Natural Product Antifoulants from the octocorals of Indian waters

Natural Product Antifoulants (NPAs) have been proposed as one of the best alternatives for the globally banned toxic biocide -TBT-in antifouling coatings. In search of NPAs from Indian waters twenty nine species of Octocorals, collected from Gulf of Mannar and Lakshadweep islands, were screened for their antifouling potential against the cyprids of the cosmopolitan biofouler, Balanus amphitrite. The crude extracts of 8 species of these corals (Cladiella krempfi, Lobophytum irregulare, Lobophytum sarcophytoides, Sarcophyton ehrenbergi, Sarcophyton glaucum, Sinularia kavarattiensis, Melitodes sp. and Subergorgia reticulata) exhibited relatively high settlement inhibition properties. The bioassay-guided purification of the crude extracts of 3 active and abundant species-Cladiella krempfi, Sinularia kavarattiensis and Subergorgia reticulata-yielded five NPAs, (l'E,5′E)-2-(2′,6′-dimethylocta-l',5′,7′-trienyl)-4-furoic acid 1, (−)-6-α-hydroxy polyanthellin A 2, (+)-(7R,10S)-2-methoxy calamenene 3, (+)-(7R,10S)-2,5-dimethoxy calamenene 4 and (+)-(7R,10S)-2-methoxy,5-acetoxy calamenene 5). Among these, 5 exhibited high future prospects on account of its low EC50 value (0.0335 μg/ml) and high therapeutic ratio (799).