Synthesis and Antimicrobial Evaluation of Novel Chiral 2‐Amino‐4,5,6,7‐tetrahydrothieno[2,3‐c]pyridine Derivatives

New N‐substituted‐2‐amino‐4,5,6,7‐tetrahydrothieno[2,3‐c]pyridine derivatives were synthesized employing a convenient one‐pot three‐component method and their structures were characterized by ¹H‐NMR and single crystal X‐ray diffraction analysis. All the synthesized compounds were in vitro screened for antimicrobial activity against Gram‐positive (Sarcina lutea) and Gram‐negative bacteria (Escherichia coli). In this work, we introduced a chiral residue on the tetrahydropyridine nitrogen, the hitherto the less investigated position on this pharmacophore in order to explore the effect. The antibacterial results showed that the synthesized compounds were active only against Gram‐positive bacteria and the (R)‐enantiomers displayed a greater antimicrobial potency than their (S)‐counterparts. The structure–activity relationship here investigated may provide some interesting clues for future development of tetrahydrothienopyridine derivatives with higher antimicrobial activity.     

Synthesis,Antimicrobial Activity and Molecular Docking Study of Novel α‐(Diphenylphosphoryl)‐ and α‐(Diphenylphosphorothioyl)cycloalkanone Oximes

A series of novel α‐(diphenylphosphoryl)‐ and α‐(diphenylphosphorothioyl)cycloalkanone oximes have been synthesized in search for novel bioactive molecules. Their structures were characterized by various spectroscopic methods including IR, NMR (¹H, ³¹P, ¹³C), mass spectrometry and single crystal X‐ray diffraction. The newly synthesized phosphorus‐containing oximes were screened for their in vitro antimicrobial activity against Gram‐positive bacteria (Staphylococcus aureus and Bacillus subtilis), Gram‐negative bacteria (Escherichia coli and Salmonella typhimurium) and fungal strains (Candida albicans and Candida glabrata). The biological assays showed that all the studied compounds exhibited high antibacterial and antifungal activities at only 0.1–2.1 μg/mL. In silico molecular docking studies in FabH enzyme active site were performed in order to predict the possible interaction modes and binding energies of the drug candidates at the molecular level.     

Synthesis of short cationic antimicrobial peptidomimetics containing arginine analogues

Worldwide efforts are underway to develop new antimicrobial agents against bacterial resistance. To identify new compounds with a good antimicrobial profile, we designed and synthesized two series of small cationic antimicrobial peptidomimetics (1–8) containing unusual arginine mimetics (to introduce cationic charges) and several aromatic amino acids (bulky moieties to improve lipophilicity). Both series were screened for in vitro antibacterial activity against a representative panel of Gram‐positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram‐negative (Escherichia coli and Klebsiella pneumoniae) bacterial strains, and Candida albicans. The biological screening showed that peptidomimetics containing tryptophan residues are endowed with the best antimicrobial activity against S. aureus and S. epidermidis in respect to the other synthesized derivatives (MIC values range 7.5–50 µg/ml). Moreover, small antimicrobial peptidomimetics derivatives 2 and 5 showed an appreciable activity against the tested Gram‐negative bacteria and C. albicans. The most active compounds (1–2 and 5–6) have been tested against Gram‐positive established biofilm, too. Results showed that the biofilm inhibitory concentration values of these compounds were never up to 200 µg/ml. The replacement of tryptophan with phenylalanine or tyrosine resulted in considerable loss of the antibacterial action (compounds 3–4 and 7–8) against both Gram‐positive and Gram‐negative bacterial strains. Furthermore, by evaluating hemolytic activity, the synthesized compounds did not reveal cytotoxic activities, except for compound 5. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Structure‐activity relationship of indolicidin,a Trp‐rich antibacterial peptide

