Catechol Siderophores from a Mangrove-Derived Bacteria Serratia marcescens F2-2 and Their Cytotoxic Activity

<i>Serratia marcescens</i> is a common Gram-negative and facultative anaerobic bacillus that produces serratiochelins with several bioactivities. In this study, four catechol siderphores (<b>1</b>-<b>4</b>), including two new ones named serratiochelins E (<b>1</b>) and F (<b>2</b>), were obtained from the fermentation of a mangrove-derived bacterium, <i>S</i>. <i>marcescens</i> F2-2. The structures were elucidated with various spectroscopic methods such as NMR and HR-ESI-MS. Absolute and geometric configurations of the new compounds were established by employing quantum NMR calculations in conjunction with DP4+ probability analysis, ECD calculations, and the advanced Marfey's method. The bioactivity test showed that serratiochelin B (<b>3</b>) displayed weak but selective cytotoxicity against HepG2 cancer cells with an IC₅₀ of 50.6 μmol/L and could trigger apoptosis through both Bcl-2/Bax/caspase-3 and Fas/FasL/caspase-8 signaling pathways. These findings deepen the understanding of siderophores of <i>S. marcescens</i> and provide a lead for research on anti-liver cancer drugs.