Liquid chromatographic method for enantiopurity control of alaptide using polysaccharide stationary phases

Separation of veterinary drug alaptide ((S)-8-methyl-6,9-diazaspiro(4,5)decane-7,10-dione) from a chiral impurity (R-enantiomer) was developed. Five chiral columns (three amylose and two cellulose type) were evaluated in a reversed-phase system. Three of them offered satisfactory enantiomeric resolution. Finally, three methods were validated and proved to be applicable for the determination of a chiral impurity content below 0.1% (method A: 3-AmyCoat column, tris-[3,5-dimethylphenyl]carbamoyl amylose; mobile phase: water/methanol/propan-2-ol/butan-2-ol=75:20:3.5:1.5 v/v, flow rate: 0.40 mL/min; column temperature: 30 °C; method B: Chiralpak AS-3R, tris-[1-phenylethyl]carbamoyl amylose; water/acetonitrile=80:20 v/v, 0.40 mL/min; 40 °C; method C: Chiralcel OZ-3R, tris-[3-chloro-4-methylphenyl] carbamoyl cellulose; water/acetonitrile=80:20 v/v, 0.40 mL/min; 40 °C). Some decrease in efficiency with repeated sample injections was observed for the 3-AmyCoat column. The resistance to mass transfer in the stationary phase increased probably due to the change in chiral selector conformation. This effect was considerably suppressed by propan-2-ol or to a greater extent by butan-2-ol added to a mobile phase. Simple regeneration was also suggested to recover efficiency of the column.