A series of Trp and Arg analogs of antibacterial indolicidin (Ind) was synthesized and the antimicrobial and hemolytic activities were investigated. [L⁹]Ind, [L¹¹]Ind, [K⁸,L⁹]Ind and [K^{6, 8},L⁹]Ind showed desirable characteristics, exhibiting negligible hemolytic activity while keeping strong antibacterial activity. The results indicated that the Trp residue at position 11 essentially contributes to both activities and one can not be exchanged for the other, whereas the Trp residues at positions 4 and 9 play important roles in antimicrobial and hemolytic activities, respectively. The Trp residues at positions 6 and 8 play no important roles in biological activities. We then found that the retro analog of Ind showed higher antibacterial activity than Ind against both Gram‐positive and Gram‐negative bacteria but remarkably lower hemolytic activity than that of Ind. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Synthesis and Antibacterial Evaluation of Mannich Bases Derived from 1,2,4‐Triazole

The series of novel Mannich bases were synthesized and evaluated for their in vitro antibacterial activity against Gram‐positive and Gram‐negative bacterial strains. The results showed that all compounds were less active than the drugs used as reference, but some of them had moderate potency against Staphylococcus epidermidis ATCC 12228 and Bacillus subtilis ATCC 6633. The presence of a phenyl ring in the position 4 of piperazine seems to be necessary for antibacterial activity in this class of compounds.     

Synthesis and in Vitro Antimicrobial Activity Screening of New 3‐Acetyl‐2,5‐disubstituted‐1,3,4‐oxadiazoline Derivatives

Thirteen new 3‐acetyl‐2,5‐disubstituted‐1,3,4‐oxadiazoline derivatives were synthesized from corresponding hydrazide‐hydrazones of isonicotinic acid in the reaction with acetic anhydride. The obtained compounds were identified with the use of spectral methods (IR, ¹H‐NMR, ¹³C‐NMR, MS). In vitro antimicrobial activity screening of synthesized compounds against a panel of bacteria and fungi revealed interesting antibacterial and antifungal activity of tested 1,3,4‐oxadiazoline derivatives, which is comparable to that of commonly used antimicrobial agents.     

Syntheses and Structure–Activity Relationships in Antibacterial Activity against Clostridium difficile and XBP1 Activation Property of 13‐[(N‐Alkylamino)methyl]‐8‐oxodihydrocoptisines

13‐[(N‐Alkylamino)methyl]‐8‐oxodihydrocoptisines were synthesized to evaluate antibacterial activity against Clostridium difficile and activating x‐box‐binding protein 1 (XBP1) activity, biological properties both associated with ulcerative colitis. Improving structural stability and ameliorating biological activity were major concerns. Different substituents on the structural modification site were involved to explore the influence of diverse structures on the bioactivities. The target compounds exhibited the desired activities with definite structure–activity relationship. In the series of 13‐[(N‐n‐alkylamino)methyl]‐8‐oxodihydrocoptisines, the length of n‐alkyl groups has a definite effect on the bioactivity, elongation of the length increasing the antibacterial activity. The synthesized compounds were determined to display strong or weak XBP1‐activating activity in vitro. The preliminary results of this study warrant further medicinal chemistry studies on these synthesized compounds.     

Evaluation of antimicrobial,antibiofilm and carbonic anhydrase inhibition profiles of 1,3‐bis‐chalcone derivatives

A series of 1,3‐bis‐chalcone derivatives ( 3a‐i, 6a‐i and 8 ) were synthesized and evaluated antimicrobial, antibiofilm and carbonic anhydrase inhibition activities. In this evaluation, 6f was found to be the most active compound showing the same effect as the positive control against Bacillus subtilis and Streptococcus pyogenes in terms of antimicrobial activity. Biofilm structures formed by microorganisms were damaged by compounds at the minimum inhibitory concentration value between 0.5% and 97%.1,3‐bis‐chalcones ( 3a‐i, 6a‐i and 8 ) showed good inhibitory action against human (h) carbonic anhydrase (CA) isoforms I and II. hCA I and II were effectively inhibited by these compounds, with K _i values in the range of 94.33 ± 13.26 to 787.38 ± 82.64 nM for hCA I, and of 100.37 ± 11.41 to 801.76 ± 91.11 nM for hCA II, respectively. In contrast, acetazolamide clinically used as CA inhibitor showed K _i value of 1054.38 ± 207.33 nM against hCA I, and 983.78 ± 251.08 nM against hCA II, respectively.     

