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

Article abstract of DOI:10.1016/j.tet.2011.06.064

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 K_ass up to 13590 M^-1 and G ⁰ 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 K_d/K_l up to 5.08 in CDCl₃ with 0.25% CD₃OD.