Chiral recognition of amino acid esters by zinc porphyrin derivatives

Three novel chiral zinc porphyrins (4a–4c) with protected chiral amino acid substituents as chiral sources were synthesized. Their chiral recognition of amino acid methyl esters was investigated using UV-vis spectrophotometric titration. Some enantioselectivities obtained are higher than that of the known system, and the highest achieved in our study is 21.54 using host 4a with PheOCH3 as guest. We also show that higher enantioselectivity can be obtained at lower temperature. Circular dichroism spectra of chiral porphyrin derivatives binding to enantiomers of guests show great shape and intensity differences. Molecular modeling was performed to understand chiral recognition on a molecular level, and the results are in good agreement with the experimental data.