Polyketide-derived Guanidines

Onnamide A (98) and several of its related derivatives have been isolated from marine sponges of the genus Theonella. Onnamide A itself was first isolated from Theondla sp. [156] and displayed potent cytotoxic activity [157]. Subsequently, a series of related derivatives have been isolated from different species of marine sponges belonging to the genus Theonella [158,159], The structure of onnamide A was 

Additional but simpler members of this class of guanidine alkaloids are the icthyotoxiccrambescins (formerly crambines) A (109), B (110), and Cl (111) isolated 

Monanchorin (120), which has been isolated from the sponge Monanchora unguiculata [238], is the last example of polyketide-derived guanidines. 

The chemistry (isolation, structures, and synthesis) and biological activities of this large class of guanidine alkaloids have been the subject of several reviews [239-243]. 

1 Chevolot, L. (1981) Guanidine derivatives, In Scheuer P. J. (Ed.) Marine Natural Products Chemical and Biolo cal Perspectives, Vol. 4, Academic Press, London, 53-91. 

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Figure 25. Selected structures of polyketide-derived guanidines alakloids.

The excellent reviews of Berlinck [1-5] have surveyed a great number of guanidine-type natural products. In addition, some guanidine-derived marine alkaloids have been reviewed by Kobayashi and Ishibashi [6,7]. Also, a recent book gave accounts of marine alkaloids including the phakellins, palau amines and oroidin-like dimers derived from bromopyrroles and polyketide-derived polycyclic guanidine alkaloids [8]. 

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