Synthesis and antimicrobial activities of structurally novel S,S'-bis(heterosubstituted) disulfides.

The central focus of this study is on the antibacterial and antifungal properties of synthetically produced S,S'-bis(heterosubstituted) disulfides as a means to control the growth of various infection-causing pathogens. Staphylococcus aureus, Francisella tularensis and Candida albicans were each found to be highly susceptible to several of these compounds by agar or broth dilution and Kirby-Bauer diffusion assays. These structurally simple, low molecular weight disulfides have shown promising bioactivities and may serve as leads to the development of effective new antibacterials for pathogenic bacteria such as methicillin-resistant S. aureus and F. tularensis.

Glyconanobiotics: Novel carbohydrated nanoparticle antibiotics for MRSA and Bacillus anthracis.

This report describes the synthesis and evaluation of glycosylated polyacrylate nanoparticles that have covalently-bound antibiotics within their framework. The requisite glycosylated drug monomers were prepared from one of three known antibiotics, an N-sec-butylthio beta-lactam, ciprofloxacin, and a penicillin, by acylation with 3-O-acryloyl-1,2-O-isopropylidene-5,6 bis((chlorosuccinyl)oxy)-d-glucofuranose (7) or 6-O-acetyl-3-O-acryloyl-1,2-O-isopropylidene-5-(chlorosuccinyl)oxy-alpha-d-glucofuranose (10). These acrylated monomers were subjected to emulsion polymerization in a 7:3 (w:w) mixture of butyl acrylate-styrene in the presence of sodium dodecyl sulfate as surfactant (3 weight %) and potassium persulfate as a radical initiator (1 weight %). The resulting nanoparticle emulsions were characterized by dynamic light scattering and found to have similar diameters ( approximately 40 nm) and size distributions to those of our previously studied systems. Microbiological testing showed that the N-sec-butylthio beta-lactam and ciprofloxacin nanoparticles both have powerful in vitro activities against methicillin-resistant Staphylococcus aureus and Bacillus anthracis, while the penicillin-bound nanoparticles have no antimicrobial activity. This indicates the need for matching a suitable antibiotic with the nanoparticle carrier. Overall, the study shows that even relatively large, polar acrylate monomers (MW>1000 amu) can be efficiently incorporated into the nanoparticle matrix by emulsion polymerization, providing opportunities for further advances in nanomedicine.

Studies on the antifungal properties of N-thiolated beta-lactams.

N-thiolated beta-lactams had previously been shown to have antibacterial activity against a narrow selection of pathogenic bacteria including Staphylococcus aureus and Bacillus anthracis, as well as apoptotic-inducing activity in a variety of human cancer cell lines. We now have found that these lactams also possess antifungal activity against Candida and other fungi by exerting powerful cytostatic effects that disrupt the structural integrity of cytoplasmic membranes. The mode of action and structure-activity trends of these lactams as antifungals parallel that previously seen in our antibacterial studies.

Unsymmetric aryl-alkyl disulfide growth inhibitors of methicillin-resistant Staphylococcus aureus and Bacillus anthracis.

This study describes the antibacterial properties of synthetically produced mixed aryl-alkyl disulfide compounds as a means to control the growth of Staphylococcus aureus and Bacillus anthracis. Some of these compounds exerted strong in vitro bioactivity. Our results indicate that among the 12 different aryl substituents examined, nitrophenyl derivatives provide the strongest antibiotic activities. This may be the result of electronic activation of the arylthio moiety as a leaving group for nucleophilic attack on the disulfide bond. Small alkyl residues on the other sulfur provide the best activity as well, which for different bacteria appears to be somewhat dependent on the nature of the alkyl moiety. The mechanism of action of these lipophilic disulfides is likely similar to that of previously reported N-thiolated beta-lactams, which have been shown to produce alkyl-CoA disulfides through a thiol-disulfide exchange within the cytoplasm, ultimately inhibiting type II fatty acid synthesis. However, the mixed alkyl-CoA disulfides themselves show no antibacterial activity, presumably due to the inability of the highly polar compounds to cross the bacterial cell membrane. These structurally simple disulfides have been found to inhibit beta-ketoacyl-acyl carrier protein synthase III, or FabH, a key enzyme in type II fatty acid biosynthesis, and thus may serve as new leads to the development of effective antibacterials for MRSA and anthrax infections.

Antibiotic-conjugated polyacrylate nanoparticles: new opportunities for development of anti-MRSA agents.

This report describes the preparation of polyacrylate nanoparticles in which an N-thiolated beta-lactam antibiotic is covalently conjugated onto the polymer framework. These nanoparticles are formed in water by emulsion polymerization of an acrylated antibiotic pre-dissolved in a liquid acrylate monomer (or mixture of co-monomers) in the presence of sodium dodecyl sulfate as a surfactant and potassium persulfate as a radical initiator. Dynamic light scattering analysis and electron microscopy images of these emulsions show that the nanoparticles are approximately 40 nm in diameter. The emulsions have potent in vitro antibacterial properties against methicillin-resistant Staphylococcus aureus and have improved bioactivity relative to the non-polymerized form of the antibiotic. A unique feature of this methodology is the ability to incorporate water-insoluble drugs directly into the nanoparticle framework without the need for post-synthetic modification. Additionally, the antibiotic properties of the nanoparticles can be modulated by changing the length or location of the acrylate linker on the drug monomer.

Penicillin-bound polyacrylate nanoparticles: restoring the activity of beta-lactam antibiotics against MRSA.

