Synthesis and pK a determination of new enantiopure dimethyl-substituted acridino-crown ethers containing a carboxyl group: Useful candidates for enantiomeric recognition studies.

New enantiopure dimethyl-substituted acridino-18-crown-6 and acridino-21-crown-7 ethers containing a carboxyl group at position 9 of the acridine ring [(S, S)-8, (S, S)9, (R,R)-10] were synthesized. The pK(a) values of the new crown ethers [(S, S)-8, (S, S)-9, (R, R)-10] and of an earlier reported macrocycle [(R, R)-2] were determined by UV-pH titrations. Crown ether (S, S)-8 was attached to silica gel by covalent bonds and the enantiomeric separation ability of the newly prepared chiral stationary phase [(S, S)-CSP-12] was studied by high-performance liquid chromatography (HPLC). Homochiral preference was observed and the best separation was achieved for the enantiomers of 1-NEA. Ligands (S, S)-9 and (R, R)-10 are precursors of enantioselective sensor and selector molecules for the enantiomers of protonated primary amines, amino acids, and their derivatives.