Anion-Binding Catalysis

For a very recent example about the combination of photoredox activation and anion binding catalysis, see G. Bergonzini,... 

A variety of organocatalyzed cascade processes based on anion-binding catalysis (Scheme 2.75) were developed recently which employed highly active Af-acyliminimn ions or oxocarbenium ions (generated from thiourea-mediated halogen abstraction) as electrophiles the resnlting A-acyliminium (oxocarbenium) anion-thiourea complex perfectly controlled the enantioselectivity [106]. 

M. W. Hosseini, A. J. Blacker, and J.-M. Lehn, Multiple molecular recognition and catalysis, nucleotide binding and ATP hydrolysis by a receptor molecule bearing an anion binding site, an intercalator group, and a catalytic site, J. Chem. Soc., Chem. Commun. 596(1988). 

Scheme 6.53 Proposed mechanism for the 53-catalyzed asymmetric Pictet-Spengler-type cyclization of P-indolyl ethyl hydroxylactams Hydroxylactam (1) forms chlorolactam (2) followed by chiral N-acyliminium chloride-thiourea complex (3) and the observed product generated by intramolecular cyclization catalysis and enantioinduction result from chloride abstraction and anion binding.

Multiple recognition and catalysis in ATP hydrolysis with increased ATP/ADP selectivity has been achieved with a multifunctional anion receptor containing a macrocyclic polyamine as anion binding site, an acridine group as stacking site and a catalytic site for hydrolysis (structure 82) [4.27]. Phosphoryl transfer is accelerated by other types of hydrogen-bonding receptors [5.24a]. 

The most thermodynamically stable and kinetically inert complexes of the trivalent lanthanides are those of the ligand DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) (42, 43). Our search for lanthanide macrocyclic complexes that would remain intact for longer time periods led us to examine derivatives of DOTA. There are two potential difficulties with the use of DOTA complexes of the trivalent lanthanides for RNA cleavage. First, the overall negative charge on the complex is not conducive to anion binding for example, Gd(DOTA)-does not bind hydroxide well (44). Second, DOTA complexes of the middle lanthanides Eu(III) and Gd(III) have only one available coordination site for catalysis. The previous lanthanide complexes that we used, e.g., Eu(L1)3+, were good catalysts and had at least two available coordination sites. 

Raheem, I.T., Thiara, P.S., Peterson, E.A. and Jacobsen, E.N. (2007) Enantioselective Pictet-Spengler-type cyclizations of hydroxy lactams H-bond donor catalysis by anion binding. Journal of the American Chemical Society, 129, 13404-13405. 

SCHEME 2.27. Hydrogen-bond donor catalysis by anion binding catalyst abstraction of a leaving group. 

Raheem IT, Thiara PS, Petersrai EA, Jacobsen EN (2007) Enantioselective Pictet-Spengler-Type Cyclizatirais of Hydroxylactams H-Bond Donor Catalysis by Anion Binding. J Am Chem Soc 129 13404... 

Allylic amines also proved to be suitable substrates for the dual catalysis/anion-binding approach developed by Seidel et al. however, the selectivities were slightly lower than that obtained with either primary aryl alkyl amines or propargylic amines [128]. This decrease in selectivily was attributed to the higher nucleophilic-... 

The anion-binding thiourea catalysis was applied further in asymmetric polycyclization of hydroxylactam derivatives 296 (Scheme 2.81). It was found that larger aromatic groups on the pyrrolidine ring of thiomea catalyst produced better results in terms of reactivity and enantioselectivity. The 4-pyrenyl-substituted thiourea 289c was found to be an optimal catalyst to promote polycyclization reactions which involved stabilizing cation-ji interactions to indnce the enantioselectivity [112]. 

Luminescence Studies of Anion Binding in Catalysis and Sensing 8.4.1 Phosphate Ester Binding and Cleavage... 

An artificial metalloenzyme (26) was designed by Breslow et al. 24). It was the first example of a complete artificial enzyme, having a substrate binding cyclodextrin cavity and a Ni2+ ion-chelated nucleophilic group for catalysis. Metalloenzyme (26) behaves a real catalyst, exhibiting turnover, and enhances the rate of hydrolysis of p-nitrophenyl acetate more than 103 fold. The catalytic group of 26 is a -Ni2+ complex which itself is active toward the substrate 1, but not toward such a substrate having no metal ion affinity at a low catalyst concentration. It is appearent that the metal ion in 26 activates the oximate anion by chelation, but not the substrate directly as believed in carboxypeptidase. 

Catalysis by flavoenzymes has been reviewed and various analogues of FAD have been prepared e.g. P -adenosine-P -riboflavin triphosphate and flavin-nicotinamide dinucleotide ) which show little enzymic activity. The kinetic constants of the interaction between nicotinamide-4-methyl-5-acetylimidazole dinucleotide (39) and lactic dehydrogenase suggest the presence of an anionic group near the adenine residue at the coenzyme binding site of the enzyme. ... 

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