| Summary: | 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. === Science, Faculty of === Chemistry, Department of === Graduate
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