Parallel Pathways and Alternative Macrocyclizations in the Biosynthesis of Largimycins by Cytochrome P450 Minus Mutants of Streptomyces argillaceus

-minus mutants suggests that a hydrolytic dehalogenation step proceeds before the peptide-polyketide chain is off-loaded from the polyketide synthase LrgJ. Remarkably, some compounds generated by these mutants bear a C-3 side chain that is cyclized into a unique β-thiolactone ring, a structural feature not seen before in natural products. Furthermore, this work has revealed alternative ways of peptide-polyketide chain off-loading by macrocyclization, unveiling the unprecedented flexibility of the thioesterase domain of LrgJ for selecting different intramolecular nucleophiles.