Science https://doi.org/10.1126/science.aax2685 (2019)

Colibactin is a secondary metabolite produced by certain gut bacteria associated with colorectal cancer. Despite many studies characterizing colibactin precursors (precolibactins) and derivatives, their biosynthetic steps, and their DNA-alkylating activity, colibactin has eluded isolation and its structure has remained incompletely defined. Using a combination of mass spectrometry, isotope labeling, and biosynthetic logic, Xue and Kim et al. determined the structure of a colibactin–diadenine adduct that results from two DNA alkylation events. Building upon that adduct, the authors predicted the full structure of colibactin, identified the metabolite in cultures of Escherichia coli Nissle 1917, and confirmed the structural prediction by chemical synthesis. These data, together with the characterization of a new advanced intermediate (precolibactin 1489) and the accumulated data from previous studies, enabled the proposal of a complete biosynthetic pathway for colibactin incorporating all of the biosynthetic enzymes encoded in the gene cluster. This structure of mature colibactin both enables further studies of its genotoxic effects and illustrates the power of a multipronged approach to the structural elucidation of natural products that are recalcitrant to isolation.