GC Quantification of Cyclopropylamine, Diethylamine and Triethylamine in Active Pharmaceutical Ingredients

Development and validation of a GC method for a key nemtabrutinib intermediate: Implementation of an in-situ free base sample preparation protocol

A novel synthetic approach to nemtabrutinib (MK-1026) was recently developed in our laboratories. The chemistry goes through a cyrene amine intermediate which does not contain any chromophore. As a result, analysis of this key chiral intermediate by HPLC-UV is not feasible. Initial attempts to develop a HPLC-CAD method were unfruitful; therefore, a gas chromatography method was developed and optimized to effectively monitor the cyrene amine free base and related impurities generated during the process. As the synthetic process continued to be optimized, the toluene sulfonic acid salt (p-TsOH) of the cyrene amine intermediate was later identified by our process chemistry group to be beneficial in terms of ease of isolation and purity upgrade. However, repeated injections of the cyrene amine p-TsOH intermediate resulted in rapid GC column deterioration. After identifying p-TsOH as the main cause of the issue, we developed a straightforward and practical procedure that involves using a resin to remove the p-TsOH counterion in-situ, which converts cyrene amine salt to its neutral form in sample solutions. This protocol was successfully demonstrated and proven to be an efficient solution. This methodology may find applications with other analytes containing counterions that need to be neutralized prior to analysis.

A simple and universal headspace GC-FID method for accurate quantitation of volatile amines in pharmaceuticals

Volatile amines are reagents commonly used in pharmaceutical manufacturing of intermediates, active pharmaceutical ingredients (APIs), and drug products as participating regents for chemical reactions and optimization of product yield. Due to their compound specific daily allowable intake, residual volatile amines are required by regulatory agencies to be monitored and controlled in pharmaceutical products intended for human consumption. However, the accurate quantification of residual volatile amines in pharmaceutical entities can often be challenging as these analytes may chemically react and/or interact with the sample matrix. Herein, we describe a simple and universal headspace gas chromatography with flame ionization detection (HS-GC-FID) method capable of separating 14 commonly used volatile amines. The chemical activity of the volatile amines with the API matrix were mitigated by using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as an additive to reduce matrix effects in conventional high-boiling diluents. The addition of DBU drastically improved the detectability and method accuracy of the residual volatile amines in an acidic API, namely, Ketoprofen®. Additionally, DBU was employed as a GC deactivation reagent to ensure interfacial adsorption of the analytes to GC components were reduced, thereby improving method precision. Method validation showed acceptable linearity, limit of detection, limit of quantitation, solution stability, precision, and robustness. Separation specificity, evaluated by observing the chromatographic resolution of the volatile amines with one-another and against a set of 23 common residual solvents, were shown to be acceptable for most peak pairs.

Method development for the acquisition of adsorption isotherm of ion pair reagents Tributylamine and Triethylamine in ion pair chromatography

Tributylamine (TBuA) and triethylamine (TEtA) are the most commonly used ion pair reagents in ion pair chromatography especially for the analysis of oligonucleotides. In order to improve the understanding of the retention and separation mechanism of oligonucleotides in ion pair chromatography, it is important to understand the retention mechanism and the nature of interaction of these ion pair reagents with the stationary phase in the chromatographic column. Adsorption isotherm is helpful in evaluating such interactions, and subsequently predicting the retention mechanism. Alkylamines are very polar molecules which lack suitable chromophore and are commonly present in charged forms. Therefore, their determination and the subsequent acquisition of their adsorption isotherms using traditional liquid chromatography is very difficult. In this study, we first developed an analytical method for the determination of TBuA and TEtA in a typical chromatographic mobile phase (acetonitrile-water) and then used the same method to acquire the adsorption isotherms for tributylammonium acetate (TBuAA) and triethylammonium acetate (TEtAA). This method started with the conversion of the alkylammonium ions to free neutral forms by treating the sample with a strong base, followed by pentane-mediated extraction and finally the analysis of the extracts using gas chromatography-flame ionization detector (GC-FID). This three-step method was validated for parameters like range, linearity, intra-day and inter-day precision and accuracy, limit of detection and limit of quantitation. For the adsorption isotherms, the C18 column was first equilibrated with the solutions having different concentrations of alkylammonium ions and then stripped with eluent devoid of alkylammonium ions. Several stripping eluents were investigated and it was discovered that the eluent requirement could be decreased by the addition of sodium chloride. The effluents from the stripping phase were collected and analyzed using the developed analytical method to acquire the adsorption data. Under the investigated conditions, adsorption of TBuAA and TEtAA showed type III and type I isotherm behavior respectively.

Separation of structurally related primary aliphatic amines using hydrophilic interaction chromatography with fluorescence detection after postcolumn derivatization with o-phthaldialdehyde/mercaptoethanol

The retention behavior of primary aliphatic amines (homologous series of aliphatic alkyl amines and cycloalkyl amines) and positional isomers of alkylamines in the hydrophilic interaction chromatography mode was studied. The study was carried out on a TSKgel Amide-80 column followed by postcolumn derivatization with fluorescence detection to describe the retention mechanism of tested compounds. The effect of chromatographic conditions including column temperature, acetonitrile content in the mobile phase, mobile phase pH (ranging from 3.5 to 6.8), and salt concentration in the mobile phase was investigated. The final mobile phase consisted of acetonitrile and solution of 20 mM potassium formate pH 3.5 in ratio 80:20 v/v. The analyses were carried out at mobile phase flow rate of 1.0 mL/min and the column temperature of 20°C. The developed method was fully validated in terms of linearity, sensitivity (limit of detection and limit of quantification), accuracy, and precision according to International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines. The proposed new methods were proved to be highly sensitive, simple, and rapid, and were successfully applied to the determinations of isopropylamine, cyclohexylamine, and cyclopropylamine in relevant active pharmaceutical ingredients.