Metabolites from fungal laccase-catalysed transformation of sulfonamides

Soil metabolism of sulfonamides is largely unknown. Hence the sulfonamides sulfanilamide (SAA), sulfadimethoxine (SDT) and sulfapyridine (SPY) were reacted in model experiments with a fungal laccase from Trametes versicolor. Enzymatic transformation after a reaction time of 15 d ranged from 10.0% for SAA up to 95.6% for SPY and the difference was attributed to the different molecular substituents. Metabolites were first tentatively assigned after LC–ESI+–MS full-scan analysis. Secondly, the proposed metabolites were further confirmed employing either multiple reaction monitoring in comparison with standard substances or precursor ion scan LC–ESI+–MS/MS experiments striving for the precursor and two to three product ions. Aniline was confirmed as a breakdown product of SPY and further metabolites of SPY and of SDT were identified as rearranged SO2 extrusion products. Thirdly, some of the metabolites matched those that were previously reported for sulfonamide photodegradation and degradation in soil. It was concluded that enzymatic metabolism as investigated here also occurs in soil.