Human UDP-glucuronosyltransferase UGT1A4 forms tertiary N-glucuronides predominately with the energetically less favored tautomer of substituted 1H-indazole (benzpyrazole)

Abstract

Background: Human UDP-glucuronosyltransferase UGT1A4 is reported to convert a range of tertiary amine substrates to the respective quaternary glucuronides. In this study, we report on the in vitro glucuronidation of a substituted 1H-indazole (benzpyrazole), a transient receptor potential ankyrin 1 antagonist. Methods: Depending on the mammalian liver used for production, two peaks with different UV spectra and slightly different MS/MS spectra were found in the LC-MS/MS analysis. An optimized HPLC method gave a baseline separation of the two glucuronides. Preparation and isolation allowed to assign their structure by 1 H-, 13 C-, and 15 N-NMR.

Gas-Phase Rearrangement of the O-Glucuronide of Vildagliptin Forms Product-Ion Fragments Suggesting Wrongly an N-Glucuronide

“…In an MS 3 experiment, the ion m/z 330 fragmented further to m/z 196, corresponding to a loss of 134 Da and m/z 154 upon loss of glucuronic acid. We have discussed earlier the loss of 134 Da or C 4 H 6 O 5 in N-glucuronides (Fredenhagen et al, 2017).…”

The Unique Human N10-Glucuronidated Metabolite Formation from Olanzapine in Chimeric NOG-TKm30 Mice with Humanized Livers

“…The glucuronidation pathway transforms small lipophilic molecules, such as steroids, bilirubin, hormones, and drugs, into water-soluble, excretable metabolites. Human UGT1A4 reportedly converts a range of tertiary amine substrates to the respective quaternary glucuronides (Fredenhagen et al, 2017;Meech et al, 2019).…”