The molecule is an ammonium ion resulting from the protonation of the secondary amino group of quinapril. It is a conjugate acid of a Phrymarolin I.
[(2S)-1-[(3S)-3-carboxy-3,4-dihydro-1H-isoquinolin-2-yl]-1-oxopropan-2-yl]-[(2S)-1-ethoxy-1-oxo-4-phenylbutan-2-yl]azanium