Synthesis and evaluation of anticancer benzoxazoles and benzimidazoles related to UK-1

UK-1 is a structurally unique bis(benzoxazole) natural product isolated from a strain of Streptomyces. UK-1 has been reported to possess anticancer activity but no activity against bacteria, yeast, or fungi. Previous work has also demonstrated the ability of UK-1 to bind a variety of di- and tri-valent metal ions, particularly Mg²⁺ ions, and to form complexes with double-stranded DNA in the presence of Mg²⁺ ions. Here we report the activity of UK-1 against a wide range of human cancer cell lines. UK-1 displays a wide spectrum of potent anticancer activity against leukemia, lymphoma, and certain solid tumor-derived cell lines, with IC₅₀ values as low as 20 nM, but is inactive against Staphylococcus aureus, a methicillin-resistant strain of S. aureus, or Pseudomonas aeruginosa. A series of analogues of the bis(benzoxazole) natural product UK-1 in which the carbomethoxy-substituted benzoxazole ring of the natural product was modified were prepared and evaluated for their anticancer and antibacterial properties. An analogue of UK-1 in which the carbomethoxy-substituted benzoxazole ring was replaced with a carbomethoxy-substituted benzimidazole ring was inactive against human cancer cell lines and the two strains of S. aureus. In contrast, a simplified analogue in which the carbomethoxy-substituted benzoxazole ring was replaced with a carbomethoxy group was almost as active as UK-1 against the four cancer cell lines examined but lacked activity against S. aureus. Metal ion binding studies of these analogues demonstrate that they both bind Zn²⁺ and Ca²⁺ ions about as well as UK-1. The non-cytotoxic benzimidazole UK-1 analogue binds Mg²⁺ ions 50-fold weaker than UK-1, whereas the simple benzoxazole analogue binds Mg²⁺ ions nearly as well as UK-1. These results support a role of Mg²⁺ ion binding in the selective cytotoxicity of UK-1 and provide a minimal pharmacophore for the selective cytotoxic activity of the natural product.     

Synthesis and evaluation of unsymmetrical bis(arylcarboxamides) designed as topoisomerase-targeted anticancer drugs.

Symmetrical dimers of lipophilic intercalating chromophores linked by cation-containing chains have recently been shown to have broad-spectrum in vivo anticancer activity. We report the preparation and evaluation of a series of both symmetric and unsymmetric dimers of a variety of intercalating chromophores of varied DNA binding strength, including naphthalimides, acridines, phenazines, oxanthrenes and 2-phenylquinolines. The unsymmetrical dimers were prepared by sequential coupling of the chromophores to linkers with selectively protected primary terminal amines to ensure high yields and unequivocal product. Protection of the internal (secondary) amines as BOC derivatives was used to ensure complete structural specificity, and was also an aid to the purification of these very polar compounds. The growth inhibitory abilities (as IC(50) values) of the compounds in a range of cell lines showed that the nature of the linker chain was important, and independent of the nature of the chromophore, with compounds containing the dicationic linker [-(CH2)2NH(CH2)2NH(CH2)2-] being on average 30-fold more potent than the corresponding compounds containing the monocationic linker [-(CH2)3NMe(CH2)3-]. However, the chromophores also play a role in determining biological activity, with the cytotoxicities of symmetric and unsymmetric dicationic dimers correlating with the overall DNA binding abilities of the chromophores.     

Synthesis of some novel phosphorylated and thiophosphorylated benzimidazoles and benzothiazoles and their evaluation for larvicidal potential to Aedes albopictus and Culex quinquefasciatus

Series of benzimidazole and benzothiazole linked phosphoramidates and phosphoramidothioates (5a–j) and benzimidazole linked phenylphosphoramidates and phenylphosphoramidothioates (10a–e) were synthesized. The title compounds were preliminary screened for mosquito larvicidal properties against Aedes albopictus and Culex quinquefasciatus at different concentration from 40 to 5 mg/L. Among the screened compounds three compounds revealed potential larvicidal effects with 100% mortality in the order of 10e > 5j > 5e. Compound 10e was found to be the most toxic compound to Ae. albopictus and Cx. quinquefasciatus. The LC₅₀ of 10e against Ae. albopictus was found to be 6.42 and 5.25 mg/L at 24 and 48 h, respectively, whereas it was 7.01 and 3.88 mg/L, respectively in Cx. quinquefasciatus. Temephos was used as positive control.     

