The anti‐Trichomonas vaginalis phloroglucinol derivative isoaustrobrasilol B modulates extracellular nucleotide hydrolysis

Trichomonas vaginalis causes trichomoniasis, a neglected sexually transmitted disease. Due to severe health consequences and treatment failure, new therapeutic alternatives are crucial. Phloroglucinols from southern Brazilian Hypericum species demonstrated anti‐T. vaginalis and anti‐Leishmania amazonensis activities. The modulation of biochemical pathways involved in the control of inflammatory response by ectonucleotidases, NTPDase, and ecto‐5′‐nucleotidase represents new targets for combating protozoa. This study investigated the activity of phloroglucinol derivatives of Hypericum species from southern Brazil against T. vaginalis as well as its ability on modulating parasite ectonucleotidases and, consequently, immune parameters through ATP and adenosine effects. Phloroglucinol derivatives screening revealed activity for isoaustrobrasilol B (IC₅₀ 38 μm ) with no hemolytic activity. Although the most active compound induced cytotoxicity against a mammalian cell lineage, the in vivo model evidenced absence of toxicity. Isoaustrobrasilol B significantly inhibited NTPDase and ecto‐5′‐nucleotidase activities, and the immune modulation attributed to extracellular nucleotide accumulation was evaluated. The production of ROS and IL‐6 by T. vaginalis‐stimulated neutrophils was not affected by the treatment. Conversely, IL‐8 levels were significantly enhanced. The associative mechanism of trophozoites death and ectonucleotidases modulation by isoaustrobrasilol B may increase the susceptibility of T. vaginalis to host innate immune cell like neutrophils consequently, contributing to parasite clearance.     

Antiproliferative activity of ester derivatives of monensin A at the C‐1 and C‐26 positions

Monensin A ( MON ) is a polyether ionophore antibiotic, which shows a wide spectrum of biological activity, including anticancer activity. A series of structurally diverse monensin esters including its C‐1 esters ( 1 – 9 ), C‐26‐O‐acetylated derivatives ( 10 – 15 ), and lactone ( 16 ) was synthesized and for the first time evaluated for their antiproliferative activity against four human cancer cell lines with different drug‐sensitivity level. All of the MON derivatives exhibited in vitro antiproliferative activity against cancer cells at micromolar concentrations. The majority of the compounds was able to overcome the drug resistance of LoVo/DX and MES‐SA/DX5 cell lines. The most active compounds proved to be MON C‐26‐O‐acetylated derivatives ( 10 – 15 ) which exhibited very good resistance index and high selectivity index.     

Efficient Synthesis and Biological Evaluation of a Novel Series of 1,5‐Benzodiazepine Derivatives as Potential Antimicrobial Agents

A series of novel 1,5‐benzodiazepine derivatives were rationally designed and synthesized following the principle of the superposition of bioactive substructures by the combination of 1,5‐benzodiazepine, pyridine (phenyl), and an ester group. The structures of the target compounds were determined by ¹H NMR, ¹³C NMR, MS, IR, and elemental analysis. All the synthesized compounds were evaluated for their antimicrobial activities in vitro against the fungi C. neoformans, C. neoformans clinical isolates (ATCC 32264), C. albicans (ATCC 10231), Gram‐negative bacterium E. coli (ATCC 44752), and Gram‐positive bacterium S. aureus (ATCC 25923). The results of the bioactive assay demonstrated that most of the tested compounds exhibited variable inhibitory effects on the growth of the tested microorganisms. All the active compounds showed better antifungal activity than antibacterial activity. Notably, compound 2b displayed the highest activity (MIC = 30 μg/mL) against C. neoformans and (MIC = 31 μg/mL) against C. neoformans clinical isolates. In addition, compound 2a also showed excellent activity against C. neoformans and C. neoformans clinical isolates with minimum inhibitory concentration of 35 and 36 μg/mL, respectively. Compounds 2a and 2b were further studied by evaluating their cytotoxicities, and the results showed that they have relatively low level cytotoxicity for BV2 and 293T cell. Preliminary structure‐activity relationship study on three diverse sets (C‐2, C‐3, and C‐8 positions) of 1,5‐benzodiazepines was performed. The results revealed that the presence of a ‐CH₃ group at the C‐8 position had a positive effect on the inhibitory activity of these compounds. Additionally, the 2‐pyridyl group at the C‐2 position may be a pharmacophore and ‐COOC₂H₅ at C‐3 position is the best substituent for the maintenance of antimicrobial activities.     

