Structural investigations of 3-acylpyrrolidine-2,4-diones by nuclear magnetic resonance spectroscopy and X-ray crystallography
The 3-acylpyrrolidine-2,4-diones (tetramic acids) can exist in solution as pairs of internal tautomers and as a pair of external tautomers. The tautomer constitution of a number of bioactive 3-acylpyrrolidine-2,4-diones, e.g. α-cyclopiazonic acid (1) and tenuazonic acid (3), has been studied. The study was facilitated by 1H and 13C n.m.r. spectroscopy and single crystal X-ray crystallography. From these results the structures of a number of natural products containing the 3-acylpyrrolidine-2,4-dione unit have been revised.