Helical chirality induction in zinc bilindiones by amino acid esters and amines

Complexation of alpha-amino acid eaters, beta-amino ethers, and amines with a series of zinc 1,19-bilindione derivatives was studied, particularly foc using on the helical chirality induction in the bilindione framework trigge red by the binding of chiral guests. Comparative studies of binding and hel ical chirality induction indicated that binding and chiral induction were m arkedly affected by polar substituents present in both zinc bilindiones and guests. 2-Hydroxyethyl groups at the 2,18-positions of zinc bilindione lar gely assisted the binding of amines and amino acid esters but not the chira l induction. 19O-Alkylation of the zinc bilindiones had inhibitory effects on the binding but enhanced efficiency of helical chirality induction. The enantiomeric excess of 19O-alkyl zinc bilindione complexed with L-Trp-OMe i n CD2Cl2 was 73% at 223 K. A COOR group and an aromatic group in the guest promoted helical chirality induction of 19O-alkylated zinc bilindiones. The patterns of H-1 NMR complexation-induced shifts of zinc bilindiones and gu ests and a molecular modeling study of the complexes showed that electrosta tic repulsion between the COOR group of amino acid eaters and the lactam ri ng of zinc bilindiones, and stacking of the side chain groups of amino acid esters on the C ring of zinc bilindione made a significant contribution to efficient helical chirality induction.