Biocidal and anti‐corrosive activities of benzoimidazol‐3‐ium cationic Schiff base surfactants

Two series of cationic Schiff base surfactants, namely, 2‐(benzylideneamino)‐3‐(2‐oxo‐2‐alkoxyethyl)‐1,3‐benzoimidazol‐3‐ium bromide (I _A–D ) and 2‐[(4‐methoxybenzylidene) amino]‐3‐(2‐oxo‐2‐alkoxyethyl)‐1,3‐benzoimidazol‐3‐ium bromide (II _A–D ) were prepared. The chemical structures of the prepared Schiff bases were recognized by elemental analysis, FTIR, H NMR, C¹³‐NMR and GC/MS spectra. The surface activities of the synthesized Schiff base cationic surfactants showed their tendency towards adsorption at the air/water interface. The adsorption tendency was estimated from the values of surface tension and the depression of surface tension at the critical micelle concentration. The studied surfactants were evaluated as antimicrobial agents against pathogenic and sulfur‐reducing bacteria using inhibition zone diameters and minimum inhibition concentration values. The synthesized cationic benzoimidazolium Schiff base cationic surfactants showed good antimicrobial activities against the tested microorganisms including Gram positive, Gram negative as well as fungi. The synthesized compounds were tested for the activity as corrosion inhibitors against carbon steel corrosion in 0.5 M HCl at 200 and 400 ppm. The promising inhibition efficiency of these compounds against the sulfur‐reducing bacteria facilitates them to be applicable in the petroleum field as new categories of Sulfur Reducing Bacteria biocides. The inhibition efficiencies of the tested compounds showed good inhibition and protection of the carbon steel. The corrosion inhibition tendency correlated to the surface activity and chemical structure of the compounds.     

Antimicrobial activity,bactericidal mechanism and LPS‐neutralizing activity of the cell‐penetrating peptide pVEC and its analogs

pVEC is a cell‐penetrating peptide derived from the murine vascular endothelial‐cadherin protein. To evaluate the potential of pVEC as antimicrobial peptide (AMP), we synthesized pVEC and its analogs with Trp and Arg/Lys substitution, and their antimicrobial and lipopolysaccharide (LPS)‐neutralizing activities were investigated. pVEC and its analogs displayed a potent antimicrobial activity (minimal inhibitory concentration: 4–16 μM) against Gram‐positive and Gram‐negative bacteria but no or less hemolytic activity (less than 10% hemolysis) even at a concentration of 200 μM. These peptides induced a near‐complete membrane depolarization (more than 80%) at 4 μM against Staphylococcus aureus and a significant dye leakage (35–70%) from bacterial membrane‐mimicking liposome at a concentration as low as 1 μM. The fluorescence profiles of pVEC and its analogs in dye leakage from liposome and membrane depolarization were similar to those of a frog‐derived AMP, magainin 2. These results suggest that pVEC and its analogs kill bacteria by forming a pore or ion channel in the cytoplasmic membrane. pVEC and its analogs significantly inhibited nitric oxide production or tumor necrosis factor‐α release in LPS‐stimulated mouse macrophage RAW264.7 cells at 10 to 50 μM, in which RAW264.7 were not damaged. Taken together, our results suggest that pVEC and its analogs with potent antimicrobial and LPS‐neutralizing activities can serve as AMPs for the treatment of microbial infection and sepsis. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

In vitro activity of novel in silico‐developed antimicrobial peptides against a panel of bacterial pathogens

