Novel 3‐Substituted Ocotillol‐Type Triterpenoid Derivatives as Antibacterial Candidates

Plant‐derived triterpenoid saponins are involved in the plant defense system by targeting bacterial membranes. A series of ocotillol‐type triterpenoid derivatives were synthesized starting from PPD, one of the main components of Panax ginseng and their antibacterial activity against several representative bacteria were evaluated. Compounds 5 and 11 exhibited excellent antibacterial activity with MIC values of 1 μg/mL against Staphylococcus aureus and 8 μg/mL and 4 μg/mL against Bacillus subtilis, respectively. Furthermore, when compounds 5 and 11 were combined with two commercial antibiotics kanamycin and chloramphenicol, they showed strong synergistic activity at sub‐MIC levels against S. aureus USA300 and B. subtilis 168. Moreover, chloramphenicol turned from a bacteriostatic to a bactericidal agent when combined with compound 11 against B. subtilis 168.     

Microwave-assisted synthesis of some new tetrazolo[1,5-a]quinoline-based benzimidazoles catalyzed by p-TsOH and investigation of their antimicrobial activity

Keeping the objective to build up a new structural class of potent antimicrobials, a series of some new 4-Benzimidazol-2-yl tetrazolo[1,5-a]quinoline derivatives has been synthesized by reaction of tetrazolo[1,5-a]quinoline-4-carbaldehyde and o-phenylenediamine in the presence of an organocatalyst p-TsOH under the influence of microwave irradiation. The identity of all the compounds has been established by ¹H NMR, ¹³C NMR, FTIR, and elemental analysis. The synthesized compounds were subjected to in vitro antimicrobial screening against a representative panel of pathogenic strains including three Gram-positive bacteria (Bacillus subtilis, Clostridium tetani, and Streptococcus pneumoniae) and three Gram-negative bacteria (Escherichia coli, Salmonella typhi, and Vibrio cholerae) as well as two fungal organisms (Aspergillus fumigatus and Candida albicans) by employing broth microdilution method. Of the compounds studied, compound 5e demonstrated significant activity against a Gram-positive bacteria Bacillus subtilis.     

Pyridazine and its related compounds. Part 36. Synthesis and antimicrobial activity of some novel pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazine derivatives

Novel derivatives of pyrimidothienopyridazine were designed and synthesized through a versatile method. Some of the target compounds bearing the sulfonamide group were evaluated for their antimicrobial activity against representative Gram-positive bacteria, Gram-negative bacteria, and fungi by applying the agar plate diffusion technique. The results showed that derivatives 11a have promising inhibitory activity against Gram-positive bacteria, and derivatives 11b and 11e have also potent inhibition against fungi. Rest of the compounds showed moderate to low activity against the examined micro-organisms.     

Oxazolidinone antimicrobials: a patent review (2012-2015)

Introduction: Antimicrobial resistance in Gram-positive bacteria is a major health care issue. This review summarizes patent publications from 2012 to 2015 that divulged novel oxazolidinones as antibacterial agents.

Areas covered: A total of 25 patents obtained from Espacenet, WIPO Patentscope and FreePatentsOnline, and AcclaimIP search engines were reviewed. The patents were scrutinized based on the novelty of the compounds, their antibacterial activity (MIC, µg/mL), and the process of preparation. The oxazolidinones with promising antibacterial activity were classified according to the following structural diversities, as biaryl heterocyclic, fused heteroaryl rings containing oxazolidinones, and others. The biaryl heterocyclic, fused heteroaryl, benzoxazine, and the 1H-pyrazol-1-yl containing oxazolidinone derivatives demonstrated potent antibacterial activities superior to linezolid against Gram-positive bacteria. Some derivatives were effective against standard strains of Gram-negative bacteria, namely Moraxella catarrhalis ATCC A894, and Escherichia coli ATCC 25922. In addition, a patent disclosed a structural isomer of linezolid with marginal activity against the aerobic Gram-negative bacteria MDR Stenotrophomonas (Xanthomonas) maltophilia, while linezolid and vancomycin did not inhibit growth. Finally, some derivatives showed activity against respiratory infectious diseases’ causative agents, such as B. anthracis, B. mallei, Y. pestis, and M. pneumoniae.

