A naphtho [1,2-b] furan derivative from the fungus Roesleria pallida

The strongly blue fluorescent compound present in the dark green extracts of the fungus Roesleria pallida (Pers.) Sacc. was obtained in a pure state and determined as 4,7-dihydroxy-2,3,3,9-tetramethyl-2,3-dihydronaphtho [1,2-b] furan-5,6-dicarboxylic anhydride.     

Design,synthesis and biological evaluation of imidazo[2,1-b]thiazole and benzo[d]imidazo[2,1-b]thiazole derivatives as Mycobacterium tuberculosis pantothenate synthetase inhibitors

In the present study, we have designed imidazo[2,1-b]thiazole and benzo[d]imidazo[2,1-b]thiazole derivatives from earlier reported imidazo[1,2-a]pyridine based Mycobacterium tuberculosis (MTB) pantothenate synthetase (PS) inhibitors. We synthesized thirty compounds and they were evaluated for MTB PS inhibition study, in vitro anti-TB activities against replicative and non-replicative MTB, in vivo activity using Mycobacterium marinum infected Zebra fish and cytotoxicity against RAW 264.7 cell line. Among them compound 2-methyl-N′-(4-phenoxybenzoyl)benzo[d]imidazo[2,1-b]thiazole-3-carbohydrazide (5bc) emerged as potent compound active against MTB PS with IC₅₀ of 0.53 ± 0.13 μM, MIC of 3.53 μM, 2.1 log reduction against nutrient starved MTB, with 33% cytotoxicity at 50 μM. It also showed 1.5 log reduction of M. marinum load in Zebra fish at 10 mg/kg.     

Selective cleavage of 10-methyl benzo[b]naphtho[2,1-d]thiophene by recombinant Mycobacterium sp. strain

Recombinant Mycobacterium sp. strain MR65 carrying dszABCD genes was used for desulfurization of 10-methylbenzo[b]naphtho[2,1-d]thiophene (10-methyl BNT) in the hexadecane phase. The specific activity was 25% of that of dibenzothiophene (DBT). One of two major metabolites of 10-methyl BNT produced by strain MR65 was identified as 1-methoxy-2-(3-methylphenyl)naphthalene by ¹H and ¹³C NMR. The other major metabolite and two minor metabolites were determined as 1-hydroxy-2-(3-methylphenyl)naphthalene, 2-(2-methoxy-3-methylphenyl)naphthalene and 2-(2-hydroxy-3-methylphenyl)naphthalene, respectively, by HPLC and GC-MS. The production ratio of the two desulfurization metabolite isomers was 0.99:0.01, calculated on the basis of peak GC areas. These results indicated that the C-S bond adjacent to the naphthalene skeleton was selectively cleaved to form the two major compounds.     

First characterization of the mutagenic specificity of 7-methoxy-2-nitronaphtho[2,1-b]furan (R7000) in Salmonella typhimurium

In order to investigate the mutational events induced by the very potent genotoxic agent 7-methoxy-2-nitronaphtho[2,1-b]furan (R7000), we evaluated its mutagenic potency in a battery of his- mutants of Salmonella typhimurium designed to study mutagenic specificity (Levin and Ames, 1986). Using this system we could show that R7000 is able to induce base-pair substitutions, mainly GC----TA transversions and, perhaps to a lower extent, AT----TA transversions. In addition, our results suggest that this chemical may be a very efficient inducer of base-pair deletions/insertions resulting in frameshifts. Whereas the induction of base-pair substitutions by R7000 is dependent on the presence of plasmid pKM101 carrying the mucA,B operon, the induction of base-pair deletions/insertions is independent of the presence of the plasmid.     

Synthesis and antiproliferative evaluation of certain iminonaphtho[2,3-b]furan derivatives

Certain iminonaphtho[2,3-b]furan derivatives were synthesized from their respective carbonyl precursors in the regiospecific and the stereospecific manners. These compounds were evaluated for their antiproliferative effects against four human carcinoma cells (MCF7, NCI-H460, SF-268, and K562) and the normal fibroblast cell line (Detroit 551). Among them, (Z)-4-(hydroxyimino)naphtho[2,3-b]furan-9(4H)-one (8) and (Z)-4-methoxy-iminonaphtho[2,3-b]furan-9(4H)-one (9) exhibited GI₅₀ values of 0.82 and 0.60 μM, respectively, against the growth of K562 cells and were inactive against the normal fibroblast Detroit 551. The selectivity index (SI) on K562 cell for 8 and 9 was >121.95 and >166.67, respectively, which is comparable to daunorubicin (SI = 239) and is more favorable than camptothecin (SI = 16.5). The cell cycle analysis on K562 indicated that these compounds arrest the cell cycle at the G2/M phase. The morphological assessment and DNA fragmentation analysis indicated that 9-induced cell apoptosis in K562 cells. The apoptotic induction may through caspase-3 activity and cleavage of PARP.     

