Turning Cucurbit[8]uril into a Supramolecular Nanoreactor for Asymmetric Catalysis

Abstract

Chiral macromolecules have been widely used as synthetic pockets to mimic natural enzymes and promote asymmetric reactions. An achiral host, cucurbit[8]uril (CB[8]), was used for an asymmetric Lewis acid catalyzed Diels–Alder reaction. We achieved a remarkable increase in enantioselectivity and a large rate acceleration in the presence of the nanoreactor by using an amino acid as the chiral source. Mechanistic and computational studies revealed that both the amino acid–Cu2+ complex and the dienophile substrate are included inside the macrocyclic host cavity, suggesting that contiguity and conformational constraints are fundamental to the catalytic process and rate enhancement. These results pave the way towards new studies on asymmetric reactions catalyzed in confined achiral cavities.

Cucurbit[7]uril as a Supramolecular Artificial Enzyme for Diels–Alder Reactions

“…[4][5][6][7][8][9][10] One class of macrocyclic host molecules,c ucurbit[n]urils (CB[n], where n = 5-8), has been utilized in the catalysis of oxidation, solvolysis,p hotochemical and metal-ion assisted reactions. [11][12][13][14][15][16][17][18][19][20] CB[n]s consist of n glycoluril units (where n is typically between 5a nd 8) that are bound via methylene bridges in aring-like arrangement (Figure 1a). [21] Thenumber of repeat units defines the portal size and cavity volume.T he dipolar nature of the carbonyl-fringed portals of CB[n]imparts ahigh cation binding affinity arising from an ion-dipole effect, whereas the inner cavity of CB[n]isremarkably hydrophobic.…”

Cooperative Activation of Cobalt–Salen Complexes for Epoxide Hydration Promoted on Flexible Porous Organic Frameworks

“…Consequently,c atalysts should possess both high activity and selectivity under mild reactionc onditions. [5] The porouss olid materials, for example, zeolites, [6] mesoporous silicas, [7] porouso rganic polymers, [8] and metal-organic frameworks (MOFs), [9] with encapsulated/immobilized/integrated active sites, tunable affinity for substrates and products, and the advantages of recycling and reuse have also been used as ap latform for artificial enzymes, though the examples are far lessi nc omparison with soft materials. [1] Enzymes are macromolecules that work in cooperative modes and have complex internal protein dynamic motions.…”

pH-responsive molecular assemblies of pyridylbutadiene derivative with cucurbit[7]uril

“…Such differential binding affinity of the dye with the host molecules have been utilized for several chemical and biological applications. 6,19,40,[43][44][45] Similar to the absorption, the emission of DABP also shows variations post interaction with CB7. In the presence of 1 mM CB7, at neutral pH and basic pH, the dye shows a hypsochromic shi (À25 nm) in emission with maxima at $690 nm (Fig.…”

“…7,12 Among all the known CBs, cucurbit [7]uril (CB7) and cucurbit [8]uril (CB8) were extensively used for these investigations because of their water solubility and suitability of their cavity size for encapsulating different guest molecules. 6,[13][14][15][16][17] Cucurbiturils have been utilized as a template for stereoselective photodimerization, 18 supramolecular catalysis, 19 inhibition and disintegration of amyloid brils for therapeutics, 20 radionuclide separation, 21 construction of supramolecular assemblies, 22,23 and to modulate photophysical properties 10,24 for several cationic pyridinium or viologen derivatives. 6,10,18,[24][25][26][27][28][29] Inspired from these earlier reports, we describe optical absorption and emission properties of a cationic pyridinium derivative [4-((1E,3E)-4-(4-(dimethylamino)phenyl)buta-1,3-dien-1-yl)-1-methylpyridin-1-ium (DABP)], in water in the absence and presence of CB7.…”