Characterization of the host-defense peptides from skin secretions of Merlin's clawed frog Pseudhymenochirus merlini: Insights into phylogenetic relationships among the Pipidae

The family Pipidae comprises the genera Hymenochirus, Pipa, Pseudhymenochirus, Silurana, and Xenopus but phylogenetic relationships within the family are unclear. Peptidomic analysis of norepinephrine-stimulated skin secretions from Pseudhymenochirus merlini Chabanaud, 1920, the single species within the genus Pseudhymenochirus, led to identification of 13 host-defense peptides with antimicrobial activity. Two peptides (hymenochirin-1Pa and -1Pb) show structural similarity to hymenochirin-1B from Hymenochirus boettgeri and eight peptides (hymenochirin-5Pa, -5Pb, -5Pc, -5Pd, -5Pe, -5Pf, 5Pg and -5Ph) are structurally similar to each other and to hymenochirin-5B from H. boettgeri. Two peptides differing by a single amino acid (IKIPSFFRNILKKVGKEAVSLM/I AGALKQS), termed pseudhymenochirin-1Pa and -1Pb, and pseudhymenochirin-2Pa (GIFPIFAKLLGKVIKVASSLISKGRTE) do not resemble host-defense peptides previously isolated from pipid frogs. Hymenochirin-5Pe was the most abundant peptide in the secretions and hymenochirin-1Pa the most potent against Staphylococcus aureus (MIC = 2.5 μM) and Escherichia coli (MIC = 10 μM). The data support a close phylogenetic relationship between Hymenochirus and Pseudhymenochirus that is distinct from the Xenopodinae (Xenopus + Silurana) clade with Pipa sister-group to all other extant pipids.     

Design,expression and characterization of the hybrid antimicrobial peptide LHP7, connected by a flexible linker,against Staphylococcus and Streptococcus

The emergence of bacterial resistance to common antibiotics poses a threat to human health and has rekindled an interest in antimicrobial peptides (AMPs). LHP7, a novel hybrid AMP containing 83 amino acid residues was designed on the basis of the LH28 and plectasin. LHP7 was expressed in Pichia pastoris, the total concentration of secreted protein reached 0.906 g/L after 108 h of methanol induction. Its antimicrobial activity was higher than that of the parent AMPs; the minimal inhibitory concentrations (MICs) of LHP7 against Staphylococcus aureus, Streptococcus pneumoniae and Streptococcus suis were 0.091, 0.023 and 0.18 μM, respectively. The antibacterial activity of LHP7 against clinical MRSA isolates (MICs = 0.73–2.91 μM) was enhanced over that of plectasin. The fractional inhibitory concentration (FIC) indicated a synergistic effect between LHP7 and ampicillin against MRSA (FIC = 0.375), and combinations of LHP7 with gentamicin, rifampin or tetracycline provided evidence of additive effects (FIC = 0.625–1.0). LHP7 exhibited a broad range of pH stability and thermostability, and a hemolytic activity of less than 5% below a concentration of 500 μg/mL. It was resistant to pepsin and papain digestion, but sensitive to trypsin digestion. These results suggest that LHP7 might have potential as a broadly applied and clinically useful antimicrobial agent.     

Synthesis of novel 4-nitropyrrole-based semicarbazide and thiosemicarbazide hybrids with antimicrobial and anti-tubercular activity

We report the synthesis and screening of forty novel 4-nitropyrrole-semicarbazide conjugates inspired from the reported bio-potential of bromopyrrole alkaloids and semicarbazide derivatives for antimicrobial activity. Herein, hybrids 5k–5o, 5r, 5s and 5t displayed four-fold increased activity (MIC = 0.39 μg/mL) against Escherichia coli compared to standard ciprofloxacin. Eight hybrids, 5k–5o and 5r–5t displayed equal antibacterial activity (MIC = 1.56 μg/mL) against Klebsiella pneumonia compared to standard ciprofloxacin. Hybrid, 5k–5o (MIC = 0.195 μg/mL) displayed highly potent antibacterial activity against MSSA as compared to standard ciprofloxacin. Eight-fold superior activity was observed for four hybrids 5k–5m and 5o (MIC = 0.39 μg/mL) against MRSA. Further, nine hybrids displayed four-fold superior antifungal activity (MIC = 0.78 μg/mL) compared to standard Amphotericin B. Encouraging MICs of these hybrids recognize them as promising leads for development of potential antimicrobial drugs.     