Synthesis of 1-(3',4',5'-trimethoxy) phenyl naphtho[2,1b]furan as a novel anticancer agent

3',4',5'-Trimethoxy benzoyl-naphthalene 2-O-acetic acid (5) underwent base catalysed intramolecular condensation to yield exclusively 1-(3',4',5'-trimethoxy) phenyl naphtho[2,1-b]furan 8. The cyclised product 8 has been characterised by spectroscopy. The product 8 showed significant anticancer activity against human cancer cell lines COLO320DM (colon), CaCO2 (colon) and WRL68 (liver) at 0.7, 0.65 and 0.50 microg/ml concentrations, respectively, in the in vitro MTT assay.     

Synthesis and anticancer evaluation of 3-aryl-6-phenylimidazo[2,1-b]thiazoles

A series of new 3,6-diphenylimidazo[2,1-b]thiazole derivatives (4a–l) are synthesized and evaluated for their anticancer activity. Some of the synthesized compounds have shown potent anti-proliferative activity against HeLa, MDA-MB-231, A549 and THP1 human cancer cell lines. Among the active compounds, 3-(3-trifluoromethylphenyl)-6-phenylimidazo[2,1-b]thiazole (4j) has caused significant cytotoxicity in HeLa cells, with IC₅₀ as low as 6.5 μM. Compound 4j has induced caspase-3 and caspase-8 activation, leading to an apoptotic cell death. FACS analysis has revealed that compound 4j arrests cells in G0/G1 phase. The presence of 3-(3-trifluoromethylphenyl)- or 3-(3-chlorophenyl)-substituent, in that order, on the 6-phenylimidazo[2,1-b]thiazole impacts more positively than other aryl-substituents, on the anti-proliferative properties of these compounds.     

Synthesis and antiproliferative activity of imidazo[2,1-b][1,3,4]thiadiazole derivatives

A series of 2,5,6-substituted imidazo[2,1-b][1,3,4]thiadiazole derivatives have been prepared and were tested for antiproliferative activity on cancer cells at the National Cancer Institute. Results showed that molecules with a benzyl group at position 2, exhibited an increase in activity for the introduction of a formyl group at the 5 position. The compound 2-benzyl-5-formyl-6-(4-bromophenyl)imidazo[2,1-b][1,3,4]thiadiazole 22 has been chosen for understanding the mechanism of action by various molecular and cellular biology studies. Results obtained from cell cycle evaluation analysis, analysis of mitochondrial membrane potential and Annexin V-FITC by flow cytometric analysis, ROS production and expression of apoptotic and DNA-repair proteins suggested that compound 22 induced cytotoxicity by activating extrinsic pathway of apoptosis, however, without affecting cell cycle progression.     

Synthesis of benzo[d]imidazo[2,1-b]thiazole-chalcone conjugates as microtubule targeting and apoptosis inducing agents

A series of benzo[d]imidazo[2,1-b]thiazole-chalcone conjugates (5a-aa) were designed, synthesized and evaluated for their cytotoxic potency against a panel of human cancer cell lines like lung (A-549), breast (MDA MB-231), prostrate (DU-145) and colon cancer (HT-29). Preliminary results revealed that some of these conjugates like 5d and 5u exhibited significant antiproliferative effect against human breast cancer (MDA MB-231) with IC₅₀ values of 1.3 and 1.2 µM respectively. To investigate the mechanistic aspects underlying the activity, the detailed biological studies of these promising conjugates (5d and 5u) were carried out on the MDA MB-231 cancer cells. Flow cytometric analysis revealed that these conjugates induce cell-cycle arrest in the G2/M phase. The tubulin polymerization assay suggests that these conjugates effectively inhibit microtubule assembly. In addition, morphological changes, reactive oxygen species (ROS) detection by 2′, 7′–dichlorofluorescin diacetate (DCFDA) and annexin V–FITC/PI assays indicate that 5d and 5u induces apoptosis. Furthermore, in silico computational studies, including molecular docking studies have been carried out to rationalise the binding modes of these conjugates with the tubulin protein.     

