Synthesis of 5-amino-4-chloro-3(2H)-pyridazinone-(4,5-14C) by microbiological dephenylation of 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone-(4,5-14C) (Pyrazon) in soil.
Earlier experiments have shown (1,2) that pyrazon (5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone), the active ingredient of the herbicide PYRAMIN®, is dephenylated in soil to form the metabolite 5-amino-4-chloro-3(2H)-pyridazinone (metabolite B). More recent investigations into the decomposition of pyrazon in the soil have shown (4,5) that soils with extreme “degradation-capacity” can be obtained by repeated additions of active ingredient to the soil, while keeping both temperature and humidity at an optimum. Soils conditioned by this method in the laboratory were capable of completely metabolizing up to 5 000 ppm pyrazon within 10–14 days.
Obviously strains of micro-organisms are selected in the soil, which use the phenyl-ring of pyrazon as their main carbon source. Dephenylation proceeds with good yield and is therefore suitable for preparation of the metabolite. Since chemical synthesis of the radioactive metabolite is rather difficult and costly, the biochemical degradation of pyrazon-(4,5-14C) was used to obtain the labelled metabolite. Recovery from soil was 53,1 % of the theoretical amount. The metabolite obtained was both chemically and radiochemically pure.
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Drescher, N., Burger, T.F. Darstellung von 5-Amino-4-chlor-3(2H)-pyridazinon-(4,5-14C) durch mikrobielle Dephenylierung von 5-Amino-4-chlor-2-phenyl-3(2H)-pyridazinon-(4,5-14C) (Pyrazon) im Boden. Bull. Environ. Contam. Toxicol. 5, 79–84 (1970). https://doi.org/10.1007/BF01545131