New class of methyl tetrazole based hybrid of (Z)-5-benzylidene-2-(piperazin-1-yl)thiazol-4(%H)-one as potent antitubercular agents

In search of potential therapeutics for tuberculosis, we describe here the synthesis and in vitro antitubercular activity of a novel series of thiazolone piperazine tetrazole derivatives. Among all the synthesized derivatives, four compounds (10, 14, 20 and 33) exhibited more potent activity (MIC = 3.08, 3.01, 2.62 and 2.51 μM) than ethambutol (MIC = 9.78 μM) and pyrazinamide (MIC = 101.53 μM) against Mycobacterium tuberculosis. Furthermore, they displayed no toxicity against Vero cells (C1008) and mouse bone marrow derived macrophages (MBMDMϕ). These investigated analogues have emerged as possible lead molecule to enlarge the scope of the study.     

Synthesis and antibiofilm activity of marine natural product-based 4-thiazolidinones derivatives

4-Thiazolidinones derivatives of marine bromopyrrole alkaloids were synthesized as potential antibiofilm compounds. Among the synthesized compounds, some showed promising antibiofilm activity. Biological data revealed that 1,3-thiazolidin-4-one derivatives are more potent antibiofilm agents compared to 1,3-thiazinan-4-ones. Antibiofilm activity of compound 4b, 4c (MIC = 0.78 μg/ml) was 3-fold superior than standard vancomycin (MIC = 3.125 μg/ml) while activity of compound 4d, 4f, 4g and 4h was 2-fold (MIC = 1.56 μg/ml) against Staphylococcus aureus biofilm. Compound 4b–4h showed equal antibiofilm activity against Staphylococcus epidermidis compared to standard Vancomycin (MIC = 3.125 μg/ml).     

Antimycobacterial and herbicidal activity of ring-substituted 1-hydroxynaphthalene-2-carboxanilides

In this study, a series of 22 ring-substituted 1-hydroxynaphthalene-2-carboxanilides were prepared and characterized. Primary in vitro screening of the synthesized compounds was performed against Mycobacterium marinum, Mycobacterium kansasii and Mycobacterium smegmatis. The compounds were also tested for their activity related to inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. Most of tested compounds showed the antimycobacterial activity against the three strains comparable or higher than the standard isoniazid. N-(3-Fluorophenyl)-1-hydroxynaphthalene-2-carboxamide showed the highest biological activity (MIC = 28.4 μmol/L) against M. marinum, N-(4-fluorophenyl)-1-hydroxynaphthalene-2-carboxamide showed the highest biological activity (MIC = 14.2 μmol/L) against M. kansasii, and N-(4-bromophenyl)-1-hydroxynaphthalene-2-carboxamide expressed the highest biological activity (MIC = 46.7 μmol/L) against M. smegmatis. This compound and 1-hydroxy-N-(3-methylphenyl)naphthalene-2-carboxamide were the most active compounds against all three tested strains. The PET inhibition expressed by IC₅₀ value of the most active compound 1-hydroxy-N-(3-trifluoromethylphenyl)naphthalene-2-carboxamide was 5.3 μmol/L. The most effective compounds demonstrated insignificant toxicity against the human monocytic leukemia THP-1 cell line. For all compounds, structure–activity relationships are discussed.     

Design,synthesis, and biological evaluation of dihydroartemisinin–fluoroquinolone conjugates as a novel type of potential antitubercular agents

Tuberculosis remains a global public health problem in recent years. To develop novel type of potential antitubercular agents, twelve novel dihydroartemisinin–fluoroquinolone (DHA–FQ) conjugates (three types of molecules) were gradually designed and conveniently synthesized. All the newly synthesized conjugates were well characterized and evaluated against different Mycobacterium tuberculosis strains in vitro. The screening results showed that five DHA–FQ conjugates were active toward M. tuberculosis H37Rv, and compound 3a exhibited the strongest inhibitory activity (MIC = 0.0625 μg/mL), which was comparable to the positive control Moxifloxacin and even stronger than Ofloxacin. Conjugates 2a and 3a also displayed comparable activities against various clinically isolated sensitive and resistant M. tuberculosis strains (MIC = 0.125–16 μg/mL) to Moxifloxacin. All target compounds possessed selective anti-M. tuberculosis ability. Preliminary structure–activity relationship demonstrated that short linker between DHA and FQ was favorable for strong antitubercular activity. This study provides a new clue for the development of novel antitubercular lead molecules.     

