Detection of the chirality of Cα-methylated α-amino acids with a dynamic helical poly(phenylacetylene) bearing aza-18-crown-6 ether pendants

A stereoregular poly(phenylacetylene) bearing the aza-18-crown-6 ether pendants (poly-1) was found to form a predominantly one-handed helix upon complexation with optically active C-alpha-methylated alpha-amino acids and their amide derivatives including typical meteoritic U-methylated alpha-amino acids such as U-methyl norvaline and C-alpha-methyl valine. The complexes exhibited an induced circular dichroism (ICD) in the UV-visible region of the polymer backbone. Therefore, poly-1 can be used as a novel probe for detection of the chirality of C-methylated alpha-amino acids. The effect of the enantiomeric excess (ee) of C-alpha-methylated a-amino acids on the helicity induction in poly-1 was also investigated.