Detection by HPLC and structural characterization by NMR and MS of a natural deuterium isotopologue of ulipristal acetate.

Herein we discuss the structure elucidation of an unknown peak detected by HPLC in the active pharmaceutical ingredient ulipristal acetate during analytical method development. An extensive chromatographic, MS and NMR spectroscopic study gave the surprising result that the detected component is the natural-abundance mono-deuterium isotopologue of the API. To the best of our knowledge this is the first example where such a mono-deuterium isotopologue could be resolved from its mother component by HPLC and structurally fully characterized by NMR and MS. The reason for this separation could be rationalized in terms of some special structural features of the molecule.