Exploring the enantioseparation of amino-naphthol analogues by supercritical fluid chromatography

The direct separation of the enantiomers of 1-(α-aminoarylmethyl)-2-naphthol, 1-(α-aminoalkyl)-2-naphthol, 2-(α-aminoarylmethyl)-1-naphthol analogues and 2-(1-amino-2-methylpropyl)-1-naphthol) was investigated in supercritical fluid chromatography. Five commercially available chiral stationary phases based on immobilized polysaccharide chiral selectors (Chiralpak IA, IB, IC, ID and IE) were evaluated. Chiralpak IB was by far the most efficient to achieve the separation of these racemates and was further selected for optimization of elution conditions. The effects of column temperature (varying between 5 and 45 °C) and co-solvent added to carbon dioxide (methanol, ethanol, isopropanol and dichloromethane) were investigated. A particular attention was paid to mobile-phase additives. Several of them, acids, bases or salts (namely water, formic acid, acetic acid, trifluoroacetic acid, diethylamine, diethanolamine, triethylamine, triethanolamine, dimethylethanolamine, ammonia and ammonium acetate), were tested in order to improve peak shapes while maintaining selectivity. With the help of other achiral naphthol derivatives, the additive effects were examined.