[Metabolism of antiparkinson drugs. An example of competitive hydroxylation]

The investigation of the metabolism of the antiparkinson drugs trihexyphenidyl (1), pridinol (2) and biperiden (3) revealed a graduate tendency for hydroxylation in the different structural elements: If alicyclic, saturated heterocyclic and aromatic ring systems are present in one compound like in 1, the alicyclic ring system is attacked predominately. The amount of metabolites with hydroxy-groups in the saturated heterocyclic ring is much lower, and no hydroxylation takes place in the aromatic ring. In drugs without alicyclic ring systems like 2 the saturated heterocyclus is attacked preferentially, but also some phenolic metabolites are formed. Consequently the following arrangement of falling hydroxylation-tendency can be established: Formula: see text. Probably this arrangement is of common validity and therefore a prediction on the hydroxylation-tendency of other compounds seems to be possible.