A high-performance, tailor-made resolving agent: remarkable enhancement ofresolution ability by introducing a naphthyl group into the fundamental skeleton

A novel resolving agent, 2-naphthylglycolic acid (2-NGA), was designed for p-substituted 1-arylethylamines on the basis of the consideration that a ri gid and large naphthyl group would be favorable for the close packing of su pramolecular hydrogen-bond sheets formed between the carboxy groups of 2-NG A and the amino groups of p-substituted 1-arylethylamines. Racemic 2-NGA wa s readily available from commercially available raw materials, and both ena ntiopure forms could be obtained by simple diastereomeric resolution with e nantiopure 1-phenylethylamine. Thus-prepared enantiopure 2-NGA was found to have an excellent resolution ability not only for p-substituted 1-arylethy lamines, but also for a wide variety of chiral primary amines. X-Ray crysta llographic analyses of the less- and more-soluble diastereomeric salts reve aled that this excellent resolution ability of 2-NGA arose from the formati on of a supramolecular hydrogen-bond sheet with the primary amine, as we ha d expected, and also from the possible achievement of an infinite chain of CH ...pi interaction between its naphthyl group and the aromatic group of t he amine, which was formed in the hydrophobic region of the supramolecular hydrogen-bond sheet.