Bacillus cereus Toxin Repertoire: Diversity of (Iso)cereulide(s).

The emetic Bacillus cereus toxin cereulide ( 1 ) poses a significant safety risk in the food industry, causing emesis and nausea after consumption of contaminated foods. Analogously to cereulide, the structures of various isocereulides, namely, isocereulides A-G, have been recently reported and could also be identified in B. cereus -contaminated food samples. The HPLC fractionation of B. cereus extracts allows us to isolate additional isocereulides. By applying MS n sequencing, post-hydrolytic dipeptide, amino acid and α-hydroxy acid analyses using UPLC-ESI-TOF-MS to purify the analytes, seven new isocereulides H-N ( 2 - 8 ) could be elucidated in their chemical structures. The structure elucidation was supported by one-dimensional and two-dimensional NMR spectra of the isocereulides H ( 2 ), K ( 5 ), L and N ( 6 + 8 ) and M ( 7 ). The toxicity of 2 - 8 was investigated in a HEp-2 cell assay to determine their respective 50% effective concentration (EC 50 ). Thus, 2 - 8 exhibited EC 50 values ranging from a 0.4- to 1.4-fold value compared to cereulide ( 1 ). Missing structure-activity correlations indicate the necessity to determine the toxic potential of all naturally present isocereulides as single compounds to be able to perform a thorough toxicity evaluation of B. cereus -contaminated foods in the future.