Total synthesis of 4 and its three diastereomers is described. The key steps involve stereoselective formation of the tetrahydrofuran ring by a cascade cyclization of hydroxy tosylate 7 and an intermolecular cross metathesis between a tetrahydrofuran 5 and a γ-lactone 6. Spectroscopic data of 4 and biosynthetic hypothesis strongly suggest it to be montanacin E. Inhibitory activities of 4 and its isomers