Insulin-releasing and cytotoxic properties of the frog skin peptide,tigerinin-1R: a structure–activity study

The frog skin host-defense peptide tigerinin-1R (RVCSAIPLPICH.NH₂) is insulinotropic both in vitro and in vivo. This study investigates the effects on insulin release and cytotoxicity of changes in cationicity and hydrophobicity produced by selected substitutions of amino acids by l-arginine, l-lysine and l-tryptophan. The [A5W], [L8W] and [I10W] analogs produced a significant (P < 0.01) increase in the rate of insulin release from BRIN-BD11 rat clonal β cells at concentration of 0.01 nM compared with 0.1 nM for tigerinin-1R. The increase in the rate of insulin release produced by a 3 μM concentration of the [S4R], [H12K], and [I10W] analogs from both BRIN-BD11 cells and mouse islets was significantly greater (P < 0.05) than that produced by tigerinin-1R. No peptide stimulated the release of lactate dehydrogenase at concentrations up to 3 μM indicating that plasma membrane integrity had been preserved. [A5W] tigerinin-1R was the only analog tested that showed cytotoxic activity against human erythrocytes (LC₅₀ = 265 ± 16 μM) and inhibited growth of Escherichia coli (MIC = 500 μM) and Staphylococcus aureus (MIC = 250 μM). The circular dichroism spectra of tigerinin-1R and [A5W] tigerinin-1R indicate that the peptides adopt a mixture of β-sheet, random coil and reverse β-turn conformations in 50% trifluoroethanol/water and methanol/water. Administration of [S4R] tigerinin-1R (75 nmol/kg body weight) to high-fat fed mice with insulin resistance significantly (P < 0.05) enhanced insulin release and improved glucose tolerance over a 60 min period following an intraperitoneal glucose load. The study supports the claim that tigerinin-1R shows potential for development into novel therapeutic agents for treatment of type 2 diabetes mellitus.     

Comparing anti-HIV,antibacterial, antifungal,micellar, and cytotoxic properties of tricarboxylato dendritic amphiphiles

Three series of homologous dendritic amphiphiles—RCONHC(CH₂CH₂COOH)₃, 1(n); ROCONHC(CH₂CH₂COOH)₃, 2(n); RNHCONHC(CH₂CH₂COOH)₃, 3(n), where R = n-C_nH_2n+1 and n = 13–22 carbon atoms—were assayed for their potential to serve as antimicrobial components in a topical vaginal formulation. Comparing epithelial cytotoxicities to the ability of these homologues to inhibit HIV, Neisseria gonorrhoeae, and Candida albicans provided a measure of their prophylactic/therapeutic potential. Measurements of the ability to inhibit Lactobacillus plantarum, a beneficial bacterium in the vagina, and critical micelle concentrations (CMCs), an indicator of the potential detergency of these amphiphiles, provided additional assessments of safety. Several amphiphiles from each homologous series had modest anti-HIV activity (EC₅₀ = 110–130 μM). Amphiphile 2(18) had the best anti-Neisseria activity (MIC = 65 μM), while 1(19) and 1(21) had MICs against C. albicans of 16 and 7.7 μM, respectively. Two measures of safety showed promise as all compounds had relatively low cytotoxic activity (EC₅₀ = 210–940 μM) against epithelial cells and low activity against L. plantarum, 1(n), 2(n), and 3(n) had MICs ? 490, 1300, and 940 μM, respectively. CMCs measured in aqueous triethanolamine and in aqueous potassium hydroxide showed linear dependences on chain length. As expected, the longest chain in each series had the lowest CMC—in triethanolamine: 1(21), 1500 μM; 2(22), 320 μM; 3(22), 340 μM, and in potassium hydroxide: 1(21), 130 μM; 3(22), 40 μM. The CMC in triethanolamine adjusted to pH 7.4 was 400 μM for 1(21) and 3900 μM for 3(16). The promising antifungal activity, low activity against L. plantarum, relatively high CMCs, and modest epithelial cytotoxicity in addition to their anti-Neisseria properties warrant further design studies with dendritic amphiphiles to improve their safety indices to produce suitable candidates for antimicrobial vaginal products.     

