Epimerization in peptide thioester condensation

Chemoenzymatic synthesis of macrocyclic peptides and polyketides via thioesterase-catalyzed macrocyclization

Chemoenzymatic strategies that combine synthetic and enzymatic transformations offer efficient approaches to yield target molecules, which have been increasingly employed in the synthesis of bioactive natural products. In the biosynthesis of macrocyclic nonribosomal peptides, polyketides, and their hybrids, thioesterase (TE) domains play a significant role in late-stage macrocyclization. These domains can accept mimics of native substrates in vitro and exhibit potential for use in total synthesis. This review summarizes the recent advances of TE domains in the chemoenzymatic synthesis for these natural products that aim to address the common issues in classical synthetic approaches and increase synthetic efficiencies, which have the potential to facilitate further pharmaceutical research.

Chemical Synthesis of a Potent Antimicrobial Peptide Murepavadin Using a Tandem Native Chemical Ligation/Desulfurization Reaction

Classical approaches for the backbone cyclization of polypeptides require conditions that may compromise the chirality of the C-terminal residue during the activation step of the cyclization reaction. Here, we describe an efficient epimerization-free approach for the Fmoc-based synthesis of murepavadin using intramolecular native chemical ligation in combination with a concomitant desulfurization reaction. Using this approach, bioactive murepavadin was produced in a good yield in two steps. The synthetic peptide antibiotic showed potent activity against different clinical isolates of P. aeruginosa. This approach can be easily adapted for the production of murepavadin analogues and other backbone-cyclized peptides.

Nonenzymatic Metabolic Reactions and Life's Origins

Prebiotic chemistry aims to explain how the biochemistry of life as we know it came to be. Most efforts in this area have focused on provisioning compounds of importance to life by multistep synthetic routes that do not resemble biochemistry. However, gaining insight into why core metabolism uses the molecules, reactions, pathways, and overall organization that it does requires us to consider molecules not only as synthetic end goals. Equally important are the dynamic processes that build them up and break them down. This perspective has led many researchers to the hypothesis that the first stage of the origin of life began with the onset of a primitive nonenzymatic version of metabolism, initially catalyzed by naturally occurring minerals and metal ions. This view of life's origins has come to be known as "metabolism first". Continuity with modern metabolism would require a primitive version of metabolism to build and break down ketoacids, sugars, amino acids, and ribonucleotides in much the same way as the pathways that do it today. This review discusses metabolic pathways of relevance to the origin of life in a manner accessible to chemists, and summarizes experiments suggesting several pathways might have their roots in prebiotic chemistry. Finally, key remaining milestones for the protometabolic hypothesis are highlighted.

Disulfide-Driven Cyclic Peptide Synthesis of Human Endothelin-2 with a Solid-Supported Npys-Cl

We report here the synthesis of human endothelin-2, a peptide of 21 amino acid residues with two disulfide bonds, based on the novel idea of a disulfide-driven cyclic peptide synthesis (DdCPS). This synthesis has two steps: (1) a one-pot solid-phase disulfide ligation of two different sulfur-containing peptide fragments using an Npys-Cl resin and (2) intramolecular cyclization of the disulfide peptide via amide bond formation using a thioester ligation. Human endothelin-2 was obtained in a total yield of 2.2% with two such DdCPS procedures and subsequent deprotection and HPLC purification. This strategy is the basis of a new solid-phase assisted practical synthesis of cyclic disulfide peptides.

Engineering of the Filamentous Fungus Penicillium chrysogenum as Cell Factory for Natural Products

Penicillium chrysogenum (renamed P. rubens) is the most studied member of a family of more than 350 Penicillium species that constitute the genus. Since the discovery of penicillin by Alexander Fleming, this filamentous fungus is used as a commercial β-lactam antibiotic producer. For several decades, P. chrysogenum was subjected to a classical strain improvement (CSI) program to increase penicillin titers. This resulted in a massive increase in the penicillin production capacity, paralleled by the silencing of several other biosynthetic gene clusters (BGCs), causing a reduction in the production of a broad range of BGC encoded natural products (NPs). Several approaches have been used to restore the ability of the penicillin production strains to synthetize the NPs lost during the CSI. Here, we summarize various re-activation mechanisms of BGCs, and how interference with regulation can be used as a strategy to activate or silence BGCs in filamentous fungi. To further emphasize the versatility of P. chrysogenum as a fungal production platform for NPs with potential commercial value, protein engineering of biosynthetic enzymes is discussed as a tool to develop de novo BGC pathways for new NPs.