Chemoenzymatic synthesis of 7-chloro-4-Dimethylallyl-L-Tryptophan, a fragment of krisynomycin

Abstract

The krisynomycins are macrocyclic depsipeptide natural products from Streptomyces that act as imipenem potentiators against methicillin-resistant Staphylococcus aureus (MRSA). The flagship molecule of this family, krisynomycin, features a unique 7-chloro-4-dimethylallyl-l-tryptophan (7-Cl-4-Pren-Trp) fragment that is both essential for biological activity and unprecedented among bacterial natural products. In silico analysis of the putative biosynthetic gene cluster revealed an aromatic prenyltransferase and a tryptophan halogenase, though the precise reaction order en route to 7-Cl-4-Pren-Trp remained ambiguous. We report herein a brief chemoenzymatic synthesis of 7-Cl-4-Pren-Trp through a prenylation-chlorination sequence, which contains the first ever C4 prenylation of tryptophan by a bacterial enzyme. Furthermore, our efforts provide tentative evidence that the same reaction sequence is operative in the biosynthesis of krisynomycin.