Metabolite proving fungal cleavage of the aromatic core part of a fluoroquinolone antibiotic

Pradofloxacin (PRA), a new fluoroquinolone (FQ) drug, is used to treat bacterial infections in cats and dogs (Litster et al. 2007);(Mueller and Stephan 2007). It shares the core structure of common cyclopropyl-type FQs (Domagala and Hagen 2003) but carries a cyano group at position C-8 and a bi-cyclic amine at C-7, S,S-pyrrolidinopiperidine ([1S,6S]-2,8-diazabicyclo[4.3.0]non-8-yl); the latter is also contained in moxifloxacin (Petersen 2006). Concerning in vitro antibacterial activity, particularly low mutant prevention concentrations of PRA suggest a high potential for preventing the emergence of resistance under therapy (Wetzstein 2005). Both substituents in combination are essential for its improved efficacy (Wetzstein and Hallenbach 2011). Furthermore, the CN group facilitates hydrolytic elimination of the amine moiety (i.e., drug inactivation) under the slightly alkaline conditions present in decaying animal waste (Wetzstein et al. 2009). Hence, PRA should be more readily biodegradable and thus ecologically favorable than conventional FQs.Fungal degradation of FQs such as ciprofloxacin (Wetzstein et al. 1999), enrofloxacin (Karl et al. 2006) and moxifloxacin (Petersen 2006) under defined in vitro conditions has been described in detail. However, all findings yet reported concerned decomposition of the amine substituent located at C-7 and the pyridone part of the FQ core. Eighty-seven metabolites of enrofloxacin produced by Gloeophyllum striatum DSM 9592, a basidiomycetous fungus causing brown rot decay of wood by employing a Fenton-type reaction mechanism (Jensen et al. 2001); (Qui and Jellison 2004), could be resolved: The chemical structures of 18 metabolites were fully elucidated, while 69 metabolites needed to be postulated based on their molecular formula, retention time and the most likely chemical context (Karl et al. 2006). Forty-eight additional metabolites were generated by seven taxonomically diverse Basidiomycetes indigenous to agricultural sites,