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

Serratia marcescens is a common Gram-negative and facultative anaerobic bacillus that produces serratiochelins with several bioactivities. In this study, four catechol siderphores (1-4), including two new ones named serratiochelins E (1) and F (2), were obtained from the fermentation of a mangrove-derived bacterium, S. marcescens 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 (3) 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 S. marcescens and provide a lead for research on anti-liver cancer drugs.