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.     

Synthesis of some thieno gamma lactam monocarboxylic acids with high antibacterial activity: A new look at an old molecular system

Synthesis and antibacterial activity of some novel monocyclic thienyl gamma lactams are reported. The compounds have been synthesized by a two-step process consisting of, first, intermolecular Michael addition, followed by intramolecular amidification between suitable arylamino malonate and 3-(2′-thienyl) acryloyl chloride and then hydrolysis cum in situ decarboxylation of the diacid. The compounds showed moderate to high antibacterial activity against gram positive and gram negative bacteria.     

N-thiolated beta-lactams: Studies on the mode of action and identification of a primary cellular target in Staphylococcus aureus

This study focuses on the mechanism of action of N-alkylthio beta-lactams, a new family of antibacterial compounds that show promising activity against Staphylococcus and Bacillus microbes. Previous investigations have determined that these compounds are highly selective towards these bacteria, and possess completely unprecedented structure-activity profiles for a beta-lactam antibiotic. Unlike penicillin, which inhibits cell wall crosslinking proteins and affords a broad spectrum of bacteriocidal activity, these N-thiolated lactams are bacteriostatic in their behavior and act through a different mechanistic mode. Our current findings indicate that the compounds react rapidly within the bacterial cell with coenzyme A (CoA) through in vivo transfer of the N-thio group to produce an alkyl-CoA mixed disulfide species, which then interferes with fatty acid biosynthesis. Our studies on coenzyme A disulfide reductase show that the CoA thiol-redox buffer is not perturbed by these compounds; however, the lactams appear to act as prodrugs. The experimental evidence that these beta-lactams inhibit fatty acid biosynthesis in bacteria, and the elucidation of coenzyme A as a primary cellular target, offers opportunities for the discovery of other small organic compounds that can be developed as therapeutics for MRSA and anthrax infections.     

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.     

Structurally designed novel furogamma lactams as inhibitors for bacterial propagations

Some novel furogamma lactams have been synthesised by one step condensation of arylaminomalonates with substituted furyl acryloyl chlorides. The annulation of substituted monocyclic gammalactams followed by cyclization produced novel tricyclic furogamma lactams. Some of these furogammalactams are found to exhibit Gram-positive and Gram-negative antibacterial activity at very high concentrations.     

Mode of action investigation for the antibacterial cationic anthraquinone analogs

Reported previously by our group, we have developed a novel class of antibacterial cationic anthraquinone analogs with superb potency (MIC <1μg/mL) against Gram positive (G+) pathogens including Methicillin-resistant Staphylococcus aureus (MRSA). However, most of these compounds only manifest modest antibacterial activity against Gram negative (G-) bacteria. Further investigation on the antibacterial mode of action using fluorogenic dyes reveals that these compounds exert two different modes of action that account for the difference in their antibacterial profile. It was found that most of the compounds exert their antibacterial activity by disrupting the redox processes of bacteria. At high concentration, these compounds can also act as membrane disrupting agents. This information can help to design new therapeutics against various bacteria.     

Preparation and antibacterial evaluation of decarboxylated fluoroquinolones

Decarboxylated ciprofloxacin (3) has been reported in the literature to have antibacterial activities against Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Bacillus subtilis, Enterobacter cloacae, Serratia marcescens and especially potent activity against Escherichia coli. Herein, we report our syntheses of 3 and five additional decarboxylated fluoroquinolones (FQs). We have re-evaluated the antibacterial activity of these FQs. In contrast to previously reported data, none of these decarboxylated fluoroquinolones showed significant antibacterial activity in our assays using both the broth dilution and agar methods. Our study confirmed that the presence of a carboxylic acid group at the 3-position of the fluoroquinolone scaffold is essential for antibacterial activity.     

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-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.     

PGRP-SB1: an N-acetylmuramoyl L-alanine amidase with antibacterial activity

The peptidoglycan recognition protein (PGRP) family is conserved from insects to mammals and is involved in immune regulation and bacterial clearance. They form at least three functional classes; receptors required for immune gene expression; amidases that degrade peptidoglycan and scavenge the tissues from immune-stimulating peptidoglycan; and as proteins with antibacterial activity. We here report that PGRP-SB1 is an N-acetylmuramoyl l-alanine amidase, which (in contrast to the previously described PGRP-amidases) shows antibacterial activity. PGRP-SB1 is highly active against peptidoglycans that have a diaminopimelic acid (DAP) residue in the cross-linking peptide, but lack activity to most lysine-containing peptidoglycans. The antibacterial activity is pronounced against Bacillus megaterium with an LD(50) of 1.5microg ml(-1). The bactericidal effect of PGRP-SB1 is dependent on its enzymatic activity, as the zinc co-factor is essential. The bactericidal mode of action is thus different from non-enzymatic vertebrate PGRPs that have been reported to be antibacterial.     

