Study of reactions induced by hydroxylamine treatment of esters of organic acids and of 3-ketoacids: Application to the study of urines from patients under valproate therapy

Abstract

Hydroxylamine used at alkaline pH as oximating agent in the search for organic aciduria by gas chromatography/mass spectrometry (GC/MS) induces other chemical reactions. Esters are partially transformed in their corresponding hydroxamic acids. GC/MS characteristics of the trimethylsilylated derivatives of the hydroxamic acids arising from alpha-unsaturated esters are here reported. Their mass spectral fragmentation helps in the recognition of peaks arising from the glucuronides of 2-ene- and probably 2,3'-diene-valproic acid. By heating in the injection port of the gas chromatograph, part of some trimethylsilylated hydroxamic acids are transformed to the corresponding isocyanates by a Lossen-like rearrangement. In addition to the corresponding hydroxamic acids, hydroxylamine treatment of alpha-unsaturated esters forms 2-isoxazolidin-3-ones by intramolecular Michael addition. GC/MS characteristics of the trimethylsilylated derivatives of these compounds are reported. Submitted to hydroxylamine, 3-ketoacids forms 2-isoxazolin-5-ones by cyclization of the oximes after acidification. This explains the existence of two GC peaks observed from urine extracts of patients under valproate therapy, which correspond to two tautomers of 2-isoxazolin-5-one originating from the oximes of the 3-keto-valproic acid.

Quantification of bile acids directly from urine by MALDI–TOF–MS

“…The present MALDI-TOF method requires no derivatization step, and allows simultaneous analysis of multiple bile acids. Furthermore, with an analysis time for unknowns of approximately 10 min, the developed method is considerably faster than the GC-MS and HPLC-MS methods [7,8]. The analysis time and limits of detection found here are comparable to the LC-ESI-MS/MS method developed by Perwaiz et al [6].…”

“…However, this method requires extensive sample pre-treatment including extraction, purification, hydrolysis of the conjugates and derivatization [3,5]. In recent years, many LC-MS techniques have been developed for the qualitative and quantitative analysis of bile acids, including FAB-MS, thermospray MS, ESI-MS/MS and ion-spray MS [2,6,7,8]. However, these methods are still somewhat restricted by low sensitivity, poor specificity, limited resolution, and/or long analysis times [3,4].…”

Targeted inactivation of sister of P-glycoprotein gene (spgp) in mice results in nonprogressive but persistent intrahepatic cholestasis

“…Briefly, bile acids were extracted with a C18 (octadecyl) reversed-phase column. For LC͞MS͞MS, bile acids were analyzed by simultaneous monitoring of parent and daughter ions for the identification of glycine and taurine conjugates (22). Identification and quantification of conjugated bile acids was achieved in 5 min.…”

Nano-electrospray tandem mass spectrometry for the analysis of neurosteroid sulphates†

“…21 Charge remote fragmentation reactions appear to be of most importance at high collision energies and studies performed at low collision energies (`100 eV) on instruments such as triple quadrupoles give product ion spectra containing less prominent CRF ions. 18,22 In recent years electrospray 23 (ES) and matrix-assisted laser desorption/ionisation 24 (MALDI) have replaced FAB as the most popular methods of desorption/ionisation of polar biological molecules. Although FAB is an excellent desorption/ionisation method for steroid sulphates, it suffers as a result of the presence of ubiquitous matrix-associated chemical noise, making low level analysis of steroid sulphates difficult if not impossible.…”

“…Particularly in combination with tandem mass spectrometry, negative-ion FAB has been well used in the structural characterisation of endogenous steroid sulphates from many physiological states. [17][18][19] Tomer and Gross 20 in their classic paper published in 1988 reported the FAB-MS/MS analysis of 19 steroid sulphates. Their experiments were performed on a hybrid magnetic sector instrument consisting of a high resolution double focusing mass spectrometer for precursor ion selection (MS 1 ) and an electrostatic analyser for product ion analysis (MS 2 …”