(3aR-cis)-Hexahydro-2-oxo-4H-furo[3,2-b]pyrrole-4-acetic Acid Ethyl Ester 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.