The chiral separation of albuterol derivatives with camphorsulfonic acid using LiChrosorb Diol and amylose chiral AD columns

This research deals with the separation of enantiomers of aminoalcohol compounds in the ion-pair chromatographic system. Separations based on formation of diastereomeric ion pairs were applied in systems with an organic mobile phase using achiral and chiral stationary phases. In this study, (+)-10-camphor-sulfonic acid (CSA) was chosen to serve as a chiral counter ion for the separation of enantiomers of albuterol (alpha-[(tert-butylamino)methyl]-4-hydroxy-m-xylene-alpha,alpha '-diol) and related compounds, monomethyl albuterol (MMEA), monoethyl albuterol (MEEA), Over-reduced Albuterol (ORAlb), Albuterol aldehyde (AA), and Benzyl Albuterol (BA). UV spectrum of each compound in a hexane-ethanol solvent mixture with and without addition of CSA was collected and spectral details were investigated. The binding constants of albuterol and related compounds with (+)-10-camphor-sulfonic acid were determined using the phase solubility technique. The experimental results indicated that Alb, MMEA, MEEA, AA, ORAlb, and BA formed fairly strong complexes with CSA. These conclusions were in fair agreement with the results obtained from chromatographic experiments. The substituent groups not only differentiated the binding powers between alcohol amines and CSA, but also influenced the complexing ability between two enantiomers with stationary phases. The effect is significant and is counted for the diastereomeric separation.; The chiral separation of albuterol and related compounds was initially performed with an achiral column, LiChrosorb Diol using the CSA chiral selector in hexane-ethanol mobile phase. In order to regulate retention and stereoselectivity, the effect of factors on the retention time and resolution including concentration of the chiral selector, the polar alcohol content in the mobile phase, and the column temperature was studied. Several parameters such as separation factor (alpha), resolution (Rs), and retention factor (k') were evaluated in order to achieve the enantiomeric separation and to define optimal conditions. With a mobile phase consisting of hexane, ethanol, triethylamine, and the complexing reagent, camphorsulfonic acid (CSA), Alb, MMEA, and MEEA were baseline resolved with the concentration of CSA at 0.01 N or greater; whereas ORAlb were only separated if the CSA concentration was below 0.02 N. AA and BA were not separated under any experimental condition explored using the LiChrosorb Diol column.; The enantioseparations of albuterols using the chiral stationary phase (CSP) of amylose tris(3,5-dimethylphenyl-carbamate), Chiralpak AD, was also investigated with and without an addition CSA in the mobile phase. In the absence of CSA, each enantiomer eluted at different retention time. However only Alb, MMEA, MEEA, and ORAlb were baseline resolved. AA and BA were partially separated using the similar mobile phase system. In the presence of CSA, the separation of two enantiomers was improved and the increase of the enantioselectivity of albuterols averaged about 20 percent. This study demonstrated interest and advantage in using a chiral stationary phase in combination of a chiral additive in the mobile phase to enhance the chiral separation.