Templated Synthesis of Enzyme Mimics How Far Can We Go

SALLY ANDERSON AND JEREMY K. M. SANDERS Cambridge Centre for Molecular Recognition University Chemical Laboratory, Lensfield Road Cambridge CB2 lEW, United Kingdom 

Watson and Crick discovered tlie DNA double helix in 1953 and realised immediately that its replication involved a templated synthesis.[1] Their work inspired Todd[2] to issue this challenge in 1956  

A template intervenes in tlie macroscopic geometry of the reaction rather than in the chemistry it provides instructions for tlie formation of a single product from a substrate or substrates which otherwise have the potential to assemble and react in a variety of ways. Changing the template should result in a different substrate assembly and consequently a different product. In general, after tlie template has directed tlie formation 

Our interest in building enzyme mimics based on porphyrins led us to synthesise cyclic porphyrin oligomers using Glaser coupling.[9] This reaction oxidatively combines two terminal acetylenes to give a butadiyne link  

The first step in this templated reaction must be the combination of two porphyrin units to yield linear dimer 5 (Fig 1). Tlien either an intramolecular cyclisation occurs or reaction witli a further monomer poiphyrin yields linear porphyrin trimer. The latter process is rendered less important by tlie Bipy template which induces the reactive ends of the linear dimer intennediate to come into close proximity and so increases the rate of intramolecular cyclisation. This reaction therefore proceeds in the same way as classical metal-cation templated macrocylisations. The yield of cyclic dimer was increased by a factor of tliree in the presence of Bipy. 

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