Expert opinion: Overall, there is limited in vivo data to support the potential clinical advancement of the currently reported novel derivatives.     

Green synthesis of novel antifungal 1,2,4-triazoles effective against γ-irradiated Candida parapsilosis

This study reports the green synthesis of 11 novel 3-substituted-4-amino-5-mercapto-1,2,4-triazole derivatives using water as a readily available nontoxic solvent. Evaluation of their antimicrobial potential against several clinical pathogenic microorganisms was carried out. The newly synthesized cysteine derivative 6 showed promising antifungal activity against both γ-irradiated and nonirradiated Candida parapsilosis 216, with the lowest MIC (minimum inhibitory concentration) value of 3.125 µg/ml, probably through inhibition of 14α-demethylase. In addition, compound 6 showed complete inhibition of gelatinase, a virulence enzyme of C. parapsilosis. Also, scanning electron microscopy was carried out. Interestingly, compound 6 acted as a dual agent as it also showed good antibacterial activity against strains of Gram-positive bacteria used in the study. The synthesized compounds showed no cytotoxicity.     

Antimicrobial Activity of the Extracts and Essential Oil of Viguiera dentata

Viguiera dentata (Cav.) Sprenguel (Asteraceae) is known as “chimalacate” in several Mexican states. Infusions of the aerial part of this species are used for the treatment of baby rash by the inhabitants of San Rafael, Coxcatlan, Puebla, Mexico. We examined the antibacterial and antifungal activities through the disk-diffusion method. The composition and antimicrobial activity of the essential oil of V. dentata is reported here for the first time. The essential oil of aerial parts of V. dentata was examined by GC-MS: it is constituted mainly by monoterpenes (57.16%), and of this the major components are 1,3,3-trimethyl-tricyclo[2.2.1.02,6] heptane (30.85%) and limonene (13.27%). Gram-positive and Gram-negative bacteria were sensitive to the essential oil. The essential oil had no antifungal activity. The hexane extract H₁ presented antibacterial activity against seven strains (four Gram-positive and three Gram-negative); this extract had no antifungal activity. One bioactive compound, ent-kaur-16-en-19-oic acid 1, was isolated. In comparison with the essential oil and H₁, the pure compound 1 showed the lowest MICs in the majority of the bacterial strains. Only the hexane partition (H₂) of the methanol extract showed antifungal activity against all tested fungi.     

Potent antibacterial activity of dihydydropyrimidine‐1,3,5‐triazines via inhibition of DNA gyrase and antifungal activity with favourable metabolic profile

The compounds were tested against panel of three Gram‐positive, viz. Staphylococcus aureus, Bacillus subtilis, Bacillus cereus and three Gram‐negative bacterial strains viz. Pseudomonas aeruginosa, Escherichia coli, and Proteus vulgaris where they showed significant to moderate antibacterial activity. The compound also showed considerable antibiofilm activity against S. aureus and B. subtilis. The most potent compounds 7l and 7m found bacteriostatic in time‐kill assay via inhibition of DNA gyrase enzyme and interacting with Glu58, Val130, Ile175 and Ile186 via numerous H‐bonds as revealed by docking. In S. aureus‐induced murine infection model, compound 7m showed dose‐dependent reduction of viability of bacteria with maximum activity in 25 mg/kg treated group. The antifungal activity against human fungal pathogens was also estimated, where these compounds showed considerable inhibitory activity as compared to standard. The metabolic liability of compound 7m was determined using RS‐Predictor and MetaPrint 2D React. The molecules were proved as effective antibacterial agent via inhibition of DNA gyrase as a mechanism together with significant antifungal activity.     

