Vijayavitthal T. Mathad

New Synthesis of Donepezil Through Palladium‐Catalyzed Hydrogenation Approach

Abstract A new, economical, and efficient process has been developed for large‐scale synthesis of donepezil 1, an anti‐Alzheimers drug. The process involves palladium‐catalyzed hydrogenation of (2E)‐5,6‐dimethoxy‐2‐(pyridin‐4‐ylmethylene)indan‐1‐one 6 to provide 5,6‐dimethoxy‐2‐(piperidin‐4‐ylmethyl)indan‐1‐one 8 as a key step. DRL‐IPD Communication No. 006.

Impurity profile study of repaglinide.

Three unknown impurities and a byproduct in repaglinide bulk drug at levels below 0.1% (ranging from 0.05 to 0.1%) were detected by a simple isocratic reversed-phase high performance liquid chromatography (HPLC) method. These impurities were isolated from crude sample of repaglinide using reversed-phase preparative high performance liquid chromatography. Based on the spectroscopic data (IR, NMR and MS) the structures of these impurities (I, II and IV) and byproduct (III) were characterised as 4-carboxymethyl-2-ethoxy-benzoic acid (I), 4-cyclohexylaminocarbamoylmethyl-2-ethoxy-benzoic acid (II), 1-cyclohexyl-3-[3-methyl-1-(2-piperidin-1-yl-phenyl)-butyl]-urea (IV) and 1,3-dicyclohexyl urea (III), respectively. Their synthesis and formation is discussed.

Efficient Synthesis of (1R)‐[3,5‐Bis(trifluoromethyl)phenyl] Ethanol, a Key Intermediate for Aprepitant, an NK‐1 Receptor Antagonist

Abstract Enzyme‐catalyzed efficient synthesis of (1R)‐[3,5‐bis (trifluoromethyl) phenyl] ethanol (R)‐(3), a key intermediate for aprepitant, via enantioselective transesterification of racemic 1‐[3,5‐bis (trifluoromethyl) phenyl] ethanol (RS)‐3 using vinyl acetate as the acyl donor in the presence of Candida antarctica lipase‐B (CAL‐B) in an overall yield of 84% with >99% ee is described.

Stress Degradation Behavior of Paliperidone, an Antipsychotic Drug, and Development of Suitable Stability-Indicating RP-LC Method

A new, simple, rapid, and stability-indicating reversed phase liquid chromatographic (RP-LC) method for the determination of both assay and related substances in paliperidone has been developed and validated. During the forced degradation at hydrolysis, oxidative, photolytic, and thermal stressed conditions, the degradation was observed in the oxidative and acid stress conditions. Five process-related impurities (Imp-A to Imp-E) in test sample of paliperidone have been detected using newly developed RP-LC method. Among the five, Imp-C and Imp-D were found to be degrdants. Good resolution between the peaks corresponding to degradation and process-related impurities from the analyte was achieved on a Hypersil BDS C18 (250×4.6 mm, 5 μm) column. The stress samples were assayed against a qualified reference standard, and the mass balance was found to be close to 99.0%. The method was validated as per ICH guideline and was found to be robust. The proposed RP-LC method was successfully applied to the analysis of commercial formulation and was found to be specific and selective.

Development and Validation of Stability-Indicating GC-FID Method for the Quantitation of Memantine Hydrochloride and Its Nonchromophoric Impurities in Bulk and Pharmaceutical Dosages

A stability-indicating method has been developed and validated for the quantitative determination of memantine hydrochloride and its nonchromophoric impurities in drug substance and drug product using gas chromatography coupled with flame ionization detector (GC-FID). The stability-indicating nature of the method has been proved by establishing peak purity and confirming the mass balance of all samples by subjecting them to stress conditions like hydrolysis, oxidation, photolysis, and thermal degradation studies. The chromatographic separation was performed on a fused silica capillary (HP-5, 30 meter, 0.32 mm and 0.25 μm film thickness) column. The method validation results indicate that the method has acceptable specificity, accuracy, linearity, precision, robustness, and high sensitivity with detection limits and quantitation limits ranging from 0.001% to 0.01% and 0.004% to 0.03%, respectively. The effectiveness of the technique was demonstrated by analysis of different bulk sample of Memantine hydrochloride. The proposed GC-FID method was also found to be specific and selective for the analysis of commercial formulation samples.

