Absolute Configuration of Pharmaceutical Research Compounds Determined by X-ray Powder Diffraction.

The absolute configuration of active pharmaceutical ingredients (APIs) was determined by generating salts of the active pharmaceutical ingredient (API) with counterions of known chirality, and determining the crystal structures by X-ray powder diffraction. This approach avoids the (often tedious) growth of single crystals, and is successful with very limited quantities of material (less than 1 mg). The feasibility of the method is demonstrated on five examples, and its limitations are discussed as well.