Phytotoxic Activity of Umbelliferone Derivatives Produced by Microbial Transformation

The search for natural herbicide alternatives is increasingly relevant in the context of environmental concerns and herbicide-resistant weeds. In this study, umbelliferone, a 7-hydroxycoumarin widely found in plants, particularly in Rutaceae and Apiaceae, was subjected to microbial biotransformation using Cunninghamella elegans and Aspergillus brasiliensis under two different culture conditions. Five structurally distinct derivatives were produced during fermentation. The structures were elucidated by 1D and 2D NMR spectroscopy and confirmed by high-resolution mass spectrometry. All compounds, including the precursor, were evaluated for phytotoxic activity against Lactuca sativa (dicot) and Agrostis stolonifera (monocot). Compound 6 exhibited the strongest inhibition, completely preventing seed germination in both species. In silico prediction of physicochemical properties using SwissADME indicated that lipophilicity, hydrogen bonding potential, and polar surface area may contribute to the observed biological effects. These findings show the potential of microbial systems to diversify natural scaffolds and support their application in the development of novel plant-derived bioherbicides.