Synthesis of Calix[4]proline Derivatives and Their Chiral Recognition for Enantiomers of Mandelic Acid

Five chiral calix[4]proline derivatives were designed and synthesized from aminocalix[4]arenes, and their structures were characterized by H-1 NMR, C-13 NMR, IR, ESI-MS and elemental analysis. The chiral recognition ability for enantiomers of mandelic acid was investigated by NMR techniques, and the results showed that 5,11-diprolinamides substituted calix[4]arene 2b could well and selectively recognize the two enantiomers of mandelic acid (K-L/K-D approximate to 94). A possible recognition mechanism was proposed, which was constructed by cooperative multi-supramolecular interactions including intermolecular acid-base, hydrogen bond and pi center dot center dot center dot pi stacking interactions.