Structure-activity relationship of buffalo antibacterial hepcidin analogs

Hepcidin is an anti-microbial peptide expressed predominantly in the liver of many species. Based on the amino acid sequence deduced from buffalo (Bubalus bubalis) hepcidin cDNA (Accession no. EU399814), six peptides Hepc(1-25), Hepc(6-25), Hepc(7-25), Hepc(9-25), Hepc(11-25) and Hepc(15-25) were synthesized using solid-phase fluorenylmethoxycarbonyl (Fmoc) chemistry. CD spectroscopy revealed different spectra of the peptides in different solvents and in all the cases beta-structure was found to be dominant with less alpha-helix as predicted. Quantitation of secondary structure indicated the highest beta-structure for all the six peptides in SDS solution, when used as mimetic for membrane-like environment. The CD spectra of all the peptides taken in water showed that degree of randomness decreased with increase in chain length of the peptide. Out of the six peptides, only Hepc(1-25), Hepc(6-25) and Hepc(7-25) showed antibacterial activity against Staphylococcus aureus (Gram-positive bacteria). The peptides did not show any sensitivity toward E. coli (Gram-negative bacteria). Minimum inhibitory concentration (MIC) showed the lowest value for Hepc(7-25) as an antibacterial agent, followed by Hepc(6-25) and Hepc(1-25). The peptides Hepc(9-25), Hepc(11-25) and Hepc(15-25) with more random structure did not show any antimicrobial activity The study demonstrated that 5 amino acids at N-terminal in buffalo hepcidin can be truncated without loss of antimicrobial activity and further reduction of length of the analog from 20 to 19 amino acids resulted increase in the activity because of increase in beta-structure of the peptide shown by CD spectroscopy.     

Hybrid molecules of estrone: new compounds with potential antibacterial, antifungal, and antiproliferative activities

New hybrid molecules of estrone were synthesized as compounds indicating promising biological activity (antibacterial, antimycobacterial, antifungal, and antiproliferative). The prepared molecules contained various heterocyclic units (pyridine, benzylsulfanyl derivatives of pyridine or derivatives of tetrazole) linked to estrone by n-heptyl bridges. The compounds with charge on molecule (the hybrid pyridinium or benzylsulfanylpyridinium salts) exhibited significant biological activity (antibacterial, antimycobacterial, antifungal, and antiproliferative). On the other hand, the compounds not in the form of salts (omega-(1-phenyl-5-tetrazolylthio)heptylethers of estrone) were inactive. The antimycobacterial activities of three different series of tetrazole derivatives (i.e., the hybrid molecules with estrone, tetrazole-5-thiols, and 5-benzylsulfanyl-1-phenyltetrazoles) with the same substituents on phenyl ring were compared. Amongst them, the 5-benzylsulfanyl-1-phenyltetrazoles were the most potent.     

N-terminal modifications of Polymyxin B nonapeptide and their effect on antibacterial activity

Polymyxin B (PMB) is a potent antibacterial lipopeptide composed of a positively charged cyclic peptide ring and a fatty acid containing tail. Polymyxin B nonapeptide (PMBN), the deacylated amino derivative of polymyxin B, is much less bactericidal but able to permeabilize the outer membrane of Gram-negative bacteria and to neutralize the toxic effects of lipopolysaccharide (LPS). In this study, we synthesized and evaluated the antibacterial and LPS neutralizing activities of four PMBN analogs modified at their N-terminal. Our results suggest that oligoalanyl substitutions of PMBN do not effect most of PMBN activities. However, a hydrophobic aromatic substitution generated a PMB-like molecule with high antibacterial activity and significant reduced toxicity.     

Synthesis and in vitro antibacterial activity of oxazolidine LBM-415 analogs as peptide deformylase inhibitors

The drug resistant bacteria pose a severe threat to human health. The increasing resistance of those pathogens to traditional antibacterial therapy renders the identification of new antibacterial agents with novel antibacterial mechanisms an urgent need. In this study, a series of (2S)-N-substituted-1-[(formyhydroxyamino)methyl]-1-oxohexyl]-2-oxazolidinecarboxamides were designed, synthesized and evaluated for in vitro antibacterial activity. Most of these compounds displayed good activities against Gram-positive organisms comparable to reference agent LBM-415.     

