7,8-Dihydroxy-4-propyl-1,2,3,4,4a,5,6,10b-octahydrobenzo[f]quinolinium bromide monohydrate, a dopamine agonist

In the crystal structure of the title dopaminergic compound, C16H24NO2+.Br-.H2O, protonation occurs at the piperidine N atom. The piperidine ring adopts a chair conformation and the cyclohexene ring adopts a half-chair conformation; together with the planar benzene ring, this results in a relatively planar shape for the whole molecule. Classical hydrogen bonds (N-H...Br, O-H...Br and O-H...O) produce an infinite three-dimensional network. Hydrogen bonds between water molecules and Br- anions create centrosymmetric rings throughout the crystal structure. Structural comparison of the molecule with the ergoline dopamine agonist pergolide shows that it is the hydrogen-bond-forming hydroxy or imino group that is necessary for dopaminergic activity, rather than the presence of a phenyl or a pyrrole ring per se.