ABSTRACT We report the synthesis of the conformationally mobile S-shaped glycoluril pentamer building block 3a and two new acyclic CB[n]-type receptors P1 and P2. P1 (9 mM) and P2 (11 mM) have moderate aqueous solubility but their host•guest complexes are poorly soluble. Host P1 does not undergo intermolecular self-association whereas P2 does (Ks = 189 ± 27 M−1). 1 H NMR titrations show that P1 and P2 are poor hosts towards hydrophobic (di)cations 6–11 (P1: Ka = 375–1400 M−1; P2: Ka = 1950–19,800 M−1) compared to Tet1 and Tet2 (Tet1: Ka = 3.09 x 106 to 4.69 × 108 M−1; Tet2: Ka = 4.59 x 108 to 1.30 × 1010 M−1). Molecular modelling shows that P1 and P2 exist as a mixture of three different conformers due to the two S-shaped methylene bridged glycoluril dimer subunits that each possess two different conformations. The lowest energy conformers of P1 and P2 do not feature a well-defined central cavity. In the presence of guests, P2 adapts its conformation to form 1:1 P2•guest complexes; the binding free energy pays the energetic price of conformer selection. This energetically unfavourable conformer selection results in significantly decreased Ka values of P1 and P2 compared to Tet1 and Tet2. GRAPHICAL ABSTRACT

中文翻译：

---

来自 S 形亚甲基桥联甘脲五聚体的构象移动无环葫芦 [n] 脲型受体

摘要 我们报告了构象移动的 S 形甘脲五聚体结构单元 3a 和两个新的无环 CB[n] 型受体 P1 和 P2 的合成。P1 (9 mM) 和 P2 (11 mM) 具有中等的水溶性，但它们的主客体复合物溶解性差。宿主 P1 不进行分子间自缔合，而 P2 进行（Ks = 189 ± 27 M-1）。1 H NMR 滴定表明，与 Tet1 和 Tet2 ( Tet1：Ka = 3.09 x 106 至 4.69 × 108 M-1；Tet2：Ka = 4.59 x 108 至 1.30 × 1010 M-1）。分子模型显示 P1 和 P2 以三种不同构象异构体的混合物形式存在，这是由于两个 S 形亚甲基桥连甘脲二聚体亚基各自具有两种不同的构象。P1 和 P2 的最低能量构象异构体没有明确定义的中心腔。在有客人存在的情况下，P2 会调整其构象，形成 1:1 P2•guest 复合体；结合自由能付出了构象异构体选择的能量代价。与 Tet1 和 Tet2 相比，这种能量上不利的构象异构体选择导致 P1 和 P2 的 Ka 值显着降低。图形概要