Synthesis, antibacterial activities and molecular docking studies of Schiff bases derived from N-(2/4-benzaldehyde-amino) phenyl-N'-phenyl-thiourea

A series of novel Schiff base derivatives have been designed and synthesized, and their biological activities were also evaluated as potential inhibitors of FabH. These compounds were assayed for antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Staphylococcus aureus. Compounds with potent antibacterial activities were tested for their E. coli FabH inhibitory activity. Compound 3v showed the most potent antibacterial activity with MIC of 1.56-6.25 μg/mL against the tested bacterial strains and exhibited the most potent E. coli FabH inhibitory activity with IC(50) of 4.3 μM. Docking simulation was performed to position compound 3v into the E. coli FabH active site to determine the probable binding conformation.     

Structure-antibacterial, antitumor and hemolytic activity relationships of cecropin A-magainin 2 and cecropin A-melittin hybrid peptides.

In order to elucidate the structure-antibiotic activity relationship of cecropin A-magainin 2 and cecropin A-melittin hybrid peptides, several truncated peptides and the analogues with amino acid substitutions were synthesized and their antibacterial, antitumor and hemolytic activities of were examined. Cecropin A-magainin 2 hybrid analog, L16-CA(1-8)-MA(1-12) (termed as L-CA-MA in this study: KWKLFKKIGIGKFLHLAKKF-NH2), is known to have potent antibacterial and antitumor activity with less hemolytic activity. We found that the C-terminal region of L-CA-MA is more involved in the alpha-helical structure on cell membrane-like environment than N-terminal one by circular dichroism analysis. Deletion of the Gly-Ile-Gly sequence, the central hinge region of L-CA-MA, produced a considerable reduction in antitumor and hemolytic activity rather than an antibacterial one. The insertion of Pro, Gly-Ile or Gly-Pro in this hinge region of L-CA-MA caused retention of both antibacterial and antitumor activity while causing a significant decrease in hemolytic activity. However, the substitution with Gly-Pro-Gly instead of the Gly-Ile-Gly in CA(1-8)-MA(1-12), CA(1-8)-ME(1-12), CA(1-13)-MA(1-13) and CA(1-13)-ME(1-13) hybrids resulted in a drastic decrease in antibacterial, antitumor and hemolytic activity. The increase of hydrophobicity at position 16 in CA(1-8)-MA(1-12) by substituting Trp or Phe induced a significant increase in hemolytic activity without a considerable change in either antibacterial or antitumor activity. Therefore, these results suggested that the appropriate flexibility in the hinge region of CA-MA and CA-ME hybrid peptides and the appropriate hydrophobicity at position 16 in the hydrophobic region of CA (1-8)-MA(1-12) are important in potent antibacterial and antitumor activity with no hemolytic effect.     

Synthesis and antibacterial activity of oxazolidinone containing sulphonyl group

A series of oxazolidinone derivatives carrying sulphonyl group was synthesized and their antibacterial activity was evaluated in vitro. Many of such compounds demonstrated potent antibacterial activity. The activity of a novel compound (YC-20) was 2-4-fold more potent than that of linezolid.     

Activation of antibacterial prodrugs by peptide deformylase

5'-Dipeptidyl derivatives of 5-fluorodeoxyuridine (FdU) (1a-d) were synthesized. These compounds are biologically inactive but can be activated by peptide deformylase, which removes the N-terminal formyl group of the dipeptide, to release the active drug FdU via an intramolecular cyclization reaction. Because the deformylase is ubiquitous among bacteria but absent in mammalian cells, 1a-d provide a novel class of potential antibacterial agents.     

Antibacterial activity of bactenecin 5 fragments and their interaction with phospholipid membranes.

Bactenecin 5 (Bac 5) is an antibacterial 43mer peptide isolated from bovine neutrophils. It consists of an Arg-rich N-terminal region and successive repeats of Arg-Pro-Pro-Ile (or Phe). We synthesized Bac 5(1-23) and several related peptides to clarify the roles these regions play in antibacterial activity. An assay of antibacterial activity revealed that such activity requires the presence of Arg residues at or near the N-terminus, as well as a chain length exceeding 15 residues. None of the peptides exhibited haemolytic activity. Polyproline II-like CD curves were observed for most of the peptides. Measurements of the membrane perturbation and fusion indicated that the perturbation and fusogenic activities of the peptides were, generally, parallel to their antibacterial activities. Amino acid substitution in the repeating region had some effect on antibacterial activity.     

