Antifouling activity exhibited by secondary metabolites of the marine sponge, Haliclona exigua (Kirkpatrick)

Abstract

Bioassay guided purification of the acetone extract of the marine sponge, Haliclona exigua, (Gulf of Mannar, India) yielded a fraction rich in bis-1-oxaquinolizidine alkaloids, active against seven strains of fouling bacteria as well as cyprids of the cosmopolitan barnacle, Balanus amphitrite. The major alkaloids in the mixture have been tentatively identified as nor-araguspongine C (33.76%), araguspongine C (6.49%), dihydroxy araguspongine (36.36%), methyl and dimethyl derivatives of the latter (12.98 and 10.38%, respectively) from HRMS studies. The lower EC sub(50) (6.6 mew g/ml as against the US Navy standard of 25 mg/ml for NPAs) and low toxicity (LC sub(50) 18 mew g/ml as compared to 0.00001 mew g/ml for TBT) values, coupled with its favourable therapeutic ratio (2.7 as against the requirement of >1) makes these compounds ideal NPAs in environmentally compatible antifouling coatings