(3R)-3-Hydroxy-1-[(4-methoxyphenyl)methyl]-2,5-pyrrolidinedione is an intermediate in synthesizing Monocrotaline-d4 (M526002), a labelled Monocrotaline (M526000) which is a toxic pyrrolizidine alkaloid isolated from Crotalaria spp. It is used for inducing pulmonary diseases in rats.