Antimycobacterial activity of new 3-substituted 5-(pyridin-4-yl)-3H-1,3,4-oxadiazol-2-one and 2-thione derivatives. Preliminary molecular modeling investigations

3H-1,3,4-Oxadiazole-2-thione and 3H-1,3,4-oxadiazol-2-one derivatives were synthesized and tested for their in vitro antimycobacterial activity. Oxadiazolone derivatives showed an interesting antimycobacterial activity against the tested strain of Mycobacterium tuberculosis H(37)Rv, whereas the corresponding thione derivatives were devoid of activity. Molecular modeling investigations showed that the active compounds may interact at the active site of the mycobacterial cytochrome P450-dependent sterol 14alpha-demethylase in the sterol biosynthesis pathway and that their binding free energy values are in agreement with their MIC values.     

Synthesis and fungicidal activity of 3,5-dichloropyrazin-2(1H)-one derivatives

We synthesized a family of 3,5-dichloropyrazin-2(1H)-one derivatives and assessed their in vitro fungicidal activity against Candida albicans. Compounds 11 and 20 were most active against C. albicans and induced accumulation of reactive oxygen species in this pathogen. Using a genome-wide approach in the yeast Saccharomyces cerevisiae, we demonstrated that genes involved in vacuolar functionality and DNA-related functions play an important role in cellular mechanisms underlying the fungicidal activity of these compounds.     

Synthesis and in vitro biological activity of new 4,6-disubstituted 3(2H)-pyridazinone-acetohydrazide derivatives

New 3(2H)-pyridazinone derivatives containing a N'-benzyliden-acetohydrazide moiety at position 2 were synthesized. The structures of these newly synthesized compounds were confirmed by IR, 1H NMR, and MS data. These compounds were tested for their antibacterial, antifungal, antimycobacterial, and cytotoxic activities. The compounds 2-[4-(4-chlorophenyl)-6-(morpholin-4-yl)-3-oxo-(2H)-pyridazin-2-yl]-N'-(4-tert-butylbenzyliden)acetohydrazide and 2-[4-(4-chlorophenyl)-6-(morpholin-4-yl)-3-oxo-(2H)-pyridazin-2-yl]-N'-(4-chlorobenzyliden) acetohydrazide exhibited activity against both Gram-positive and Gram-negative bacteria. Most of the compounds were active against E. coli ATCC 35218. The preliminary results of this study revealed that some target compounds exhibited promising antimicrobial activities.     

Quantitative structure-activity relationships of 1,3,4-thiadiazol-2(3H)-ones and 1,3,4-oxadiazol-2(3H)-ones as human protoporphyrinogen oxidase inhibitors

Protoporphyrinogen oxidase (Protox, EC 1.3.3.4) has attracted great interest during the last decades due to its unique biochemical characteristics and biomedical significance. As a continuation of our research work on the development of new PPO inhibitors, 23 new 1,3,4-thiadiazol-2(3H)-ones bearing benzothiazole substructure were designed and synthesized. The in vitro assay indicated that the newly synthesized compounds 1a-w displayed good inhibition activity against human PPO (hPPO) with K(i) values ranging from 0.04μM to 245μM. To the knowledge, compound 1a, O-ethyl S-(5-(5-(tert-butyl)-2-oxo-1,3,4-thiadiazol-3(2H)-yl)-6-fluorobenzothiazol-2-yl)carbonothioate, with the K(i) value of 40nM, is so far known as the most potent inhibitor against hPPO. Based on the molecular docking and modified molecular mechanics/Poisson-Boltzmann surface area (MM-PBSA) calculations, the quantitative structure-activity relationships of 1,3,4-thiadiazol-2(3H)-ones and 1,3,4-oxadiazol-2(3H)-one derivatives were established with excellent correlation relationships (r(2)=0.81) between the calculated and experimental binding free energies. Some important insights were also concluded for guiding the future rational design of new hPPO inhibitors with improved potency.     

Antifungal activity of a series of 1,2-benzisothiazol-3(2H)-one derivatives

A series of broad-spectrum antifungal agents based on the 1,2-benzisothiazol-3(2H)-one scaffold is reported. Preliminary structure-activity relationship studies have established the importance of the presence of the heterocyclic ring, a methyl group, and a phenyl ring for optimal manifestation of antifungal activity.     