Zinc potentiates the antibacterial effects of histidine-rich peptides against Enterococcus faecalis

Antimicrobial peptides are effector molecules of the innate immune system. We have recently shown that peptides containing multiples of the heparin-binding Cardin and Weintraub motifs AKKARA and ARKKAAKA exert antimicrobial activities. Here, we show that replacement of lysine and arginine in these motifs by histidine abrogates the antibacterial effects of these peptides. Antibacterial activity of the histidine-rich peptides against the Gram-positive bacterium Enterococcus faecalis was restored by the addition of Zn2+. Fluorescence microscopy experiments showed that Zn2+ enabled binding of the histidine-rich peptides to Enterococcus faecalis bacteria. Similar Zn2+-dependent antibacterial activities were shown for histatin 5 as well as histidine-containing peptides derived from the Zn2+- and heparin-binding domain 5 of human kininogen. Thus, the results demonstrate a previously undisclosed Zn2+-dependent antibacterial activity of kininogen-derived peptides and indicate an important role for Zn2+ in regulating the antimicrobial activities of histidine-rich peptides.     

Definition of the heterocyclic pharmacophore of bacterial methionyl tRNA synthetase inhibitors: potent antibacterially active non-quinolone analogues

Potent inhibitors of bacterial methionyl tRNA synthetase (MRS) have previously been reported. Through SAR of the quinolone moiety, the right hand side pharmacophore for MRS inhibition has now been defined as an NH-C-NH functionality in the context of a bicyclic heteroaromatic system. Potent antibacterial fused-pyrimidone and fused-imidazole analogues have been obtained and enantioselective activity demonstrated. Compound 46 demonstrated very good antibacterial activity against panels of antibiotic-resistant staphylococci and enterococci.     

Comparative study of SCE induction and cytostatic effects by homo-azasteroidal esters of N,N-bis(2-chloroethyl)aminobenzoic acid in human lymphocytes

The effect of homo-azasteroidal esters of benzoic acid mustard isomers and the 4-methyl derivatives, which have steroidal lactams as a biological basis, on cytogenetic damage was studied. Twenty compounds were comparatively studied, on a molar basis, as regards their ability to induce sister-chromatid exchanges (SCEs) and cell division delays.A correlation between potency for SCE induction, effectiveness in cell division delay and previously established antitumor activity of these compounds was observed.     

Antibacterial activity, structure and CMC relationships of alkanediyl alpha,omega-bis(dimethylammonium bromide) surfactants

Some alpha,omega-alkanediyl bis-dimethylammonium bromide compounds (gemini surfactants) referred as "m-s-m" have been synthesized, purified and characterized by usual spectroscopic methods. These compounds have been screened for antibacterial activity against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Their activity was compared. The compounds tested showed excellent in vitro antibacterial activity against Staphylococcus aureus ranging from 1.5 to 20 microg/ml and had variable activity against E. coli with minimum minimum inhibitory concentration (MIC) of 50 microg/ml. These compounds are less active against P. aeruginosa. On the other hand, contrary to the antibacterial activity of these products against S. aureus, a relation between the MIC and the critical micellar concentration (CMC) was found and relationship between chain's Length and antibacterial activity was found.     

The iturin-like lipopeptides are essential components in the biological control arsenal of Bacillus subtilis against bacterial diseases of cucurbits

