Synthesis and pKa 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 pKa 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.