Kinetic analysis and subambient temperature on-line on-column derivatization of an active aldehyde

Accurate Mass Identification of an Interfering Water Adduct and Strategies in Development and Validation of an LC-MS/MS Method for Quantification of MPI8, a Potent SARS-CoV-2 Main Protease Inhibitor, in Rat Plasma in Pharmacokinetic Studies

MPI8, a peptidyl aldehyde, is a potent antiviral agent against coronavirus. Due to unique tri-peptide bonds and the formyl functional group, the bioassay of MPI8 in plasma was challenged by a strong interference from water MPI8. Using QTOF LC-MS/MS, we identified MPI8•H2O as the major interference form that co-existed with MPI8 in aqueous and biological media. To avoid the resolution of MPI8 and MPI8•H2O observed on reverse phase columns, we found that a Kinetex hydrophilic interaction liquid chromatography (HILIC) column provided co-elution of both MPI8 and MPI8•H2O with a good single chromatographic peak and column retention of MPI8 which is suitable for quantification. Thus, a sensitive, specific, and reproducible LC-MS/MS method for the quantification of MPI8 in rat plasma was developed and validated using a triple QUAD LC-MS/MS. The chromatographic separation was achieved on a Kinetex HILIC column with a flow rate of 0.4 mL/min under gradient elution. The calibration curves were linear (r2 > 0.99) over MPI8 concentrations from 0.5−500 ng/mL. The accuracy and precision are within acceptable guidance levels. The mean matrix effect and recovery were 139% and 73%, respectively. No significant degradation of MPI8 occurred under the experimental conditions. The method was successfully applied to a pharmacokinetic study of MPI8 after administration of MPI8 sulfonate in rats.

Photochemical stability of 4'-azido-2'-deoxy-2'-methylcytidine hydrochloride: structural elucidation of major degradation products by LC-MS and NMR analysis

The photochemical stability of (1'R,2'S,3'S,4'R)-4'-azido-2'-deoxy-2'-methylcytidine hydrochloride, a new anti-HCV agent, was investigated. Aqueous solutions and bulk drug powder of the drug candidate were exposed to UV-visible light, complying with ICH requirements. The nucleoside analog decomposed via loss of nitrogen to yield products derived from a highly reactive azide intermediate. Major photolysis products were identified by LC-MS and NMR analysis, revealing three main photodegradation pathways. The first one led to the formation of a ring-expanded imidate ester. The other degradation pathways involved exocyclic or endocyclic bond cleavage with imine or imino lactone formation. The latter were prone to rapid hydrolysis, eventually resulting in the release of cytosine, 2-methyl malonaldehyde and (E)-cytosyl-2-methylpropenal.

Kinetic study on the epimerization of trityloxymethyl butyrolactol by liquid chromatography

The epimerization of trityloxymethyl butyrolactol has been investigated using dynamic chromatography and an approximation function introduced by Trapp and Schurig that is based on stochastic and theoretical plate models. The epimerization rate constants and Gibbs activation energies of epimerization are directly calculated from chromatographic peak parameters, i.e. retention times of the interconverting species, peak width at half height and the relative plateau height by using the approximation function. The relationships between peak shape and chromatographic conditions, such as flow-rate, temperature and pH are investigated.