Synthesis and SAR of 2-arylbenzoxazoles, benzothiazoles and benzimidazoles as inhibitors of lysophosphatidic acid acyltransferase-beta

2-Arylbenzoxazoles, benzothiazoles and benzimidazoles were identified as new classes of potent, isoform specific inhibitors of lysophosphatidic acid acyltransferase-beta (LPAAT-beta). Effects of selected inhibitors on proliferation of tumor cells in vitro were investigated.     

Some benzoxazoles and benzimidazoles as DNA topoisomerase I and II inhibitors

Some novel fused heterocyclic compounds of 2, 5-disubstituted-benzoxazole and benzimidazole derivatives, which were previously synthesized by our group, were investigated for their inhibitory activity on both eukaryotic DNA topoisomerase I and II in a cell free system. 2-Phenoxymethylbenzimidazole (17), 5-amino-2-(p-fluorophenyl)benzoxazole (3), 5-amino-2-(p-bromophenyl)benzoxazole (5), 5-nitro-2-phenoxymethyl-benzimidazole (18), 2-(p-chlorobenzyl)benzoxazole (10) and 5-amino-2-phenylbenzoxazole (2) were found to be more potent as eukaryotic DNA topoisomerase I poisons than the reference drug camptothecin having IC(50) values of 14.1, 132.3, 134.1, 248, 443.5, and 495 microM, respectively. 5-Chloro-2-(p-methylphenyl)benzoxazole (4), 2-(p-nitrobenzyl)benzoxazole (6) and 5-nitro-2-(p-nitrobenzyl)benzoxazole (8) exhibited significant activity as eukaryotic DNA topoisomerase II inhibitors, having IC(50) values of 22.3, 17.4, 91.41 microM, respectively, showing higher potency than the reference drug etoposide.     

Synthesis and anticancer evaluation of thiazolyl-chalcones

Thirty-seven (E)-1-(4-methyl-2-arylaminothiazol-5-yl)-3-arylprop-2-en-1-ones were synthesized via Claisen-Schmidt condensation of 1-(4-methyl-2-(arylamino)thiazol-5-yl)ethanone with the corresponding arylaldehydes. All these thiazolyl-chalcones were characterized and evaluated by MTT assay on human cancer cell lines BGC-823, PC-3, NCI-H460, BEL-7402 in vitro. Compounds 5, 8, 26, 37 and 41 are effective against cancer cell lines with IC(50)s below 10 μM. The antitumor activity in ICR mice bearing sarcoma 180 tumors indicates compounds 10 and 41 have moderate in vivo activity with 22-25% tumor-weight inhibition.     

Parameters affecting the degradation of benzothiazoles and benzimidazoles in activated sludge systems

It was found that benzothiazole, 2-oxybenzothiazole and 2-benzothiazolesulphonate were degraded in activated sludge systems. 2-Mercaptobenzothiazole (MBT) was more resistant, although the first step in MBT degradation seemed to be transformation to the sulphonate form. At higher MBT concentrations, it was transformed into a disulphide, which accumulated in the sludge. MBT was also found to be mainly responsible for the toxicity of rubber chemical waste-water towards activated sludges. It inhibited the degradation of the other hetrocycles. Only at concentrations of around 20 ppm was MBT degraded. Mercaptobenzimidazole ranked second in resistance to degradation. Correspondence to: H. Verachtert     

QSAR of anticancer compounds. Bis(11-oxo-11H-indeno[1,2-b]quinoline-6-carboxamides), bis(phenazine-1-carboxamides), and bis(naphthalimides)

QSAR have been developed for the anticancer activity (growth inhibition) of various tumor cells by bis(11-oxo-11H-indeno[1,2-b]quinoline-6-carboxamides), bis(phenazine-1-carboxamides), and bis(naphthalimides). Of the seven QSAR, positive hydrophobic interactions are found in only two examples: bis(naphthalimides) versus human colon cancer cells. This is consistent with other QSAR of anticancer compounds where hydrophobic interactions are found to be unimportant.     

Synthesis and anticancer evaluation of vitamin K(3) analogues

Novel vitamin K(3) analogues were synthesized and evaluated for their anticancer activity. Compound 6, 9, 10, 11, 14, and (+/-)15 demonstrated a strong inhibitory activity against the tumor cells of A-549, Hep G2, MCF7, MES-SA, MES-SA/Dx5, MKN45, SW-480, and TW-039. Compound (+/-)15 displayed potent tumor cell cytotoxicity, and compound 14 selectively affected MCF7, even though it did not influence normal cells Detroit551 and WI-38. Compound (+/-)15 inhibited MES-SA and MES-SA/Dx5, and this specific result shows that compound (+/-)15 may become a good anticancer drug candidate.     

