DEGRADATION OF THE FLUOROQUINOLONE ENROFLOXACIN BY THE BROWN-ROT FUNGUS GLOEOPHYLLUM-STRIATUM - IDENTIFICATION OF METABOLITES

The degradation of enrofloxacin, a fluoroquinolone antibacterial drug used in veterinary medicine, was investigated with the brown rot fungu s Gloeophyllum striatum. After 8 weeks, mycelia suspended in a defined liquid medium had produced 273, 18.5, and 6.7% (CO2)-C-14 from [C-14] enrofloxacin labeled either at position C-2, at position C-4, or in t he piperazinyl moiety, respectively. Enrofloxacin, applied at 10 ppm, was transformed into metabolites already after about 1-week The most s table intermediates present in 2-day old supernatants were analyzed by high-performance liquid chromatography combined with electrospray ion ization mass spectrometry. Eight of 11 proposed molecular structures c ould be confirmed by H-1 nuclear magnetic resonance spectroscopy or by cochromatography with reference compounds. We identified (i) 3-, 6-, and 8-hydroxylated congeners of enrofloxacin, which have no or only ve ry little residual antibacterial activity; (ii) 5,6-(or 6,8-), 5,8-, a nd 7,8-dihydroxylated congeners, which were prone to autoxidative tran sformation; (iii) an isatin-type compound as well as an anthranilic ac id derivative, directly demonstrating cleavage of the heterocyclic cor e of enrofloxacin; and (iv) 1-ethylpiperazine, the 7-amino congener, a nd desethglene-enrofloxacin, representing both elimination and degrada tion of the piperazinyl moiety. The pattern of metabolites implies fou r principle routes of degradation which might be simultaneously employ ed. Each route, initiated by either oxidative decarboxylation, defluor ination, hydroxylation at C-8, or oxidation of the piperazinyl moiety, may reflect an initial attack by hydroxyl radicals at a different sit e of the drug. During chemical degradation of [4-C-14]enrofloxacin wit h Fenton's reagent, five confirmatory metabolites, contained in groups i and iv, were identified. These findings provide new evidence in sup port of the hypothesis that brown rot fungi may be capable of producin g hydroxyl radicals, which could be utilized to degrade wood and certa in xenobiotics.