Antimicrobial‐peptide‐based therapies could represent a reliable alternative to overcome antibiotic resistance, as they offer potential advantages such as rapid microbicidal activity and multiple activities against a broad spectrum of bacterial pathogens. Three synthetic antimicrobial peptides (AMPs), AMP72, AMP126, and also AMP2041, designed by using ad hoc screening software developed in house, were synthesized and tested against nine reference strains. The peptides showed a partial β‐sheet structure in 10‐mM phosphate buffer. Low cytolytic activity towards both human cell lines (epithelial, endothelial, and fibroblast) and sheep erythrocytes was observed for all peptides. The antimicrobial activity was dose dependent with a minimum bactericidal concentration (MBC) ranging from 0.17 to 10.12 μM (0.4–18.5 µg/ml) for Gram‐negative and 0.94 to 20.65 μM (1.72‐46.5 µg/ml) for Gram‐positive bacteria. Interestingly, in high‐salt environment, the antibacterial activity was generally maintained for Gram‐negative bacteria. All peptides achieved complete bacterial killing in 20 min or less against Gram‐negative bacteria. A linear time‐dependent membrane permeabilization was observed for the tested peptides at 12.5 µg/ml. In a medium containing Mg²⁺ and Ca²⁺, the peptide combination with EDTA restores the antimicrobial activity particularly for AMP2041. Moreover, in combination with anti‐infective agents (quinolones or aminoglycosides) known to bind divalent cation, AMP126 and AMP2041 showed additive activity in comparison with colistin. Our results suggest the following: (i) there is excellent activity against Gram‐negative bacteria, (ii) there is low cytolytic activity, (iii) the presence of a chelating agent restores the antimicrobial activity in a medium containing Mg²⁺ and Ca²⁺, and (iv) the MBC value of the combination AMPs–conventional antibiotics was lower than the MBC of single agents alone. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

Peptide dendrimers as antifungal agents and carriers for potential antifungal agent—N3‐(4‐methoxyfumaroyl)‐(S)‐2,3‐diaminopropanoic acid—synthesis and antimicrobial activity

A series of peptide dendrimers and their conjugates with antimicrobial agent FMDP (N³‐(4‐methoxyfumaroyl)‐(S)‐2,3‐diamino‐propanoic acid) were synthesized. The obtained compounds were tested for the antibacterial and antifungal activity. All novel dendrimers displayed much better activity against the tested strains than FMDP itself. Moreover, their conjugates with FMDP also exhibited antimicrobial activity. The most promising molecules were tested against a broad selection of fungal strains. The analysis of their antifungal properties indicates that the examined molecules are efficient growth inhibitors of fluconazole‐resistant hospital‐acquired strains. Moreover, an application of amphiphilic branched peptides such as FMDP carriers suggests that transport mechanism involves more likely the cell membrane perturbation than the mediation of the specific transport proteins. The activity of obtained compounds strongly depends on the specific structure of the molecule.     

Defensin‐like peptide3 from black solder fly: Identification,characterization, and key amino acids for anti‐Gram‐negative bacteria

An antibacterial peptide was isolated from a black soldier fly, Hermetia illucens. The molecular mass of this peptide was established as 4247.37 by matrix‐assisted laser desorption/ionization‐time of flight mass (MALD‐TOF MS) spectrometry. The amino acid sequence of the mature peptide was determined by N‐terminal sequencing using Edman degradation, combined with cDNA sequencing of the previously reported defensin‐like peptide (DLP) 3. Analysis of the minimal inhibitory concentration (MIC) revealed that DLP3 had potent activity against Gram‐positive and negative bacteria, but DLP4 had only anti‐Gram‐positive activity as previously reported. Recombinant DLP3 and DLP4 were overexpressed in Escherichia coli, and antibacterial activities were identical to DLPs purified from H. illucens hemolyph. In silico analysis revealed that only six amino acid sequences were different between DLP3 and DLP4, but antibacterial activity against Gram‐negative bacteria differed. Therefore these amino acid variants may be key amino acids (Gly‐10, Val‐18, Met‐23, Arg‐25, Asp‐32, Arg‐40) related to killing Gram‐negative bacteria.     

