First synthesis and characterization of key stereoisomers related to Ezetimibe

Ezetimibe: A Review of Analytical Methods for the Drug Substance, Pharmaceutical Formulations and Biological Matrices

Ezetimibe (EZM) is a selective inhibitor of the sterol transporter Niemann-Pick C1-Like 1 in the small intestine used as an adjunctive therapy to lower cholesterol levels in cases of hyperlipidemia. The goal of this work was to summarize the main physical-chemical, pharmacological and pharmacokinetic characteristics of EZM, as well as to describe the main analytical methodologies for the quantification of the drug. Methods described in the United States Pharmacopeia for EZM raw material and tablets were also presented. The drug has a large number of process-related impurities and degradation products and needs strict quality control of its impurities. Specific chiral methods for the evaluation of its chiral impurities are also a need for EZM. The main advantages and disadvantages of the compiled analytical methods were presented, as well as the limits of detection and quantitation. The fastest and most efficient methods were highlighted. Most methods for analyzing EZM used C₈ or C₁₈ stationary phases in gradient mode with binary mobile phases containing acetonitrile and an acidic buffer solution with ultraviolet detection. For analysis of EZM in biological matrices, liquid chromatography-tandem mass spectrometry is generally employed using electron spray ionization in negative ionization mode using multiple reaction monitoring. Different methods in the literature evaluate a large number of impurities for EZM, however new stability-indicating high-performance liquid chromatography methods for the drug are still needed.

Development of a Simple, Highly Selective RP-LC Method for the Quantification of Diastereomers and Other Related Substances of Ezetimibe Using Multivariate Analysis

A simple reverse phase method for the selective quantification of ezetimibe (EZM), its diastereomers and other related substances was developed. The method demonstrated an excellent separation between each of the 14 impurities (including diastereomers, specified impurities and degradation products) and EZM within a runtime of 45 min. The developed method was evaluated against the reported USP method, other literature methods found that none of them was able to separate/show the absence of all the diastereomers and degradation products. The critical method parameters were optimized using central composite design. Forced degradation studies proved the method to be highly specific and the structure of all the major degradation products were confirmed by LC-MS study. The results of validation proved the method to be precise (% RSD < 4), accurate (recoveries in range of 100 ± 6%), linear (R2 > 0.999) and sensitive (LOQ ≤ 0.04% and LOD ≤ 0.01%) for all the impurities and drug. The method is suitable for both drug substance and oral solid dosage form.

Identification, synthesis and characterization of process related desfluoro impurity of ezetimibe and HPLC method validations

Ezetimibe, which selectively inhibits cholesterol absorption across the intestinal wall and is used as an antihyperlipidemic agent, is synthesized for commercial use as a drug substance in highly pure form. During the synthetic process development studies of ezetimibe, an impurity was detected in the final product at levels ranging from 0.05% to 0.15% in reverse phase gradient high performance liquid chromatography (HPLC) method and its molecular weight was determined by LC-MS analysis. The impurity was identified as (3R,4S)-3-((S)-3-(4-fluorophenyl)-3-hydroxypropyl)-4-(4-hydroxyphenyl)-1-phenylazetidin-2-one which is called desfluoro ezetimibe (lactam-related) impurity, synthesized and characterized, the mechanism of its formation was discussed in detail. After all standardization procedures, it was used as a reference standard during validation of HPLC method and routine analyses. In addition, content of Eze-1 desfluoro impurity in Eze-1 intermediates was specified as 0.10% to keep the formation of desfluoro ezetimibe impurity under control and the related substances HPLC method was validated accordingly.