Identification of an N-(hydroxysulfonyl)oxy metabolite using in vitro microorganism screening, high-resolution and tandem electrospray ionization mass spectrometry

Preliminary metabolic profiling of a drug under pre-clinical development revealed the presence of a minor unknown metabolite with a positive ion electrospray ionization (ESI) mass spectrum identical to that of the unchanged compound. Since the low concentration of the compound did not allow any additional experiments, preparative bioconversion using fungi was used to obtain a substantial amount of the molecule. Negative ion ESI-MS and tandem mass spectrometry (MS/MS) in combination with accurate mass measurements obtained on a quadrupole/time-of-flight instrument (Q-TOF) led to the positive identification of a hydroxylamide sulfoconjugated metabolite.