Stability-Indicating Gradient RP-LC Method for the Determination of Process and Degradation Impurities in Bosentan Monohydrate: An Endothelin Receptor Antagonist

Described is a simple, rapid, selective, and stability-indicating RP-LC method for the determination of process and degradation-related impurities of bosentan monohydrate. Chromatographic separation was achieved on Zorbax SB-Phenyl column thermostated at 35∘C under gradient elution by a binary mixture of solvent A (60% phosphate buffer, pH 2.5, and 40% methanol) and solvent B (acetonitrile) at a flow rate of 1.0 mL/min. Forced degradation was carried out under acidic, alkaline, oxidative, photolytic, and thermal conditions. Significant degradation is observed in acid and alkali stress conditions. Process- and degradation-related impurities were characterized by mass spectrometry, 1H NMR, and FT-IR spectral data. Validation of the developed method was carried out as per ICH requirements. Regression analysis shows an “𝑟” value (correlation coefficient) of greater than 0.999 for bosentan and five potential impurities. This method was capable to detect the five impurities at 0.01% of the test concentration of 1.0 mg mL−1.

Development and Validation of New Chromatographic Method for the Determination of Enantiomeric and Diastereomeric Purity of Solifenacin Succinate: An Antimuscarinic Agent

A new, simple, and rapid stereoselective normal phase-liquid chromatographic (NP-LC) method was developed to separate and quantify the solifenacin succinate and its three stereoisomers. The stereoisomeric separation was achieved on Chiralpak IC (250×4.6 mm ID) column. The mobile phase was consisting of n-hexane, ethanol, isopropyl alcohol, and diethylamine in the ratio (60 : 15 : 25 : 0.1, v/v/v/v), and the flow rate was maintained at 1.0 mL min−1. UV detection was carried out at 220 nm. In addition, chiroptical detection was carried out using laser polarimeter to understand the elution orders. Resolution between all the stereoisomers was not less than 3. Effect of column temperature on resolution between the stereoisomers was studied. The method was validated as per ICH guideline and found to be robust. The proposed NP-LC method was successfully applied to the analysis of commercial formulation. The method could be of use not only for routine evaluation of the quality of solifenacin succinate in bulk drug manufacturing unit but also for detection of impurities in pharmaceutical formulations.

Efficient Synthesis and Practical Resolution of 1-(Naphthalen-1-yl)ethanamine, a Key Intermediate for Cinacalcet

An efficient synthesis of 1-(naphthalen-1-yl)ethanamine ( RS -2) and its practical resolution to optically pure (1R)-(naphthalen-1-yl)ethanamine ( R -(+)-2), a key intermediate in the synthesis of cinacalcet hydrochloride (1), is described. The resolution of RS -2 using R-(−)-mandelic acid as a resolving agent in ethanol was established on an industrial scale to give pure R -(+)-2 with >99.8% ee after liberation of the amine from its mandelate salt. An efficient process for the racemization of undesired isomer S -(−)-2 is also provided to maximize the yield of desired enantiomer.

Synthesis and Spectral Characterization of Related Substances of Lacidipine, an Antihypertensive Drug

Abstract Five related substances (impurities) were detected in lacidipine bulk drug substance by a simple high-performance liquid chromatographic method (HPLC) and were identified by liquid chromatography–mass spectrometry (LC-MS). These related substances were independently synthesized, characterized, and co-injected with the sample containing impurities.

Improved and single-pot process for the synthesis of macitentan, an endothelin receptor antagonist, via lithium amide-mediated nucleophilic substitution

An improved, simple, efficient, and telescoped synthesis of macitentan, an endothelin receptor antagonist, starting from 5-(4-bromophenyl)-4,6-dichloropyrimidine in an overall yield of around 62% is described.Graphical abstract