The novel title macrocycles, based
on methylene-bridged 1,5-naphthalene
units, have been obtained by template effect in a thermodynamically
controlled synthesis. In detail, the prism[5]arene
1
or
the prism[6]arene
3
was selectively removed from the
equilibrium mixture by using the complementary ammonium-templating
agent. When only the solvent 1,2-DCE was used, the 1,4-confused derivative
2
was obtained. The prism[5]arene here described shows a deep
π-electron-rich aromatic cavity that exhibits a great affinity
for the quaternary ammonium guests, originating from favorable cation···π
and
+
NC–H···π interactions.
This recognition motif is the basis of the templated synthesis of
the prism[
n
]arenes here reported.
A novel catalytic feature of a hexameric resorcinarene capsule is highlighted. The self-assembled cage was exploited to promote the Friedel-Crafts benzylation of several arenes and heteroarenes with benzyl chloride under mild conditions. Calculations showed that there are catalytically relevant hydrogen-bonding interactions between the bridging water molecules of the capsule and benzyl chloride, which is fundamental for the activation of the C-Cl bond. The capsule controls the reaction outcome. Inside the inner cavity of the capsule, N-methylpyrrole is preferentially benzylated in the unusual β-position while mesitylene reacts faster than 1,3-dimethoxybenzene despite the greater π-nucleophilicity of the latter compound.
In this paper, we discuss the remarkable CO2 absorption properties of a new solvent-free porous organic solid, 1,2-dimethoxyp-tert-butylcalix[4]dihydroquinone. Exposure of 1 to H2 gas at 20 atm did not result in
detectable absorption of this gas. High selectivity for CO2
over H2 is a requirement if these materials are to be used
for CO2 separations from synthesis gas mixtures exiting, for
example, a water-gas shift reactor
Cyclosporin A (CsA), a potent immunosuppressant, is known to bind with high specificity to cyclophilin (CyP), a 17.7 kDa protein with peptidyl-prolyl isomerase activity. In order to investigate the three-dimensional structure of the CsA/CyP complex, we have applied a variety of multidimensional NMR methods in the study of uniformly 13C-labeled CsA bound to cyclophilin. The 1H and 13C NMR signals of cyclosporin A in the bound state have been assigned, and from a quantitative interpretation of the 3D NOE data, the bound conformation of CsA has been determined. Three-dimensional structures of CsA calculated from the NOE data by using a distance geometry/simulated appealing protocol were found to be very different from previously determined crystalline and solution conformations of uncomplexed CsA. In addition, from CsA/CyP NOEs, the portions of CsA that interact with cyclophilin were identified. For the most part, those CsA residues with NOEs to cyclophilin were the same residues important for cyclophilin binding and immunosuppressive activity as determined from structure/activity relationships. The structural information derived in this study together with the known structure/activity relationships for CsA analogues may prove useful in the design of improved immunosuppressants. Moreover, the approach that is described for obtaining the structural information is widely applicable to the study of small molecule/large molecule interactions.
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