Novel 3-arylfuran-2(5H)-one-fluoroquinolone hybrid: Design,synthesis and evaluation as antibacterial agent

3-Arylfuran-2(5H)-one, a novel antibacterial pharmacophore targeting tyrosyl-tRNA synthetase (TyrRS), was hybridized with the clinically used fluoroquinolones to give a series of novel multi-target antimicrobial agents. Thus, twenty seven 3-arylfuran-2(5H)-one-fluoroquinolone hybrids were synthesized and evaluated for their antimicrobial activities. Some of the hybrids exhibited merits from both parents, displaying a broad spectrum of activity against resistant strains including both Gram-negative and Gram-positive bacteria. The most potent compound (11) in antibacterial assay shows MIC₅₀ of 0.11 μg/mL against Multiple drug resistant Escherichia coli, being about 51-fold more potent than ciprofloxacin. The enzyme assays reveal that 11 is a potent multi-target inhibitor with IC₅₀ of 1.15 ± 0.07 μM against DNA gyrase and 0.12 ± 0.04 μM against TyrRS, respectively. Its excellent inhibitory activities against isolated enzymes and intact cells strongly suggest that 11 deserves to further research as a novel antibiotic.     

Secretory expression of functional barley limit dextrinase by Pichia pastoris using high cell-density fermentation

Heterologous production of large multidomain proteins from higher plants is often cumbersome. Barley limit dextrinase (LD), a 98 kDa multidomain starch and α-limit dextrin debranching enzyme, plays a major role in starch mobilization during seed germination and is possibly involved in starch biosynthesis by trimming of intermediate branched α-glucan structures. Highly active barley LD is obtained by secretory expression during high cell-density fermentation of Pichia pastoris. The LD encoding gene fragment without signal peptide was subcloned in-frame with the Saccharomyces cerevisiae α-factor secretion signal of the P. pastoris vector pPIC9K under control of the alcohol oxidase 1 promoter. Optimization of a fed-batch fermentation procedure enabled efficient production of LD in a 5-L bioreactor, which combined with affinity chromatography on β-cyclodextrin–Sepharose followed by Hiload Superdex 200 gel filtration yielded 34 mg homogenous LD (84% recovery). The identity of the recombinant LD was verified by N-terminal sequencing and by mass spectrometric peptide mapping. A molecular mass of 98 kDa was estimated by SDS–PAGE in excellent agreement with the theoretical value of 97419 Da. Kinetic constants of LD catalyzed pullulan hydrolysis were found to K_m,app = 0.16 ± 0.02 mg/mL and k_cat,app = 79 ± 10 s^?1 by fitting the uncompetitive substrate inhibition Michaelis–Menten equation, which reflects significant substrate inhibition and/or transglycosylation. The resulting catalytic coefficient, k_cat,app/K_m,app = 488 ± 23 mL/(mg s) is 3.5-fold higher than for barley malt LD. Surface plasmon resonance analysis showed α-, β-, and γ-cyclodextrin binding to LD with K_d of 27.2, 0.70, and 34.7 μM, respectively.     

Synthesis and antimicrobial profile of N-substituted imidazolium oximes and their monoquaternary salts against multidrug resistant bacteria

