Averica Discovery Services, Inc.
October 17, 2018–October 19, 2018
Jeff Kiplinger will attend and present recent work at SFC 2018, the 11th annual International SFC Conference. Averica presentations have frequently appeared on the agenda of this meeting.
Dr. Kiplinger will discuss an approach, developed at Averica, that simplifies the complex chiral resolution of compounds with multiple stereocenters. The process leverages the chiral selectivity and preparative efficiency of SFC, and the precise resolution of reversed-phase UPLC chromatography.
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Rapid Resolution of Isomers from Chiral Molecules with Multiple Stereocenters
Jeffrey P. Kiplinger, Paul M. Lefebvre, Lei Yu (Averica Discovery Services, Marlborough MA); Keith Galyan (Novartis Institute for Biomedical Research, Cambridge MA)
Molecular complexity is an important concept in drug discovery. It is highly associated with target specificity and with limiting toxicity. Key descriptors of molecular complexity include “three dimensionality”, side chain/molecular size ratio, fraction of sp3 atoms, and number of chiral centers(1). In probing molecular complexity, increasing the number of stereocenters is of high importance but has been little explored due to complexity of synthesis and of resolution(2).
Traditionally, single chiral center racemic compounds are easily resolved chromatographically by screening stationary and mobile phase conditions until a pair of peaks with an abundance ratio of 1:1 is observed. Many chromatographers attempt to resolve a 2-center compound similarly, by screening until 4 peaks are observed as matched pairs and setting separation conditions accordingly.
A molecule with n chiral centers has 2n isomers, present in a mixture as 2n-1 diastereomeric pairs of enantiomers. Synthetic schemes to make molecules with two or more stereocenters often have diastereomeric selectivity even if the reagents are not chiral, so commonly the abundance of each diastereomeric pair in a final product varies. Thus in a 3 chiral center molecule the product may include 8 isomers in a ratio of (e.g.) 100 10:10:2:2:75:75. Chiral selectors available on chromatographic stationary phases today are diverse, but unlikely to be universally selective. The chromatogram from such a mixture is nearly impossible to interpret. When we evaluate samples with the frequent presence of chemical impurities or side products, developing a separation scheme for a 3-center compound is a formidable task.
We have developed a process that avoids the need to obtain clear resolution of the individual isomers of a multicenter compound. The process leverages the selectivity of reversed phase achiral media by high resolution HPLC for the diastereomeric pairs of enantiomers, coupled to preparative SFC using chiral media. The process is fast and easily manages the resolution and clear assignment of all the isomers present in synthetic compounds with 3 and 4 stereocenters. While the orthogonal chromatographies are performed sequentially – not directly coupled – the minimal method development makes the analytical and preparative parts of the cycle efficient and fast. We will present detailed examples to illustrate the technique.
- Lovering, F. (2013) Escape from flatland 2: complexity and promiscuity. MedChemComm 4, 515–519
- Mendez-Lucio, O. et al. (2017) The many roles of molecular complexity in drug discovery. Drug Discovery Today 22:1; 121-126