SELECTIVE SYNTHESES AND DERIVATISATION OF A 2 B- TYPE meso-TRIARYLCORROLES

1. SELECTIVE SYNTHESES AND DERIVATISATION OF A2B- TYPE meso-TRIARYLCORROLES • E. Dolusica, H. Radeckab, J. Radeckib and W. Dehaena • aDept. of Chemistry, University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium • bInstitute of Animal Reproduction and Food Research of Polish Academy of Sciences, Division of Food Science, Tuwima 10, 10-747 Olsztyn, Poland • e-mail : eduard.dolusic@chem.kuleuven.ac.be Introduction Corroles are porphyrin analogues, lacking one meso carbon. Until recently they were rather rare chemicals, but in the last few years a number of publications have appeared describing the synthesis of corroles and core-modified corroles.1-3 This has made these interesting compounds much more available than before, allowing the study of their coordination chemistry, applications of metallocorroles in catalysis and their photophysical behaviour. In this work a two-step synthesis of sterically encumbered triarylcorroles 2 by an acid catalysed [2+1] condensation of dipyrromethanes 1 and aromatic aldehydes followed by oxidation with p-chloranil is described. Preparation of bifunctional corrole-indole reagents, which should serve to monitor binding of indolic compounds to proteins in living plant cells, is in progress. Application of the corroles Samples of some of the corroles 2 were incorporated in membranes or self-assembled monolayers. The modified membranes show very significant response to small neutral phenol analytes. The response towards these analytes is much higher than for the porphyrin and calixpyrroles that were used previously in the framework of our collaboration,4 since the basicity of the corroles is much higher. Alternatively, conjugates of 2c with derivatives 4 of plant hormone (auxin) indole-3-acetic acid are currently being prepared (according to the scheme below) in order to give rise to novel probes 7 for indole-binding proteins in living cells. This work is being done in collaboration with Prof. V. Magnus, Zagreb, Croatia. Synthesis of the corroles The general procedure for the synthesis of the corroles was as outlined in the scheme above. The aldehyde was subjected to an acid catalysed reaction with an excess of 1 in CH2Cl2 to produce the intermediate tetrapyrromethane 1a which was not isolated. Instead, the entire reaction mixture was subjected to oxidation with p-chloranil to yield the corrole 2. Three methods were tried out within the scope of the procedure: method A generally follows the procedure described by Asokan et al.1 With lowering the ratio of dipyrromethane and aldehyde the yields of corrole decreased and some porphyrin (bearing two pentafluorophenyl moieties) could be isolated. Method B was essentially as described by Gryko and Jadach.2 We also carried out the reaction at 0ºC rather than at room temperature, which should slow down the formation of the by-product tris(2,6-dichlorophenyl) corrole, otherwise formed in a substantial amount. Better results were obtained by choosing method C, basically the same as method B except for catalysing the reaction with trichloro- (TCA) rather than trifluoroacetic acid, and this in a concentration as low as about 1/75 that of the aldehyde. The corroles, which in most cases were not prepared previously, and possible by-products were isolated by careful column- or plate chromatography in mixtures of CH2Cl2 and heptane and characterized by 1H and 13C NMR spectroscopy, electrospray mass spectrometry and UV spectroscopy. The details can be seen in the Table. References 1. C. V. Asokan, S. Smeets, W. Dehaen, Tetrahedron Lett. 2001, 42, 4483-4485. 2.D. T. Gryko, K. Jadach, J. Org. Chem. 2001, 66, 4267-4275. 3. D. T. Gryko, Eur. J. Org. Chem. 2002, 1735-1743. 4. T. Piotrowski, H. Radecka, J. Radecki, S. Depraetere, W. Dehaen, Mat. Sci. Eng. C 2001, 18, 223-228.