Bioactive Peptide Natural Products as Lead Structures for Medicinal Use

The need for new drugs for the treatment of various diseases is enormous. From the previous century until the present, numerous peptide and peptide-derived natural products have been isolated from bacteria and fungi. Hence, microorganisms play a pivotal role as sources for novel drugs with an emphasis on anti-infective agents. Various disciplines from biology, chemistry, and medicine are involved in early stages of the search for peptide natural products including taxonomy, microbiology, bioanalytics, bioinformatics, and medicinal chemistry. Under biochemical aspects, small peptide drugs are basically either ribosomally synthesized and post-translationally modified (RiPPs) or synthesized by multimodular nonribosomal peptide synthetases (NRPSs). Within the context of current developments on bioactive peptide natural products, this Account predominantly highlights recent discoveries, approaches, and research from our laboratory on RiPPs and NRPSs from bacteria and fungi. In our search for peptides showing bioactivities of interest, different approaches were applied: classical screening, in silico prediction, in vitro reconstitution, site-directed mutagenesis, chemoenzymatics, heterologous expression, and total synthesis including structure-activity relationship (SAR) studies in the research on the labyrinthopeptins, albicidin, and the cyclodepsipeptides (CDPs). The ribosomally synthesized labyrinthopeptins, class III lanthipeptides, which have been discovered in a classical screening campaign, display highly attractive antiallodynic (against neuropathic pain caused by dysfunction of the nervous system) and antiviral activities. Therefore, the biosynthetic assembly was investigated by extensive enzymatic studies of the modifying enzymes, and site-directed mutagenesis was performed for the generation of analogs. By genome mining, other class III lanthipeptides have been uncovered, while synthetic access proved to be an unmet challenge for the labyrinthopeptins. In contrast, for the gyrase inhibitor albicidin, the establishment of a chemical synthesis followed by medicinal chemistry studies was the only viable option to gain access to derivatives. Albicidin, which has been discovered investigating plant host-pathogen interactions, has a strong activity against Gram-negative bacteria, for example, Escherichia coli and Pseudomonas aeruginosa, and a future synthetic derivative may become a lead structure for development of an anti-Gram-negative drug. The compound class of the cyclodepsipeptides contributes already two marketed drugs, enniatin (fusafungine) and emodepside. Cyclodepsipeptides show general antibacterial and antifungal effects, whereas specific insecticidal and anthelmintic activities provide lead structures for drug development. Hence, exploiting the chances of reprogramming NRPSs, the generation of chimeric or otherwise designed synthetases could render a new untapped structural space and thus novel bioactivities. While current developments in the fields of genomics, bioinformatics, and molecular biology facilitate the search for new natural products and the design of new peptide structures, the next decade will show which compounds have been carried on further applications and whether current developments have led to an increase in drug candidates.