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

Four novel C(2)-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 (1)H 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 Delta G(0) up to 23.3 kJ mol(-1) and selectivity ratio: 80:20) by (1)H 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 CDCl(3) with 0.25% CD(3)OD. (C) 2011 Elsevier Ltd. All rights reserved.