Synthesis,crystal structure,and ADME prediction studies of novel imidazopyrimidines as antibacterial and cytotoxic agents

In the present study, a novel series of polyfunctionalized imidazopyrimidines 6a–u and 9a–d were efficiently constructed by a domino reaction between 2-imino-6-substituted-2,3-dihydropyrimidin-4(1H)-ones 4a–d or 8a–c and 2-bromoacetophenones 5a–i under mild basic conditions. The synthesized series were screened for their antibacterial activity against Staphylococcus aureus and Bacillus subtilis as Gram-positive (+) bacteria, as well as against Gram-negative (−) bacteria Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Salmonella typhi. Most of the synthesized derivatives of imidazopyrimidines 6 and 9 showed remarkable selectivity against Gram(−) bacteria over the Gram(+) ones. Compounds 6c , 6f , and 6g displayed potent and broad-spectrum antibacterial activity against all tested strains. Compounds 6f and 6g displayed promising inhibitory activity on GryB ATPase from E. coli with IC₅₀ = 1.14 and 0.73 μM, respectively. Simultaneously, some of the synthesized imidazopyrimidines were screened for their antiproliferative activity against 60 cancer cell lines at a concentration of 10 μM. Compound 9d showed potent activity against most of the tested cell lines, with a mean growth inhibition of 37%. The ADME (absorption, distribution, metabolism, and excretion) prediction study demonstrated that the synthesized hits have, in addition to their promising chemotherapeutic activity, acceptable pharmacokinetic properties, and a drug-likeness nature to be further developed.     

A facile route for the synthesis 1,4-disubstituted tetrazolone derivatives and evaluation of their antimicrobial activity

A facile route for the synthesis of 20 new 1,4-disubstituted tetrazolone derivatives from allyl bromides of Baylis–Hillman adducts and various 1-substituted tetrazolones is described. All the synthesized compounds were screened for in vitro antibacterial and antifungal activity. Out of 20 newly synthesized compounds 16 compounds showed very good activity against the Gram-positive bacteria Bacillus subtilis compare to the standard drug ciprofloxacin. The compounds 7b, 7n and 7o showed remarkable activity against both the Gram-positive bacteria B. subtilis and Staphylococcus aureus. Two compounds 7l and 7o showed very good activity against the Gram-negative bacteria Escherichia coli. The compounds, when tested for antifungal activity four compounds— 7b, 7l, 7o and 7s— showed very good activity against the strain Aspergillus niger, whereas seven compounds— 7e, 7g, 7h, 7l, 7o and 7s— display good activity against Candida albicans. Compounds 7b, 7e, 7g, 7l and 7o exhibited very good-to-high activity towards all the strains tested.     

Enhancement of anti-bacterial and anti-tumor activities of pentacyclic triterpenes by introducing exocyclic α,β-unsaturated ketone moiety in ring A

Ursolic acid, oleanolic acid, glycyrrhetinic acid, and betulinic acid, the representatives of pentacyclic triterpenes, were modified by introducing 2-methylene-3-oxo group as exocyclic α,β-unsaturated ketone moiety in ring A. The anti-bacterial and anti-tumor activities of these derivatives were assayed by comparing with the parent compounds. Results indicated that pentacyclic triterpenes carrying 2-methylene-3-oxo group in the ring A exhibited a significant improvement in anti-bacterial activity that was limited to Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis. The four derivatives also showed an increased cytotoxicity against leukemia, lung, and breast cancer cell lines in a dose-dependent manner in vitro. U2 and O2 compounds showed strong apoptotic activities to lung carcinoma cell lines. The results for the first time provided scientific evidence for improvement of anti-bacterial and anti-tumor activities of pentacyclic triterpenes using derivatives of these compounds.     

