Synthesis and biological evaluation of gramicidin S dimers

Advancements in peptide-based antimicrobials: A possible option for emerging drug-resistant infections

In recent years, multidrug-resistant pathogenic microorganisms (MDROs) have emerged as a severe threat to human health, exhibiting robust resistance to traditional antibiotics. This has created a formidable challenge in modern medicine as we grapple with limited options to combat these resilient bacteria. Despite extensive efforts by scientists to develop new antibiotics targeting these pathogens, the quest for novel antibacterial molecules has become increasingly arduous. Fortunately, nature offers a potential solution in the form of cationic antimicrobial peptides (AMPs) and their synthetic counterparts. AMPs, naturally occurring peptides, have displayed promising efficacy in fighting bacterial infections by disrupting bacterial cell membranes, hindering their survival and reproduction. These peptides, along with their synthetic mimics, present an exciting alternative in combating antibiotic resistance. They hold the potential to emerge as a formidable tool against MDROs, offering hope for improved strategies to protect communities. Extensive research has explored the diversity, history, and structure-properties relationship of AMPs, investigating their amphiphilic nature for membrane disruption and mechanisms of action. However, despite their therapeutic promise, AMPs face several documented limitations. Among these challenges, poor pharmacokinetic properties stand out, impeding the attainment of therapeutic levels in the body. Additionally, some AMPs exhibit toxicity and susceptibility to protease cleavage, leading to a short half-life and reduced efficacy in animal models. These limitations pose obstacles in developing effective treatments based on AMPs. Furthermore, the high manufacturing costs associated with AMPs could significantly hinder their widespread use. In this review, we aim to present experimental and theoretical insights into different AMPs, focusing specifically on antibacterial peptides (ABPs). Our goal is to offer a concise overview of peptide-based drug candidates, drawing from a wide array of literature and peer-reviewed studies. We also explore recent advancements in AMP development and discuss the challenges researchers face in moving these molecules towards clinical trials. Our main objective is to offer a comprehensive overview of current AMP and ABP research to guide the development of more precise and effective therapies for bacterial infections.

Tuning the Effects of Bacterial Membrane Permeability through Photo-Isomerization of Antimicrobial Cationic Amphiphiles

Several important antimicrobial drugs act by permeabilizing cell membranes. In this study, we showed that the intensity of membrane permeability caused by antimicrobial cationic amphiphiles can be modified not only by their concentration but also through light-induced isomerization of their lipid segment. Two types of photo-isomerizable cationic amphiphiles were developed and the effects of photo-isomerization on bacterial growth and membrane permeability were evaluated. One photo-isomer inhibited cell growth and division, whereas the other photo-isomer led to a rapid and lethal bacterial membrane-disrupting effect. The switch from "on" to "off" can be obtained by either the cis- or trans-isomer depending on the bacterial strain and the type of cationic amphiphile. These cationic amphiphiles offer a novel tool for research and industrial applications that require light-controlled bacterial membrane permeabilization.

Solvent-free thermocyclization of the unactivated linear gramicidin S precursor and analogues

A convenient thermocyclization of the linear gramicidin S precursor and its analogues is demonstrated. With the preorganized β-sheet conformation, the unactivated linear precursors can cyclize into the corresponding head-to-tail cyclic products in high yield after being heated under solvent-free conditions.

Cyclic modular beta-sheets

The development of peptide beta-hairpins is problematic, because folding depends on the amino acid sequence and changes to the sequence can significantly decrease folding. Robust beta-hairpins that can tolerate such changes are attractive tools for studying interactions involving protein beta-sheets and developing inhibitors of these interactions. This paper introduces a new class of peptide models of protein beta-sheets that addresses the problem of separating folding from the sequence. These model beta-sheets are macrocyclic peptides that fold in water to present a pentapeptide beta-strand along one edge; the other edge contains the tripeptide beta-strand mimic Hao [JACS 2000, 122, 7654] and two additional amino acids. The pentapeptide and Hao-containing peptide strands are connected by two delta-linked ornithine (deltaOrn) turns [JACS 2003, 125, 876]. Each deltaOrn turn contains a free alpha-amino group that permits the linking of individual modules to form divalent beta-sheets. These "cyclic modular beta-sheets" are synthesized by standard solid-phase peptide synthesis of a linear precursor followed by solution-phase cyclization. Eight cyclic modular beta-sheets 1a-1h containing sequences based on beta-amyloid and macrophage inflammatory protein 2 were synthesized and characterized by 1H NMR. Linked cyclic modular beta-sheet 2, which contains two modules of 1b, was also synthesized and characterized. 1H NMR studies show downfield alpha-proton chemical shifts, deltaOrn delta-proton magnetic anisotropy, and NOE cross-peaks that establish all compounds but 1c and 1g to be moderately or well folded into a conformation that resembles a beta-sheet. Pulsed-field gradient NMR diffusion experiments show little or no self-association at low ( Collapse

