Abstract
The first chemical study of the Indo-Pacific dorid nudibranch Aldisa andersoni resulted in the isolation of five chlorinated phenyl-pyrrolyloxazoles belonging to the phorbazole series. Two new molecules, 9-chloro-phorbazole D and N1-methyl-phorbazole A, co-occurring with known phorbazoles A, B and D, have been characterized. Phorbazoles were found to be present mainly in the external part of the mollusc. The structures of the new compounds were determined by interpretation of spectroscopic data, mainly NMR and mass spectrometry and by comparison with the literature data. Evaluation of feeding-deterrence activity as well as in vitro growth inhibitory properties in human cancer cells was also carried out.
Highlights
Opisthobranchs are marine molluscs in which the shell is reduced or completely absent
Phorbazoles have been reported to date only from the sponge Phorbas aff. clathrata [10,11,12]. The origin of these metabolites in A. andersoni could be ascribed to a diet based on Phorbas sponges de novo biosynthesis could not be excluded
Six specimens of A. andersoni were caught by scuba diving off Muttom coast (South India) during
Summary
Opisthobranchs are marine molluscs in which the shell is reduced or completely absent. The tubercles are separated by black areas of pigment, the upper part of the skin is crossed by a bright yellow saddle behind the rhinophores and other yellow marks on the dorsum [6] These features appear to be indicative of aposematism (warning coloration), closely resembling the shape and the color pattern of unpalatable nudibranch species belonging to the genus Phyllidia, which are known to contain toxic isonitrile molecules [7]. Two feeding-deterrent sterols featuring cholic acid side chain have been reported from Aldisa cooperi [8], whereas an unusual 24-norchol-4-ene-3,22-dione has been isolated from Aldisa smaragdina [9] It seems that the source of steroids in Aldisa cooperi should be the sponge Anthoarcuata graceae but the animal is able to modify the inactive cholestenone into two active compounds. The origin of these metabolites in A. andersoni could be ascribed to a diet based on Phorbas sponges de novo biosynthesis could not be excluded
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