D. Q. Liu, C. E. C. A. Hop, M. G. Beconi, A. Mao, S.-H. Lee ‘Use of on-line hydrogen/deuterium exchange to facilitate metabolite identification’ Rapid Communications in Mass Spectrometry, 15(19), 2001, 1832-1839

The structures of two compounds, M4 and M5 were assigned incorrectly as the N-glucuronide and N-glucoside, respectively. Both compounds were present in in vitro and in vivo samples of compound I at trace levels. In an investigation of biotransformations of a series of compounds containing a primary amino group, we observed that many of them tend to form adducts with glucose and/or glucuronic acid (at trace levels though). Careful examination of the collision-induced dissociation (CID) spectra of M4 and M5 suggested that it's unlikely that they are N-glucuronide and glucoside conjugates. Typically, electrospray ionization CID spectra of O- or N-glucosides and glucuronides produce intense fragment ions for the corresponding aglycones (in this case, the parent compound at m/z 203). However, m/z 203 was only a minor signal in the CID spectra of both M4 and M5. Thus, they are more appropriately assigned as the Schiff base adducts (see the illustration) presumably formed chemically. Further examination of the available data indicated that they were also present in rat hepatocytes spiked with compound I without any incubation. For the revised structures, formation of the minor signal at m/z 203 in the CID spectra is not obvious and it may have been generated through rearrangement. We sincerely regret that any confusion this may have caused. The original article to which this Erratum refers was published in Rapid Communications in Mass Spectrometry 15:(19) 2001, 1832–1839

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