Stereocontrolled facile synthesis and antimicrobial activity of oximes and oxime ethers of diversely substituted bispidines

A small library of diversely substituted 2,4,6,8-tetraaryl-3,7-diazabicyco[3.3.1]nonan-9-ones, their oximes and O-methyloximes were achieved in a stereocontrolled manner by an easiest synthetic strategy as single isomers with high yields. Stereochemistry of all the synthesized compounds was established by their 1D/2D NMR spectral studies, further, witnessed by single-crystal XRD analysis. Accordingly, the compounds exist in a chair-boat conformation with equatorial orientation of the substituents in the chair part and boat-axial orientation in the boat part. Finally, all the synthesized oximes and oxime ethers were evaluated for their in vitro antimicrobial activity against a panel of pathogenic bacteria and fungi, and as a result of the structure-activity correlations, some lead molecules were known for further optimization.     

Synthesis,antimicrobial and antiviral activity of substituted benzimidazoles

In the present study we have synthesized (4-nitrophenyl)-[2-(substituted phenyl)-benzoimidazol-1-yl]-methanones, (2-bromophenyl)-[2-(substituted phenyl)-benzoimidazol-1-yl]-methanone analogues (1–14) and evaluated them for their antimicrobial and antiviral potential. The results of antimicrobial screening indicated that none of the synthesized compounds were effective against the tested bacterial strains. Compounds 3, 11, 13 and compounds 5, 11, 12 were found to be active against Aspergillus niger and Candida albicans respectively, and may be further developed as antifungal agents. Furthermore, evaluation against a panel of different viruses pointed out the selective activity of compounds 5 and 6 against vaccinia virus and Coxsackie virus B4.     

Synthesis and antimicrobial activity of some novel phenyl and benzimidazole substituted benzyl ethers

In this study, a series of novel phenyl- and benzimidazole-substituted benzyl ethers were synthesized and evaluated for antibacterial and antifungal activities against Staphylococcus aureus, Methicillin-resistant S. aureus (MRSA), Escherichia coli, Candida albicans, and Candida krusei. Compound 6g exhibited the most potent antibacterial activity with lowest MIC values of 3.12 and 6.25 microg/mL against S. aureus and MRSA, respectively.     

Structural aspects of antioxidant activity of substituted pyridoindoles

Stobadine and its two structural analogues, dehydrostobadine and N-acetylated stobadine were used to examine how structural alteration in the close proximity of the indolic nitrogen would influence the antioxidant activity of the substituted pyridoindoles. The compounds were tested for their efficiency to scavenge stable free radicals of alpha,alpha'-diphenyl-beta-picrylhydrazyl as well as for their ability to prevent 2,2'-azobis-(2-amidinopropane)hydrochloride induced peroxidation of dioleoyl phosphatidylcholine liposomes. The results proved that the substituted pyridoindoles can act as potent scavengers of peroxyl radicals both in aqueous and lipid phases, the antioxidant activity being comparable with that of Trolox. Structural changes in the proximity of the indolic nitrogen were found crucial for the radical scavenging efficiency: aromatisation of the pyridoindole skeleton in dehydrostobadine lowered the antioxidant activity, while acetylation of the indolic nitrogen completely abolished the ability to scavenge peroxyl radicals. The results are in agreement with the notion that the antioxidant activity of stobadine and of the related pyridoindoles may be mediated via the indolic nitrogen centre. When stobadine and Trolox were present simultaneously in liposomal incubations, Trolox spared stobadine in a dose-dependent manner; a direct interaction of Trolox with stobadinyl radical appears to be a plausible explanation with possible consequences for the antioxidant capacity of stobadine under in vivo conditions, where re-cycling of stobadine by vitamin E might occur.     

Synthesis of multisubstituted quinolines from Baylis-Hillman adducts obtained from substituted 2-chloronicotinaldehydes and their antimicrobial activity

Baylis-Hillman acetates were synthesized from substituted 2-chloronicotinaldehydes and were conveniently transformed into multisubstituted quinolines and cyclopenta[g]quinolines on reaction with nitroethane or ethyl cyanoacetate via a successive S(N)2'-S(N)Ar elimination strategy. Thus, synthesized quinolines were evaluated for antimicrobial activity and found having substantial antibacterial and antifungal activity.     

Synthesis and antimicrobial evaluation of some new substituted purine derivatives

A series of 8,9-disubstituted adenines (4, 5, 8), 6-substituted aminopurines (10–13) and 9-(p-fluorobenzyl/cyclopentyl)-6-substituted aminopurines (16, 17, 19–30) have been prepared and the antimicrobial activities of these compounds against Staphylococcus aureus, methicillin-resistant S. aureus (MRSA, standard and clinical isolate), Bacillus subtilis, Escherichia coli and Candida albicans were evaluated. 6-[(N-phenylaminoethyl)amino]-9H-purine (12) which has no substitution at N-9 position and 9-cyclopentyl-6-[(4-fluorobenzyl)amino]-9H-purine (24) exhibited excellent activity against C. albicans with MIC 3.12 μg/mL. These compounds displayed better antifungal activity than that of standard oxiconazole. Furthermore, compound 22 carrying 4-chlorobenzylamino group at the 6-position of the purine moiety exhibited comparable antibacterial activity with that of the standard ciprofloxacin against both of the drug-resistant bacteria (MRSA, standard and clinical isolate).     

