Melophlins C−O, Thirteen Novel Tetramic Acids from the Marine Sponge Melophlus sarassinorum

Thirteen new metabolites, melophlins C-O (1-13), were identified from the marine sponge Melophlus sarassinorum. Compounds 1-13 represent tetramic acid derivatives that differ with regard to the nature of their alkyl side chains. The structures of the new compounds were elucidated on the basis of comprehensive spectral analysis (H-1, C-13, H-1-H-1 COSY, HMQC, and HMBC NMR, as well as low- and high-resolution ESIMS and EIMS). The absolute configurations of 1, 8, 10, 11, 12, and 13 were determined by ESI LC/MS analysis of chiral derivatives obtained upon oxidation and hydrolysis of the respective parent compounds. Melophlin C (1) displayed pronounced antibacterial activity against Bacillus subtilis and Staphylococcus aureus, together with antifungal activity against Candida albicans.