollusk to protect it from predators (Ciavatta et al, 1993). 

Three new chlorinated diterpenes of the lissoclimide family (labdanes) were isolated from Pleurobranchus albi-guttatus and Pleurobranchus forskalii collected in the Philippines (Fu et al, 2004). These notaspids are known to feed on ascidians of the genus Lissoclinum and the new lisso-climides in these mollusks are probably of dietary origin (see Chapter 28). 

---