The Development of One New Normal Phase Liquid Chromatography Method and Thermodynamic Investigation of Olodaterol Hydrochloride Enantiomer.

In order to improve and replace the enantiomer method outlined in the olodaterol hydrochloride draft monograph (From the European Pharmacopoeia forum), one new, simple, and fast enantioselective normal phase high-performance liquid chromatography chiral method was developed on polysaccharide-based Chiral MX (2) (4.6 × 250 mm, 5 µm) column. n-Hexane, ethanol, and diethylamine in the ratio of 40:60:0.1 (V/V/V) were selected as mobile phase at a flow rate of 0.8 mL/min, and the detection was performed on a photodiode array detector at 225 nm with 5 µL injection volume. The column temperature was set at 40°C for better peak shape and sensitivity. The analysis time can be shortened to 15 min, whereas the resolution between enantiomer and olodaterol was found to be even more than 10.0, which was far better than that obtained with the reported method in this draft monograph. The developed chiral method was validated in accordance with ICH Q2 (R1), including specificity, LOD&LOQ, precision, linearity, accuracy, and robustness. Thereby, the proposed method was demonstrated to be suitable for the determination of enantiomer in olodaterol hydrochloride bulk drug and drug product. Besides, the thermodynamic parameters were evaluated on the basis of Van't Hoff plots that was used to explain correlative chiral recognition mechanisms with the chiral stationary phase.

Development and validation of a stability-indicating RP-HPLC method for the determination of fifteen impurities in rivaroxaban.

A simple and stability-indicating reverse phase high-performance liquid chromatographic (RP-HPLC) method for the determination of rivaroxaban (RIX) and its related substances was developed. Fifteen impurities of RIX, including three unreported isomers, were identified, synthesized, purified, and confirmed using MS, 1H NMR, 13C NMR, and HSQC spectral methods. This new method offered baseline separation for all monitored impurities, and was fast and reliable when compared to the European Pharmacopoeia method. Optimum separation for RIX and its related impurities was achieved on an octyldecyl silica column (YMC Core C18, 4.6 ×100 mm, 2.7 µm) by using a gradient HPLC method in 38 min. The final method was validated with respect to precision, LOD and LOQ, linearity, accuracy, and robustness. This developed method was suitable for routine quality control and drug analysis of RIX active substance.

Ruthenium-Catalyzed Highly Enantioselective Synthesis of cis-3-Quinuclidinols via DKR Asymmetric Transfer Hydrogenation.

A method for the enantioselective synthesis of cis-3-quinuclidinols by Ru-catalyzed asymmetric transfer hydrogenation via dynamic kinetic resolution is described. The reaction proceeded under mild conditions using ammonium formate as the hydrogen donor, affording the products in high yields (up to 99%) with excellent diastereoselectivity (up to 99:1 dr) and enantioselectivity (95-99% ee). This protocol was applicable to gram-scale preparation with perfect enantioselectivity through simple recrystallization.

Peak distortion in reversed-phase liquid chromatography separation of active carbonyl-containing compounds: Mechanism and solution for this overlooked phenomenon.

Peak distortion is frequently encountered for compounds containing active carbonyl groups during reversed-phase (RP) LC separation. However, as being commonly overlooked or misdiagnosed, this problem is rarely reported in the literature and lacks an effective solution. In the present study, six pharmaceutical-related compounds containing keto or aldehyde groups, that exhibited severe peak distortion in early method development, were selected as the model compounds for further investigation. Systematic pH-screening experiments and a series of LC quadrupole-time of flight (Q-TOF) MS and NMR experiments were conducted on each model compound. The underlying chemical behavior of this type of compound during RP-LC separation was explicitly revealed. The formation of gem-diol/hemiketal/hemiacetal species via nucleophilic addition with H2O/MeOH will occur in a low pH eluent, but will be completely suppressed when the pH is higher than an analyte-specific value. As further validated by twelve other pharmaceutical-related compounds belonging to this type, we confirmed that increasing the eluent pH using buffers without nucleophilicity is a simple and effective method to solve this peak distortion problem.