Synthesis and antibacterial activity of novel 6-fluoro-1-[(1R,2S)-2-fluorocyclopropan-1-yl]-4-oxoquinoline-3-carboxylic acids bearing cyclopropane-fused 2-amino-8-azabicyclo[4.3.0]nonan-8-yl substituents at the C-7 position

A series of novel 6-fluoro-1-[(1R,2S)-2-fluorocyclopropan-1-yl]-4-oxoquinoline-3-carboxylic acids bearing cyclopropane-fused 2-amino-8-azabicyclo[4.3.0]nonan-8-yl substituents at the C-7 position were synthesized to obtain potent drugs for the treatment of Gram-positive infections. Some compounds exhibited excellent antibacterial activity, and potent inhibitory activity against bacterial DNA topoisomerase IV. In addition, some of the potent compounds showed reduced inhibitory activity against human DNA topoisomerase II compared with the corresponding noncyclopropane-fused compounds.     

Efficient microwave-assisted synthesis, antibacterial activity and high fluorescence of 5 benzimidazolyl-2'-deoxyuridines

A series of novel C-5 benzimidazolyl-2'-deoxyuridines was synthesized in good yields under solvent-free conditions and microwave irradiation from 5-formyl-2'-deoxyuridine and arylenediamine derivatives in the presence of NaHSO(3) as catalyst. Their absorption and fluorescence spectra were measured. They showed intense fluorescence around 400-500nm with quantum yields between 0.3 and 0.5. All compounds studied in this work were screened for their antibacterial activities against a series of Gram positive and negative bacteria. The trifluoromethyl substituted benzimidazole derivatives showed some antibacterial activity.     

Synthesis of a series of novel 2,5-disubstituted-1,3,4-oxadiazole derivatives as potential antioxidant and antibacterial agents

A series of novel 2,5-disubstituted-1,3,4-oxadiazole derivatives were synthesized and screened for their antimicrobial and antioxidant activities. The assay indicated that compounds 3c, 3d, and 3i exhibited comparable antibacterial and antioxidant activity with first-line drugs. The structure activity relationship and molecular docking study of the synthesized compounds are also reported.     

Synthesis and biological evaluation of novel benzoxazinyl-oxazolidinones as potential antibacterial agents

A number of benzoxazinyl-oxazolidinones bearing 3-trizolylmethyl or 3-carboxamide side chain were designed and synthesized with the aim to develop antibacterial agents with improved properties. In vitro antibacterial activities of these novel compounds were evaluated against a panel of resistant and susceptible Gram-positive bacteria. Most analogues bearing 3-trizolylmethyl showed good to moderate antibacterial activities. Compound 12a exhibited a fourfold increase in activity compared with linezolid against all the tested strains, which was identified to be a promising antibacterial agent for further evaluation.     

Design,synthesis and antibacterial activity of novel andrographolide derivatives

A series of andrographolide derivatives were synthesized through a facile condensation reaction with different carboxylic acids. The new compounds were characterized and screened for their antibacterial activities. A number of the new compounds significantly reduced bacterial quorum sensing virulence factors production in Pseudomonas aeruginosa, essential for pathogenesis. Compound 11b showed the best activity among all the new compounds.     

Synthesis and SAR evaluation of oxadiazolopyrazines as selective Haemophilus influenzae antibacterial agents

The parallel synthesis and antibacterial activity of 5-hydroxy[1,2,5] oxadiazolo[3,4-b]pyrazines is reported. The compounds were synthesized by condensing diaminofurazan with alpha-keto acids to give a variety of aryl-substituted analogues. Halogenated phenyl groups at C-6 give rise to the greatest Haemophilus influenzae antibacterial activity.     

A hybrid protein of urokinase growth-factor domain and plasminogen-activator inhibitor type 2 inhibits urokinase activity and binds to the urokinase receptor.

