Title
Conformational Properties of Aromatic Oligoamides Bearing Pyrrole Rings
Author
Yukiko Tojo, Ko Urushibara, Sawori Yamamoto, Hirotoshi Mori, Hyuma Masu, Mayumi Kudo, Tomoya Hirano, Isao Azumaya, Hiroyuki Kagechika, Aya Tanatani
Year
2018
Journal
The Journal of Organic Chemistry
Abstract
N-Alkylbenzanilides generally exist in cis conformation both in the crystalline state and in various solvents, and this cis conformational preference can be utilized to construct dynamic helical oligoamides. Here, we synthesized the pyrrole-containing amides 2–5 and their oligomers 6–8 and examined their conformations in the crystalline state and in solution. All the N-methylated amides showed cis conformational preference in solution, but the ratio of the cis isomer was decreased when the amide bond was attached at the 4-position of the pyrrole ring, probably because the destabilization of the trans conformer due to electronic repulsion between the pyrrole π electrons and the amide carbonyl lone-pair electrons is reduced due to the small torsion angle between the 5-membered N-pyrrole and the amide bond. In the crystalline state, N-methylated amides showed cis structure, except for compound 5, and cis conformational preference was observed for the pyrrole amides. The CD spectra of oligoamides 15–18 bearing chiral N-substituents were consistent with the presence of dynamic and well-defined chiral foldamers, which were structurally distinct from N-alkylated poly(p-benzamide)s 1.
Full Article
Instrument
J-820
Keywords
Circular dichroism, Stereochemistry, Chemical stability, Thermal stability, Organic chemistry, Biochemistry