Two different series of N-substituted imidazolium oximes and their monoquaternary salts were synthesized and biologically tested with respect to their ability to inhibit growth a diverse panel of antibiotic susceptible Gram-positive and antibiotic resistant Gram-negative bacteria as well fungal strains. The newly synthesized compounds were analyzed by spectral studies to confirm their structure. The preliminary results showed that all compounds tested possess promising antimicrobial potential against both susceptible Gram-positive and antibiotic resistant Gram-negative isolates, exhibiting a wide range of MIC values from 0.14 to 100.0 μg/mL. The structure–activity relationship demonstrates that the p-methylphenyl and p-fluorophenyl groups in monoquaternary salts 6 and 7 attached directly to the imidazolium ring could be essential for observed remarkable inhibitory profiles against clinically important pathogens Pseudomonas aeruginosa (MIC = 0.14 μg/mL) and Klebsiella pneumoniae (MIC = 1.56 μg/mL). Furthermore, the broth microdilution assay was then used to investigate the antiresistance efficacy of compound 7 against fourteen extended-spectrum β-lactamase (ESBL)-producing strains in comparison to eight clinically relevant antibiotics. Compound 7 exhibited a remarkable antiresistance profiles ranging between 0.39 and 12.50 μg/mL against all of ESBL-producing strains, which leads to the suggestion that may be interesting candidate for development of new antimicrobials to combat multidrug resistant Gram-negative bacteria.     

Anticancer activities of an antimicrobial peptide derivative of Ixosin-B amide

In nature, antimicrobial peptides (AMPs) represent the first line of defense against infection by pathogens; thus, they are generally good candidates for the development of antimicrobial agents. Recently, we reported two potent antimicrobial peptides, KWLRRVWRWWR-amide (MAP-04-03) and KRLRRVWRRWR-amide (MAP-04-04), which were derived from a fragment of Ixosin-B-amide (KSDVRRWRSRY). Since some cationic AMPs exhibited cytotoxic activity against cancer cells, in the current study, we further investigated the anticancer activity of these potent antimicrobial peptides by antiproliferative assays and wound-healing assays, and the effect of peptide on the cytoskeleton alteration and cell morphology were analyzed by confocal microscopy. Results indicated that MAP-04-03 not only exhibited inhibitory effects on the proliferation (IC₅₀ = 61.5 μM) and on the cell migration of MCF-7 breast cancer cells (at a concentration of 5 μM), but also affected the cytoskeleton at the concentration of 25 μM. These results demonstrated that MAP-04-03 can serve as a lead peptide analog for developing potent anticancer agents.     

Synthesis and antimicrobial activity of novel amphiphilic aromatic amino alcohols

We report in this work the preparation and in vitro antimicrobial evaluation of novel amphiphilic aromatic amino alcohols synthesized by reductive amination of 4-alkyloxybenzaldehyde with 2-amino-2-hydroxymethyl-propane-1,3-diol. The antibacterial activity was determined against four standard strains (Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa) and 21 clinical isolates of methicillin-resistant Staphylococcus aureus. The antifungal activity was evaluated against four yeast (Candida albicans, Candida tropicalis, Candida glabrata and Candida parapsilosis). The results obtained showed a strong positive correlation between the lipophilicity and the antibiotic activity of the tested compounds. The best activities were obtained against the Gram-positive bacteria (MIC = 2–16 μg ml^?1) for the five compounds bearing longer alkyl chains (4c–g; 8–14 carbons), which were also the most active against Candida (MIC = 2–64 μg ml^?1). Compound 4e exhibited the highest levels of inhibitory activity (MIC = 2–16 μg ml^?1) against clinical isolates of MRSA. A concentration of twice the MIC resulted in bactericidal activity of 4d against 19 of the 21 clinical isolates.     

Esculentin-2CHa: A host-defense peptide with differential cytotoxicity against bacteria,erythrocytes and tumor cells

