A LIQUID-CHROMATOGRAPHIC METHOD FOR THE DETERMINATION OF THE ENANTIOMERIC PURITY OF THE ANTICANCER DRUG, 9-AMINO-20(S)-CAMPTOTHECIN

A method was developed for determining the enantiomeric purity of 9-amino-20(S)-camptothecin (9-A-20(S)-CAM). The chiral derivatizing reagent, 1-(1-naphthyl)ethyl isocyanate (NEI) was used to derivatize the enantiomers of 9-A-CAM, and H-1-NMR, LC-MS, and LC-UV were used to identify and quantitate the two diastereomers produced. During the first 24 h, derivatization was exclusively at the 9-amino nitrogen. The much slower reaction involving reaction of NEI with the 20-hydroxy oxygen could be prevented by quenching the reaction within the first 24 h with methanol. NMR analysis provided useful information about the site of derivatization; however. the partial separation of the signals was insufficient for quantitative analysis of the two diastereomers. Whereas baseline resolution of the two diastereomers was achieved by reversed-phase LC, the reproducibilities of the resolution and the peak area ratios were dependent on the nature and composition of the mobile phase, the flow rate, the column temperature. sample concentration and sample preparation.