Synthesis and evaluation of novel bacterial rRNA-binding benzimidazoles by mass spectrometry

A series of novel benzimidazoles were efficiently synthesized using both solution- and solid-phase chemistry. These compounds were found to bind to the bacterial 16S ribosomal RNA A-site with micromolar affinities using unique mass spectrometry-based assays.     

Synthesis and evaluation of antioxidant and antibacterial activities of new substituted bis(1,3,4-oxadiazoles), 3,5-bis(substituted) pyrazoles and isoxazoles

Two series of five membered heterocyclic bis(1,3,4-oxadiazole) derivatives 2(a-h) and 3,5-bis(substituted)pyrazoles, isoxazoles 3(a,b,d-i), 4(a-c) were synthesized via oxidative cyclization of some diaroylhydrazones using chloramine-T and cyclocondensation reaction with hydrazine hydrate and hydroxylamine hydrochloride, respectively. The newly synthesized compounds were screened for antioxidant and anti-microbial activities. Compounds 2(b), 3(b), and 4(a) showed higher antioxidant activity at 10 μg/ml while compounds 2(a), 3(a), 3(f), and 4(a) exhibited better anti-microbial activity at 100 μg/ml compared with standard vitamin C and ciprofloxacin, respectively. Structures of newly synthesized compounds were confirmed by elemental analysis and spectral IR, ¹H NMR, and ¹³C NMR data.     

Synthesis and antiviral evaluation of benzimidazoles, quinoxalines and indoles from dehydroabietic acid

Several heterocycles, such as benzimidazoles, quinoxalines and indoles incorporated into a hydrophenanthrene and naphthalene skeleton, were synthesised from two useful ortho-bromonitro precursors derived from dehydroabietic acid: methyl 12-bromo-13-nitro-deisopropyldehydroabietate and methyl 12-bromo-13,14-dinitro-deisopropyldehydroabietate. The new heterocycles were evaluated for their activity in vitro against several RNA and DNA viruses.     

Methylsulfonyl benzothiazoles (MSBT) derivatives: Search for new potential antimicrobial and anticancer agents

A series of novel 4 and 5-substituted methylsulfonyl benzothiazole (MSBT) compounds having amide, alkoxy, sulfonamide, nitro and amine functionality were synthesized from sequential reactions on 5-ethoxy-2-(methylsulfonyl)benzo[d]thiazole such as nitration, reduction, sulfonation, dealkylation, etc. All synthesized compounds were screened against antimicrobial and selected screened for anticancer activity. Antimicrobial activities studies reveled that among all compounds screened, out of MSBT-07, MSBT-11, MSBT-12, MSBT-14, MSBT-19, and MSBT-27 were found to have promising antimicrobial activity at MIC range of 4–50 μg/ml against selected bacterial as well as fungal species. Compounds having good antimicrobial activity were screened for cervical cancer (HeLA cell lines). Of these MSBT-07 and MSBT-12 significantly reduced the cell growth. Consequently their calculated GI₅₀ values were found to be 0.1 or <0.1 μM.     

Synthesis and biological evaluation of thiobenzanilides as anticancer agents

A series of novel thiobenzanilides is described. These compounds have been previously found to show strong biological activity such as antimycotic and antifungal actions. This is the first demonstration on the mechanism of the anticancer effect of thiobenzanilide agents (4a–c) on human melanoma A375 cells. The cytotoxic studies of compounds 4a–c on human melanoma A375 cells indicate thiobenzanilides induced higher cytotoxicity than nitrobenzanilides (3a–c). In addition, DNA flow cytometric analysis shows that 4a–c displays a significant G2/M phase arrest, which progresses to early apoptosis as detected by flow cytometry after double-staining with annexin V and propidium iodide (PI). Because cellular apoptosis is often preceded by the disruption of mitochondrial function, the assessment of mitochondrial function in 4a–c-treated cells is worthy of investigation. Our data revealed that treatment of A375 cells with 4a–c resulted in the loss of mitochondrial membrane potential (ΔΨ_mt), a reduction of ATP synthesis, increased reactive oxygen species (ROS) generation, and activation of caspase-3. Thus, we suggest that 4a–c agents are potent inducers of cell apoptosis in A375 cells.     