Cytotoxic and trypanocidal activities of cinchona alkaloid derivatives

A series of 27 cinchona alkaloid derivatives ( 1f–w , 2a–e and 3a–d ) were investigated for their cytotoxic and trypanocidal activities using seven different cancer cell lines (KB, HeLa, MCF‐7, A‐549, Hep‐G2, U‐87 and HL‐60), two normal cell lines (HDF and CHO) and bloodstream forms of Trypanosoma brucei brucei, respectively. Four compounds ( 1u , 1w , 2e and 3d ) were identified with promising cytotoxic activity with 50% growth inhibition (GI₅₀) values below 10 μM. Two ( 2e and 3d ) of the four compounds also exhibited potent anti‐trypanosomal activity with GI₅₀ values of 0.3–0.4 μM. All four active compounds represented derivatives modified at their C‐9 hydroxy group. With respect to anti‐proliferative activity and selectivity, 2e (epi‐N‐quinidyl‐N′‐bis(3,5‐trifluoromethyl)phenylthiourea) proved to be the most promising derivative for both cancer cells and bloodstream forms of T. b. brucei. The cytotoxic activity of compounds 1u , 1w , 2e and 3d was attributed to their ability to induce apoptosis in cancer cells. The results demonstrate the potential of cinchona alkaloid derivatives as novel anti‐cancer and anti‐trypanosome drug candidates.     

Synthesis and Antimicrobial Evaluation of 6‐Alkylamino‐N‐phenylpyrazine‐2‐carboxamides

This work presents synthesis and antimicrobial evaluation of nineteen 6‐alkylamino‐N–phenylpyrazine‐2‐carboxamides. Antimycobacterial activity was determined against Mycobacterium tuberculosis H37Rv, M. kansasii and two strains of M. avium. Generally, the antimycobacterial activity increased with prolongation of simple alkyl chain and culminated in compounds with heptylamino substitution ( 3e , 4e ) with MIC = 5–10 μm against M. tuberculosis H37Rv. On the contrary, derivatives with modified alkyl chain (containing e.g. terminal methoxy or hydroxy group) as well as phenylalkylamino derivatives were mainly inactive. The most active compounds (with hexyl to octylamino substitution) were evaluated for their in vitro activity against drug‐resistant strains of M. tuberculosis and possessed activity comparable to that of the reference drug isoniazid. None of the tested compounds were active against M. avium. Some derivatives exhibited activity against Gram‐positive bacteria including methicillin‐resistant Staphylococcus aureus (best MIC = 7.8 μm ), while Gram‐negative strains as well as tested fungal strains were completely unsusceptible. Active compounds were tested for in vitro toxicity on various cell lines and in most cases were non‐toxic up to 100 μm .     

Potential of bisbenzimidazole‐analogs toward metronidazole‐resistant Trichomonas vaginalis isolates

A bisoxyphenylene‐bisbenzimidazole series with increasing aliphatic chain length (CH₂ to C₁₀H₂₀) containing a meta‐ (m) or para (p)‐benzimidazole linkage to the phenylene ring was tested for ability to inhibit the growth of metronidazole‐susceptible (C1) and metronidazole‐refractory (085) Trichomonas vaginalis isolates under aerobic and anaerobic conditions. Compound 3m , 2,2′‐[α,ω‐propanediylbis(oxy‐1,3‐phenylene)]bis‐1H‐benzimidazole, displayed a 5.5‐fold lower minimum inhibitory concentration (MIC) toward T. vaginalis isolate 085 than metronidazole under aerobic growth conditions, (26 μm compared to 145 μm ). A dose of 25 mg/kg per day for four days of compound 3m cured a subcutaneous mouse model infection using T. vaginalis isolates 286 (metronidazole susceptible) and 085 (metronidazole refractory). Compound 3m was weakly reduced by pyruvate:ferredoxin oxidoreductase, but unlike metronidazole was not dependent upon added ferredoxin. It is concluded from structure‐activity relationships that there was no obvious trend based on the length of the central aliphatic chain, or the steric position of the bisbenzimidazole enabling prediction of biological activity. The compounds generally fulfill Lipinski's rile of five, indicating their potential as drug leads.     

