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Colibactin is a pseudo--symmetric gut microbiome metabolite that induces DNA interstrand cross-links and plays a causal role in colorectal cancer. Since efforts to isolate colibactin have not been successful, we developed colibactin 742 () as a stable colibactin mimetic. However, colibactin 742 () exists as a mixture of ring and chain isomers, which complicates analysis of its activity. We report here the discovery of colibactin 686 () as a superior colibactin mimetic. Colibactin 686 () is more potent than colibactin 742 () and recapitulates the bacterial genotoxic phenotype. Colibactin 686 () possesses a -symmetric structure, which will expedite its synthesis, and is incapable of ring-chain isomerization, which will simplify analysis of its biological activity. We additionally establish that colibactins do not passively diffuse into cells, and are substrates for monocarboxylate transporter pumps. These latter findings have implications for trafficking of natural colibactin, which remains poorly understood.