Synthesis of Enantiomers of Chiral Ester Derivatives Containing an Amide Group and Their Chiral Recognition by 1H NMR Spectroscopy

Enantiomers of chiral ester derivatives containing an amide group, and possessing one or two stereogenic centers were prepared from L- and D-alpha-amino acids, and glycine with (S)- and (R)-mandelic acid for probing their chiral recognition as a new class of chiral guests by H-1 NMR spectroscopy, since chiral ester derivatives have been rarely used as chiral substrates for chiral recognition by H-1 NMR technology. The results indicated that these chiral ester derivatives have been successfully differentiated in the presence of tetraaza macrocyclic chiral solvating agents (TAMCSAs) 1 a-1 c. In order to better understand their chiral discriminating behavior, Job plots, association constants (K-a), and theoretical calculations of (S,S)-G1 and (R,R)-G1, as a representative example, were performed, respectively. In order to evaluate their practical application, the H-1 NMR spectra of G1 and G9 with various optical purities were measured (up to 98 % ee). In this work, a practical strategy has been effectively established for chiral recognition of chiral ester derivatives containing an amide group and possessing one or two chiral centers in the presence of tetraaza macrocyclic chiral solvating agents 1 a-1 c by means of H-1 NMR spectroscopy.