7-(3-氨基-4-烷氧亚胺基-1-哌啶基)喹诺酮类化合物的合成与抗菌作用

为寻找新的更加优秀的喹诺酮类抗菌药，设计合成了21个7-(3-氨基-4-烷氧亚胺基-1-哌啶基)喹诺酮类化合物，并测定其体内外抗菌活性。化合物结构经¹H NMR和HRMS得到确证，并用单晶X-衍射分析确定其双键构型。化合物14a和14m表现出优秀的广谱抗菌活性，它们对所实验的12株革兰氏阳性菌的活性，总体上明显优于3个对照药，特别是对包括MRSA和MRSE在内的金葡菌和表葡菌的活性是吉米沙星和巴罗沙星的4～16倍、左氧氟沙星的8～64倍。它们对金葡菌的MIC值分别是0.25～1 mg·L^-1和0.125～1 mg·L^-1，对表葡菌的MIC值分别是0.5～4 mg·L^-1和1～8 mg·L^-1，对小鼠系统感染的体内保护作用与吉米沙星、莫西沙星基本相当(P>0.05)。     

Screening for antimicrobial activity of some essential oils by the agar overlay technique

Fifty-three essential oils were tested against five micro-organisms (Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans) using the agar overlay technique. The essential oils were randomly selected and not on the basis of a supposed activity. It was found that all oils showed an activity against at least one micro-organism, and that substantial activities againstP. aeruginosa were scarce. Combined activities againstC. albicans, the Gram-positive bacteria andE. coli, and an activity againstC. albicans were most often observed. Secondly a combined activity againstC. albicans, B. subtilis andS. aureus was found. The differences between the inhibition zones were too small for a differentiation of the antimicrobial activities of the essential oils. A correlation matrix shows the relationships of the micro-organisms as to the activity patterns of the essential oils. High correlations were found for all the micro-organisms, except forP. aeruginosa.     

Anti-inflammatory activity of the constituents of the roots of <Emphasis Type="Italic">Aralia continentalis</Emphasis>

To assess the anti-inflammatory activity of the constituents of the roots of Aralia continentalis, ent-pimara-8(14),15-diene-19-oic acid (continentalic acid, pimaradienoic acid, compound I), 7β-hydroxy-ent-pimara-8(14),15-diene-19-oic acid (compound II), 7-oxo-ent-pimara-8(14),15-diene-19-oic acid (compound III), 15α,16α-epoxy-17-hydroxy-ent-kauran-19-oic acid (compound IV) and ent-kaura-16-en-19-oic acid (kaurenoic acid, compound V), their inhibitory effects against cyclooxygenase-2 (COX-2)-catalyzed PGE₂ and inducible nitric oxide synthase (iNOS)-catalyzed NO production by lipopolysaccharide-treated RAW 264.7 cells were examined. Among the compounds tested, compound III and V moderately inhibited NO production. In addition, compound III weakly inhibited PGE₂ production, while treatment with compounds II and IV at concentrations of up to 100 μM had no significant effects. Conversely, compound I only weakly inhibited PGE₂ and NO production. To elucidate the mechanism by which these changes occurred, the iNOS down-regulating capacity of compound III was investigated. Western blot analysis and an electrophoretic mobility shift assay demonstrated that compound III weakly inhibited COX-2 and iNOS expression at 50–100 μM, and inhibited NF-κB activation. When in vivo anti-inflammatory activities of compounds I, III and V were examined, intraperitoneal injection of 4–100 mg/kg of compound I and V significantly inhibited carrageenaninduced paw edema in mice, whereas compound III did not. Taken together, the results of this study suggest that some constituents of A. continentalis, especially compounds I, III and V, exert significant anti-inflammatory activity, which suggests that these constituents contribute, at least in part, to the anti-inflammatory action of the roots of A. continentalis.     

Alignment-based design and synthesis of new antimicrobial Aurein-derived peptides with improved activity against Gram-negative bacteria and evaluation of their toxicity on human cells

