A heterobicylic compound that is (2S,3aR,7aS)-1-[(2S)-2-aminopropanoyl]octahydro-1H-indole-2-carboxylic acid in which the hydrogen of the amino group is substituted by a (2R)-1-ethoxy-1-oxo-4-phenylbutan-2-yl group. It is a angiotensin-converting enzyme inhibitor and a prodrug used for the treatment of hypertension.