Synthesis and biological evaluation of imidazo[2,1-b]thiazole-benzimidazole conjugates as microtubule-targeting agents

A series of imidazo[2,1-b]thiazole-benzimidazole conjugates were synthesized and evaluated for their antiproliferative activity against four human cancer cell lines i.e.; HeLa (cervical), A549 (lung), MCF-7 (breast) and DU-145 (prostate) along with normal HEK-293 cell line. Amongst them, conjugate 6d displayed significant cytotoxicity against human lung cancer cell line, A549 with IC₅₀ value 1.08 µM. Further, cell cycle analysis revealed that this compound arrested the cell cycle at G2/M phase in A549 cells. Furthermore, the tubulin polymerization assay results suggest that this conjugate (6d) exhibits significant inhibitory effect on the tubulin assembly with an IC50 value of 1.68 µM. Moreover, the apoptotic inducing properties of compound 6d was confirmed by Hoechst staining, measurement of mitochondrial membrane potential (ΔΨm) and annexin V-FITC assay. Further, molecular docking studies revealed that compound 6d occupied the colchicine binding site.     

Naphtho[2,1-b][1,5] and [1,2-f][1,4]oxazocines as selective NK1 antagonists

Previously we reported on the synthesis and properties of a series of highly potent piperidinyl 2-subsituted-3-cyano-1-naphthamide NK1 antagonists that includes 3 and 4. Here we report our efforts to alleviate a troublesome atropisomeric property of those derivatives by introduction of a tethering bridge that, in addition, could be used to lock the resulting cyclic derivatives in a purported NK1 pharmacophore conformation. Using 3 as a starting point, the naphtho[2,1-b][1,5]oxazocine, 17, was found to contain the optimal ring tether size (8) for retaining NK1 activity, was more NK1 versus NK2 selective, and reduced the number of atropisomers from four to two. Cyclic derivatives 29 and 32, which exist as essentially single atropisomers in the purported pharmacophore conformation, were prepared in the closely related naphtho[1,2-f][1,4]oxazocine series as part of an effort to use mono methyl substitution of the tethering bridge as a conformation stabilizing factor. Both 29 and 32 were found to be less active as NK1 antagonists than the non-methylated parent 28 possibly due to methyl group destabilization of receptor interaction. We discuss the above findings in the context of a previously proposed NK1 pharmacophore model and present a further refinement of that model.     

Synthesis and evaluation of antitubercular activity of imidazo[2,1-b][1,3,4]thiadiazole derivatives

A series of 2,6-disubstituted and 2,5,6-trisubstituted imidazo[2,1-b][1,3,4]thiadiazoles were synthesized, the structures of the compounds were elucidated and screened for antitubercular activity against Mycobacterium tuberculosis H37Rv using the BACTEC 460 radiometric system, antibacterial activity against Escherichia coli and Bacillus cirrhosis, and antifungal activity against Aspergillus niger and Penicillium wortmanni. Among the tested compounds 2-(2-furyl)-6-phenylimidazo[2,1-b][1,3,4] thiadiazole-5-carbaldehyde (6c) and (2-cyclohexyl-6-phenylimidazo[2,1-b][1,3,4]thiadiazol-5-yl)methanol (7a) have shown the highest (100%) inhibitory activity. Compounds 6a, 6b, 7c, and 8a exhibited moderate antitubercular activity with percentage inhibition 36, 30, 15, and 20, respectively, at a MIC of >6.25 microg/ml.     

Identification of 5,6-dihydroimidazo[2,1-b]thiazoles as a new class of antimicrobial agents

In an effort to develop novel antimicrobial agents against drug-resistant bacterial infections, 5,6-dihydroimidazo[2,1-b]thiazole compounds were synthesized and tested for their antimicrobial activity. Eight compounds comprised by two sub-scaffolds were identified as hits against methicillin-resistant Staphylococcus aureus (MRSA). These hits were modified at 6-position by replacing (S)-6 to (R)-6 configuration and the (R)-isomers increased their antimicrobial activities by two-fold. The most active compound showed a MIC₉₀ value of 3.7 μg/mL against MRSA in a standard microdilution bacterial growth inhibitory assay. This compound protected wax moth worms against MRSA at a dose of 5× MIC using a worm infectious model. This compound also exhibited inhibition of DNA gyrase activity in a DNA gyrase supercoil assay, suggesting the 5,6-dihydroimidazo[2,1-b]thiazoles may target DNA gyrase for the antimicrobial action.     

Synthesis and biological activity of anticoccidial agents: 5,6-diarylimidazo[2,1-b][1,3]thiazoles

Novel 5,6-diarylimidazo[2,1-b][1,3]thiazoles bearing an amine substituent at the imidazothiazole 2-position have been synthesized and evaluated as anticoccidial agents in both in vitro and in vivo assays. Both subnanomolar in vitro activity and broad spectrum in vivo potency were detected for several compounds, particularly compound 10.     

