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Development of new carceplexes and hemicarceplexes and the dynamic combinatorial library study Sun, Jianyu

Abstract

New disulfide linked [4]carceplex 54»guests was synthesized. This kind of carceplex has diastereotopic protons that can be used in the study of "twistomers" of the carceplex. The twisting process was studied by variable temperature NMR spectroscopy. The activation energy barrier AG* of the twisting on 54 depends on the size of guest molecules. The smaller the guest molecule, the higher the AG* is. We proposed an explanation for the observation. The location of guests inside the host molecule was also studied. The reversibility of disulfide bond formation in this series of compounds and the self-assembly during the formation of carceplexes suggest 54 and the previously synthesized 32 are excellent candidates for the study of the first dynamic combinatorial libraries of carceplexes. Using the disulfide linked [4]carceplexes 54 and disulfide linked [5]carceplexes 32, we worked out reversible conditions to synthesize the corresponding carceplexes from dynamic combinatorial libraries. The yield of disulfide linked [5]carceplexes is improved significantly from 14% (kinetic condition) to 50% (thermodynamic condition). The result on disulfide linked [4]carceplexes is not as good as on disulfide linked [5]carceplexes. We believe the reason is that we haven't found a good template for the disulfide [4]carceplex. Guest exchange was also observed in the library, which confirmed that this library is dynamic. The preparation of [5]cavitand benzylthiol 31 was modified. Using the modified reaction condition, 31 can be synthesized in 40% yield from [5]cavitand, which is much higher than the yield with old reaction condions (10%). This improvement made 32 a more useful template in the study of DCLs. During the synthesis of disulfide linked [4]carceplexes, we synthesized a hemicarcerand, 58, with new trithiacarbonate linkers in very high yield (80%). An X-ray crystal structure was obtained. Based on template studies, we propose the template for the self-assembly of this hemicarcerand can be an inorganic salt, an unprecedented template for such a system.

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