Cytotoxic polyketides containing tetramic acid moieties isolated from the fungus Myceliophthora Thermophila: elucidation of the relationship between cytotoxicity and stereoconfiguration

Five new polyketides that contain tetramic acids, myceliothermophins A-E, were isolated from the thermophilic fungus Myceliophthora thermophila. Two sets of 5-alkyl-5-hydroxyl (or 5-methoxyl)-1H-pyrrol-2(5H)-one diastereomers, myceliothermophins A/B and C/D, were separated as pure compounds by using silica-gel column chromatography and recycling reverse-phase high-performance liquid chromatography (RP-HPLC). The relative configurations of the chiral centers in 5-alkyl-5-hydroxyl (or 5-methoxyl)-1H-pyrrol-2(5H)-one moieties were deduced from NOESY correlations. In the cytotoxic assay, the 5-(2-methylpropyldiene)-1H-pyrrol-2(5H)-one analogue (myceliothermophin E) exhibited inhibition against four cancer cell lines. In addition, the significant inhibitory effect of myceliothermophins A and C and the inactivity of myceliothermophins B and D revealed the importance of the relative configurations of 5-alkyl-5-hydroxyl (or 5-methoxyl)-1H-pyrrol-2(5H)-one moieties on their cytotoxicity potency against cancer cells.