Phototransformation of the drug rivastigmine: Photoinduced cleavage of benzyl-nitrogen sigma bond

The photochemical behaviour of rivastigmine has been investigated under UV-B irradiation by HPLC and NMR. Kinetic data have been obtained irradiating aqueous solutions (5 × 10−5 M). For mechanistic purposes and products studies irradiation has also been carried out on concentrated solutions (1 × 10−3 M) in water/acetonitrile, acetonitrile, methanol, methanol/acetonitrile, in the presence and absence of oxygen. Photoproducts, isolated by chromatographic processes, have been identified by spectroscopic means. Photochemical cleavage of the benzyl-nitrogen bond occurs and leads to radical-derived and, mainly, ion-derived products. Mechanistic pathways have been hypothesised on the basis of both steady-state irradiation and laser flash photolysis experiments.

► By UV-B radical and/or ionic cleavage of the benzyl amine group of the drug occurs.
► Mechanistic routes are based on steady-state and laser flash photolysis experiments.
► Water as solvent plays a determinant role in favouring electron-transfer reactions.
► The main photoproduct, an aryl ketone, is a photosensitizer.