New C2-symmetric 2,2′-bipyridine crown macrocycles for enantioselective recognition of amino acid derivatives

A series of new C2-symmetric 2,2′-bipyridine-contaning crown macrocycles 1-4 has been developed for enantiomeric recognition of amino acid derivatives. These new macrocycles have been showed to be strong complexing agents for primary organic ammonium salts (with K up to 4.83×10 5 M-1 and -ΔG0 up to 32.4 kJ mol -1) and also useful chromophores for UV-vis titration studies. These macrocyclic hosts exhibited enantioselective binding towards the (S)-enantiomer of phenylglycine methyl ester hydrochloride (Am1) with K(S)/K (R) up to 2.10 (ΔΔG0=-1.84 kJ mol -1) in CH2Cl2 with 0.25% CH3OH. The structure-binding relationship studies showed that the aromatic subunit and the ester group of the ammonium guests are both important for good enantioselectivity. In addition, the host-guest complexes have been studied using various NMR experiments.Department of Applied Biology and Chemical Technolog