Direct high-performance liquid chromatographic separation of penbutolol enantiomers on a cellulose tris-3,5-dimethylphenyl carbamate chiral stationary phase

Penbutolol is a β-adrenoceptor blocking agent, and it contains the clinically relevant (?)-S-enantiomer. It was reported that the (+)-R-enantiomer of penbutolol is pharmacologically 50 times less active than the (?)-S-isomer in β-sympatholysis and without intrinsic sympathomimetic activity and refractory period in the heart muscle. Furthermore, the (+)-R-enantiomer does possess mutagenic activity. A high-performance liquid chromatographic (HPLC) method is described for direct identification, stereochemical separation, and quantitation of (+)-R-enantiomer in the clinically used (?)-S-isomer. The method involves the use of cellulose tris-3,5-dimethylphenyl carbamate chiral stationary phase coated on silica gel (OD-Chiralcel column). The capacity factors (k′) for the first eluted enantiomer and stereochemical separation factor (α) obtained were 1.32 and 1.98, respectively. The maximum stereochemical resolution factor (R) was 5.05. The method could be applied for optical purity determination of (?)-(S)-penbutolol in pharmaceutical formulation to detect for the presence of the undesirable (+)-R-enantiomer.