Highly Stable,Amide‐Bridged Autoinducing Peptide Analogues that Strongly Inhibit the AgrC Quorum Sensing Receptor in Staphylococcus aureus

Blocking quorum sensing (QS) pathways has attracted considerable interest as an approach to suppress virulence in bacterial pathogens. Toward this goal, we recently developed analogues of a native autoinducing peptide (AIP‐III) signal that can inhibit AgrC‐type QS receptors and attenuate virulence phenotypes in Staphylococcus aureus. Application of these compounds is limited, however, as they contain hydrolytically unstable thioester linkages and have only low aqueous solubilities. Herein, we report amide‐linked AIP analogues with greatly enhanced hydrolytic stabilities and solubilities relative to our prior analogues, whilst maintaining strong potencies as AgrC receptor inhibitors in S. aureus. These compounds represent powerful tools for the study of QS.     

Amino Acid‐Specific,Ribonucleotide‐Promoted Peptide Formation in the Absence of Enzymes

Nucleic acids and polypeptides are at the heart of life. It is interesting to ask whether the monomers of these biopolymers possess intrinsic reactivity that favors oligomerization in the absence of enzymes. We have recently observed that covalently linked peptido RNA chains form when mixtures of monomers react in salt‐rich condensation buffer. Here, we report the results of a screen of the 20 proteinogenic amino acids and four ribonucleotides. None of the amino acids prevent phosphodiester formation, so all of them are compatible with genetic encoding through RNA chain growth. A reactivity landscape was found, in which peptide formation strongly depends on the structure of the amino acid, but less on the nucleobase. For example, proline gives ribonucleotide‐bound peptides most readily, tyrosine favors pyrophosphate and phosphodiester formation, and histidine gives phosphorimidazolides as dominant products. When proline and aspartic acid were allowed to compete for incorporation, only proline was found at the N‐terminus of peptido chains. The reactivity described here links two fundamental classes of biomolecules through reactions that occur without enzymes, but with amino acid specificity.     

AJIPHASE®: A Highly Efficient Synthetic Method for One‐Pot Peptide Elongation in the Solution Phase by an Fmoc Strategy

We previously reported an efficient peptide synthesis method, AJIPHASE®, that comprises repeated reactions and isolations by precipitation. This method utilizes an anchor molecule with long‐chain alkyl groups as a protecting group for the C‐terminus. To further improve this method, we developed a one‐pot synthesis of a peptide sequence wherein the synthetic intermediates were isolated by solvent extraction instead of precipitation. A branched‐chain anchor molecule was used in the new process, significantly enhancing the solubility of long peptides and the operational efficiency compared with the previous method, which employed precipitation for isolation and a straight‐chain aliphatic group. Another prerequisite for this solvent‐extraction‐based strategy was the use of thiomalic acid and DBU for Fmoc deprotection, which facilitates the removal of byproducts, such as the fulvene adduct.     

The Kalimantacin Polyketide Antibiotics Inhibit Fatty Acid Biosynthesis in Staphylococcus aureus by Targeting the Enoyl‐Acyl Carrier Protein Binding Site of FabI

The enoyl‐acyl carrier protein reductase enzyme FabI is essential for fatty acid biosynthesis in Staphylococcus aureus and represents a promising target for the development of novel, urgently needed anti‐staphylococcal agents. Here, we elucidate the mode of action of the kalimantacin antibiotics, a novel class of FabI inhibitors with clinically‐relevant activity against multidrug‐resistant S. aureus. By combining X‐ray crystallography with molecular dynamics simulations, in vitro kinetic studies and chemical derivatization experiments, we characterize the interaction between the antibiotics and their target, and we demonstrate that the kalimantacins bind in a unique conformation that differs significantly from the binding mode of other known FabI inhibitors. We also investigate mechanisms of acquired resistance in S. aureus and identify key residues in FabI that stabilize the binding of the antibiotics. Our findings provide intriguing insights into the mode of action of a novel class of FabI inhibitors that will inspire future anti‐staphylococcal drug development.