High‐yield recombinant expression of the chicken antimicrobial peptide fowlicidin‐2 in Escherichia coli

The antimicrobial peptide fowlicidin‐2 identified in chicken is a member of the cathelicidins family. The mature fowlicidin‐2 possesses high antibacterial efficacy and lipopolysaccharide (LPS) neutralizing activity, and also represents an excellent candidate as an antimicrobial agent. In the present study, the recombinant fowlicidin‐2 was successfully produced by Escherichia coli (E. coli) recombinant expression system. The gene encoding fowlicidin‐2 with the codon preference of E. coli was designed through codon optimization and synthesized in vitro. The gene was then ligated into the plasmid pET‐32a(+), which features fusion protein thioredoxin at the N‐terminal. The recombinant plasmid was transformed into E. coli BL21(DE3) and cultured in Luria‐Bertani (LB) medium. After isopropyl‐β‐D‐thiogalactopyranoside (IPTG) induction, the fowlicidin‐2 fusion protein was successfully expressed as inclusion bodies. The inclusion bodies were dissolved and successfully released the peptide in 70% formic acid solution containing cyanogen bromide (CNBr) in a single step. After purification by reverse‐phase high‐performance liquid chromatography (RP‐HPLC), ～6.0 mg of fowlicidin‐2 with purity more than 97% was obtained from 1 litre of bacteria culture. The recombinant peptide exhibited high antibacterial activity against the Gram‐positive and Gram‐negative bacteria, and even drug‐resistant strains. This system could be used to rapidly and efficiently produce milligram quantities of a battery of recombinant antimicrobial peptides as well as for large‐scale production. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:369–374, 2015     

Experimental and molecular docking investigation on DNA interaction of N‐substituted phthalimides: antibacterial,antioxidant and hemolytic activities

A series of Schiff base molecules derived from a phthalimide scaffold was investigated as efficient antibacterial, antioxidant and DNA‐interacting agents. The spectroscopic characterization of these derivatives was studied in detail using elemental analysis and spectroscopic techniques. The DNA‐binding profile of title molecules against Ct‐DNA (calf thymus) was investigated by absorbance, fluorescence, hydrodynamics and thermal denaturation investigations. The bacterial inhibition potential of these molecules was investigated against Escherichia coli and Staphylococcus aureus. Molecule 3c emerged as the most active against S. aureus (IC₅₀: 14.8 μg/mL), whereas compounds 3a and 3b displayed potential antibacterial activities against E. coli (IC₅₀: 49.7 and 67.6 μg/mL). Molecular docking studies of these compounds against GlcN‐6‐P synthase were carried out to rationalize antibacterial efficiency of these molecules. These newly synthesized molecules were screened for their scavenging capacity against 2,2‐diphenyl‐1‐picryl‐hydrazyl (DPPH) and H₂O₂ free radicals and the results were compared with ascorbic acid as synthetic antioxidant. The title molecules 3a, 3b and 3e showed less than 20% hemolysis, which indicated their significant non‐toxic behavior.     

Enzymatic Resolution of α‐Methyleneparaconic Acids and Evaluation of their Biological Activity

Both enantiomers of three biologically relevant paraconic acids—MB‐3, methylenolactocin, and C75—were obtained with enantioselectivities up to 99% by kinetic enzymatic resolutions. Good enantiomeric excesses were obtained for MB‐3 and methylenolactocin, using α‐chymotrypsin and aminoacylase as enantiocomplementary enzymes, while C75 was resolved with aminoacylase. They all were evaluated for their antiproliferative, antibacterial, and antifungal activities, showing weak effects and practically no difference between enantiomers in each case. At high concentrations (16–64 µg/mL), (–)‐ C75 acted as an antimicrobial agent against Gram‐positive bacteria. Chirality 27:239–246, 2015. © 2015 Wiley Periodicals, Inc.     

