Protonated Amino Acid-Induced One-Handed Helicity of Polynorbornene Having Monoaza-18-crown-6 Pendants

Abstract

Upon complexation with protonated amino acids, one-handed helical polynorbornenes appended with monoaza-18-crown-6 (7a) are obtained. The cooperativity is observed as revealed by the sergeant−soldier effect and the majority rule. When sterically hindered amino acids such as phenylalanine, isovaline or proline, esters of amino acids, and aminoalcohols are used, the Δε values in CD spectra are significantly reduced. The protonated ammonium ion may form complex with a crown ether moiety whereas the carboxylic acid may form hydrogen bonding with the adjacent crown ether pendant resulting in unidirectional orientation of the pendants leading to a helical scaffold. The corresponding dimer 10 with the same isotactic stereochemistry as that of polynorbornene 7a behaves similarly to exhibit bisignate CD curve upon treatment with protonated alanine. On the other hand, polynorbornene with monoaza-15-crown-5 (7b) does not exhibit any CD response under the same conditions.