Design of Conformationally Constrained Azole Antifungals: Efficient Synthesis and Antifungal Activity of trans‐3‐Imidazolylflavanones

An efficient protocol has been developed for the preparation of a series of trans‐3‐imidazolylflavanones and (Z)‐trans‐3‐imidazolylflavanone oximes, as potential antifungal agents, by the reaction of 2‐imidazolyl‐2′‐hydroxyacetophenone with different benzaldehyde derivatives and subsequence oximation reaction. The stereochemical and conformational aspects of compounds were also assigned by ¹H NMR spectroscopy. The aryl group present at C‐2 and the imidazole ring present at C‐3 were assigned to occupy equatorial position in trans‐3‐imidazolylflavanones 3 and axial position in (Z)‐trans‐3‐imidazolylflavanone oximes 4 . Most of the 3‐imidazolylflavanone derivatives containing a substituent on phenyl ring showed significant antifungal activity and modification of the 4‐oxo group to oxime or substituent on phenyl ring produced changes in the antifungal activity profile of these compounds. Generally, 3′‐chloro‐ analog of 3‐imidazolylflavanone 3c exhibited better profile of antifungal activity against strains of fungi tested, superior than reference drug fluconazole.     

Synthesis of nicotinamide derivatives having a hydroxy‐substituted benzene ring and the influence of their structures on the apoptosis‐inducing activity against leukemia cells

With the view of developing novel apoptosis‐inducing agents against malignant cells, nicotinamide derivatives containing substituted O‐benzoyl‐tyrosine, dopamine, and norepinephrine residues were synthesized. Antiproliferative activity measurements using leukemia U937 cells revealed that the benzoyl‐tyrosine derivative having two hydroxys at C‐2 and C‐3 on the benzoyl group, and the one having a hydroxy at C‐2 and a methoxy at C‐4 proved the most potent among the 9 nicotinamide derivatives. The IC₅₀ values of these compounds were 0.87 and 3.15 µM, which indicates their noteworthy activity compared with epigallocatechin gallate, a catechin component in green tea known for its noticeable activity. The cell death process was confirmed to be the result of apoptosis by agarose gel electrophoresis and dye staining, suggesting the high potential of these compounds as apoptosis‐inducing anticancer agents. Drug Dev Res 72: 289–297, 2011. © 2010 Wiley‐Liss, Inc.     

Synthesis of Novel Heterocyclic Ring‐Fused 18β‐Glycyrrhetinic Acid Derivatives with Antitumor and Antimetastatic Activity

Glycyrrhetinic acid (GA) is one of the most important triterpenoic acids shows many pharmacological effects, especially antitumor activity. GA triggers apoptosis in various tumor cell lines. However, the antitumor activity of GA is weak, thus the synthesis of new synthetic analogs with enhanced potency is needed. By introducing various five‐member fused heterocyclic rings at C‐2 and C‐3 positions, 18 novel GA derivatives were obtained. These compounds were evaluated for their inhibitory activity against the growth of eight different tumor cell lines using a SRB assay. The most active compound 37 showed IC₅₀ between 5.19 and 11.72 μm , which was about 11‐fold more potent than the lead compound GA. An apoptotic effect of GA and 37 was determined using flow cytometry and trypan blue exclusion assays. We also demonstrated here for the first time that GA and the synthetic derivatives exhibited inhibitory effect on migration of the tested tumor cells, especially 37 which was about 20‐fold more potent than GA on antimetastatic activity.     

Synthesis of valproate,valerate, and 1‐methyl‐1, 4‐dihydropyridyl‐3‐carbonyloxy ester derivatives of Hantzsch 1,4‐dihydropyridines as potential prodrugs and their evaluation as calcium channel antagonist and anticonvulsant agents

