Mimics, enzyme crown ethers

Finally, chiral crown ethers have been utilized successfully both as enzyme mimics and as enzyme analogs. Important examples in the literature include... 

The preparation of phenazine crown ether derivatives was reported by Huszthy and coworkers in their investigation of the use of these heterocycles as enzyme mimics <99T1491,... 

Biological activity refers to a compound s ability either to alter or to mimic a living system or one of its components. A living system could be an entire animal, or even a cell in a Petri dish. Components of a living system would include organelles, proteins, or DNA. Crown ether compounds have been studied to determine their effects at these various levels of life. Crown ethers interact directly with such molecules as DNA and enzymes. Numerous crowns have also been tested for their toxic effects to various mammalian and bacterial cell lines, as well as animals including mice. 

This article sets out to highlight briefly some of the contributions that have been made by synthetic molecular receptors of the crown ether type to the development of enzyme mimics and analogues. However, before this aspect involving essentially binding at the transition state is reviewed, it is necessary to survey the ground-state phenomenon of complexation and decomplexation which characterises the first and last steps in an enzyme-catalysed reaction. 

While cyclodextrins are used as enzyme mimics in aqueous media, crown ethers can act as a key component of artificial enzymes in organic solutions (Fig. 2). Crown ether was discovered by Pedersen in 1967. which... 

The Allosteric Effect, p. 20 Artificial Enzymes, p. 76 Catalytic Antibodies, p. 193 Crown Ethers, p. 326 Cyclodextrins, p. 398 DNA Nanotechnology, p. 475 Enzyme Mimics, p. 546... 

Carcerands and Hemicarcerands, p. 189 Concave Reagents, p. i /1 Crown Ethers, p. 326 Cryptophanes, p. 340 Cyclodextrins, p. 398 Cyclodextrins, Applications, p. 405 Cyclophanes Definition and Scope, p. 414 Enzyme Mimics, p. 546 Macrocycle Synthesis, p. 830 Organometallic Anion Receptors, p. 1006 Soft and Smart Materials, p. 1302 X-Ray Crystallography, p. 1586... 

Biological Ligands, p. 88 Crown Ethers, p. 326 Cryptands, p. 334 Enzyme Mimics, p. 546 lonophores, p. 760 Micelles and Vesicles, p. 861... 

Classification and Nomenclature of Supramolecular Compounds, p. 261 Crown Ethers, p. 326 Cryptands, p. 334 Dendrimers, p. 432 Electrochemicul Sensors, p. 505 Enzyme Mimics, p. 546 Fluorescent Sensors, p. 572 Imaging and Targeting, p. 687 Ion-Selective Electrodes, p. 747 lonophores, p. 760 Kinetics of Complexation, p. 776 Lariat Ethers, p. 782... 

Classical Descriptions of Inclusion Compounds, p. 253 Clathrate Hydrates, p. 274 Concepts in Crystal Engineering, p. 319 Crown Ethers, p. 326 Cryptands, p. 334 DNA Nanotechnology, p. 475 Enzyme Mimics, p. 546 The Lock and Key Principle, p. 809 Molecular-level Machines, p. 931 Selectivity Thermodynamic and Kinetic, p. 1225 Self-Assembly Definition and Kinetic and Thermodynamic Considerations, p. 1248 Self-Assembly Terminology, p. 1263 Soft and Smart Materials, p. 1302 Spherands, p. 1344... 

Leznoff has published further on the solid-phase synthesis of insect sex attrac-tants. The advantages and uses of enzymes attached to solid supports have been reviewed. Aspects of triphase catalysis (organic layer-water-polymer) have been discussed by Regen, while advances in phase-transfer catalysis have been reviewed. A crown ether NAD(P)H mimic has been described,bringing synthetic chemists nearer to the objective of artificial enzyme systems. 

Acyl transfer processes are of immense strategic and synthetic importance in synthesis and biology. In Fignre 12, the ability of peptidases snch as chymotrypsin to cleave amide bonds using a nncleophilic serine-195 residne to generate an activated acyl-enzyme intermediate was described. Numerous supramolecular structures have been designed that mimic these natural enzymatic acyl transfer processes, such as Lehn s crown ether/ammonium ion complexation... 

There have been numerous synthetic supramolecular structures created to mimic the various aspects of the natural enzymes that catalyze acyl transfers. Here, we only show two with their respective binding geometries and electron pushing for the nucleophilic attack. The first shown below was developed by Lehn, and uses the well precedented binding between crown ethers and ammonium ions to form a complex between the catalyst and the substrate. The second example was developed by Bres-low, where cyclodextrin (the toroid see Chapter 4) is used to drive hydrophobic binding of the substrate to the catalyst. These two examples do indeed catalyze their respective acyl transfers, but with orders of magnitude lower... 

---