β-Cyclodextrin (β-CD) dimers have been prepared using the bioorthogonal Staudinger ligation for the first time. In addition to a known linker, methyl 2-(diphenylphosphanyl)terephthalate, a doubly active linker was specifically developed that enabled connection of two β-CD units in a single step and in aqueous/organic media, under mild conditions and with good yields. A three-carbon spacer between the β-CD torus and the azido group was required for facile dimer formation. The products, as studied by NMR spectroscopy, were found to adopt closed conformations by intramolecular self-inclusion. On the other hand, association via intermolecular binding was also observed in aqueous solution, confirmed by DOSY NMR experiments. Despite self-inclusion, the β-CD cavities were capable of guest encapsulation, as shown by titration experiments: the binding constant with 1-adamantylamine was similar to that of natural β-CD. Theoretical calculations for isolated molecules (PM3 level of theory) and in the presence of solvent [water, PM3(COSMO)] as well as DFT calculations suggested that the compounds prefer to adopt conformations which bring the phenyl groups either inside the β-CD cavity (inclusion) or over its narrow side (vicinal). Thus, Staudinger ligation could be the method of choice for linking CDs exhibiting (i) ease of preparation in aqueous media, in short steps, under mild conditions and in good yields, (ii) satisfactory aqueous solubility and independent binding capacity of the cavities.
β-
环糊精(β-CD)二聚体首次利用
生物正交斯道辛格缩合法制备。除已知的连接剂甲基2-(
二苯基膦基)
对苯二甲酸酯外,还专门开发了一种具有双重活性的连接剂,能够在温和条件下,在
水/有机介质中一步连接两个β-CD单元,且产率良好。β-
CD环和
叠氮基团之间需要一个三碳间隔才能便于形成二聚体。通过核磁共振光谱研究,发现产品通过分子内自包含采用闭合构象。另一方面,在
水溶液中也观察到了分子间结合,通过
DOSY核磁共振实验证实。尽管存在自包含,β-CD中空腔仍能够包裹客体,通过滴定实验证明:与1-
金刚烷胺的结合常数与天然β-CD相似。对于孤立分子的理论计算(PM3理论
水平)和在溶剂存在下的计算(
水,PM3(COSMO))以及密度泛函理论计算表明,这些化合物更倾向于采用将苯基团置于β-CD中空腔内(包含)或位于其窄侧(邻近)的构象。因此,斯道辛格缩合可能是连接表现出易于在
水介质中制备、在短步骤中、在温和条件下和高产率下、以及具有令人满意的
水溶性和空腔独立结合能力的
环糊精的首选方法。