Cellulose tris(3,5-dimethylphenylcarbamate)-based chiral stationary phases as effective tools for enantioselective HPLC separation of structurally different disubstituted binaphthyls.

ABSTRACT

Cellulose tris(3,5-dimethylphenylcarbamate)-based chiral stationary phases (CSPs) were used for a study of the HPLC retention and enantioseparation behavior of 2,2'-disubstituted or 3,2,2'-trisubstituted 1,1'-binaphthyls and 8,3'-disubstituted 1,2'-binaphthyls. The effects of the mobile phase composition in normal- (NP) and reversed-phase (RP) separation modes were investigated. The NP mobile phases contained n-hexane and propane-2-ol at various volume ratios, the RP ones were obtained by mixing acetonitrile with water or a 20 mM phosphate buffer of pH 6.0 or 3.0. The RP separation mode has been found more suitable for enantioresolution of most of the analytes. The best enantioseparation of 2,2'-diacetyl-1,1'-binaphthyl, 2-hydroxy-2'-(phenylamino)-1,1'-binaphthyl-3-carboxylic acid and 2-amino-2'-hydroxy-1,1'-binaphthyl-3-carboxylic acid was obtained in the mobile phase of ACN/20 mM phosphate buffer, pH 3.0, 40/60 (v/v), whereas N-(2'-hydroxy-1,1'-binaphthyl-2-yl)acetamide, N-(3'-methoxy-1,2'-binaphthyl-8-yl)acetamide, and N-(3'-hydroxy-1,2'-binaphthyl-8-yl)acetamide yielded better results in ACN/water at the same v/v ratio. The analyte-CSP interaction mechanism was found to be temperature independent but the enantioresolution improved at an elevated temperature. The mechanism of the enantioselective discrimination is discussed on the basis of the thermodynamic parameters obtained. Semi-preparative separation conditions have been proposed for 2-amino-2'-hydroxy-1,1'-binaphthyl-3-carboxylic acid, N-(3'-methoxy-1,2'-binaphthyl-8-yl)acetamide, and N-(3'-hydroxy-1,2'-binaphthyl-8-yl)acetamide.