Synthesis and antitumoral activity of novel 3-(2-substituted-1,3,4-oxadiazol-5-yl) and 3-(5-substituted-1,2,4-triazol-3-yl) beta-carboline derivatives

Several novel 1-substituted-phenyl beta-carbolines bearing the 2-substituted-1,3,4-oxadiazol-5-yl and 5-substituted-1,2,4-triazol-3-yl groups at C-3 were synthesized and evaluated for their in vitro anticancer activity. The assay results pointed thirteen compounds with growth inhibition effect (GI(50)<100 microM) for all eight different types of human cancer cell lines tested. The beta-carbolines 7a and 7h, bearing the 3-(2-metylthio-1,3,4-oxadiazol-5-yl) group, displayed high selectivity and potent anticancer activity against ovarian cell line with GI(50) values lying in the nanomolar concentration range (GI(50)=10 nM for both compounds). The 1-(N,N-dimethylaminophenyl)-3-(5-thioxo-1,2,4-triazol-3-yl) beta-carboline (8g) was the most active compound, showing particular effectiveness on lung (GI(50)=0.06 microM), ovarian and renal cell lines. The potent anticancer activity presented for synthesized compounds 7a, 7h, and 8g, together with their easiness of synthesis, makes these compounds promising anticancer agents.     

Antimycobacterial and H1-antihistaminic activity of 2-substituted piperidine derivatives

2-Substituted derivatives of the antihistaminic agents Bamipine, Diphenylpyraline and of their 1-phenyl analogues were tested for their antimycobacterial and H(1)-antagonistic activities. They are strong H1-receptor antagonists and also inhibit the growth of mycobacterials with a maximum MIC of 6.25 microg/mL against Mycobacterium tuberculosis H(37)Rv. H1-receptor antagonistic potency was slightly decreased by substitution in ring position 2 and distinctly diminished by N-aryl substitution. The antimycobacterial potency of Diphenylpyraline was in general increased by substitution in ring position 2, whereas only a few Bamipine derivatives showed markedly improved activity. A correlation between the two activities was not detected for those compounds.     

Synthesis and antimicrobial activity of polyhalobenzonitrile quinazolin-4(3H)-one derivatives

A novel series of polyhalobenzonitrile quinazolin-4(3H)-one derivatives were synthesized and characterized by NMR, IR, MS, and HRMS spectra. All of the newly prepared compounds were screened for antimicrobial activities against four strains of bacteria (Gram-positive bacterial: Staphylococcus aureus and Bacillus cereus; Gram-negative bacterial: Escherichia coli and Pseudomonas aeruginosa) and one strain of fungi (Candida albicans). Among the synthesized compounds, 5-(dimethylamino)-8-(2,4,5-trichloro-isophthalonitrile) quinazolin-4(3H)-one (7k) exhibited significant activity towards Gram-positive bacterial, Gram-negative bacterial, and the fungi strains. The MIC (0.8–3.3 μg/mL) and MBC (2.6–7.8 μg/mL) for this compound were close to those of nofloxacin, chlorothalonil, and fluconazole, making it the most potent antimicrobial agents in the series.     

Novel and orally active 5-(1,3,4-oxadiazol-2-yl)pyrimidine derivatives as selective FLT3 inhibitors

5-(1,3,4-Oxadiazol-2-yl)pyrimidine derivative 1 was identified as a new class of FLT3 inhibitor from our compound library. With the aim of enhancement of antitumor activity of 2 prepared by minor modification of 1, structure optimization of side chains at the 2-, 4-, and 5-positions of the pyrimidine ring of 2 was performed to improve the metabolic stability. Introduction of polar substituents on the 1,3,4-oxadiazolyl group contributed to a significant increase in the metabolic stability. As a result, a series of compounds showed increased efficacy against MOLM-13 xenograft model in mice by oral administration.     

Anticancer potential of 3-(arylideneamino)-2-phenylquinazoline-4(3H)-one derivatives

Different quinazoline derivatives have showed wide spectrum of pharmacological activities. Some 3-(arylideneamino)-phenylquinazoline-4(3H)-ones have been reported to possess antimicrobial activity. The present study has been undertaken to evaluate the anticancer effect of these quinazolinone derivatives. The quinazolinone derivatives were synthesized as reported earlier. Compounds containing NO(2), OH, OCH(3), or OH and OCH(3) as substituent(s) on the arylideneamino group were named as P(3a), P(3b), P(3c), and P(3d) respectively. Out of these, P(3a) and P(3d) showed better cytotoxic activity than P(3b) and P(3c) on a panel of six cancer cell lines of different origin, namely, B16F10, MiaPaCa-2, HCT116, HeLa, MCF7, and HepG2, though the effect was higher in B16F10, HCT116, and MCF7 cells. P(3a) and P(3d) induced death of B16F10 and HCT116 cells was associated with characteristic apoptotic changes like cell shrinkage, nuclear condensation, DNA fragmentation, and annexin V binding. Also, cell cycle arrest at G1 phase, alteration of caspase-3, caspase-9, Bcl-2 and PARP levels, loss of mitochondrial membrane potential, and enhanced level of cytosolic cytochrome c were observed in treated B16F10 cells. Treatment with multiple doses of P(3a) significantly increased the survival rate of B16F10 tumor bearing BALB/c mice by suppressing the volume of tumor while decreasing microvascular density and mitotic index of the tumor cells.     

