title: Convergent and Modular Synthesis of Candidate Precolibactins. Structural Revision of Precolibactin A.
abstract: The colibactins are hybrid polyketide-nonribosomal peptide natural products produced by certain strains of commensal and extraintestinal pathogenic Escherichia coli. The metabolites are encoded by the clb gene cluster as prodrugs termed precolibactins. clb(+) E. coli induce DNA double-strand breaks in mammalian cells in vitro and in vivo and are found in 55-67% of colorectal cancer patients, suggesting that mature colibactins could initiate tumorigenesis. However, elucidation of their structures has been an arduous task as the metabolites are obtained in vanishingly small quantities (μg/L) from bacterial cultures and are believed to be unstable. Herein we describe a flexible and convergent synthetic route to prepare advanced precolibactins and derivatives. The synthesis proceeds by late-stage union of two complex precursors (e.g., 28 + 17 → 29a, 90%) followed by a base-induced double dehydrative cascade reaction to form two rings of the targets (e.g., 29a → 30a, 79%). The sequence has provided quantities of advanced candidate precolibactins that exceed those obtained by fermentation, and is envisioned to be readily scaled. These studies have guided a structural revision of the predicted metabolite precolibactin A (from 5a or 5b to 7) and have confirmed the structures of the isolated metabolites precolibactins B (3) and C (6). Synthetic precolibactin C (6) was converted to N-myristoyl-d-asparagine and its corresponding colibactin by colibactin peptidase ClbP. The synthetic strategy outlined herein will facilitate mechanism of action and structure-function studies of these fascinating metabolites, and is envisioned to accommodate the synthesis of additional (pre)colibactins as they are isolated.
authors.affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520, United States.|Chemical Biology Institute, Yale University , West Haven, Connecticut 06516, United States.
authors.forename: Alan R
authors.initials: AR
authors.lastname: Healy
authors.affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520, United States.|Chemical Biology Institute, Yale University , West Haven, Connecticut 06516, United States.
authors.forename: Maria I
authors.initials: MI
authors.lastname: Vizcaino
authors.affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520, United States.|Chemical Biology Institute, Yale University , West Haven, Connecticut 06516, United States.|Department of Microbial Pathogenesis, Yale School of Medicine , New Haven, Connecticut 06536, United States.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Crawford
authors.affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520, United States.|Department of Pharmacology, Yale School of Medicine , New Haven, Connecticut 06520, United States.
authors.forename: Seth B
authors.initials: SB
authors.lastname: Herzon
mesh_terms: D060326:Chemistry Techniques, Synthetic; D003500:Cyclization; D004926:Escherichia coli / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D015394:Molecular Structure; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D061065:Polyketides / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D010455:Peptides; D061065:Polyketides; C569566:colibactin