Optical Rotation Study on Solvent Dependence of Diastereomeric Salt Discrimination Properties

The optical rotation properties have been studied for two diastereomeric salts of four kinds of amine–carboxylic acid salt systems, and the results have been compared among them and their chiral salts. The diastereomeric salts of 2-(4-methylphenyl)-1-phenylethylamine/mandelic acid (1-phenyl-2-(4-methylphenyl)ethylamine; PTE/MA) and α-amino-ε-caprolactam/N-tosylphenylalanine (ACL/TPA) exhibited relatively large differences in optical rotation values and solvent dependency. In contrast, the diastereomeric salts of α-methylbenzylamine/MA and piperazine-2-carboxylic acid t-butylamide/TPA possessed similar optical rotation behavior; the values and solvent dependency were almost identical. These results were discussed in relation to the dielectrically controlled resolution phenomenon for the formers, PTE/MA and ACL/TPA, and were also compared with the crystal structures.