Determination of the site of glucuronidation in an N-(3,5-dichlorophenyl)succinimide metabolite by electrospray ionization tandem mass spectrometry following derivatization to picolinyl esters

Derivatization using 3-pyridylcarbinol coupled with liquid chromatography electrospray ionization tandem mass spectrometry (LC/MS/MS) was used to characterize a novel Phase II metabolite of the nephrotoxic agricultural fungicide, N-(3,5-dichlorophenyl)succinimide (NDPS). A glucuronide conjugate of N-(3,5-dichlorophenyl)-2-hydroxysuccinamic acid (2-NDHSA) was identified in the urine from a rat dosed with 14C]NDPS. However, 2-NDHSA contains an aliphatic hydroxyl group and a carboxylic acid group, both of which are potential sites for glucuronidation. Mass spectrometry alone was unable to distinguish between these possibilities. Since the position of glucuronidation may be important in the mechanism of NDPS-induced nephrotoxicity, chemical derivatization in conjunction with mass spectrometry was used to characterize the glucuronide. The 2-NDHSA glucuronide conjugate was isolated from rat urine, derivatized with 3-pyridylcarbinol, and the derivatized metabolite was then analyzed by LC/MS/MS. Two known NDPS metabolites, 2-NDHSA and N-(3,5-dichlorophenyl)succinamic acid (NDPSA), were also isolated from rat urine and derivatized similarly. 3-Pyridinylcarbinol reacted rapidly with the carboxylic acid groups and formation of the picolinyl esters increased the ionization potential under positive ion conditions. The urinary glucuronide of 2-NDHSA was identified as an alcohol-linked glucuronide by examination of the molecular ions and the collision-induced dissociation (CID) product ion spectra of the derivatized products. When used in combination with mass spectrometry, derivatization of carboxylic acids with 3-pyridylcarbinol provided useful mass fragmentations and is a rapid way to obtain structural information about the position of glucuronidation of NDPS metabolites.