Synthesis and antioxidant properties of substituted 2-phenyl-1H-indoles

In this study, we report the design, synthesis and antioxidant activity of a series of substituted 2-(4-aminophenyl)-1H-indoles and 2-(methoxyphenyl)-1H-indoles. The new compounds are structurally related to the known indole-based antioxidant lead compound melatonin (MLT), and the antitumour 2-(4-aminophenyl)benzothiazole and 2-(3,4-dimethoxyphenyl)benzothiazole series. Efficient access to the target 2-phenylindoles was achieved via Fischer indole synthesis between substituted phenylhydrazines and acetophenones. 2-(4-Aminophenyl)indoles (such as the 6-fluoro analogue 3b) in particular showed potent antioxidant activity in the DPPH and superoxide radical scavenging assays (80% and 81% inhibition at 1 mM concentration of 3b, respectively), at a level comparable with the reference standard MLT (98% and 75% at 1 mM).     

Synthesis and antiviral activity of substituted quercetins

Influenza viruses are important pathogens that cause respiratory infections in humans and animals. In addition to vaccination, antiviral drugs against influenza virus play a significant role in controlling viral infections by reducing disease progression and virus transmission. Plant derived polyphenols are associated with antioxidant activity, anti-carcinogenic, and cardio- and neuro-protective actions. Some polyphenols, such as resveratrol and epigallocatechin gallate (EGCG), showed significant anti-influenza activity in vitro and/or in vivo. Recently we showed that quercetin and isoquercetin (quercetin-3-β-d-glucoside), a glucoside form of quercetin, significantly reduced the replication of influenza viruses in vitro and in vivo (isoquercetin). The antiviral effects of isoquercetin were greater than that of quercetin with lower IC(50) values and higher in vitro therapeutic index. Thus, we investigated the synthesis and antiviral activities of various quercetin derivatives with substitution of C3, C3', and C5 hydroxyl functions with various phenolic ester, alkoxy, and aminoalkoxy moieties. Among newly synthesized compounds, quercetin-3-gallate which is structurally related to EGCG showed comparable antiviral activity against influenza virus (porcine H1N1 strain) to that of EGCG with improved in vitro therapeutic index.     

Synthesis and antimicrobial activity of squalamine analogue

Synthesis and antimicrobial activity of squalamine analogue 2 are reported. The synthesis of 2 was accomplished from bisnoralcohol 3. The spermidine moiety was introduced via reductive amination of an appropriately functionalized 3beta-aminosterol with spermidinyl aldehyde 17 utilizing sodium triacetoxyborohydride as the reducing agent. Compound 2 shows weaker antimicrobial activity than squalamine.     

Synthesis, characterization and antimicrobial activity of a series of substituted coumarin-3-carboxylatosilver(I) complexes

A series of new coumarin-derived carboxylate ligands and their silver(I) complexes have been synthesized, characterized and screened for their in vitro antibacterial activity against a range of Gram-positive and Gram-negative bacteria as well as for their antifungal activity against a clinical isolate of Candida albicans. The ligands were synthesised by either acid or base hydrolysis of their corresponding esters, which in turn were synthesised via the Knoevenegal reaction. The reaction of silver(I) nitrate with the coumarin carboxylate ligands in either aqueous or aqueous/ethanol solutions allowed the isolation of a series of novel Ag(I) carboxylate complexes. Whilst none of the ligands showed any antimicrobial activity, a number of the Ag(I) complexes exhibited potent activity. In particular, Ag(I) complexes of hydroxy-substituted coumarin carboxylates demonstrated potent activity against the clinically important methicillin-resistant Staphylococcus aureus (MRSA) bacterium (MIC₈₀ = 0.63 μM).     

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.     

Synthesis and antioxidant activity of olivil-type lignans

Olivil-type lignans, an enantiomeric type of natural olivil, were synthesized for the first time to evaluate the relationship between the structure of olivil and its antioxidant activity. A comparison of the antioxidant activity with that of other synthesized tetrahydrofuran lignans indicated reduced activity with the tertiary hydroxy group. A different effect of the two phenolic groups of olivil on the antioxidant activity was also observed.     

