Triterpene glycosides associated antifouling activity from Holothuria tubulosa and H. polii

Antifouling paints in the current markets contain toxic biocides for fouling organisms in aquatic ecosystems. Therefore, there is a great need for development of eco-friendly booster biocides. Fouling-deterrent bio-active molecules in sea cucumbers were studied by qualitative and semi-quantitative experiments in the present study. The antifouling activities of the semi-purified triterpene glycosides and zinc-pyrion as positive control were tested in rosin-based self-polishing antifouling paints. An in-silico analysis was also carried out to estimate possible role of triterpene glycosides on photosystem Q(B) protein 1 (PSQ). The triterpene glycosides found in Holothuria polii were also characterized by using mass spectrometry. For a possible evaluation of the sea cucumber residues, vitamin C, protein, carbohydrate, lipid contents and fatty acid composition were also studied. According to the results, the highest triterpene glycoside concentration was observed within methanol-dichloromethane extract of H. polii. In silico tests showed that holothurinoside A and DCA (3,4-dichloroaniline) had highest and lowest docking scores for cyanobacterial photosystem II, respectively. Although the most successful biocide was commercial biocide, zinc pyrion in the antifouling tests, the semi-purified triterpene glycosides based plates showed excellent antifouling properties. The control plates were heavily fouled by sea worms whereas the plates including semi-purified triterpene glycosides and zinc-pyrion prevented macro fouling settlement. The results revealed that triterpene glycosides can bind PSQ and they may prevent photosynthesis. In conclusion, organic synthesis of triterpene glycosides can open a new door to development of eco-friendly antifouling bioactive agents. Further investigations related to active metabolites from sea cucumbers are strongly recommended to understand the full picture.