The host-defense peptide, esculentin-2CHa (GFSSIFRGVA¹⁰KFASKGLGK D²⁰LAKLGVDLVA³⁰ CKISKQC) shows potent (MIC ≤ 6 μM) growth inhibitory activity against clinical isolates of multidrug-resistant strains of Staphylococcus aureus, Acinetobacter baumannii, and Stenotrophomonas maltophilia and differential cytotoxic activity against human erythrocytes (LC₅₀ = 150 μM) and human non-small cell lung adenocarcinoma A549 cells (LC₅₀ = 10 μM). Esculentin-2CHa significantly (P < 0.01) stimulates the release of the anti-inflammatory cytokine IL-10 by mouse lymphoid cells and elevates its production after stimulation with concanavalin A and significantly (P < 0.05) stimulates TNF-α production by peritoneal macrophages. Effects on IL-6 and IL-1β production were not significant. Removal of the hydrophobic N-terminal hexapeptide (GFSSIF) from esculentin-2CHa results in abolition of growth inhibitory activity against S. aureus and cytotoxic activity against erythrocytes and A549 cells as well as a marked (≥16-fold) reduction in potency against A. baumannii and S. maltophilia. The primary structure of esculentin-2 has been poorly conserved between frog species but evolutionary pressure has acted to maintain the hydrophobic character of this N-terminal hexapeptide sequence. Removal of the cyclic C-terminal domain (CKISKQC) and replacement of the Cys³¹ and Cys³⁷ residues by serine resulted in appreciable decreases in cytotoxicity against all microorganisms and against mammalian cells. The more cationic [D20K, D27K] analog showed a modest increase in potency against all microorganisms (up to 4-fold) but a marked increase in cytotoxicity against erythrocytes (LC₅₀ = 11 μM) and A549 cells (LC₅₀ = 3 μM).     

Characterization of bioactive recombinant antimicrobial peptide parasin I fused with human lysozyme expressed in the yeast Pichia pastoris system

Parasin I (PI) is a 19 amino acid peptide with potent antimicrobial activities against a broad spectrum of microorganisms and is a good candidate for development as a novel antimicrobial agent. The objective of this study was to express and characterize a codon optimized parasin I peptide fused with human lysozyme (hLY). A 513 bp cDNA fragment encoding the mature hLY protein and parasin I peptide was designed and synthesized according to the codon bias of Pichia pastoris. A 4 × Gly flexible amino acid linker with an enterokinase cleavage (DDDDK) was designed to link the PI to the C-terminal of hLY. The codon optimized recombinant hLY-PI was cloned into the pPICZαA vector and expressed in P. pastoris. The over-expressed extracellular rehLY-PI was purified using Ni sepharose affinity column and exhibited a molecular mass of approximately 18 kDa. After digested with enterokinase the rehLY-PI protein release its corresponding rehLY and rePI, with molecular mass of 16 kDa and 2 kDa, respectively, on Tricine-SDS-PAGE. The released rehLY exhibited similar lytical activity against Micrococcus lysodeikticus to its commercial hLY. The digested rehLY-PI product exhibited antimicrobial activities against Bacillus subtilis, Staphylococcus aureus and Escherichia coli, and synergism has been found between the released rePI and rehLY. In conclusion, we successfully optimized a rehLY-PI fusion protein encoding gene and over-expressed the rehLY-PI in P. pastoris. The recombination protein digested with enterokinase released functional hLY and antimicrobial parasin I, which demonstrates a potential for future use as an animal feed additive to partly replace antibiotic.     

A family of antimicrobial and immunomodulatory peptides related to the frenatins from skin secretions of the Orinoco lime frog Sphaenorhynchus lacteus (Hylidae)

Peptidomic analysis of norepinephrine-stimulated skin secretions of the Orinoco lime tree frog Sphaenorhynchus lacteus (Hylidae, Hylinae) revealed the presence of three structurally related host-defense peptides with limited sequence similarity to frenatin 2 from Litoria infrafrenata (Hylidae, Pelodryadinae) and frenatin 2D from Discoglossus sardus (Alytidae). Frenatin 2.1S (GLVGTLLGHIGKAILG.NH₂) and frenatin 2.2S (GLVGTLLGHIGKAILS.NH₂) are C-terminally α-amidated but frenatin 2.3S (GLVGTLLGHIGKAILG) is not. Frenatin 2.1S and 2.2S show potent bactericidal activity against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MIC ≤16 μM) but are less active against a range of Gram-negative bacteria. Frenatin 2.1S (LC₅₀ = 80 ± 6 μM) and 2.2S (LC₅₀ = 75 ± 5 μM) are cytotoxic against non-small cell lung adenocarcinoma A549 cells but are less hemolytic against human erythrocytes (LC₅₀ = 167 ± 8 μM for frenatin 2.1S and 169 ± 7 μM for 2.2S). Weak antimicrobial and cytotoxic potencies of frenatin 2.3S demonstrate the importance of C-terminal α-amidation for activity. Frenatin 2.1S and 2.2S significantly (P < 0.05) increased production of proinflammatory cytokines IL-1β and IL-23 by lipopolysaccharide (LPS)-stimulated mouse peritoneal macrophages and frenatin 2.1S also enhanced production of TNF-α. Effects on IL-6 production were not significant. Frenatin 2.2S significantly downregulated production of the anti-inflammatory cytokine IL-10 by LPS-stimulated cells. The data support speculation that frenatins act on skin macrophages to produce a cytokine-mediated stimulation of the adaptive immune system in response to invasion by microorganisms. They may represent a template for the design of peptides with therapeutic applications as immunostimulatory agents.     