Synthesis and evaluation of spiroisoxazoline oxindoles as anticancer agents

Restoring p53 levels through disruption of p53–MDM2 interaction has been proved to be a valuable approach in fighting cancer. We herein report the synthesis and evaluation of eighteen spiroisoxazoline oxindoles derivatives as p53–MDM2 interaction inhibitors. Seven compounds showed an antiproliferative profile superior to the p53–MDM2 interaction inhibitor nutlin-3, and induced cell death by apoptosis. Moreover, proof-of-concept was demonstrated by inhibition of the interaction between p53 and MDM2 in a live-cell bimolecular fluorescence complementation assay.     

Preclinical in vitro screening of newly synthesised amidino substituted benzimidazoles and benzothiazoles

Newly synthesised benzimidazole/benzotiazole derivatives bearing amidino, namely 3,4,5,6-tetrahydropyrimidin-1-ium chloride, substituents have been evaluated for their potential antitumor activity in vitro. Compounds and standard drugs (doxorubicin, staurosporine and vandetanib) were tested on three human lung cancer cell lines A549, HCC827 and NCI-H358. We tested compounds in MTS citotoxicity assay and in BrdU proliferative assay performed on 2 D and 3 D assay format. Because benzmidazole scaffold is similar to natural purines, we tested the most active compounds for ability to induce cell apoptosis of A549 by binding to DNA in comparison with doxorubicin and saturosporine. Additionally, the ADME properties of the most active benzothiazole/benzimidazole and non-active compounds were determined to see if the different ADME properties are the cause of different activity in 2 D and 3 D assays, as well as to see if the tested active compounds have drug like properties and potency for further profilation. ADME characterisation included solubility, lipophilicity, permeability, metabolic stability and binding to plasma proteins. In general, the benzothiazole derivatives were more active in comparison to their benzimidazole analogues. The exception was 2-phenyl substituted benzimidazole 6a being active with very pronounced activity especially towards HCC827 cells. All active compounds have similar mode of action on A549 cell line as standard compound doxorubicin, which binds to nucleic acids with the DNA double helix. Tested active benzothiazole compounds were characterised by moderate to good solubility, good metabolic stability, low permeability and high binding to plasma proteins. One tested active benzimidazole derivative showed ADME properties, but lower lipophilicity resulted in low PPB and higher metabolic instability. In addition, no significant difference was observed in ADME profile between active and non-active compounds.     

Synthesis, antimicrobial and antioxidant evaluation of quinolines and bis(indolyl)methanes

An improved and practical synthesis of substituted quinolines and bis(indolyl)methanes was achieved under microwave condition using Zn(OTf)(2) as catalyst. The synthesized compounds have been screened for antimicrobial and antioxidant activities.     

Synthesis and biological evaluation of novel benzodioxinocarbazoles (BDCZs) as potential anticancer agents

We report the efficient synthesis and biological evaluation of new benzodioxinoindolocarbazoles heterocycles (BDCZs) designed as potential anticancer agents. Indolic substitution and maleimide variations were performed to design a new library of BDCZs and their cytotoxicity were evaluated on two representative cancer cell lines. Several derivatives have shown a marked cytotoxicity with IC₅₀ values in the nanomolar range. Results are reported in this Letter.     

Synthesis and biological evaluation of novel pyrrolopyrrolizinones as anticancer agents

We herein describe the synthesis of novel 3-(het)aryl-pyrrolo[2,3-b]pyrrolizin-8(1H)-ones starting from commercial (het)aryl-acetonitriles. A more convergent route was also described through the first synthesis of ethyl 3-amino-4-bromo-1H-pyrrole-2-carboxylate 17. The antiproliferative activities of these compounds were tested toward various cell lines and one of them 10k shows interesting cytotoxic properties, although it was less potent than our lead compound in thiophene series 1k.     

Synthesis and biological evaluation of novel anticancer bivalent colchicine-tubulizine hybrids

A series of novel antimitotic hybrids were synthesized in good yields by linking of azide-containing colchicine congeners with acetylene-substituted tubulizine-type derivatives using copper-mediated 1,3-dipolar cycloaddition. Obtained compounds exhibit good cytotoxicity against HBL100 epithelial cell lines (IC(50)=0.599-2.93 μМ). Several newly synthesized compounds are the substoichiometric inhibitors of microtubule assembly (R=0.41-0.78). The results highlight the importance of the length of spacer linking the tubulin binding ligands in heterodimeric molecules.