A group of 3‐(hydroxyalkyl) 5‐alkyl 1,4‐dihydro‐2,6‐dimethyl‐4‐aryl‐3,5‐pyridinedicarboxylates ( 11–15 ) were prepared using a modified Hantzsch reaction, which were then elaborated to valproate ( 16–18 ), valerate ( 19, 20 ), and 1‐methyl‐1,4‐dihydropyridyl‐3‐carbonyloxy ( 25, 26 ) derivatives. Alternatively, the valproate derivative 3‐(2‐n‐propylpentanoyloxymethyl) 5‐isopropyl 1,4‐dihydro‐2,6‐dimethyl‐4‐(2,3‐dichlorophenyl)‐3,5‐pyridinedicarboxylate ( 34 ) was prepared by the reaction of isopropyl 1,4‐dihydro‐2,6‐dimethyl‐4‐(2,3‐dichlorophenyl)‐3,5‐pyridinedicarboxylate ( 30 ) with chloromethyl valproate ( 33 ). This class of lipophilic compounds possess partition coefficients (Kp) in the 149–452 range, relative to the reference drug nimodipine (Kp = 187). All compounds exhibited potent calcium channel antagonist (CCA) activity (IC₅₀ = 10^–7 to 10^–10 M range), relative to the reference drug nimodipine (IC₅₀ = 1.49 × 10^–8 M). CCA structure–activity relationships showed the parent C‐3 2‐hydroxyethyl compounds were more potent than their valproate derivatives, but less active than their valerate derivatives. Compounds having a 1‐methyl‐1,4‐dihydropyridyl‐3‐carbonyloxy chemical delivery system (CDS) were approximately equiactive to the parent C‐3 2‐hydroxyethyl compounds. Anticonvulsant activity was determined in the maximal electroshock (MES) and subcutaneous metrazol (scMet) screens. 3‐(2‐Hydroxyethyl) 5‐isopropyl 1,4‐dihydro‐2,6‐dimethyl‐4‐(2,3‐dichlorophenyl)‐3,5‐pyridinedicarboxylate ( 12 ) provided modest protection in the MES and scMet screens. In the C‐3 valproate [CO₂(CH₂)nO₂CCH(n‐Pr)₂] group of compounds, those possessing an ethylene spacer (n = 2) provided protection in the MES screen, whereas those having a propylene spacer (n = 3) or methylene spacer (n = 1) were inactive. Related C‐3 valerate esters [CO₂(CH₂)₂O₂C‐n‐Bu] also provided protection in the MES screen, whereas those having a 1‐methyl‐1,4‐dihydropyridyl‐3‐carbonyloxy CDS moiety were inactive. Drug Dev. Res. 48:26–37, 1999. © 1999 Wiley‐Liss, Inc.     

In‐vitro evaluation of the P‐glycoprotein interactions of a series of potentially CNS‐active Amaryllidaceae alkaloids

Objectives Drug compounds interacting with the blood–brain barrier efflux transporter P‐glycoprotein (P‐gp) might have limited access to brain tissue. The aim of the present study was to evaluate whether nine potentially CNS‐active Amaryllidaceae alkaloids of the crinine, lycorine and galanthamine types interact with P‐gp. Methods Alkaloids with inhibitory activity towards either the serotonin reuptake transporter or acetylcholinesterase, or both, were investigated using the calcein‐AM efflux assay in Madin‐Darby canine kidney cells transfected with human multidrug resistance transporter 1. Key findings Powelline and 6‐hydroxycrinamine showed an interaction with P‐gp, with IC50 values between 300 and 500 µm . 3‐O‐Acetylhamayne showed a weaker interaction, with an IC50 value above 3 mM. Epibuphanisine, lycorine, 1‐epi‐deacetylbowdenisine, papyramine and galanthamine all showed weak or no interaction with P‐gp. There was no observed correlation between alkaloid type and P‐gp interaction. Conclusions Structurally similar compounds such as crinine and epibuphanisine showed very different P‐gp interactions, highlighting the difficulty in predicting P‐gp interactions. Epibuphanisine has previously shown activity in the serotonin reuptake transporter assay and may therefore serve as a lead for serotonin reuptake transporter active compounds. The most potent compound in the acetylcholinesterase assay, the marketed drug compound galanthamine (Reminyl), showed no interaction with P‐gp.     

Synthesis and antimalarial activity of ethylene glycol oligomeric ethers of artemisinin

Objectives The aim of this study was to synthesize a series of ethylene glycol ether derivatives of the antimalarial drug artemisinin, determine their values for selected physicochemical properties and evaluate their antimalarial activity in vitro against Plasmodium falciparum strains. Methods The ethers were synthesized in a one‐step process by coupling ethylene glycol moieties of various chain lengths to carbon C‐10 of artemisinin. The aqueous solubility and log D values were determined in phosphate buffered saline (pH 7.4). The derivatives were screened for antimalarial activity alongside artemether and chloroquine against chloroquine‐sensitive (D10) and moderately chloroquine‐resistant (Dd2) strains of P. falciparum. Key findings The aqueous solubility within each series increased as the ethylene glycol chain lengthened. The IC50 values revealed that all the derivatives were active against both D10 and Dd2 strains. All were less potent than artemether irrespective of the strain. However, they proved to be more potent than chloroquine against the resistant strain. Compound 8 , featuring three ethylene oxide units, was the most active of all the synthesized ethers. Conclusions The conjugation of dihydroartemisinin to ethylene glycol units of various chain lengths through etheral linkage led to water‐soluble derivatives. The strategy did not result in an increase of antimalarial activity compared with artemether. It is nevertheless a promising approach to further investigate and synthesize water‐soluble derivatives of artemisinin that may be more active than artemether by increasing the ethylene glycol chain length.     

