Ecotoxicological Evaluation of Simple Xanthone, Cinnamic Acid, and Chalcone Derivatives Using the Microtox Assay for Sustainable Synthetic Design of Biologically Active Molecules

The increasing emphasis on green chemistry and environmentally responsible organic synthesis highlights the need to evaluate not only the biological activity but also the ecological safety of bioactive molecules. Xanthone, cinnamic acid, and chalcone scaffolds are widely explored in pharmaceutical and cosmetic research, yet their environmental profiles remain insufficiently characterized. This study assessed the ecotoxicity of simple derivatives from these three structural classes using the Microtox assay with the bioluminescent bacteria Aliivibrio fischeri. Test compounds were synthesized or obtained commercially, dissolved in dimethyl sulfoxide (DMSO), and evaluated at two exposure times (5 and 15 min), with half maximal effective concentration (EC50) values calculated based on luminescence inhibition. The results revealed substantial differences between the investigated groups: chalcone derivatives exhibited uniformly high ecotoxicity, whereas cinnamic acid derivatives showed the most favorable environmental profile with low variability in EC50 values. Xanthone derivatives displayed the widest ecotoxicity range, with toxicity strongly dependent on substituent type and substitution position. Notably, chloro-substitution in cinnamic acid derivatives correlated with lower toxicity, while positional effects were critical in the xanthone series. A comparison with in silico predictions generated using the ADMETlab platform showed poor correlation with the experimental outcomes. The predictive model did not distinguish the differing ecotoxicological behavior of α,β-unsaturated systems in chalcones versus cinnamic acids and systematically flagged halogenation as a toxicity-driving feature, contrary to several of our in vitro observations. Together, these findings provide new insights into structure–ecotoxicity relationships and underscore the need to complement computational predictions with validated experimental assays when designing bioactive compounds with improved environmental safety.