Pyridine containing chiral macrocycles: synthesis and their enantiomeric recognition for amino acid derivatives

Four novel C2-symmetric enantiomerically pure, chiral pyridine-18-crown-6 type macrocycles containing lipophilic chains at the stereogenic centers were prepared. The enantioselectivity of the new ligands toward the enantiomers of d-,l-amino acid methyl ester derivatives were also determined by 1H NMR titration method. These novel macrocycles have been showed to be strong complexing agents for d- and l-amino acid methyl ester hydrochloride salts (with Kass up to 13590 M−1 and ∆G0 up to 23.3 kJ mol−1 and selectivity ratio: 80:20) by 1H NMR titration methods. These macrocyclic hosts exhibited enantioselective binding towards the d-enantiomer of valine methyl ester hydrochloride with Kd/Kl up to 5.08 in CDCl3 with 0.25% CD3OD.