This report describes the preparation of antibacterially active emulsified polyacrylate nanoparticles in which a penicillin antibiotic is covalently conjugated onto the polymeric framework. These nanoparticles were prepared in water by emulsion polymerization of an acrylated penicillin analogue pre-dissolved in a 7:3 (w:w) mixture of butyl acrylate and styrene in the presence of sodium dodecyl sulfate (surfactant) and potassium persulfate (radical initiator). Dynamic light scattering analysis and atomic force microscopy images show that the emulsions contain nanoparticles of approximately 40 nm in diameter. The nanoparticles have equipotent in vitro antibacterial properties against methicillin-susceptible and methicillin-resistant forms of Staphylococcus aureus and indefinite stability toward beta-lactamase.

N-thiolated 2-oxazolidinones: a new family of antibacterial agents for methicillin-resistant Staphylococcus aureus and Bacillus anthracis.

In this report, we describe a new family of N-thiolated 2-oxazolidinones having antibacterial activity against methicillin-resistant Staphylococcus aureus and Bacillus anthracis. The effect of ring substituents and stereochemistry on antibacterial activity of these oxazolidinones closely parallels that previously reported for N-thiolated beta-lactam antibiotics.

N-Thiolated beta-lactam antibacterials: effects of the N-organothio substituent on anti-MRSA activity.

A study on the structure-activity profiles of N-thiolated beta-lactams 1 is reported which demonstrates the importance of the N-organothio moiety on antibacterial activity. Our results indicate that elongation of the N-alkylthio residue beyond two carbons, or extensive branching within the organothio substituent, diminishes antibacterial effects. Of the derivatives we examined, the N-sec-butylthio beta-lactam derivative 5g possesses the strongest growth inhibitory activity against methicillin-resistant Staphylococcus aureus strains. Sulfur oxidation state is important, as the N-sulfenyl and N-sulfinyl groups provide for the best antibacterial activity, while lactams bearing the N-sulfonyl or N-sulfonic acid functionalities have much weaker or no anti-MRSA properties. Stereochemistry within the organothio chain does not seem to be a significant factor, although for N-sec-butylthio beta-lactams 15a-d, the 3R,4S-lactams 15c, d are more active than the 3S,4R-stereoisomers 15a, b in agar diffusion experiments. The N-methylthio lactams are the most sensitive to the presence of glutathione, followed by N-ethylthio and N-sec-butylthio lactams, which indicates that bioactivity and perhaps bacterial selectivity of the lactams may be related to the amount of organothiols in the bacterial cell. These results support the empirical model for the mechanism of action of the compounds in which the lactam transverses the bacterial membrane to deliver the organothio moiety to its cellular target.

N-thiolated beta-lactams: a new family of anti-Bacillus agents.

This report describes the evaluation of N-thiolated beta-lactam antibiotics as potential anti-Bacillus agents. N-Thiolated beta-lactams are a new family of antibacterials that previously have been found to selectively inhibit the growth of Staphylococcus bacteria over many other genera of microbes. From the data presented herein, these lactams similarly inhibit a variety of Bacillus species, including Bacillus anthracis. The preliminary structure-activity studies suggest that there is a need to balance the lipophilic character of the C3/C4 groups in order to obtain optimal anti-Bacillus activity. Elongation or extensive branching of the organothio substituent diminishes antibacterial effects, with the sec-butylthio derivative providing the strongest activity.

N-Methylthio beta-lactam antibacterials: effects of the C3/C4 ring substituents on anti-MRSA activity.

N-Thiolated beta-lactams are a new family of antibacterials that inhibit the growth of Staphylococcus bacteria. Unlike other beta-lactam drugs, these compounds retain their full antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) strains and operate through a different mode of action. The structural features, which give these lactams their biological activity, have not yet been completely defined. Earlier efforts in our laboratory established that the N-organothio substituent is essential for antimicrobial activity while other groups at C(3) and C(4) on the lactam ring play a more subtle role. In this present study, we investigate these effects by varying the polar and steric nature of the ring substituents at these two centers. From the data presented herein, it appears that there is a need to balance the lipophilic character of the C(3)/C(4) groups to obtain an optimal anti-MRSA activity. The structure-bioactivity profiles more closely relate to the compound's ability to penetrate the bacterial cell membrane to sites of action within the cytoplasm rather than to any specific non-bonding interactions with a biological target. Based on these results, a model for the compounds' mode of action is presented.

N-Thiolated beta-lactam antibacterials: defining the role of unsaturation in the C4 side chain.

N-Methylthio beta-lactams represent a novel family of antibacterial agents for methicillin-resistant Staphylococcus aureus (MRSA). The structure-activity functions and mechanism of action of these compounds, although still largely undefined, differ dramatically from those of all previously reported beta-lactam antibiotics. Prior work has established that the N-alkylthio moiety is required for antibacterial activity, and that a variety of unsaturated groups can be tolerated at C(4) of the lactam ring. This report describes the effect that unsaturation within the C(4) substituent has on antibacterial activity of these interesting new N-thiolated beta-lactams.

N-thiolated beta-lactams: novel antibacterial agents for methicillin-resistant Staphylococcus aureus.

In this report we describe a new family of N-thiolated beta-lactams that have antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). The compounds show unprecedented structure-activity features and an unusual mode of action for a beta-lactam antibiotic.

Effect of aryl ring fluorination on the antibacterial properties of C4 aryl-substituted N-methylthio beta-lactams.

4-Aryl-substituted N-thiolated beta-lactams are a new family of antibacterial agents possessing unique structure-activity profiles and a mode of action. Unlike traditional beta-lactam antibiotics, which require highly polar enzyme-binding groups, these lactams bear hydrophobic groups on their side chains. In this study, we examine the effect that increasing hydrophobicity, through fluorine substitution in the C(4) aryl ring, has on the antibacterial properties.