Melophlins A and B, Novel Tetramic Acids Reversing the Phenotype of ras-Transformed Cells, from the Marine Sponge Melophlus sarassinorum

Two novel tetramic acids named melophlins A (1) and B (2) were isolated from the marine sponge Melophlus sarassinorum, and the absolute stereostructures were elucidated on the basis of chemical and physicochemical evidence. Melophrins A (1) and B (2) induced reversion of the tumorous phenotype of ras-transformed NIH3T3 cells to normal at the concentration of 5 μg mL−1.