Combined Approach of Backbone Amide Linking and On-Resin N‑Methylation for the Synthesis of Bioactive and Metabolically Stable Peptides

Rhabdopeptides are a large class of nonribosomal peptides from the bacteria Xenorhabdus and Photorhabdus with low micromolar activity against different protozoa, which are the causative agents of several tropical diseases. The development of a facile and flexible synthesis combining backbone amide linking with on-resin peralkylation for the synthesis of permethylated rhabdopeptides is described. This strategy allows the fast generation of permethylated naturally occurring and artificial rhabdopeptides for a structure–activity study. Furthermore, in vitro experiments revealed their superior properties regarding their stability and passive membrane diffusion.