Isolation and identification of four major impurities in capreomycin sulfate.

Capreomycin has good clinical utility to treat multidrug resistant tuberculosis, but it is only used as a second line drug due to its adverse reactions. Literature has demonstrated that the toxicity of capreomycin product is significantly influenced by the impurities in it. Unfortunately, so far, no one impurity in capreomycin has ever been isolated and definitely identified due to its extremely strong basic character and high polarity. An ion-pair method reported in literature can provide separation of capreomycin and its impurities, but it is hard to be used for the preparative purpose. In this study, this ion-pair method was further improved to detect more impurities in capreomycin sulfate substance. Besides the four main components (IA, IB, IIA and IIB), four impurities (impurity A-D) with their contents much higher than the identification threshold were observed. Furthermore, a two dimensional (2D) LC quadrupole-time of flight (Q-TOF) MS method was established to realize high resolution MS analysis of these impurities. For the purpose of preparative isolation, a hydrophilic interaction chromatography (HILIC) method was established. The four main components were well isolated, but unfortunately, the four impurities were co-eluted with each other or with IB by the HILIC method. Fortunately, the degradation experiments revealed that IA and IB could yield clean impurity A and B respectively in acidic medium, and can yield clean impurity D and C respectively in alkaline medium. Therefore, IA and IB were first isolated by the preparative HILIC method, then pure IA and IB underwent acid degradation and base degradation separately and followed by re-isolation by the HILIC method to obtain pure impurity A-D respectively. Based on Q-TOF MS and NMR analysis, the structures (including absolute configuration) of the four isolated impurities were definitely identified.

Stereogenic cis-2-substituted-N-acetyl-3-hydroxy-indolines via ruthenium(ii)-catalyzed dynamic kinetic resolution-asymmetric transfer hydrogenation.

Ruthenium(ii)-catalyzed dynamic kinetic resolution-asymmetric transfer hydrogenation of racemic 2-substituted-N-acetyl-3-oxoindolines to cis-2-substituted-N-acetyl-3-hydroxyindolines is reported. Using the homochiral {Ru[TfDPEN](p-cymene)} catalyst with S/C = 400 in a HCO2H/Et3N mixture, up to >99.9% ee and >99 : 1 dr are obtained with high yields (79-98%). This method provides the first example of preparing enantiomerically pure indolines through asymmetric transfer hydrogenation (ATH).

Matrix precipitation: a general strategy to eliminate matrix interference for pharmaceutical toxic impurities analysis.

Matrix interference, which can lead to false positive/negative results, contamination of injector or separation column, incompatibility between sample solution and the selected analytical instrument, and response inhibition or even quenching, is commonly suffered for the analysis of trace level toxic impurities in drug substance. In this study, a simple matrix precipitation strategy is proposed to eliminate or minimize the above stated matrix interference problems. Generally, a sample of active pharmaceutical ingredients (APIs) is dissolved in an appropriate solvent to achieve the desired high concentration and then an anti-solvent is added to precipitate the matrix substance. As a result, the target analyte is extracted into the mixed solution with very less residual of APIs. This strategy has the characteristics of simple manipulation, high recovery and excellent anti-interference capability. It was found that the precipitation ratio (R, representing the ability to remove matrix substance) and the proportion of solvent (the one used to dissolve APIs) in final solution (P, affecting R and also affecting the method sensitivity) are two important factors of the precipitation process. The correlation between R and P was investigated by performing precipitation with various APIs in different solvent/anti-solvent systems. After a detailed mathematical reasoning process, P=20% was proved to be an effective and robust condition to perform the precipitation strategy. The precipitation method with P=20% can be used as a general strategy for toxic impurity analysis in APIs. Finally, several typical examples are described in this article, where the challenging matrix interference issues have been resolved successfully.