Chiral macrocycles with eight (R)- and (S)-methylbenzylurea residues on the resorcinarene skeleton linked through a hexyl or dodecyl spacer having amide linkages have been prepared by the reactions of the corresponding octaamine derivative with (R)- and (S)-α-methylbenzylisocyanate, respectively. In chloroform, the urea-functionalized resorcinarenes with hexyl spacers form intramolecular hydrogen bonds by bundling the urea and amide residues in a cyclic fashion to give a self-folding cavitand. The urea and amide residues are cooperatively oriented in the same direction to result in asymmetric hydrogen-bonding belts. Unique circular dichroism (CD) bands are induced in the absorption wavelength ranges of the macrocyclic skeleton, caused by a chirality transmission from their chiral urea termini through hexyl spacers in the self-folded conformation. On the other hand, urea-functionalized resorcinarenes with a longer dodecyl spacer do not show such unique CD bands on the macrocycle, because of their weaker propensity for hydrogen bond formation. The characteristic CD bands of the urea-functionalized self-folding macrocycles disappeared upon complexation with anions such as chloride and bromide, reflecting breaking of the intramolecular hydrogen-bonding belts.
通过相应的八胺衍
生物分别与(R)-和(S)-α-甲基苄基
异氰酸酯的反应,制备出了在
间苯二酚骨架上有八个(R)-和(S)-甲基苄基
脲残基的手性大环,这些残基通过具有酰胺键的己基或
十二烷基间隔物连接。在
氯仿中,带有己基间隔的
脲官能化
间苯二酚通过将
脲和酰胺残基以环状方式捆绑在一起形成分子内氢键,从而得到一种自折叠空穴剂。
脲和酰胺残基在同一方向上相互配合,形成不对称的氢键带。在大环骨架的吸收波长范围内,会出现独特的圆二色性(CD)带,这是由于在自折叠构象中,手性
脲末端通过己基间隔产生了手性传递。另一方面,具有较长
十二烷基间隔的
脲官能化
间苯二酚由于氢键形成的倾向性较弱,在大环上不会显示出这种独特的 CD 带。
脲官能化自折叠大环与
氯化物和
溴化物等阴离子络合后,其特征性 CD 带消失,这反映了分子内氢键带的断裂。