Sequence-specific peptidomimetics are molecules that mimic the structure and function of peptides and proteins. With new backbones and molecular frameworks, peptidomimetics are of considerable interest in addressing challenges encountered in chemical biology and biomedical sciences. Based on the γ-PNA backbone, a new class of peptidomimetics - “γ-AApeptides” were recently developed. Both linear and cyclic γ-AApeptides can be synthesized with high efficiency. Compared with α-peptides, γ-AApeptides are resistant to enzymatic degradation, and amendable to diversification with a variety of chemical groups. Moreover, they could mimic primary and secondary structure, as well as the function of peptides, and show promise in biological applications, such as the development of new agents combating bacteria, cancer, and Alzheimer's disease. A few research outcomes of γ-AApeptides are highlighted in this Concept article, and a future perspective is also proposed.

Foldamers offer an attractive opportunity for the design of novel molecules that mimic the structures and functions of proteins and enzymes including biocatalysis and biomolecular recognition. Herein we report a new class of nonnatural helical sulfono-γ-AApeptide foldamers of varying lengths. The crystal structure of the sulfono-γ-AApeptide monomer S6 illustrates the intrinsic folding propensity of sulfono-γ-AApeptides, which likely originates from the bulkiness of tertiary sulfonamide moiety. The two-dimensional solution NMR spectroscopy data for the longest sequence S1 demonstrates a 10/16 right-handed helical structure. Optical analysis using circular dichroism further supports well- defined helical conformation of sulfono-γ-AApeptides in solution containing as few as five building blocks. Future development of sulfono-γ-AApeptides may lead to new foldamers with discrete functions, enabling expanded application in chemical biology and biomedical sciences.

Herein we report a highly efficient new method for preparing γ-AApeptides capable of theoretically containing any functionality; the method uses a few common N-alloc γ-AApeptide building blocks. More importantly, using the same approach, new classes of peptidomimetics bearing novel backbone scaffolds can also be readily generated. Our results not only demonstrate the versatility of this new synthetic method, but also highlight the possibility that the resulting novel peptidomimetics may find discrete biomedical/biomaterial applications in the future.

The tripeptide N-formyl-Met-Leu-Phe (fMLF) is a potent neutrophil chemoattractant and the reference agonist for the G protein-coupled N-formylpeptide receptor (FPR). As it plays a very important role in host defense and inflammation, there has been considerable interest in the development of fMLF analogues in the hope of identifying potential therapeutic agents. Herein we report the design, synthesis, and evaluation of AApeptides that mimic the structure and function of fMLF. The lead AApeptides induced calcium mobilization and mitogen-activated protein kinase (MAPK) signal transduction pathways in FPR-transfected rat basophilic leukemic (RBL) cells. More intriguingly, at high concentrations, certain AApeptides were more effective than fMLF in the induction of calcium mobilization. Their agonistic activity is further supported by their ability to stimulate chemotaxis and the production of superoxide in HL-60 cells. Similarly to fMLF, these AApeptides are much more selective towards FPR1 than FPR2. These results suggest that the fMLF-mimicking AApeptides might emerge as a new class of therapeutic agents that target FPRs.

Herein we describe the development of a new class of antimicrobial and anti-inflammatory peptidomimetics: cyclic lipo-α-AApeptides. They have potent and broad-spectrum antibacterial activity against a range of clinically relevant pathogens, including both multidrug-resistant Gram-positive and Gram-negative bacteria. Fluorescence microscopy suggests that cyclic lipo-α-AApeptides kill bacteria by disrupting bacterial membranes, possibly through a mechanism similar to that of cationic host-defense peptides (HDPs). Furthermore, the cyclic lipo-α-AApeptide can mimic cationic host-defense peptides by antagonizing Toll-like receptor 4 (TLR4) signaling responses and suppressing proinflammatory cytokines such as tumor necrosis factor-α (TNF-α). Our results suggest that by mimicking HDPs, cyclic lipo-α-AApeptides could emerge as a new class of antibiotic agents that directly kill bacteria, as well as novel antiinflammatory agents that act through immunomodulation.

The last two decades have seen the rise of antimicrobial peptides (AMPs) to combat emerging antibiotic resistance. Herein we report the solid-phase synthesis of short lipidated α/γ-AA hybrid peptides. This family of lipo-chimeric peptidomimetics displays potent and broad-spectrum antimicrobial activity against a range of multi-drug resistant Gram-positive and Gram-negative bacteria. These lipo-α/γ-AA hybrid peptides also demonstrate high biological specificity, with no hemolytic activity towards red blood cells. Fluorescence microscopy suggests that these lipo-α/γ-AA chimeric peptides can mimic the mode of action of AMPs and kill bacterial pathogens via membrane disintegration. As the composition of these chimeric peptides is simple, therapeutic development could be economically feasible and amenable for a variety of antimicrobial applications.