Synthesis and antimycobacterial activity of 4-(5-substituted-1,3,4-oxadiazol-2-yl)pyridines

4-(5-Substituted-1,3,4-oxadiazol-2-yl)pyridine derivatives 1-12 were synthesized and evaluated for their in vitro antimycobacterial activity. Some compounds showed an interesting activity against Mycobacterium tuberculosis H(37)Rv and five clinical isolates (drug-sensitive and -resistant strains). Compound 4 [4-(5-pentadecyl-1,3,4-oxadiazol-2-yl)pyridine] was 10 times more active than isoniazid, 20 times more active than streptomycin, and 28 times more potent than ethambutol against drug-resistant strain CIBIN 112. Compound 5 [4-(5-heptadecyl-1,3,4-oxadiazol-2-yl)pyridine] showed the same behavior as compound 4. Both of the above structures bear a high lipophilic chain bonded to the 5-position of the oxadiazole moiety. This fact implies that there exists a contribution of lipophilicity, which could facilitate the entrance of these molecules through lipid-enriched bacterial cell membrane.     

Search for anticonvulsant and analgesic active derivatives of dihydrofuran-2(3H)-one

A series of derivatives of dihydrofuran-2(3H)-one (γ-butyrolactone, GBL) was synthesized and tested for anticonvulsant, neurotoxic and analgesic activity. In the anticonvulsant screening 10 lactones were effective in the maximal electroshock test (MES) at the highest doses (300 and 100 mg/kg, 0.5 h, ip, mice). Statistical analysis showed correlation between the anticonvulsant activity and relative lipophilicity parameters determined by experimental and computational methods (R_M0, C log P and M log P). Preliminary antinociceptive evaluation of selected derivatives revealed strong analgesic activity. The majority of the tested compounds showed high efficacy in animal models of acute pain (hot plate and writhing tests) and strong local anesthetic activity (modified tail immersion test). The obtained ED₅₀ values were comparable with such analgesics as acetylsalicylic acid and morphine.     

Synthesis,biological evaluation and molecular modeling study of new (1,2,4-triazole or 1,3,4-thiadiazole)-methylthio-derivatives of quinazolin-4(3H)-one as DHFR inhibitors

A new series of 2-mercapto-quinazolin-4-one analogues was designed, synthesized and evaluated for their in vitro DHFR inhibition, antitumor and antimicrobial activity. Compound 17 proved to be the most active DHFR inhibitor with IC₅₀ value of 0.01 μM, eight fold more active than methotrexate (MTX). Compounds 16 and 24 showed antitumor activity against human Caco2 colon and MCF-7 breast tumor cell lines with IC₅₀ values of 25.4 and 9.5 μg/ml, respectively. Compounds 15, 20, 21 and 30 showed considerable activity against the Gram-positive bacteria Staphylococcus aureus while 24 and 30 proved active against Bacillus subtilis with a magnitude of potency comparable to the broad spectrum antibiotic Ciprofloxacin. Strong activity was observed for 13, 14, 19, 20 and 24 against Candida albicans and Aspergillus flavus. Compound 17 shared a similar molecular docking mode with MTX and made a critical hydrogen bond and arene-arene interactions via Ala9 and Phe34 amino acid residues, respectively.     

Synthesis and elastase-inhibiting activity of 2-pyridinyl-isothiazol-3(2H)-one 1,1-dioxides

The synthesis of a series of new isothiazol-3(2H)-one 1,1-dioxides with halogenated (mostly fluorinated) pyridinyl and pentafluorophenyl substituents at 2-position is reported. These compounds (18-24) became easily accessible from 2-thiocyanato-1-carboxaldehydes and aminopyridines, pentafluoroaniline, respectively, by an isothiazolium cyclization-oxidation route. Compound 21 exhibited an IC(50) value of 3.1 microM toward human leukocyte elastase. The proteases cathepsin G, trypsin, cathepsin L, and angiotensin-converting enzyme, and the serine esterases acetylcholinesterase and cholesterol esterase were not inhibited by 21.     