Salicylanilide N-monosubstituted carbamates: Synthesis and in vitro antimicrobial activity

The research of innovative antimicrobial agents represents a cutting edge topic. Hence, we synthesized and characterised novel salicylanilide N-monosubstituted carbamates. Twenty compounds were evaluated in vitro against eight bacterial strains and eight fungal species. The lowest minimum inhibitory concentrations (MICs) were found to be ⩽0.49 μM. Genus Staphylococcus, including methicillin-resistant Staphylococcus aureus, and fungus Trichophyton mentagrophytes showed uniformly the highest rate of susceptibility, whilst Gram-negative bacteria and most of the fungi were less susceptible. A wide range of carbamates provided comparable or superior in vitro antimicrobial activity in comparison to established drugs. Interestingly, extended-spectrum β-lactamase producing strain of Klebsiella pneumoniae was inhibited with MICs starting from 31.25 μM. With respect to Staphylococci, 2-[(4-bromophenyl)carbamoyl]-4-chlorophenyl phenylcarbamate exhibited the lowest MIC values (⩽0.98 μM). 2-[(4-Bromophenyl)carbamoyl]-4-chlorophenyl benzylcarbamate showed the widest spectrum of antifungal action. The results indicate that some salicylanilide carbamates can be considered to be promising candidates for future investigation.     

Salicylanilide diethyl phosphates: Synthesis,antimicrobial activity and cytotoxicity

A series of 27 salicylanilide diethyl phosphates was prepared as a part of our on-going search for new antimicrobial active drugs. All compounds exhibited in vitro activity against Mycobacterium tuberculosis, Mycobacterium kansasii and Mycobacterium avium strains, with minimum inhibitory concentration (MIC) values of 0.5–62.5 μmol/L. Selected salicylanilide diethyl phosphates also inhibit multidrug-resistant tuberculous strains at the concentration of 1 μmol/L. Salicylanilide diethyl phosphates also exhibited mostly the activity against Gram-positive bacteria (MICs ⩾1.95 μmol/L), whereas their antifungal activity is significantly lower. The IC₅₀ values for Hep G2 cells were within the range of 1.56–33.82 μmol/L, but there is no direct correlation with MICs for mycobacteria.     

Synthesis and antioxidant properties of substituted 3-benzylidene-7-alkoxychroman-4-ones

A series of 3-benzylidene-7-alkoxychroman-4-one derivatives were synthesized and evaluated for their antioxidant activities. The antioxidant activity was assessed using three methods, namely, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, ferric reducing antioxidant power (FRAP), and thiobarbituric acid reactive substances (TBARS) assays. 3-Benzylidene-7-alkoxychroman-4-one derivatives bearing catecholic group on benzylidene moiety exhibited excellent antioxidant activity. Compounds having catechol moiety exhibited potent antioxidant activities in all tested methods and they were more active than the reference drug, Trolox.     

Synthesis,antimicrobial activity and molecular modeling study of substituted 5-aryl-pyrimido[5,4-c]quinoline-2,4-diones

A series of pyrimido[5,4-c]quinoline-2,4-dione derivatives 5a–k were synthesized in moderate yields via a thermolysis reaction of equimolar ratio of 5-arylidine-1,3-dimethylbarbituric acid derivatives 3a–d with aniline derivatives 4a–d at 150–180 °C for 1–2?h. Eight of the synthesized compounds were chosen for a primary in vitro one-dose anticancer assay performed using the full NCI 60 cell panel. Only compound 5b showed moderate GI% at the used dose (10 μM) against four of the tested cell lines corresponding to leukemia SR (GI%: 51), non small-cell lung cancer HOP-92 (GI%: 63), melanoma UACC-62 (GI%: 53) and renal cancer UO-31 (GI%: 69). On the other hand, antimicrobial screening of the whole set of the synthesized compounds was performed against three Gram +ve and two Gram ?ve bacterial strains. Results of the antimicrobial screening showed that compounds 5d, 5e, 5f, 5h and 5k have broad-spectrum antibacterial efficacy being moderately active against all the tested Gram +ve and two Gram ?ve bacteria. Also, compound 5a showed interesting results being only active against Streptococcus faecalis and both tested Gram ?ve strains viz. E. coli and P. aeruginosa. In order to compare the binding mode of the most active compounds 5e and 5f along with the inactive compound 5c we docked these compounds into the empty binding site of topoisomerase II DNA gyrase (PDB ID: 1KZN), and results were compared with the bound inhibitor Clorobiocin.     

Synthesis and antimicrobial activity of brominated resorcinol dimers

Dibrominated resorcinol dimers were synthesized by reaction of 4-bromoresorcinol with aldehydes under reflux in ethanol in the presence of HCl. Subsequent dehalogenation yielded the corresponding monobrominated compounds and a fully dehalogenated dimer. Of the dimers, 6,6'-((4-hydroxyphenyl)methylene)bis(4-bromobenzene-1,3-diol) (4) displayed potent antibacterial activity and inhibitory activity against isocitrate lyase Candida albicans.     

Synthesis and antimicrobial activity of erythromycin-A oxime analogs

A series of erythromycin-A oxime ether as well as esters have been synthesized. Ether derivatives were synthesized through the epoxy ether intermediate of erythromycin-9-oxime, followed by opening of the epoxy linkage through various amines, whereas esters have been prepared through DCC mediated protocol. These derivatives have been evaluated for antibacterial activity and found to be as active as erythromycin-A.