Application of electrospray mass spectrometry in the identification of intact glucuronide and sulphate conjugates of clozapine in rat

Abstract

1. The phase II metabolites in the bile, urine and faeces of rat dosed with clozapine were investigated by means of electrospray mass spectrometry (ESMS) in both positive and negative ion modes.

2. When operated at a cone voltage of 45 V, this soft ionization technique permitted the detection of quasi molecular ions of both sulphate and glucuronide conjugates of hydroxylated phase I metabolites of clozapine. With the cone voltage set at 90 V, however, the ESMS also contained highly diagnostic ions resulting from the loss of 80 Daltons (sulphur trioxide) or 176 Daltons (the glucuronide moiety) from sulphates and O-glucuronides respectively.

3. A sufficient quantity of one metabolite was isolated from rat bile to permit further analysis by ¹H-nmr. This metabolite, which was also found in rat urine, was proved to be 7-O-glucuronyl-7-hydroxyclozapine. The analogous sulphate metabolite was also identified in bile by ESMS.

4. Corresponding glucuronide and sulphate conjugates of a hydroxylated N-desmethyl clozapine were similarly detected in rat bile. There was insufficient material to permit analysis by ¹H-NMR, but it appears likely that conjugation was also at the 7-position of N-desmethylclozapine.

5. Finally, the sulphate conjugate of a hydroxy dechlorinated derivative of clozapine was identified by ESMS in both urine and bile. By analogy with a previous report of a similar metabolite in man, the metabolite was tentatively identified as 8-hydroxy-8-deschloroclozapine.