Imitation of phase I metabolism reactions of MAO-A inhibitors by titanium dioxide photocatalysis

The imitation of phase I metabolism of moclobemide and toloxatone, two monoamine oxidase type A (MAO-A) inhibitors, was performed with the use of titanium dioxide photocatalytic process. Ultra high pressure liquid chromatography system coupled with an accurate hybrid ESI-Q-TOF mass spectrometer was used for the evaluation of metabolic profiles, structural elucidation of the identified transformation products and quantitative analysis of the process. Based on high resolution MS and MS/MS data, eleven transformation products were characterized in photocatalytic experiments for moclobemide and seven products for toloxatone. A significant number of these products were found as hepatic metabolites under the incubation of the selected MAO-A inhibitors with human liver microsomes (HLM). What is important, some of these HLM metabolites are not yet described in the literature. It was also found that the multivariate chemometric analysis allowed an effortless characterization of the registered metabolic profiles which can be a useful method for a fast preliminary drug metabolism study. Additionally, principal component analysis (PCA) of the registered TOF (MS) photocatalytic and HLM profiles of moclobemide and toloxatone shows that shorter irradiation time is preferred for photocatalytic metabolism experiments. A heterogeneous photocatalysis with the use of titanium dioxide was found to be a powerful tool for mimicking phase I metabolic reactions, as a fast, sensitive and inexpensive method.