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MESH Headings

• Amino Acid Sequence
• Amyloid beta-Peptides/chemistry
• Chemokine CXCL2
• Chromatography, High Pressure Liquid
• Hydrogen Bonding
• Magnetic Resonance Spectroscopy
• Molecular Conformation
• Molecular Sequence Data
• Monokines/chemistry
• Oligopeptides/chemical synthesis
• Ornithine/chemistry
• Peptides, Cyclic/chemistry
• Protein Folding
• Protein Structure, Secondary
• Water/chemistry

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Grants

• R01 GM049076-12 NIGMS NIH HHS
• 5T32 CA 009054 NCI NIH HHS
• R01 GM049076-13 NIGMS NIH HHS
• T32 CA009054 NCI NIH HHS
• GM 49076 NIGMS NIH HHS
• R01 GM049076 NIGMS NIH HHS
• 5T15 LM 07443 NLM NIH HHS
• R01 GM049076-11 NIGMS NIH HHS
• T15 LM007443 NLM NIH HHS

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Affiliation(s)

R. Jeremy Woods Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025, Phone: 949-824-6091, FAX: 949-824-9920
Justin O. Brower Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025, Phone: 949-824-6091, FAX: 949-824-9920
Elena Castellanos Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025, Phone: 949-824-6091, FAX: 949-824-9920
Mehrnoosh Hashemzadeh Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025, Phone: 949-824-6091, FAX: 949-824-9920
Omid Khakshoor Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025, Phone: 949-824-6091, FAX: 949-824-9920
Wade A. Russu Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025, Phone: 949-824-6091, FAX: 949-824-9920
James S. Nowick Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025, Phone: 949-824-6091, FAX: 949-824-9920

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Synthesis of Low-Hemolytic Antimicrobial Dehydropeptides Based on Gramicidin S

The synthesis and biological activity of a novel cyclic beta-sheet-type antimicrobial dehydropeptide based on gramicidin S (GS) is described. The GS analogue, containing two (Z)-(beta-3-pyridyl)-alpha,beta-dehydroalanine (DeltaZ3Pal) residues at the 4 and 4' positions (2), was synthesized by solution-phase methodologies using Boc-Leu-DeltaZ3Pal azlactone. Analogue 2 exhibited high antimicrobial activity against Gram-positive bacteria and had much lower hemolytic activity than wild-type GS and the corresponding (Z)-alpha,beta-dehydrophenylalanine (DeltaZPhe) analogue (1).

Apidaecin-type peptides: biodiversity, structure-function relationships and mode of action

Apidaecins (apidaecin-type peptides) refer to a series of small, proline-rich (Pro-rich), 18- to 20-residue peptides produced by insects. They are the largest group of Pro-rich antimicrobial peptides (AMPs) known to date. Structurally, apidaecins consist of two regions, the conserved (constant) region, responsible for the general antibacterial capacity, and the variable region, responsible for the antibacterial spectrum. The small, gene-encoded and unmodified apidaecins are predominantly active against many gram-negative bacteria by special antibacterial mechanisms. The mechanism of action by which apidaecins kill bacteria involves an initial non-specific binding of the peptides to an outer membrane (OM) component. This binding is followed by invasion of the periplasmic space, and by a specific and essentially irreversible combination with a receptor/docking molecule that may be a component of a permease-type transporter system on inner membrane (IM). In the final step, the peptide is translocated into the interior of the cell where it meets its ultimate target. Evidence that apidaecins are non-toxic for human and animal cells is a prerequisite for using them as novel antibiotic drugs. This review presents the biodiversity, structure-function relationships, and mechanism of action of apidaecins.