Bis‐2(5H)‐furanone derivatives as new anticancer agents: Design,synthesis, biological evaluation,and mechanism studies

New bis‐2(5H)‐furanone derivatives containing a benzidine core were synthesized via a one‐step transition‐metal‐free reaction of benzidine with 5‐substituted 3,4‐dihalo‐2(5H)‐furanones. Their antitumor activities against various tumor cells have been evaluated by MTT assay. Among them, compound 4e exhibits significant inhibitory activity against C6 glioma cells with an IC₅₀ value of 12.1 μm and low toxicity toward HaCaT human normal cells. Studies on the antitumor mechanism reveal that cell cycle arrest at S‐phase in C6 cells is induced by compound 4e . Furthermore, investigations with electronic, fluorescence emission and circular dichroism spectra show that compound 4e can significantly interact with C6‐DNA. These data indicate that DNA may be one of the potential targets for bis‐2(5H)‐furanone derivatives as anticancer drugs.     

Kinetics of killing or growth of Trichomonas vaginalis in the presence of aminoglycosides, neomycin and geneticin (G418)

Few therapeutic drugs, other than metronidazole and close derivatives, are currently available to treat trichomoniasis. Trichomonas vaginalis is known to have a primitive ribosome based on small subunit ribosomal DNA sequence comparisons. Targeting ribosomal subunits, the aminoglycosides neomycin and geneticin (G418, distinct from gentamycin) were tested for activity against T. vaginalis. While neomycin had no effect, G418 was effective in killing cultured T. vaginalis cells at doses intermediate between those previously effective against prokaryotes and eukaryotes. G418 cytotoxicity requires further study before recommending this agent as topically applied therapy in refractory patients.     

Effect of the lipophilic parameter (log <Emphasis Type="Italic">P</Emphasis>) on the anti-parasitic activity of imidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]pyridine derivatives

A number of imidazo[1,2-a]pyridine derivatives were selected and investigated in relation to anti-parasitic (Trichomonas vaginalis) activity. After treatment with derivatives, biological activity was assessed by determination of the in vitro viability of cell cultures, using alamar blue as a metabolic indicator. A good correlation was found between the anti-parasitic activity and the partition coefficient log P determined experimentally on the tested compounds, which explained up to 84% of the measured activity. A favorable interval (0.9 ± 0.3 log P) was found for optimum biological response.     

Synthesis and anti-bacterial activity of some heterocyclic chalcone derivatives bearing thiofuran, furan, and quinoline moieties

36 Novel heterocyclic chalcone derivatives were synthesized and tested for their anti‐bacterial activity. Some compounds presented good anti‐microbial activities against Gram‐positive bacteria (including the multidrug‐resistant clinical isolates). This class of compounds presented high potency against Streptococcus mutans, among which the derivatives F2 with an MIC of 2 µg/mL was as active as the standard drug (norfloxacin) and less active than oxacillin. All the compounds did not inhibit the growth of Gram‐negative bacteria (Escherichia coli CCARM 1924 or Escherichia coli CCARM 1356) at 64 µg/mL.     

Novel 3‐substituted N‐methylcarbazole–imidazolium salt derivatives: Synthesis and cytotoxic activity

A series of novel 3‐substituted N‐methylcarbazole–imidazolium salt derivatives has been prepared and evaluated in vitro against a panel of tumor cell lines (Hep G‐2, Hela and PC12). The results suggest that the presence of substituted 2‐methyl‐imidazole or imidazole ring and substitution of the imidazolyl‐3‐position with a naphthylacyl or 4‐bromophenacyl group were important for improving cytotoxic activity. Compounds 17 , 18 , 27, and 28 with 4‐bromophenacyl and naphthylacyl groups displayed good activities with IC₅₀ values of 0.09–7.20 μm against three tumor cell lines investigated and more active than DDP. Compound 35 exhibited cytotoxic activity selectively against Hela cell.     

