SERS IDENTIFICATION OF QUINONE-IMINE SPECIES AS OXIDATION-PRODUCTS OFANTITUMOR ELLIPTICINES

Oxidative transformations of 9-hydroxyellipticine (9-OH-E) and N-2-met hyl-9-hgdroxyeUipticinium (NMHE) were performed in aqueous solutions. Electrochemical oxidation of 9-OH-E and biochemical and chemical oxida tion of NMHE, were monitored by UV-visible absorption and their reacti on products characterized by surface-enhanced Raman scattering (SERS). Spectroscopic analyses of the oxidation product obtained from the 2e( -) electrochemical process of 9-OH-E at Pt and Ag electrodes permitted the identification of the quinone-imine function. Comparison with the spectra of products resulting from the biooxidation of NMHE by the pe roxidase-H2O2 system revealed the occurrence of the same reactive spec ies. On the other hand, UV-visible and SERS analyses of the chemical o xidation of NMHE by sodium hypochlorite seem to indicate that this pat hway is not efficient enough to generate such a primary quinone-imine oxidation species. In this case, only di-o-quinones were detected and identified as the main oxidation products. All the spectroscopic resul ts of this study confirm the crucial role of the electrophilic quinone -imine function in the bio-oxidative metabolic transformation which le ads to covalent adducts by trapping biological nucleophiles.