Bioactive Isoquinoline Quinone from an Undescribed Philippine Marine Sponge of the Genus Xestospongia

An undescribed Philippine marine sponge of the genus Xestospongia afforded four isoquinoline quinones: the new N -ethylene methyl ketone derivative of renierone ( 1 ), as well as the known compounds 1,6-dimethyl-7-methoxy-5,8-dihydroisoquinoline-5,8-dione ( 2 ), renierone ( 3 ), and mimosamycin ( 4 ). Compound 2 exhibited insecticidal activity toward neonate larvae of the polyphagous pest insect Spodoptera littoralis (EC 50 of 35 ppm and LC 50 of 521 ppm) when incorporated into artificial diet. Compounds 1 and 3 were only weakly active toward S. littoralis, while compound 4 was found to be inactive. All four isolated compounds were active against the Gram-positive bacteria Bacillus subtilis and Staphyloccoccus aureus . Compound 4 was also active against the fungus Cladosporium cucumerinum.