Tenuazonic acid (mixture of diastereomers) in Methanol

(5S)-3-Acetyl-1,5-dihydro-4-hydroxy-5-[(1S)-1-methylpropyl]-2H-pyrrol-2-one
(S)-3-Acetyl-5-(S)-sec-butyltetramic acid, (S)-3-Acetyl-5-sec-butyl-4-hydroxy-3-pyrrolin-2-one