Enantiomeric Recognition of Racemic 4‐Aryl‐1,4‐dihydropyridine Derivatives via Chiralpak AD‐H Stationary Phases

The chromatographic chiral resolution of two new series of racemic 4‐substituted‐1,4‐dihydropyridine derivatives was studied on a commercial Chiralpak AD‐H column. Analytes without 5,5‐dimethyl substituents ( 1–15 ) are more efficiently resolved than analytes with 5,5‐dimethyl groups ( 16–30 ). The AD‐H column discriminated between enantiomers through both hydrogen bonding attractions and π–π interactions. This interpretation is in accord with plots of the logarithm of separation factors, log(α), versus σ (Hammett–Swain substituent parameter) and σ⁺ (Brown substituent constant) plots. By elucidating the effects of the remote substituents on these chiral separations, it was shown that the influence of π–π interaction forces increase when steric bulk effects act to decrease the hydrogen bonding attractive forces on the AD‐H column. Chirality 24:854–859, 2012. © 2012 Wiley Periodicals, Inc.