Phototransformation of the drug rivastigmine. Photoinduced cleavage of benzyl-nitrogen sigma bound

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 x 10-5 M). For mechanistic purposes and products studies irradiation has also been carried out on concentrated solutions (1 x 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.