Template catalysis

J. Am. Chem. Soc., 126, 16280-16281 Zelder, F.H. and Rebek, J. Jr. (2006) Cavitand templated catalysis of acetylcholine. Chem. Commun., 753-754 Purse, B.W. and Rebek, J. Jr. (2005) Supramolecular structure and dynamics special feature Functional cavitands Chemical reactivity in structured environments. Proc. Nail. Acad. Sci. U.S.A., 102, 10777-10782. 

Radical A-exo cyclizations can also be catalyzed without recourse to the Thorpe-Ingold effect by applying the concept of template catalysis (Fig. 24) [157]. Here, 20 mol% of a cationic titanocene(IV) precatalyst 82 is applied, which contains a coordinating neutral tether. After reductive opening of epoxide 81, a cationic titanocene(III) complexed radical 83 is formed, in which both the epoxide and the xfi-un saturated carboxamide radical acceptor are coordinated. This provides the template to accelerate the slow A-exo radical cyclization step considerably. Cyclobutanes 84 were isolated in 46-84% yield with mostly good / / [Pg.145]

Fig. 24 Template-catalysis in radical 4-exo cyclizations (only major trans-diastereomers shown)...

Neumann R, Shaik S, de Visser SP, Kaneti J (2003) Fluorinated alcohols enable olefin epoxidationby H2O2 template catalysis. J Org Chem 68 2903-2912... 

But what is it about this system that makes us call it self-replicating How could we show that the system progresses through directed template catalysis rather than through simple chemical autocatalysis After all, (6) bristles with functional groups. The imide, amide, ribose and purine functionalities must all be considered as possible explanations for the autocatalysis observed. For example, imidazole is a well-known catalyst for acylation reactions, and the purine contains such a subunit. Could not this functionality be the cause The potentially catalytic functions of the product molecule had to be individually tested in the structural context of (6) and under the conditions where (6) acts as an autocatalyst. 

Even in the light of these experiments, another laboratory contended that the system did not replicate through directed template catalysis [32], instead asserting a mechanism of simple amide catalysis by the product (6). Control experiments with molecules (17), (19) and (22) - all amides - had already excluded this pathway, and controls with (18) and (20) had further excluded a more subtle pathway of internal amide catalysis (Figure 16). Nevertheless, additional evidence against amide catalysis by product (6) was desired, and thus experiments were conducted that involved coupling (4) with molecule (26)... 

The very special properties of DNA, one of the icons of modem science, make it one of the most versatile molecules in chemistry. In nature, it serves as the carrier of genetic information and as such is one of the cornerstones of life [1]. In vitro, a very diverse set of applications have been explored, ranging from programmable building blocks in bionanotechnology [2] to scaffolds for catalysis. In this review, we will focus on this last aspect, with a particular emphasis on metal catalysis. Three approaches will be discussed DNAzymes, DNA-templated catalysis, and DNA-based asymmetric catalysis (Fig. 1). Artificial DNA-metal base pairing [3] will not be covered, as no catalysis using these systems has been reported to date. 

Fig. 8 Schematic representation of the concepts of DNA-directed catalysis (a) and DNA-templated catalysis (b)...

This chapter has presented an overview of applications of DNA in metal ion catalysis. Three general approaches were outlined metal-dependent DNAzymes, DNA-directed and templated catalysis, and DNA-based asymmetric catalysis. 

Degens RT., Matheja J. and Jackson T.A. (1970) Template catalysis asymmetric polymerization of amino acids on clay minerals, Nat. Ill, 492 -493. 

F. H. Zelder, J. Rebek Jr., Cavitand templated catalysis of acetylcholine, Chem Comm., 2006, 753-754. 

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