Selective Modification of Ribosomally Synthesized and Post-Translationally Modified Peptides (RiPPs) through Diels-Alder Cycloadditions on Dehydroalanine Residues.

Ruben Oudshoorn,Reinder H De Vries,Gerard Roelfes,Oscar P Kuipers,Jakob H Viel

doi:10.1002/chem.201902907

Abstract

We report the late‐stage chemical modification of ribosomally synthesized and post‐translationally modified peptides (RIPPs) by Diels–Alder cycloadditions to naturally occurring dehydroalanines. The tail region of the thiopeptide thiostrepton could be modified selectively and efficiently under microwave heating and transition‐metal‐free conditions. The Diels–Alder adducts were isolated and the different site‐ and endo/exo isomers were identified by 1D/2D 1H NMR. Via efficient modification of the thiopeptide nosiheptide and the lanthipeptide nisin Z the generality of the method was established. Minimum inhibitory concentration (MIC) assays of the purified thiostrepton Diels–Alder products against thiostrepton‐susceptible strains displayed high activities comparable to that of native thiostrepton. These Diels–Alder products were also subjected successfully to inverse‐electron‐demand Diels–Alder reactions with a variety of functionalized tetrazines, demonstrating the utility of this method for labeling of RiPPs.

Highlights

We report the late-stage chemical modification of ribosomally synthesized and post-translationally modified peptides (RIPPs) by Diels–Alder cycloadditions to naturally occurring dehydroalanines
Progress has been made towards latestage chemical modification of antimicrobial peptides isolated from producing strains, achieving selective derivatization of these structurally diverse and complex natural products often poses a major synthetic challenge.[9]
Many thiopeptides and lanthipeptides contain one or more uniquely reactive dehydroamino acids such as dehydroalanine (Dha) and dehydrobutyrine (Dhb), which are the result of posttranslational enzymatic dehydration of Ser and Thr residues, respectively.[10]

Summary

Introduction

We report the late-stage chemical modification of ribosomally synthesized and post-translationally modified peptides (RIPPs) by Diels–Alder cycloadditions to naturally occurring dehydroalanines. The unactivated, strained alkene in the formed norbornene product could be employed in Inverse Electron Demand Diels–Alder (IEDDA, “click”) reactions with tetrazines (Scheme 1), a popular labeling tool in chemical biology.[31]

Results

Conclusion