THE IDENTIFICATION OF IN-VITRO METABOLITES OF BUPROPION USING ION-TRAP MASS-SPECTROMETRY

We have identified in vitro metabolites of bupropion (Wellbutrin(R)) f rom incubations with human liver S9 fraction and human liver microsome s based on molecular weight information from full scan experiments usi ng a liquid chromatograph coupled to a quadrupole ion trap mass spectr ometer capable of multi-stage operation (LC/MS(n)). Preliminary experi ments have shown that this instrument provides comparable sensitivity to conventional LC-coupled triple quadrupole instruments for metabolic studies, while allowing detailed structural studies using MS(n) exper iments and routine on-line coupling with high performance liquid chrom atography via an external atmospheric pressure chemical ionization (AP CI) source. The LC/MS analysis of human S9 showed the presence of thre e isomeric monohydroxylated metabolites of bupropion, These were furth er characterized in a series of MS/MS experiments which gave character istic spectra for the three isomers. A minor dihydroxylated species wa s also identified in the human S9 sample and further characterized in a series of MS(n) experiments. Detailed structural information was gen erated by the use of on-line LC/MS(n) type experiments. We have follow ed the fragmentation pathways of several molecular ion species in a se ries of sequential LC/MS(n) experiments, extending as far as MS(6) wit h scan cycle times of less than 1.5 s. Such experiments have provided insights into the structure of specific fragment ions. Additional meta bolic products were identified in the rat liver microsomes incubation sample.