Metabolite Identification in Drug Discovery

Early knowledge on the structures of metabolites from in vitro and in vivo metabolism studies is very useful for improving the biopharmaceutical, efficacy and safety properties of lead candidates in drug discovery. The recognition of the value in what metabolite identification brings to drug discovery led to its inclusion in ADMET toolbox and recent trend to multiplex assessment of metabolic stability and metabolite identification. In this chapter, we will cover the in vitro and in vivo systems typically used for metabolite identification. Fast LC-MS/MS with capability of data-dependent multiple-stage mass analysis is the instrument of choice and the workhorse for multiplexing assessment of metabolic stability and metabolite identification from a single analysis. Therefore, various LC-MS/MS instruments and techniques used for metabolite identification including software to speed up data-mining along with estimating major metabolites based on UV methods will be discussed. In general, the exact site of biotransformation is difficult to obtain based solely on MS data. As a result, microchemistry will also be discussed to help narrowing down site of modification in metabolites.