The binding of urokinase-type plasminogen activator (uPA) to its specific cell-surface receptor (uPAR) localises the proteolytic cascade initiated by uPA to the pericellular environment. Inhibition of uPA activity or prevention of uPA binding to uPAR might have a beneficial effect on disease states wherein this activity is deregulated, e.g. cancer and some inflammatory diseases. To this end, a bifunctional hybrid molecule consisting of the uPAR-binding growth-factor domain of uPA (amino acids 1-47; GFuPA) at the N-terminus of plasminogen-activator inhibitor type 2 (PAI-2) was produced in Saccharomyces cerevisiae. The purified protein inhibited uPA with kinetics similar to placental or recombinant PAI-2 and was also found to bind to U937 cells and to FL amnion cells. GFuPA-PAI-2 competed with uPA, the N-terminal fragment of uPA and a proteolytic fragment of uPA (amino acids 4-43) in cell binding experiments, indicating that the molecule bound to the cells via uPAR. Hence, both the uPA-inhibitory and uPAR-binding domains of the hybrid molecule were functional, demonstrating the feasibility of the novel concept of introducing an unrelated, functional domain onto a member of the serine-protease-inhibitor superfamily.     

Synthesis and antibacterial activity of 5-substituted oxazolidinones

A series of 5-substituted oxazolidinones with varying substitution at the 5-position of the oxazolidinone ring were synthesized and their in vitro antibacterial activity was evaluated. The compounds demonstrated potent to weak antibacterial activity. A novel compound (PH-027) demonstrated potent antibacterial activity, which is comparable to or better than those of linezolid and vancomycin against antibiotic-susceptible standard and clinically isolated resistant strains of gram-positive bacteria. Although the presence of the C-5-acetamidomethyl functionality at the C-5 position of the oxazolidinones has been widely claimed and reported as a structural requirement for optimal antimicrobial activity in the oxazolidinone class of compounds, our results from this work identified the C-5 triazole substitution as a new structural alternative for potent antibacterial activity in the oxazolidinone class.     

Design, synthesis and antibacterial activity of cecropin-like model peptides

In order to investigate structure-activity relationships of cecropins, model peptides that mimic certain structural features of the cecropin molecules were designed and synthesized. The conformational analysis of cecropins and the design of the model peptides were based on Chou-Fasman calculations. The peptides were synthesized by solid-phase methods and purified by reverse-phase liquid-chromatography on C18-silica columns. Their secondary structures were studied by circular dichroism measurements. Antibacterial activities against seven test organisms were determined and compared to the activities of the natural cecropins A and B. These results were discussed on the basis of structural features of the model peptides and on model mechanisms. It was concluded that high antibacterial activity for this class of compounds requires a basic helical amphipathic N-terminal segment that is connected to a hydrophobic helical C-terminal segment by a flexible non-helical hinge region.     

Amino acids conjugated quinazolinone-Schiff’s bases as potential antimicrobial agents: Synthesis,SAR and molecular docking studies

A series of amino acids conjugated quinazolinone-Schiff’s bases were synthesized and characterized by analytical and spectroscopic methods. All the synthesized analogues (8–43) and the intermediates (1–7) were screened for their in vitro antibacterial and antifungal activities. In antimicrobial activity, compounds 12–16, 21–25, 30–34 and 39–43 showed excellent antibacterial activity which is better than the antibacterial standard Streptomycin. Compounds 15, 23–25, 30–34, 36 and 38–43 showed excellent antifungal activities which is more active than the reference antifungal drug Bavistin. Further, to understand the correlation of biological activity with that of drug-receptor interaction, molecular docking was performed on active site ofglucosamine-6-Phosphate (GlcN-6-P) synthase (PDB ID: 2VF5) which showed good binding profile. Molecular docking studies and Preliminary structure-activity (SAR) relationship revealed that the tryptophan and phenylalanine conjugated quinazolinones with electron donating groups (OH and OCH₃) were found to be excellent antimicrobial activities which is better than the glycine and alanine conjugated derivatives. This may be explained by the contribution of aromaticity and hydrophobicity of amino acids. Among the series, compounds 41 and 43 showed the highest docking scores for antimicrobial activity. The conjugation plays a major role in improving the biological activities of those compounds.     

Synthesis and biological evaluation of novel 1,4-naphthoquinone derivatives as antibacterial and antiviral agents

A series of 1,4-naphthoquinone derivatives were synthesized and evaluated for antibacterial and antiviral activities. The structure-activity relationships of these compounds were also studied. The results suggest that compounds 9-22 showed in vitro marked antibacterial activity. Compounds 4c and 7a showed inhibitory effect against RNA dependent RNA polymerase induced poliovirus type 2 infected HeLa cells.