Discovery of potent anti-tuberculosis agents targeting leucyl-tRNA synthetase

Tuberculosis is a serious infectious disease caused by human pathogen bacteria Mycobacterium tuberculosis. Bacterial drug resistance is a very significant medical problem nowadays and development of novel antibiotics with different mechanisms of action is an important goal of modern medical science. Leucyl-tRNA synthetase (LeuRS) has been recently clinically validated as antimicrobial target. Here we report the discovery of small-molecule inhibitors of M. tuberculosis LeuRS. Using receptor-based virtual screening we have identified six inhibitors of M. tuberculosis LeuRS from two different chemical classes. The most active compound 4-{[4-(4-Bromo-phenyl)-thiazol-2-yl]hydrazonomethyl}-2-methoxy-6-nitro-phenol (1) inhibits LeuRS with IC₅₀ of 6 μM. A series of derivatives has been synthesized and evaluated in vitro toward M. tuberculosis LeuRS. It was revealed that the most active compound 2,6-Dibromo-4-{[4-(4-nitro-phenyl)-thiazol-2-yl]-hydrazonomethyl}-phenol inhibits LeuRS with IC₅₀ of 2.27 μM. All active compounds were tested for antimicrobial effect against M. tuberculosis H37Rv. The compound 1 seems to have the best cell permeability and inhibits growth of pathogenic bacteria with IC₅₀ = 10.01 μM and IC₉₀ = 13.53 μM.     

3-Aryl-4-acyloxyethoxyfuran-2(5H)-ones as inhibitors of tyrosyl-tRNA synthetase: Synthesis,molecular docking and antibacterial evaluation

Thirty-eight 3-aryl-4-acyloxyethoxyfuran-2(5H)-ones were designed, prepared and tested for antibacterial activities. Some of them showed significant antibacterial activity against Gram-positive organism, Gram-negative organism and fungus. Out of these compounds, 4-(2-(3-chlorophenylformyloxy)ethoxy)-3-(4-chlorophenyl)furan-2(5H)-one (d40) showed the widest spectrum of activity with MIC₅₀ of 2.0 μg/mL against Staphylococcus aureus, 4.3 μg/mL against Escherichia coli, 1.5 μg/mL against Pseudomonas aeruginosa and 1.2 μg/mL against Candida albicans. Our data disclosed that MIC₅₀ values against whole cell bacteria are positive correlation with MIC₅₀ values against tyrosyl-tRNA synthetase. Meanwhile, molecular docking of d40 into S. aureus tyrosyl-tRNA synthetase active site was also performed, and the inhibitor tightly fitting the active site might be an important reason why it has high antimicrobial activity.     

Design,synthesis and evaluation of 6-(4-((substituted-1H-1,2,3-triazol-4-yl)methyl)piperazin-1-yl)phenanthridine analogues as antimycobacterial agents

Focus in this Letter is made to design and synthesize a series of nineteen new 6-(4-((substituted-1H-1,2,3-triazol-4-yl)methyl)piperazin-1-yl)phenanthridine analogues employing click chemistry and evaluated for their anti-tubercular activity against Mycobacterium tuberculosis H₃₇Rv. Among the tested compounds, 7f and 7j exhibited good activity (MIC = 3.125 μg/mL), while 8a displayed excellent activity (MIC = 1.56 μg/mL) against the growth of M. tuberculosis H₃₇Rv. In addition, 7f, 7j and 8a compounds were subjected to cytotoxic studies against mouse macrophage (RAW264.7) cell lines and the selectivity index values are >15 indicating suitability of compounds for further drug development.