Anti-cancer potential of (1,2-dihydronaphtho[2,1-b]furan-2-yl)methanone derivatives

A series of 1,2-dihydronaphtho[2,1-b]furan derivatives were synthesized by cyclizing 1-(aryl/alkyl(arylthio)methyl)-naphthalen-2-ol and pyridinium bromides in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in very good yield. The synthesized compounds were evaluated for their anti-proliferative potential against human triple negative MDA-MB-468 and MCF-7 breast cancer cells and non-cancerous WI-38 cells (lung fibroblast cell) using MTT experiments. Among 21 synthesized compounds, three compounds (3a, 3b and 3 s) showed promising anti-cancer potential and compound 3b was found to have best anti-proliferative activities based on the results of several biochemical and microscopic experiments.     

Specific stabilization of DNA triple helices by indolo[2,1-b]quinazolin-6,12-dione derivatives

Derivatives of indolo[2,1-b]quinazolinone containing aminoalkylamino side chains were synthesized as specific DNA triplex stabilizing agents. The aminoalkylamino side chains are essential for triplex stabilization. The position-8 fluorine atom or a methyl group to the nitrogen adjacent to the planar core can enhance triplex stability by 6 degrees C and the effect is additive. Conformational analysis reveals that the orientation of the side chain underlies the ability of this compound to stabilize a DNA triplex.     

Mutagenic activity of benzofurans and naphthofurans in the Salmonella/microsome assay: 2-nitro-7-methoxynaphtho[2,1-b]furan (R7000), a new highly potent mutagenic agent

A series ¹ of benzofurans and naphthofurans was examined through the Salmonella/microsome assay. (i) With one possible exception, only 2-nitro derivatives give a mutagenic response. However, it appears that the mutagenic potency depends notably on the nature and the position of the other substituents in the molecule. (ii) The mutagenic response occurs in strains TA1537, TA1538, TA98 and TA100 but not in strain TA1535. Reversion of the missense mutation of TA1535 is thus induced only in presence of the plasmid pKM101. (iii) This mutagenic response is at least partially dependent on the bacterial nitroreductase activities and is usually lower in presence of activating mixture from rat liver. (iv) One of the compounds tested, 2-nitro-7-methoxynaphtho-[2,1-b]furan (R7000), may be the most potent mutagen examined so far in the Salmonella/microsome assay. It yields about 200 000 revertants/nanomole on strain TA100 in the standard plate test.The relation between structure, mutagenic potency and other biological activities of the compounds are briefly discussed.     

Cytotoxic activity toward KB cells of 2-substituted naphtho[2,3-b]furan-4,9-diones and their related compounds

We investigated the cytotoxic activity of 2-substituted naphtho[2,3-b]furan-4,9-diones. We have previously synthesized 33 types of 2-substituted and related compounds, and the cytotoxic activity of these compounds was then examined by a KB cell culture assay. 2-(3-Furanoyl)benzoic acids and 1,4-naphthoquinones had no activity. 2-Acetyl-4,9-dimethoxynaphtho[2,3-b]furan 4 showed low activity. However, parent naphtho[2,3-b]furan-4,9-dione 2 and most 2-substituted derivatives exhibited cytotoxic activity. The parent structure was therefore for cytotoxicity. 2-Formylnaphtho[2,3-b]furan-4,9-dione 11 had particularly potent activity (ED50=0.09 microg/ml).     

Efflux pump inhibition by 11H-pyrido[2,1-b]quinazolin-11-one analogues in mycobacteria

Mycobacterium tuberculosis infection causes 1.8 million deaths worldwide, of which half a million has been diagnosed with resistant tuberculosis (TB). Emergence of multi drug resistant and extensive drug resistant strains has made all the existing anti-TB therapy futile. The major involvement of efflux pump in drug resistance has made it a direct approach for therapeutic exploration against resistant M. tuberculosis. This study demarcates the role of 11H-pyrido[2,1-b]quinazolin-11-one (quinazolinone) analogues as efflux pump inhibitor in Mycobacterium smegmatis. Sixteen quinazolinone analogues were synthesized by treating 2-aminopyridine and 2-fluorobenzonitrile with K^tOBu. Analogues were tested, and 3a, 3b, 3c, 3g, 3j, 3l, 3m, and 3p were found to modulate EtBr MIC by >4 whereas 3a, 3g, 3i and 3o showed >4 modulation on norfloxacin MIC. 3l and 3o in addition to their very low toxicity they showed high EtBr and norfloxacin accumulation respectively. Time kill curve showed effective log reduction in colony forming unit in presence of these analogues, thus confirming their role as efflux pump inhibitor. Through docking and alignment studies, we have also shown that the LfrA amino acid residues that the analogues are interacting with are present in Rv2333c and Rv2846c of M. tuberculosis. This study have shown for the first time the possibility of developing the 11H-pyrido[2,1-b]quinazolin-11-one analogues as efflux pump inhibitors for M. smegmatis and hence unbolts the scope to advance this study against resistant M. tuberculosis as well.