(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.