The antibacterial potential of four strains of Bacillus subtilis, UMAF6614, UMAF6619, UMAF6639, and UMAF8561, previously selected on the basis of their antifungal activity and efficacy against cucurbit powdery mildew, was examined. Among these strains, UMAF6614 and UMAF6639 showed the highest antibacterial activity in vitro, especially against Xanthomonas campestris pv. cucurbitae and Pectobacterium carotovorum subsp. carotovorum. These strains produced the three families of lipopeptide antibiotics known in Bacillus spp.: surfactins, iturins, and fengycins. Using thin-layer chromatography analysis and direct bioautography, the antibacterial activity could be associated with iturin lipopeptides. This result was confirmed by mutagenesis analysis using lipopeptide-defective mutants. The antibacterial activity was practically abolished in iturin-deficient mutants, whereas the fengycin mutants retained certain inhibitory capabilities. Analyses by fluorescence and transmission electron microscopy revealed the cytotoxic effect of these compounds at the bacterial plasma membrane level. Finally, biological control assays on detached melon leaves demonstrated the ability of UMAF6614 and UMAF6639 to suppress bacterial leaf spot and soft rot; accordingly, the biocontrol activity was practically abolished in mutants deficient in iturin biosynthesis. Taken together, our results highlight the potential of these B. subtilis strains as biocontrol agents against fungal and bacterial diseases of cucurbits and the versatility of iturins as antifungal and antibacterial compounds.     

2β-Acetoxyferruginol—A new antibacterial abietane diterpene from the bark of Prumnopitys andina

As part of an on-going project to isolate antibacterial compounds from rare conifer species, a new abietane diterpene, 2β-acetoxyferruginol was isolated from the stem bark of Prumnopitys andina. Molecular modelling studies were conducted to explain some of the NOEs observed in the A-ring of this compound and to support assignment of relative stereochemistry. This new compound had antibacterial activity at 8 μg/ml against two effluxing strains of Staphylococcus aureus, but interestingly was inactive at 128 μg/ml against a wild-type strain and against a methicillin-resistant (MRSA) clinical isolate. We have previously demonstrated that ferruginol is active against these four S. aureus stains and therefore the results indicate that the presence of the acetoxy group has a detrimental effect on antibacterial activity against certain strains. 2β-Acetoxyferruginol was also assayed against Propionibacterium acnes and was active at 4 μg/ml.     

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.     

Antibacterial activity of soluble pyridinium-type polymers.

Cross-linked poly(N-benzyl-4-vinylpyridinium halide) (designated insoluble BVP) was previously reported to capture bacterial cells alive by contact with them. The corresponding linear polymer poly(N-benzyl-4-vinylpyridinium salt) (designated soluble BVP) was found to exhibit antibacterial activity. This soluble pyridinium-type polymer showed strong antibacterial activity against gram-positive bacteria, whereas it was less active against gram-negative bacteria. The antibacterial activity of this cationic, polymeric disinfectant was considerably greater than that of the corresponding monomeric compound and was approximately equal to that of conventional disinfectants such as benzalkonium chloride and chlorohexidine.     

Antibacterial activity of soluble pyridinium-type polymers

Cross-linked poly(N-benzyl-4-vinylpyridinium halide) (designated insoluble BVP) was previously reported to capture bacterial cells alive by contact with them. The corresponding linear polymer poly(N-benzyl-4-vinylpyridinium salt) (designated soluble BVP) was found to exhibit antibacterial activity. This soluble pyridinium-type polymer showed strong antibacterial activity against gram-positive bacteria, whereas it was less active against gram-negative bacteria. The antibacterial activity of this cationic, polymeric disinfectant was considerably greater than that of the corresponding monomeric compound and was approximately equal to that of conventional disinfectants such as benzalkonium chloride and chlorohexidine.     

Antibacterial, antifungal and cytotoxic properties of some sulfonamide-derived chromones

A series of antibacterial and antifungal sulfonamide (sulfanilamide, sulfaguanidine, sulfamethaxozole, 4-aminoethylbenzene-sulfonamide and 4-amino-6-trifluoromethyl-benzene-1,3-disulfonamide) derived chromones, previously reported as inhibitors of carbonic anhydrase, have been screened for in-vitro antibacterial activity against four Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi and Shigella flexener) and two Gram-positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains, and for in-vitro antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani, Candida glaberata. All compounds (1)-(5) showed significant antibacterial activity against all four Gram-negative species and both Gram-positive species. However, three of them, (1), (4) and (5), were found to be comparatively much more active compared to (2) and (3). Of these, (5) was found to be the most active one. For antifungal activity, generally compounds (1) and (2) showed significant activity against more than three strains whereas (3)-(5) also showed significant activity against varied fungal strains. In the brine shrimp bioassay for in-vitro cytotoxic properties, only two compounds, (4) and (5) displayed potent cytotoxic activity, LD50 = 2.732 x 10(-4)M) and LD50 = 2.290 x 10(-4)M) respectively, against Artemia salina.