Department of Chemistry and Biochemistry, Graduate School of Humanities and Sciences , Ochanomizu University , 2-1-1 Otsuka , Bunkyo-ku, Tokyo 112-8610 , Japan.
Center for Analytical Instrumentation , Chiba University , 1-33 Yayoi , Inage, Chiba 263-8522 , Japan.
J Org Chem. 2018 Dec 7;83(23):14338-14349. doi: 10.1021/acs.joc.8b02045. Epub 2018 Nov 15.
Alternately N-alkylated aromatic amides such as 1-3 bearing various side chains were designed and synthesized as novel helical foldamers. The CD spectra of oligomers with chiral side chains showed a positive Cotton effect, which indicates that these oligomers take helical conformations in solution. The CD intensity gradually increased with increasing chain length, and pentamer 3d showed remarkably strong CD signals in chloroform. The absorption maxima of the UV spectra were increasingly red shifted with increasing chain length, in contrast to the case of poly( p- N-alkylbenzamide)s. Structure optimization of the oligomers based on the crystal structure of 1a as the monomer unit supported the formation of helical structure with a large cavity and also suggested intramolecular hydrogen bond formation between secondary amides. The results of calculation were consistent with the observed spectroscopic features.
交替 N-烷基化的芳香酰胺，如 1-3，带有各种侧链，被设计并合成作为新型的螺旋折叠体。具有手性侧链的低聚物的 CD 谱显示出正的科顿效应，这表明这些低聚物在溶液中采取螺旋构象。CD 强度随着链长的增加而逐渐增加，并且五聚体 3d 在氯仿中表现出显著强的 CD 信号。与聚（对 N-烷基苯甲酰胺）的情况相反，紫外光谱的吸收最大值随着链长的增加而逐渐红移。基于单体单元 1a 的晶体结构对低聚物的结构优化支持了具有大空腔的螺旋结构的形成，并且还表明在仲酰胺之间形成分子内氢键。计算结果与观察到的光谱特征一致。
