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Strategy for structure elucidation of drug metabolites derived from protonated molecules and (MS)n fragmentation of zotepine, tiaramide and their metabolites.

TSQ ESI MS/MS and ion trap ESI MS(2) cleave protonated molecules. MS(2) at m/z 332 of zotepine cleaved m/z 245 (10%), m/z 287 (5%) and m/z 315 (100%) fragment ions at protonated positions. MS(2) at m/z 356 of tiaramide cleaved m/z 338 (18%), 313 (10%), 226 (100%), 198 (78%) and 131 (60%) fragment ions at protonated positions. The ESI ion trap MS produced new internal protonated molecules in an ion trap, such as m/z 113 and m/z 88 from m/z 131 protonated piperazinonium, and m/z 245 protonated 8-chloro dibenzo[b,f]thiepin. ESI ion trap (MS)(n) (n>or=3) cleaved new internal protonated molecules. It also causes carbocation cleavage, alpha cleavage, onium cleavage and McLafferty cleavage. We can easily elucidate the structure of metabolites from the difference in m/z of corresponding fragments between unchanged compound and its metabolite. Reactive oxygen diradicals involved in cytochrome P-450 cycles react with electron rich groups and reactive C-H bonds of zotepine and tiaramide to produce metabolites of 2-hydroxyzotepine, 3-hydroxyzotepine, norzotepine, zotepine-N-oxide, zotepine-S-oxide, Tiaramide carboxylic acid, dehydroxyethyltiaramide and tiaramide-N-oxide. The strategy for structure elucidation of drug metabolites was established on the basis of the reactivity of unchanged drug with reactive oxygen diradicals involved in cytochrome P-450 cycles and theory associated with protonated molecules and (MS)(n) fragmentation of drug metabolites.[1]

References

  1. Strategy for structure elucidation of drug metabolites derived from protonated molecules and (MS)n fragmentation of zotepine, tiaramide and their metabolites. Tozuka, Z., Kaneko, H., Shiraga, T., Mitani, Y., Kawamura, A., Kagayama, A., Aoba, A. Drug Metab. Pharmacokinet. (2002) [Pubmed]
 
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