Recent Studies on Gramicidin S Analog Structure and Antimicrobial Activity

Late-stage installation and functionalization of alkyl pyridiniums: a general HTE amenable strategy to access diverse aryl alanine containing macrocyclic peptides

This manuscript describes a strategy to readily access diverse aryl and homoaryl alanine-containing pharmaceutically relevant macrocyclic peptides. A two-step sequence involving the late-stage installation of the pyridinium functionality on macrocyclic peptides followed by reductive couplings was implemented. These transformations are amenable to microscale high-throughput experimentation (HTE) and enable rapid access to aryl alanine-containing macrocyclic peptides that would otherwise be inaccessible via solid-phase peptide synthesis using commercially available amino acids. Numerous aryl and heteroaryl derivatives can be effectively used in these reactions. In addition, a systematic investigation was undertaken using an "informer" set of macrocyclic peptides which revealed the compatibility of the late-stage diversification with peptides containing diverse side chain functionalities.

Gramicidin-S-Inspired Cyclopeptidomimetics as Potent Membrane-Active Bactericidal Agents with Therapeutic Potential

Antimicrobial peptides (AMPs) are promising antibacterial agents often hindered by their undesired hemolytic activity. Inspired by gramicidin S (GS), a well-known cyclodecapeptide, we synthesized a panel of antibacterial cyclopeptidomimetics using β,γ-diamino acids (β,γ-DiAAs). We observed that peptidomimetic CP-2 displays a bactericidal activity similar to that of GS while possessing lower side-effects. Moreover, extensive studies revealed that CP-2 likely kills bacteria through membrane disruption. Altogether, CP-2 is a promising membrane-active antibiotic with therapeutic potential.

Synthesis and Biological Studies of Dodecameric Cationic Antimicrobial Peptides Containing Tetrahydrofuran Amino Acids

We report here a concise route to synthesize various stereoisomers of tetrahydrofuran amino acids (TAAs) and the synthesis of TAA-containing linear cationic dodecapeptides. Some of these linear peptides show slightly better antimicrobial activities than their tetra- and octameric congeners, but no activity against Mycobacterium tuberculosis, for which octapeptides exhibited by far the best results; this implies that antibacterial activity is dependent on the length of these linear peptides. All the dodecapeptides described here were found to be toxic in nature against Vero cells. The study helps to delineate the optimal length of this series of linear peptides and select potential leads in the development of novel cationic peptide-based antibiotics.

Stabilization of Cyclic β-Hairpins by Ugi-Reaction-Derived N-Alkylated Peptides: The Quest for Functionalized β-Turns

A solid-phase approach including on-resin Ugi reactions was developed for the construction of β-hairpins. Various N-alkylated dipeptide fragments proved capable of aligning antiparallel β-sheets in a macrocyclic scaffold, thus serving as β-hairpin templates. Gramicidin S was used as the model β-hairpin to compare the Ugi-derived β-turns with the type-II' β-turn. The results show that the multicomponent incorporation of such N-alkylated residues allows for the simultaneous stabilization and exo-cyclic functionalization of cyclic β-hairpins.