Considering the worldwide increasing prevalence of resistance to traditional antibiotics, it is necessary to find new antibiotics to deal with this issue. Recently, antimicrobial peptides (AMPs) have been proposed as new antimicrobial agents. Aureins are a family of AMPs that are isolated from Green and Golden Bell Frogs. These peptides have a favorable antibacterial activity against Gram-positive bacteria. We designed two peptides derived from natural Aurein enjoying alignment-based design method. After synthesis of the peptides, their secondary structure was checked by circular dichroism. Consequently, the antibacterial effects of these peptides were investigated by determining the minimum inhibitory concentration (MIC) and bactericidal concentration. Eventually, the toxicity of these peptides was determined by MTT (3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide) assay on normal human skin cells (Hu02 cell line). Natural Aurein1.2 was used as a natural control to compare the properties in all stages. The results indicated that these new peptides had medium-upward antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, and Bacillus subtilis (MIC of 8–64 μg/mL) and weak bactericidal activity against Staphylococcus aureus (MIC of 128–256 μg/mL). Also, MTT assays results showed that AureinN2 is less toxic than AureinN1 and Aurein1.2. Toxicity of AureinN2 for Hu02 cell lines was between 20 and 40% at the concentration of 8–500 μg/mL. In this study, we were able to improve antimicrobial activity of two synthetic derivatives of the Aurein family against Gram-negative bacteria by using machine-learning algorithm and other in silico methods.     

Synthesis and in?vitro antimicrobial activity of benzo[b][1,4]thiazin-3(4H)-ones via smiles rearrangement

New benzo[b][1,4]thiazin-3(4H)-one derivatives (compounds 12a–p) were synthesized via Smiles rearrangement and assayed in vitro for their antimicrobial activity against Gram-positive, Gram-negative bacteria and fungi. The antimicrobial activity of the benzo[b][1,4]thiazin-3(4H)-ones showed, on the whole, potent toward all tested Gram-positive and Gram-negative microorganism (minimal inhibitory concentration ranging from 16 to 64 μg/ml), whereas weak effectiveness was exhibited against fungi. Data obtained suggested that 12g, 12i, and 12o exerted the best antibacterial activity against Gram-positive bacteria and compound 12b demonstrated the best inhibition of Gram-negative bacteria. These observations provide some predictions to design further antimicrobial active compounds prior to their synthesis following with molecular modeling studies.     

Synthesis and antibacterial activity of novel levofloxacin derivatives containing a substituted thienylethyl moiety

Background and the purpose of the study

Piperazinyl quinolones such as ciprofloxacin, ofloxacin and levofloxacin are an important group of quinolone antimicrobials which are widely used in the treatment of various infectious diseases. In the present study, we synthesized a new series of levofloxacin derivatives and evaluated their antibacterial activities.

Methods

The N-substituted analogs of levofloxacin 6a–j were prepared by nucleophilic reaction of N-desmethyl levofloxacin 11 with thienylethyl bromide derivatives 8 or 9. All target compounds were tested using conventional agar dilution method in comparison to levofloxacin and N-desmethyl levofloxacin and their MIC values were determined against a panel of Gram-positive and Gram-negative bacteria.

Results

All compounds showed significant antibacterial activities against Gram-positive bacteria (MIC = 0.04-6.25 μg/mL); however, the activity against Gram-negative bacteria was lower (MIC = 1.56–100 μg/mL). As is evident from the data, oxime derivatives 6e, 6h and 6i are superior in inhibiting the growth of Gram-positive bacteria (MIC = 0.04–0.19 μg/mL), and their activities were found to be 5–25 times better than N-desmethyl levofloxacin 11 and equal or better than levofloxacin 4.

Conclusion

We have designed and synthesized novel quinolone derivatives bearing functionalized thienylethyl moiety on the piperazine ring of levofloxacin. The results of antibacterial screening against Gram-positive and Gram-negative bacteria revealed that the introduction of functionalized thienylethyl moiety on the piperazine ring of levofloxacin can improve the activity against Gram-positive bacteria. Gram-positive bacteria are responsible for a wide range of infectious diseases, and rising resistance in this group is causing increasing concern. Thus, this study introduces structural features of levofloxacin scaffold for development of new candidates in the field of anti-Gram positive chemotherapy     

Chemoselective N-benzylation of 2-thiohydantoins and 2-thiobarbituric acids catalyzed by PEG-stabilized Ni nanoparticles and their anti-microbial activities

An efficient one pot chemoselective N-benzylation of 2-thiohydantoins and 2-thiobarbituric acids catalyzed by PEG-stabilized Ni nanoparticles has been reported, wherein the NH group of thiohydantoins and thiobarbituric acids is selectively benzylated and no S-benzylation is observed. Mildness and environment friendly approach of the protocol gives it an edge over other conventional methods. These compounds were tested in vitro for their antibacterial activity against Gram-positive bacteria namely, Staphylococcus aureus and Bacillus subtilis and their inhibitory action against two strains of fungus.     

