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

Abstract 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 .