Abstract
A chiral procedure based on EKC was developed and validated for determination of the enantiomeric purity of PHA‐543613, a drug candidate that was under development for treatment of the cognitive deficits of Alzheimer's disease and schizophrenia. Separation of enantiomers is accomplished via differential, enantiospecific complexation with a single‐isomer, precisely sulfated beta‐CD and heptakis‐6‐sulfato‐β‐CD (HpS‐β‐CD). Both neutral and sulfated CDs were screened before selecting HpS‐β‐CD as the chiral selector. The separation is conducted in a 61 cm×50 μm uncoated fused silica capillary with 25 mM HpS‐β‐CD in pH 2.50, 25 mM lithium phosphate as the separation buffer with detection at 220 nm. Application of reverse polarity at –30 kV results in an elution time of about 12 min for PHA‐543613 and 13 min for the undesired S‐enantiomer. Quantification is versus an authentic reference S‐enantiomer as an external standard in combination with an internal standard. The procedure was validated over the range 0.1–2.0% w/w. The detection limit is 0.01–0.02%. The amount of distomer intrinsic to the drug substance is about 0.1% or less. The developed method was used to generate stability data on multiple lots: in one case for up to 3 years.