Hermann Keith, Pratumyot Yaowalak, Polen Shane, Hardin Alex M, Dalkilic Erdin, Dastan Arif, Badjić Jovica D
Department of Chemistry and Biochemistry, The Ohio State University, 100 West 18th Avenue (USA).
Chemistry. 2015 Feb 23;21(9):3550-5. doi: 10.1002/chem.201406492. Epub 2015 Jan 21.
A preparative procedure for obtaining a pair of twisted molecular baskets, each comprising a chiral framework with either right ((P)-1syn) or left ((M)-1syn) sense of twist and six ester groups at the rim has been developed and optimized. The racemic (P/M)-1syn can be obtained in three synthetic steps from accessible starting materials. The resolution of (P/M)-1syn is accomplished by its transesterification with (1R,2S,5R)-(-)-menthol in the presence of a Ti(IV) catalyst to give diastereomeric 8(P) and 8(M). It was found that dendritic-like cavitands 8(P) and 8(M), in CD2Cl2, undergo self-inclusion ((1)H NMR spectroscopy) with a menthol moiety occupying the cavity of each host. Importantly, the degree of inclusion of the menthol group was ((1)H NMR spectroscopy) found to be greater in the case of 8(P) than 8(M). Accordingly, it is suggested that different folding characteristic of 8(P) and 8(M) ought to affect the physicochemical characteristics of the hosts to permit their effective separation by column chromatography. The absolute configuration of 8(P)/8(M), encompassing right- and left-handed "cups", was determined with the exciton chirality method and also verified in silico (DFT: B3LYP/TZVP). Finally, the twisted baskets are strongly fluorescent due to three naphthalene chromophores, having a high fluorescence quantum yield within the rigid framework of 8(P)/8(M).
已开发并优化了一种制备方法，用于获得一对扭曲的分子篮，每个分子篮都包含具有右旋（(P)-1syn）或左旋（(M)-1syn）扭曲方向的手性骨架以及六个位于边缘的酯基。外消旋体（P/M）-1syn可以从易得的起始原料通过三个合成步骤获得。（P/M）-1syn的拆分是通过在钛（IV）催化剂存在下与（1R,2S,5R）-（-）-薄荷醇进行酯交换反应，得到非对映异构体8(P)和8(M)来实现的。研究发现，树枝状空穴化合物8(P)和8(M)在CD2Cl2中会发生自包结（通过1H NMR光谱），薄荷醇部分占据每个主体的空穴。重要的是，通过1H NMR光谱发现，8(P)中薄荷醇基团的包结程度大于8(M)。因此，有人认为8(P)和8(M)不同的折叠特性应该会影响主体的物理化学特性，从而允许通过柱色谱法对它们进行有效分离。8(P)/8(M)的绝对构型，包括右手和左手“杯状”结构，通过激子手性方法确定，并通过理论计算（密度泛函理论：B3LYP/TZVP）进行了验证。最后，由于三个萘发色团，扭曲的分子篮具有很强的荧光性，在8(P)/8(M)的刚性骨架内具有很高的荧光量子产率。