Synthesis and molecular docking study of some novel 2,3-disubstituted quinazolin-4(3H)-one derivatives as potent inhibitors of urease

A new series of 2,3-disubstituted quinazolin-4(3H)-one compounds including oxadiazole and furan rings was synthesized. Their inhibitory activities on urease were assessed in vitro. All newly synthesized compounds exhibited potent urease inhibitory activity in the range of IC₅₀ = 1.55 ± 0.07–2.65 ± 0.08 µg/mL, when compared with the standard urease inhibitors such as thiourea (IC₅₀ = 15.08 ± 0.71 µg/mL) and acetohydroxamic acid (IC₅₀ = 21.05 ± 0.96 µg/mL). 2,3-Disubstituted quinazolin-4(3H)-one derivatives containing furan ring (3a-e) were found to be the most active inhibitors when compared with the compounds 2a-e bearing oxadiazole ring. Compound 3a, bearing 4-chloro group on phenyl ring, was found as the most effective inhibitor of urease with the IC₅₀ value of 1.55 ± 0.11 µg/mL. The molecular docking studies of the newly synthesized compounds were performed to identify the probable binding modes in the active site of the Jack bean urease (JBU) enzymes.     

Synthesis and biological activity of 2,5-diaryl-3-methylpyrimido[4,5-c]quinolin-1(2H)-one derivatives

A series of 2,5-diaryl-3-methylpyrimido[4,5-c]quinolin-1(2H)-ones (7-30), variously substituted at the 2- and 5-phenyl moieties, were synthesized and evaluated for their in vitro cytotoxic activity against a PC3 cancer cell line. Cytotoxicity data revealed that the type of substituent as well as substitution pattern have variable influence on cytotoxic activity. Among the compounds tested, compounds (9), (13), (18), (19), and (23) demonstrated appreciable cytotoxic activity with mean IC(50) values of 2.0, 1.4, 1.6, 2.2, and 1.9microM, respectively. Methyl substitution at the 2-phenyl ring was found to yield the least active compounds. Two of the most potent compounds (13) and (18) were further investigated for inhibition of tubulin polymerization and found to have no activity at the concentrations used in the assay.     

Discovery of novel antitubercular 1,5-dimethyl-2-phenyl-4-([5-(arylamino)-1,3,4-oxadiazol-2-yl]methylamino)-1,2-dihydro-3H-pyrazol-3-one analogues

In search of potential therapeutics for tuberculosis, we describe herewith the synthesis, characterization and antimycobacterial activity of 1,5-dimethyl-2-phenyl-4-([5-(arylamino)-1,3,4-oxadiazol-2-yl]methylamino)-1,2-dihydro-3H-pyrazol-3-one analogues. Among the synthesized compounds, 4-[(5-[(4-fluorophenylamino]-1,3,4-oxadiazol-2-yl)methylamino]-1,2-dihydro-1,5-dimethyl-2-phenylpyrazol-3-one (4a) was found to be the most promising compound active against Mycobacterium tuberculosis H(37)Rv and isoniazid resistant M. tuberculosis with minimum inhibitory concentrations, 0.78 and 3.12μg/mL, respectively, free from any cytotoxicity (>62.5μg/mL).     

Synthesis, biological evaluation and molecular docking studies of novel 2-(1,3,4-oxadiazol-2-ylthio)-1-phenylethanone derivatives

In present study, a series of new 2-(1,3,4-oxadiazol-2-ylthio)-1-phenylethanone derivatives (6a-6x) as potential focal adhesion kinase (FAK) inhibitors were synthesized. The bioassay assays demonstrated that compound 6i showed the most potent activity, which inhibited the growth of MCF-7 and A431 cell lines with IC(50) values of 140 ± 10 nM and 10 ± 1 nM, respectively. Compound 6i also exhibited significant FAK inhibitory activity (IC(50)=20 ± 1 nM). Docking simulation was performed to position compound 6i into the active site of FAK to determine the probable binding model.     

Fluorescent 2-styrylpyridazin-3(2H)-one derivatives as probes targeting amyloid-beta plaques in Alzheimer's disease

Amyloid plaques, which are primarily composed of aggregated amyloid-beta (Aβ) peptide, are the neuropathological hallmarks of Alzheimer's disease (AD). Fluorescent markers containing 2-styrylpyridazin-3(2H)-ones were developed to detect intracellular aggregated Aβ peptides. Nine compounds exhibited a greater than 10-fold increase of in emission spectra before and after mixing with Aβ aggregates compared with before mixing. Among these compounds, compound 9n exhibited the highest affinity for Aβ aggregates (K(d)=1.84 μM) and selectively stained both aggregated intracellular Aβ and Aβ plaques in the transgenic AD model mice (APP/PS1). These preliminary results indicate that 2-styrylpyridazin-3(2H)-one derivatives are promising alternative fluorescence imaging agent for the study of AD.