Synthesis,Characterization, and Anti‐Amoebic Activity of N‐(Pyrimidin‐2‐yl)benzenesulfonamide Derivatives

A new series of N‐(pyrimidin‐2‐yl)benzenesulfonamide derivatives, 3a – 3i and 4a – 4i , was synthesized from pyrimidin‐2‐amines, 2a – 2i , with the aim to explore their effects on in vitro growth of Entamoeba histolytica. The chemical structures of the compounds were elucidated by elemental analysis, FT‐IR, ¹H‐ and ¹³C‐NMR, and ESI mass‐spectral data. In vitro anti‐amoebic activity was evaluated against HM1 : IMSS strain of Entamoeba histolytica. The IC₅₀ values were calculated by using the double dilution method. The results were compared with the IC₅₀ value of the standard drug ‘metronidazole’. The selected compounds were tested for their cytotoxic activities by cell‐viability assay using H9C2 cardiac myoblasts cell line, and the results indicated that all the compounds displayed remarkable >80% viabilities to a concentration of 100 μg/ml.     

Antibacterial spectrum and cytotoxic activities of serrulatane compounds from the Australian medicinal plant Eremophila neglecta

Aims: To determine the antibacterial spectrum and cytotoxic activities of serrulatane compounds from the Australian plant Eremophila neglecta. Methods and Results: Antimicrobial activities of serrulatane compounds 8,19‐dihydroxyserrulat‐14‐ene ( 1 ) and 8‐hydroxyserrulat‐14‐en‐19‐oic acid ( 2 ) were tested against Gram‐negative and Gram‐positive bacteria including human and veterinary pathogens and some multidrug‐resistant isolates. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of the compounds were determined by broth microdilution assay. Both compounds exhibited antibacterial activity against all Gram‐positive test strains. They showed antimycobacterial activity against isolates of Mycobacterium fortuitum and Mycobacterium chelonae. Of the five Gram‐negative bacteria tested, only Moraxella catarrhalis showed susceptibility to the compounds. Cytotoxic activities were tested in the Vero cell line. Compound 1 showed more activity than 2 in both antibacterial and cytotoxicity assays with cytotoxicity at concentrations similar to the MBC. Conclusions: Serrulatane compounds showed significant activity against medically important bacteria, with 1 exhibiting stronger antibacterial activity. However, they also displayed toxicity to mammalian cells. Significance and Impact of the Study: Serrulatanes are of interest as novel antibacterial compounds for use in biomedical applications; this study reports data obtained with a range of bacterial strains and mammalian cells, essential for assessing the capabilities and limitations of potential applicability of these compounds.     

Total synthesis and biological evaluation of spirotryprostatin A analogs

Based on the spirotryprostatin A structure, a series of compounds belonging to spiro‐indolyl diketopiperazine structural class were designed and synthesized, which embody an oxindole with an all‐carbon quaternary stereocenter. The total synthesis can efficiently be accessed in a seven‐step reaction sequence with 18–28% overall yield from commercially available materials, and a highly enantioselective 1,3‐dipolar cycloaddition, N ‐acylation of the resulting stereochemically complex spiro[pyrrolidin‐3,3′‐oxindole]s core with Fmoc‐L ‐pro‐Cl and spontaneous ring closure upon N ‐deprotection were obtained. The synthesized compounds 13a–e and 15a–e were evaluated for their antibacterial activities. The result showed that compounds 13b and 15b were active only against Gram‐positive bacteria, and selective antibacterial activity was exhibited by compounds 13d and 13e against Streptococcus lactis . Further, all the remaining compounds showed a certain degree of antibacterial activity. In addition, the structure–activity relationship is also discussed.