Structure–activity Relationship Studies of Microbiologically Active Thiosemicarbazides Derived from Hydroxybenzoic Acid Hydrazides

Forty-five derivatives of thiosemicarbazide were synthesized, and their antibacterial activity against Gram-positive and Gram-negative bacteria was evaluated. Some of the described compounds exhibited interesting activity against reference strains of Gram-positive bacteria, whereas only two derivatives had the ability to inhibit the growth of Gram-negative species (Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 13883, Proteus mirabilis ATCC 12453). The most potent antimicrobial activity was observed in the cases of salicylic acid hydrazide derivatives. The differences in activity inspired us to conduct conformational analysis using molecular mechanics level. The obtained results suggest that the molecule geometry, especially at the N4–terminus of thiosemicarbazide skeleton, determines the antibacterial activity. Unfortunately, in opposition to what we expected, only one of the tested compounds inhibited the activity of the topoIV enzyme, and none of them was active against DNA gyrase.     

Synthesis,characterization and antimicrobial activity of 4-((1-benzyl/phenyl-1<Emphasis Type="Italic">H</Emphasis>-1,2,3-triazol-4-yl)methoxy)benzaldehyde analogues

A diverse series of 4-((1-benzyl/phenyl-1H-1,2,3-triazol-4-yl)methoxy)benzaldehyde analogues has been synthesized in good yield by the click reaction between 4-O-propargylated benzaldehyde and various organic bromides/azides. All the synthesized compounds were tested in vitro for their antimicrobial activity against Gram-positive bacteria (Staphylococcus epidermidis and Bacillus subtilis), Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and fungi (Candida albicans and Aspergillus niger). Most of the compounds exhibited good-to-excellent antimicrobial activity. Compound 7b was found to be more potent than ciprofloxacin against B. subtilis, whereas it showed activity comparable to ciprofloxacin against E. coli. Compounds 4h and 4i showed activity comparable to fluconazole against A. niger. Further, the binding mode of compound 7b into the active site of E. coli topoisomerase II DNA gyrase B has also been investigated.     

Synthesis and antibacterial activity of new tetracyclic quinolone antibacterials.

A series of 8-substituted-9,1-(epoxymethano)-7-fluoro-5-oxo-5H- thiazolo[3,2-a]quinoline-4-carboxylic acids having a novel tetracyclic structure was synthesized and tested for antibacterial activity. The nature of the heteroatom (N, O, or S) substituted at the 8-position had little influence on the antibacterial activity. Among the six pyrrolidinyl derivatives and the five piperazinyl derivatives, the 8-(3-hydroxy-1-pyrrolidinyl) derivative 6h and the hydrochloride of the 8-(4-methyl-1-piperazinyl) derivative 6l showed the most potent activity against both Gram-positive and Gram-negative bacteria. Against nalidixic acid resistant strains, isolated from Escherichia coli KC-14, compound 6h was less potent than 6l. Replacement of the piperazinyl nitrogen atom by a carbon atom, an oxygen atom, or a sulfur atom (corresponding to the piperidino, morpholino, or thiomorpholino group, respectively) enhanced the activity against Gram-positive bacteria, but reduced the activity against Gram-negative bacteria. Compound 6l also showed potent in vivo antibacterial activity against Gram-positive and Gram-negative bacteria, and did not cause convulsions in mice with the concomitant administration of fenbufen. Replacement of the carboxy group by a sulfonic acid group in 6l resulted in a complete loss of antibacterial activity.