A chiral liquid chromatographic method is developed for the enantiomeric resolution of racemic 1-(4-Methoxybenzyl)-1,2,3,4,5,6,7,8-octahydroisoquinoline, a key starting material in the synthesis of the antitussive agent dextromethorphan hydrobromide. The enantiomers are resolved on a Chiralpak ID-3 column using gradient elution of mobile phase A and B containing a mixture of 0.1% diethylamine in acetonitrile and 0.1% diethylamine in methanol respectively. The resolution between the enantiomers is found to be three. The developed method is extensively validated and proved to be robust. The limit of detection and limit of quantification of unwanted (R)-enantiomer is found to be 0.0075% and 0.025% with respect to test concentration, respectively. The percentage recovery of (R)-enantiomer is ranged from 88.6 to 106.6 in (S)-(-)-1-(4-Methoxybenzyl)-1,2,3,4,5,6,7,8-octahydroisoquinoline sample solution. The proposed method is found to be suitable and accurate for the quantitative determination of (R)-enantiomer in the key starting material of the dextromethorphan hydrobromide bulk drugs.
Key words: HPLC; chiral purity; dextromethorphan; development; validation
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