(S)-1-(1-Methylpyridin-2-yl)-3-aminopiperidine as a novel derivatization reagent capable of enantiomeric separation and enhanced ESI-MS/MS detection for chiral carboxylic acids

A novel derivatization reagent, (S)-1-(1-methylpyridin-2-yl)-3-aminopiperidine (MPAPp), was designed and developed for the enantiomeric separation by conventional reversed-phase liquid chromatography (LC) and the sensitive electrospray ionization-tandem mass spectrometry (ESI-MS/MS) detection of chiral carboxylic acids. MPAPp reacted with the carboxylic acids at 60 degrees C within 5 min in the presence of a condensation agent to produce the positively-charged and diastereomeric derivatives. The MPAPp-derivatization enabled the satisfactory enantiomeric separation not only of the alpha- and beta-chiral carboxylic acids [ketoprofen (KET), etodolac and 3-hydroxypalmitic acid], but also of the gamma-chiral carboxylic acid [2-(gamma-carboxyethyl)-6-hydroxy-2,7,8-trimethylchroman (gamma-CEHC)] with the resolution (Rs) values of 1.35-1.82. The derivatization also worked for the enantiomeric separation of the epsilon-chiral carboxylic add [alpha-lipoic acid, separation factor (alpha) = 1.04]. The detection responses of the MPAPp-derivatives were 25-500-times greater than the intact carboxylic acids, therefore, the low femtomolar derivatives were fully detected. The trace detection of a gamma-CEHC enantiomer (limit of detection, 1.9 fmol on column) in saliva was achieved by the MPAPp-derivatization followed by LC/ESI-MS/MS. The pharmacokinetic profiles of the KET enantiomers during/after the MOHRUS (R) patch application were also obtained from the saliva analysis using the MPAPp-derivatization based LC/ESI-MS/MS method, which was precise (intra- and inter-assay relative standard deviations, < 6.6% and < 4.6%, respectively) and accurate (96.2-105.3%) within the range of 35-280 pg/mL for each enantiomer.