Beiträge zur Biosynthese von Strobilurin A und Oudemansin A sowie Gewinnung neuer halogenierter Strobilurine durch vorläufer-dirigierte Biosynthese

Abstract

The integral part of this thesis are studies of the biosynthesis of the antifungal strobilurin A as well as experiments to modify the metabolite by precurser directed biosynthesis.Earlier studies with strobilurin A using two different strains did not allow a conclusion about the starter-unit and the biosynthetic pathway. In this thesis Strobilurus tenacellus are used. Feeding experiments with [1-13C]acetate at two different times clearly indicated an incorporation. By feeding of acetate the incorporation rate from the second to the third day of cultivation was in excess compared with a feeding from the fifth to the sixth day. Any further experiments with labelled precursors were done at the earlier time. The results clearly showed the origin of all C-atoms in the side chain. The origin of the starter unit could be clarified by feeding [D8]phenylalanine, [3-13C]phenylalanine and [2,3-13C2]phenylalanine. The amino acid is degraded to benzoic acid. On the base of the proven incorporation pattern a complete mechanism of the biosynthetic pathway of Strobilurin A could be established. Furthermore a mechanism of the rearrangement to the methoxacrylate unit has been suggested and discussed. The formation of an acetate-pool is supposed following the strength of time-dependent feeding experiments with [1-13C]acetate. This seems to be a characteristic in the metabolism of basidiomycetes.2-, 3- and 4-fluorbenzoicacid, as well as cinnamic acid in form of their N-acetylcysteaminethioester have been made available as precurser by Prof. Dr. T.J. Simpson FRS (University of Bristol, School of Chemistry, Organic and Biological Chemistry). The feeding experiments lead to the analogous fluorstrobilurin A derivatives and also proved the degradation of phenylalanine to benzoic acid which acts as starter unit. Another variation of the starter unit arose after feeding nicotinic acid and led to 3-azastrobilurin A. The fluoroderivatives as well as the azoderivative were isolated and characterised for the first time. Tandem feeding experiments with 4-hydroxy-benzoic acid with the present of different halogen salts increased the amounts of strobilurin B and the new 4-dechloro-4-bromo-strobilurin B and resulted in the already known strobilurin H could be isolated. The results of the experiments are the base of a hypothetic mechanism for the halogenation.The thesis also deals with the comparison of the biosynthetic pathways leading to strobilurin A and oudemansin A. Experiments were done with Oudemansiella mucidia. Feeding of [1-13C]Acetat, [1,2-13C2]Acetat, [D8]phenylalanine, [3-13C]phenylalanine and [2,3-13C2]phenylalanine lead to the same incorporation pattern as had already been found in the case of strobilurin A. Based on these data a similar biosynthetic pathway was assumed.