Synthesis and preliminary structural and binding characterization of new enantiopure crown ethers containing an alkyl diarylphosphinate or a proton-ionizable diarylphosphinic acid unit

New enantiopure crown ethers containing either an ethyl diarylphosphinate moiety [(S,S)-4 to (S,S)-7] or a proton-ionizable diarylphosphinic acid unit [(S,S)-8 to (S,S)-11] have been synthesized. Electronic circular dichroism (ECD) studies on the complexation of these new enantiopure crown ethers with the enantiomers of α-(1-naphthyl)ethylammonium perchlorate (1-NEA) and with α-(2-naphthyl)ethylammonium perchlorate (2-NEA) were also carried out. These studies showed appreciable enantiomeric recognition with heterochiral [(S,S)-crown ether plus either (R)-1- or (R)-2-NEA] preference. Theoretical calculations found three significant intermolecular hydrogen bonds in the complexes of (S,S)-9. Furthermore, preference for heterochiral complexes was also observed, in good agreement with ECD results. Complex formation constants were determined by NMR titration for four selected crown ether/NEA pairs. Enantiopure crown ethers containing either an ethyl phosphinate [(S,S)-4 to (S,S)-7] or a phosphinic acid moiety [(S,S)-8 to (S,S)-11] were synthesized and complexation with the enantiomers of 1- and 2-NEA was studied. Calculations showed three important hydrogen bonds between (S,S)-9 and each enantiomer of 1-NEA and 2-NEA. Appreciable enantiomeric recognition and heterochiral preference were found.