Efficient Process for Obeticholic Acid: Synthesis, Structural Assignment, and Control Strategy for Diastereoisomeric Impurities

An efficient process for the preparation of chirally pure obeticholic acid [1, (6α, 7α), OCA] with an overall yield of 30.78% from compound 5 (CDCA) is presented in this article. During the process development, there is a requirement for characterization of physical samples of all the possible diastereomers of 1 such as 2 (6β, 7α), 3 (6β, 7β), and 4 (6α, 7β) to designate the peaks for the quantitative measurement of their contents in high-performance liquid chromatography (HPLC). All these diastereomers (2, 3, and 4) are synthesized, separated using preparative HPLC, and characterized using various spectroscopic techniques. This paper describes the fate and control mechanism of the diastereomeric and process- and degradation-related impurities in detail.