Screening approach for chiral separation of pharmaceuticals

High-throughput and performance analysis and purification of enantiomers are important parts of drug discovery and provide high-quality compounds for pharmacological testing. We have previously reported two parts describing chiral chromatographic screens using normal-phase (NPLC) and reversed-phase (RPLC) liquid chromatography, in order to cope with increasing numbers of new compounds generated by chemistry programs. We present in this part the development and implementation of a third faster screen using supercritical fluid chromatography (SFC) to maximize chance in achieving rapid enantiomer resolution of large numbers of compounds in a minimum of time. The SFC screen utilizes a narrow combination of only four columns (Chirlapak AD and AS, and Chiralcel OD and OJ) and two solvent modifiers (methanol and isopropanol). A modifier and column-switching setup was employed to allow the entire screening process to be serially run in the order AD > OD > OJ > AS and methanol > isopropanol, so that the screening for a given molecule can be stopped when separation is achieved. The switching system was fully automated for unattended operation of multiple compounds. An optimization procedure was also defined, which can be performed if needed for unsuccessful separations in the screening step. The chiral SFC strategy proved its performance and robustness in resolution of hundreds proprietary chiral molecules generated by drug discovery programs, with a success rate exceeding 95%. In addition, the generic capability of the strategy was evaluated by applying the screen and optimization methodology to a test set comprising 40 marketed drugs differing from proprietary compounds in terms of chemical diversity, revealing a similar high success rate of 98%. Chiral separations developed at the analytical scale work easily and equally well at the semi-preparative level, as illustrated with an example. The SFC screen allows resolution of compounds that were partially separated by NPLC or not separated at all by RPLC, demonstrating the utility of implementing complementary chromatographic techniques. The SFC screen is currently an integral part of our analytical support to discovery chemical programs and is considered the first try for chiral separations of new compounds, because it offers a higher success rate, performance and throughput.