Novel semi-synthetic glycopeptide antibiotics active against methicillin-resistant staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE): doubly-modified water-soluble derivatives of chloroorienticin B

Alternatives to Fight Vancomycin-Resistant Staphylococci and Enterococci

Gram positive pathogens are a significant cause of healthcare-associated infections, with Staphylococci and Enterococci being the most prevalent ones. Vancomycin, a last resort glycopeptide, is used to fight these bacteria but the emergence of resistance against this drug leaves some patients with few therapeutic options. To counter this issue, new generations of antibiotics have been developed but resistance has already been reported. In this article, we review the strategies in place or in development to counter vancomycin-resistant pathogens. First, an overview of traditional antimicrobials already on the market or in the preclinical or clinical pipeline used individually or in combination is summarized. The second part focuses on the non-traditional antimicrobials, such as antimicrobial peptides, bacteriophages and nanoparticles. The conclusion is that there is hitherto no substitute equivalent to vancomycin. However, promising strategies based on drugs with multiple mechanisms of action and treatments based on bacteriophages possibly combined with conventional antibiotics are hoped to provide treatment options for vancomycin-resistant Gram-positive pathogens.

Exploration of the site-specific nature and generalizability of a trimethylammonium salt modification on vancomycin: A-ring derivatives

Vancomycin analogues bearing an A-ring trimethylammonium salt modification were synthesized and their antimicrobial activity against vancomycin-resistant Enterococci (VRE) was evaluated. The modification increased antimicrobial potency and provided the capability to induce bacteria cell membrane permeabilization, but both properties were weaker than that found with our earlier reported similar C-terminus modification. The results provide further insights on the additive effect and generalizability of the structural and site-specific nature of a peripheral quaternary trimethylammonium salt modification of vancomycin.

Recent advances in the synthesis of new glycopeptide antibiotics

The vancomycin family of glycopeptide antibiotics has been inspiring research in the field of synthetic chemistry since the 1980s. Recent studies have moved away from the focus of total synthesis into new territory: the design and evaluation of novel compounds based on the natural products which exhibit improved antibacterial activity. Modern approaches to drug synthesis draw together investigations into the nature of the binding environment, and innovative synthetic methodologies which provide solutions to the challenging structural features and stereochemistry associated with this intriguing class of compounds. New analogues, derivatives and dimers of the natural products, as well as recent successes in the total synthesis of the complestatins are described in this tutorial review, covering literature from the last decade.

Polymerizable vancomycin derivatives for bactericidal biomaterial surface modification: structure-function evaluation

Surface modification of implantable biomaterials with biologically active functionalities, including antimicrobials, has wide potential for addressing implant-related design problems. Here, four polymerizable vancomycin derivatives bearing either acrylamide or poly(ethylene glycol) (PEG)-acrylate were synthesized and then polymerized through a surface-mediated reaction. Functionalization of vancomycin at either the V₃ or the X₁ position decreased monomeric activity by 6−75-fold depending on the modification site and the nature of the adduct (P < 0.08 for all comparisons). A 5000 Da PEG chain showed an order of magnitude decrease in activity relative to a 3400 Da counterpart. Molecular dynamics computational simulations were used to explore the mechanisms of this decreased activity. Assays were also conducted to demonstrate the utility of a living radical photopolymerization to create functional, polymeric surfaces with these monomers and to demonstrate surface-based activity against Staphylococcus epidermidis. In particular, the vancomycin−PEG-acrylate derivatives demonstrated a 7−8 log reduction in bacterial colony forming units (CFU) with respect to nonfunctionalized control surfaces.

Solubilization of dipropofol, an antibacterial agent, using saccharide and ascorbic acid

Dipropofol has a strong antibacterial activity against Gram-positive bacteria. However, it lacked the solubility in water and this property was supposed to limit its efficacy. We tried to improve the solubility and found a new solubilization method of dipropofol in water by the addition of a monosaccharide or ascorbic acid.

Anti-MRSA agents: under investigation, in the exploratory phase and clinically available

Staphylococcal infections are difficult to treat due to the rapid emergence of methicillin-resistant staphylococci and, unfortunately, vancomycin-intermediate or -resistant staphylococci. Numerous alternative treatments are urgently required. In this special report, intensive research of new molecules is highlighted--in known antibacterial families and new medicinal chemical entities.

Glycopeptides: Update on an old successful antibiotic class

The natural product glycopeptides vancomycin and teicoplanin have come to play a significant role in the therapy for Gram-positive bacterial infections. In particular vancomycin is the choice for empiric therapy of these infections primarily due to its activity against and the significance of methicillin-resistant Staphylococcus aureus. While high-level problematic glycopeptide resistance among enterococci was observed initially and continues to increase, the slow creep of vancomycin intermediate susceptibility and the fear of frank resistance among the staphylococci have precipitated increasing work leading to creation of new semisynthetic analogs. These new agents, including dalbavancin and telavancin, are within 1-2 years availability in the clinic. Interestingly, chemical modifications resulting in these second-generation analogs and additional characterization have revealed new mechanisms of antibacterial action, and plasticity regarding additional properties including pharmacokinetics for the drug candidates. The unique beneficial properties of the near term vancomycin replacements, semisynthesis of additional important analogs, and advances in metabolic engineering resulting in novel scaffolds signal a new era for the glycopeptide antibiotics.

Design and synthesis of macrocycles active against vancomycin-resistant enterococci (VRE): the interplay between d-Ala-d-Lac binding and hydrophobic effect

A modified vancomycin binding pocket (D-O-E ring) incorporating a CHNHCOR function at the AA4 position is designed and synthesized. Potent bioactivities against both sensitive- and resistant-strain are found for some of these compounds (MIC 4 microg/mL against VREF). From this preliminary SAR studies, it was speculated that the D-Ala-D-Ala binding was required for this series of compounds since the corresponding des-leucine derivative is inactive. The presence of long aliphatic chain was important for the desired activities and such hydrophobic effect is specific as no beneficial effect is observed when the same aliphatic chain was attached to the other part of the molecule.

Semi-synthetic glycopeptide antibacterials

Studies leading to the discovery of TD-6424 and their relevance to other hydrophobically-substituted glycopeptides are reviewed along with a brief comparison of properties for related agents currently undergoing clinical evaluation.

An efficient and practical method for solid-phase synthesis of tripeptide-bearing glycopeptide antibiotics: combinatorial parallel synthesis of carboxamide derivatives of chloroorienticin B

An efficient and practical method was established for solid-phase parallel synthesis of the peptide-bearing carboxamide derivatives of chloroorienticin B, and over 80 compounds were synthesized simultaneously. Among the derivatives prepared, compounds having both tryptophan and tyrosine residues (1-3) were found to possess potent antibacterial activity against VRE.