Isolation and structure elucidation of the major photodegradation products of pirmenol hydrochloride

Column chromatography, thin-layer chromatography, high-performance liquid chromatography, nuclear magnetic resonance spectrometry, and high-resolution mass spectrometry were employed to separate and identify the photodegradation products of pirmenol hydrochloride [(+/-)-cis-alpha-[3-(2,6-dimethyl-1-piperidinyl)propyl]-alpha-phenyl-2- pyridinemethanol monohydrochloride monohydrate], a new antiarrhythmic drug. A methanol solution of pirmenol was irradiated using a low-pressure mercury lamp. The solution afforded four major degradation products, three of which were identified as 3-(cis-2,6-dimethylpiperidinyl)propyl 2-(2-pyridyl)phenyl ketone, 2-(2-pyridyl)benzoic acid, and methyl 2-(2-pyridyl)-benzoate. The degradation followed apparent-first-order reaction kinetics. In addition, the possible photodegradation pathways are discussed with reference to reaction mechanisms.