Obeticholic acid Impurity 4, an isomer sharing the exact elemental composition as its parent drug, Obeticholic acid, is likely a stereoisomer or a positional isomer. Obeticholic acid is a 6ฮฑ-ethyl derivative of chenodeoxycholic acid, possessing a 3ฮฑ,7ฮฑ-dihydroxy-5ฮฒ-cholan-24-oic acid skeleton. Impurity 4 may arise from epimerization at one of the chiral centers, such as the C-3 or C-7 hydroxyl groups, or potentially the C-6 ethyl substituent, resulting in an altered spatial arrangement without changing the connectivity of atoms. Alternatively, it could represent a subtle rearrangement within the bile acid framework. This compound serves as a crucial HPLC reference standard for assessing the purity profile of Obeticholic acid.
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