Synthesis and characterization of new impurities in obeticholic acid

Novel and efficient synthetic strategies are developed for the first synthesis of two new impurities found in obeticholic acid. The synthetic routes to the impurities are designed without column purification using 4-nitrobenzoyl chloride as a selective protecting group. The impurities, which are obtained in good yields and high purity, are identified and characterized using high-resolution mass spectrometry, Fourier transform infrared, one-dimensional nuclear magnetic resonance (¹H, ¹³C, distortionless enhancement by polarization transfer), and two-dimensional nuclear magnetic resonance (Correlated Spectroscopy, heteronuclear single quantum coherence, heteronuclear multiple bond correlation, and rotating-frame Overhauser effect spectroscopy) techniques.