Antifouling steroids isolated from red alga epiphyte filamentous bacterium Leucothrix mucor

Active antifouling steroids were isolated from the filamentous bacterium . Bioactivity-guided isolation by silica gel column chromatography and high-performance liquid chromatography generated two compounds. The chemical constituents having the antifouling activities were identified as 17-(1,2-dihydroxyl-5-methyl-hexane)-2,3-dihydroxyl-cholest-4-en-6-one [compound (a)] and 13-acetate-17-(1,5-dimethylhexane)-cholest-7-en-3,5,6,15-tetraol [compound (b)] by interpreting one- and two-dimensional nuclear magnetic resonance and mass spectroscopy data. The two compounds were isolated from 780 mg of crude extract, yielding 12 and 14 mg, respectively. Antifouling activities were determined against a representative soft fouling macroalgae (), a biofouling diatom (), and the bacteria KNP-3 and sp. KNS-8. The two compounds were able to inhibit the spore settlement of zoospores with a low half maximal effective concentration (EC50) (1.2-2.1 mu g/ml) and inhibit diatom growth with an EC50 of 5.2-7.5 mu g/ml. Compound (a) showed activity with minimum inhibitory concentration values of 32-56 mu g/ml and compound (b) showed an activity of 66-90 mu g/ml. Among the two compounds, compound (a) is a new compound, whereas compound (b) was previously reported to have been isolated from a marine invertebrate.