Identification of a Novel Animal Metabolite of Methomyl Insecticide

Abstract

In studies conducted to determine the fate of methomyl in goat, chicken, and monkey, an unknown highly polar, acidic metabolite was found in the urine/excreta of all three animals. The metabolite was purified by HPLC and analyzed by microcolumn LC/MS with electrospray ionization and by NMR. A Hypercarb porous graphitic carbon HPLC column was used for purification and LC/MS, since the unknown was unretained on conventional reversed phase HPLC columns. [ 14 C]Methomyl was used as radiotracer, and [ 13 C]methomyl was added at the 50% level to facilitate metabolite identification. The molecular weight of the metabolite was determined by LC/MS-electrospray, using positive and negative ionization, and structurally useful fragment ions were obtained in both modes by in-source collision-induced dissociation (CID). High-resolution accurate mass measurements of the MH + doublet allowed assignment of the elemental composition. NMR data showed the presence of methyl, methylene, and methine protons with coupling observed between 13 C and the methyl and methine protons. From these data, the structure was determined to be an unusual double conjugate of acetonitrile (a degradate of methomyl), involving conjugation with both cysteine and sulfate.

Structure elucidation of phase II metabolites by tandem mass spectrometry: an overview

“…Hydroxyl groups (in particular phenolic groups) are readily conjugated with sulfuric acid (activated as 3 -phosphoadenosine-5 -phosphosulfate (PAPS)) in the presence of sulfotransferases, as shown in Scheme 4 for phenol [14,16,17,19,22,23,[38][39][40]. Less frequently, amino groups (in particular aromatic amines) are conjugated with sulfuric acid.…”

“…ESI in negative-ion mode is preferred, although for some conjugated metabolites positive-ion ESI spectra were also reported (e.g. in [14,19,23]). Introduction of a sulfate group increases the m/z value of the quasi-molecular ion by 80 ( Table 1).…”

Even‐electron ions: a systematic study of the neutral species lost in the dissociation of quasi‐molecular ions

“…Nevertheless, a host of studies focussing on selected protonated or deprotonated compounds have been reported 18–50. In particular, there are numerous reports on the CI mass spectra of various compound classes as summarized by Harrison 4.…”

Parameters for Carbamate Pesticide QSAR and PBPK/PD Models for Human Risk Assessment

“…Information on the metabolic pathway was taken from Harvey et al (1973), Huhtanen and Dorough (1976), and Reiser et al (1997). In the study by Harvey et al (1973) Harvey et al (1973); however the absence of methomyl, S-methyl N-hydroxythioacetimidate, the N N S-oxide of methomyl, and the S,S-dioxide of methomyl and conjugates was demonstrated.…”

“…Information on the pathway was obtained from WHO/FAO (2000), and the metabolic work on methomyl in Table 29 (Appendix B) (Harvey et al 1973;Huhtanen and Dorough 1976;Reiser et al 1997). Thiodicarb (acetamide-14 C) is rapidly absorbed from the gastrointestinal tracts of rats, metabolized to unstable intermediates (i.e., methomyl, methomyl oxime, etc.…”