Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan.
J Org Chem. 2010 Jan 15;75(2):417-23. doi: 10.1021/jo902158v.
A series of monomeric strands consisting of m-terphenyl backbones with chiral rigid C-linked (3) and flexible N-linked (5) formamidines and achiral carboxylic acid (4) and flexible carboxymethyl (6) residues were synthesized, and their duplex formations through amidinium-carboxylate salt bridges were investigated by NMR, circular dichroism (CD), and UV-visible spectroscopies. The salt bridge-derived duplex formation was largely dependent on the structures of the formamidine and carboxylic acid strands, and the C-linked formamidine strand 3 formed a more stable duplex with the complementary carboxylic acid strands (4 and 6) than did the flexible N-linked formamidine strand 5. The single crystal X-ray analysis revealed that the duplex 5.4 has a skewed right-handed double helical structure. A complementary duplex dimer was also synthesized from the dimers of 5 and 4 joined by diacetylene linkers. Variable-temperature CD measurements indicated that the duplex possesses a dynamic double helical structure resulting from the flexible N-linked formamidine units.
一系列由 m-三联苯骨架组成的单体链,具有手性刚性 C 连接(3)和柔性 N 连接(5)的甲脒以及非手性羧酸(4)和柔性羧甲基(6)残基,其通过脒基-羧酸盐桥形成的双链体通过 NMR、圆二色性(CD)和紫外可见光谱进行了研究。盐桥衍生的双链体形成在很大程度上取决于甲脒和羧酸链的结构,并且 C 连接的甲脒链 3 与互补的羧酸链(4 和 6)形成更稳定的双链体,而柔性 N 连接的甲脒链 5 则形成更稳定的双链体。单晶 X 射线分析表明,双链体 5.4 具有扭曲的右手双螺旋结构。还通过二乙炔接头将 5 和 4 的二聚体连接合成了互补的双链体二聚体。变温 CD 测量表明,双链体具有动态双螺旋结构,这是由于柔性 N 连接的甲脒单元。