Pyridine-containing chiral macrocycles for the enantioselective recognition of amino acid derivatives and their molecular dynamics simulations

Two novel C-2-symmetric optically active pyridine-15-crown-5 type ligands containing lipophilic chains at the stereogenic centres, macrocycles 5 and 6, were prepared from (S)-1,2-propanediol and (S)-3-aryloxy-1,2-propanediol for the enantiomeric recognition of amino acid ester derivatives. These novel macrocycles have been shown to be strong complexing agents for primary organic ammonium salts (with K values of up to 1363.5 M-1, Delta G degrees of up to 17.86 kJ mol(-1) and a selectivity ratio of 80:20) by H-1 NMR titration method. These macrocyclic host exhibited enantioselective binding towards the L-enantiomer of phenylalanine methyl ester hydrochloride with K-L/K-D up to 8.57 in CDCl3 containing 0.25% CD3OD. Experimental results have been detailed with molecular dynamic calculations at atomic level concerning the molecular recognition and discrimination properties of a chiral pyridino-15-crown-5. The binding free energies were calculated as similar to-25 kJ mol(-1). The results indicated that the host binds and discriminates valine salts better than phenylalanine salts. The molecular dynamics, MM/PBSA calculations are consistent with the H-1 NMR results. (C) 2010 Elsevier Ltd. All rights reserved.