Enzyme mimics based on cyclic porphyrin oligomers: strategy, design and exploratory synthesis

This paper is the first of a series' describing in detail our project to create enzyme mimics based on oligomeric porphyrins. The ultimate aim is to create systems which are capable of binding two or more substrates within a cavity, catalysing reaction between them and releasing the product(s). The long-term aim is not to mimic any particular natural enzyme. However, inspired by the example of nature, we want to understand the principles of how to design and create homogeneous catalytic systems. Although we are still a long way from achieving that goal, the key porphyrin trimer described in this paper effectively and stereoselectively accelerates an intermolecular Diels-Alder reaction 6 * 7 and catalyses acyl transfers,'.* proving that the basic concept is viable. Since completion of the work described in this series, the basic design has undergone further evolution in several directions.' In this paper we set the scene at the outset of this work in 1987, describe our overall strategy, discuss our molecular and synthetic design, give details of early syntheses of the butadiynelinked cyclic porphyrin oligomers which were our initial targets, l o and present spectroscopic evidence in support of the extraordinary structures created. These exploratory syntheses generated sufficient material for the ligand-binding studies which form the basis of the second paper in the series.' The resulting ligand-templated syntheses of oligomers ranging from dimers to an octamer are described in the following two papers,'.3 while the remaining papers in the series cover oligomers which are extended by platinumor octatetraynelinks.4,'