Application of¹⁹F.n.m.r. spectroscopy to the identification of dog urinary metabolites of imirestat, a spirohydantoin aldose reductase inhibitor

Abstract

1. Urine from a dog dosed orally at 20 mg/kg with 14C-imirestat, a spirohydantoin aldose reductase inhibitor, contained 17.7 and 12.5% of the administered radioactivity at 0-48 and 48-72 h respectively. 2. Radio-h.p.l.c. of the 0-48 h urine revealed a complex mixture of metabolites and a small proportion of parent drug (1.6% of dose). Direct 19F-n.m.r. spectroscopy of this urine showed the fluoride ion, numerous metabolites which were predominantly glucuronide conjugates and, as a minor component, the parent drug. 3. After incubation with beta-glucuronidase the 0-48 h urine gave a 19F-n.m.r. spectrum showing fewer signals. This finding is consistent with aromatic ring hydroxylation followed by glucuronidation being the major metabolite pathways. 4. Deconjugated urine was analysed by proton-coupled 19F-n.m.r. and two-dimensional 19F-19F correlated spectroscopy. Results indicate that major components included three monohydroxy metabolites, a diphenol with both phenolic functions in the same ring, and a phenolic metabolite containing only one fluorine atom. 5. Semi-preparative h.p.l.c. of 0-48 h dog urine gave individual glucuronides isolated as mixtures of C-9 epimers. These fractions were hydrolysed and purified a second time by h.p.l.c. to give aglycones which were analysed by multi-nuclear n.m.r. and g.l.c.-mass spectrometry. The 3- and 4-hydroxy derivatives of imirestat were identified, as was the 2-hydroxy product obtained during or following defluorination. The other major aglycone was postulated to be the 3-fluoro-2-hydroxy metabolite. This represents a novel 'NIH-shift' type pathway for the metabolism of fluorobenzenes.

Formation of a defluorinated metabolite of a quinoxaline antiviral drug catalysed by human cytochrome P450 1A2

“…This migration is postulated to proceed via arene oxide formation followed by subsequent NIH shift rearrangement and conjugation with glucuronic acid, but other potential mechanisms for NIH rearrangement have been postulated, such as via a ketone intermediate (Vannelli & Hooper 1995). Similar NIH shift rearrangements for fluorinated aromatics have been reported in dog for the spirohydantoin aldose inhibitor, imirestat (Gilbert et al 1992), and in rat and dog for the antipsychotic, sertindole (Sakamoto et al 1995).…”

19F-NMR as an analytical tool for fluorinated agrochemical research.

“…More recently, Mortimer and Dawson (1991) successfully utilized a 9.4 T magnet with a dedicated 19F 5 mm probe as a residue technique to analyze a number of fluorinated pesticides in a variety of matrices. 19F NMR has also been utilized to identify metabolites of a fluorinated drug (Imirestat) in dog urine (Gilbert et al, 1992) and the monodealkylated trifluralin metabolite in carrots (Mortimer et al, 1994). However, no comparable investigations have been reported for agrochemical degradation under realistic environmental conditions.…”

Comparative Detection of Fluorinated Xenobiotics and Their Metabolites through 19F NMR or 14C Label in Plant Cells

“…More recently, this method has been used in humans for the detection of flurbiprofen and its metabolites in urine (Wade et al, 1990), of antidepressors and antipsychotic agents (Karson et al, 1993;Komoroski, 1994), and also of 5-fluorouracil and its metabolites in tumors (Presant et al, 1994). It has also been used for metabolism studies of fluorinated drugs in animals (Hashimoto et al, 1991;Gilbert et al, 1992) or plants (Parisot et al, 1991).…”