Synthesis and Biological Evaluation of Novel Pyrazoles and Pyrazolo[3,4‐d]pyrimidines Incorporating a Benzenesulfonamide Moiety

Synthesis and biological evaluation of novel pyrazoles and pyrazolo[3,4‐d]pyrimidines are reported. Fourteen compounds were selected by the NCI and tested for their preliminary in‐vitro anticancer activity, whereas all the synthesized compounds were evaluated for their in‐vitro antimicrobial activity. Compound 12a was proven to possess the highest anticancer activity with a broad spectrum profile. It showed particular effectiveness towards leukemia HL‐60 (TB), K‐562, non‐small cell lung cancer NCI‐H23, and colon cancer HT 29, KM 12 cell lines (GI₅₀ = 6.59, 4.44, 1.37, 3.33, and 9.63 μM, respectively). Out of the synthesized compounds, thirteen derivatives were found to display pronounced antimicrobial activity especially against P. aeruginosa. Compounds 2c , 5b , 10 , 11b , 17b , 18b , and 19 were proven to be the most active with a broad spectrum of activity. Compound 19 was found to be equipotent to ampicillin against B. subtilis, whereas compounds 11b and 19 were four times superior to ampicillin against P. aeruginosa, while compounds 5b and 18b were equipotent to ampicillin against the same organism. Moreover, compounds 2c , 10 , and 11b were nearly equipotent to ampicillin against E. coli. On the other hand, compounds 2c , 5b , 10 , 11a , 17b , and 18b exerted nearly half the activity of clotrimazole against C. albicans.     

Synthesis and Biological Evaluation of Some Novel Polysubstituted Pyrimidine Derivatives as Potential Antimicrobial and Anticancer Agents

Synthesis and evaluation of the antimicrobial and cytotoxic activity of two series of polysubstituted pyrimidines comprising the thioether functionality and other pharmacophores, reported to contribute to various chemotherapeutic activities are described. All newly synthesized compounds were subjected to in‐vitro antibacterial and antifungal screening. Out of the compounds tested, 18 derivatives displayed an obvious inhibitory effect on the growth of the tested Gram‐positive and Gram‐negative bacterial strains, with special effectiveness against the Gram‐positive strains. Compounds 1 , 2 , 6 , 7 , 9 , 10 , 11 , 21 , and 24 revealed remarkable broad antibacterial spectrum profiles. Among those, compounds 1 , 2 , 6 , 7 , 9 , and 24 exhibited an appreciable antifungal activity against C. albicans. Compound 2 proved to be the most active antimicrobial member identified here as it showed twice the activity of ampicillin against B. subtilis and the same activity of ampicillin against M. Luteus and P. aeruginosa together with a moderate antifungal activity. Further, eleven analogs were evaluated for their in‐vitro cytotoxic potential utilizing the standard MTT assay against a panel of three human cell lines: breast adenocarcinoma MCF7, hepatocellular carcinoma HePG2, and colon carcinoma HT29. The obtained data revealed that six of the tested compounds 1 , 3 , 7 , 12 , 13 , and 15 showed a variable degree of cytotoxic activity against the tested cell lines at both the LC₅₀ and LC₉₀ levels. Compound 7 proved to be the most active cytotoxic member in this study with special effectiveness against the colon carcinoma HT29 and breast cancer MCF7 human cell lines for LC₅₀ and LC₉₀. Thus, compounds 1 and 7 could be considered as possible dual antimicrobial‐anticancer agents.     

Synthesis and Biological Evaluation of Some Polymethoxylated Fused Pyridine Ring Systems as Antitumor Agents

A series of 3,5‐bis(arylidene)‐4‐piperidones like chalcone analogues carrying variety of methoxylated aryl groups, pyrazolo[4,3‐c]pyridines, pyrido[4,3‐d]pyrimidines, and pyrido[3,2‐c]pyridines, carrying an arylidene moiety, and some pyrano[3,2‐c]pyridines, like flavone and coumarin isosteres, were synthesized and screened for their in‐vitro antitumor activity at the National Cancer Institute (NCI, USA). The tested compounds 7 , 9 , 10 , 12, 13, 15, 17 , and 19 exhibited a broad spectrum of antitumor activity. Compounds belonging to the pyrazolo[4,3‐c]pyridine series proved to be more active than those of the pyrido[3,2‐c]pyridine and pyrano[3,2‐c]pyridine analogues, in which the monomethoxylated derivatives showed better antitumor activity when compared with their corresponding dimethoxylated congeners. Compound 7 is considered to be the most active member identified in this study with a broad spectrum of activity against 22 different tumor cell lines belonging to the nine subpanels employed, and a particular effectiveness against the breast cancer T‐47D cell line (GI 54.7%). The pyrano[3,2‐c]pyridine heterocyclic system 19 proved to be the most active antitumor agent among the six‐membered fused pyridines, with variable activity against 18 different tumor cell lines, and special activity against the non‐small cell lung cancer Hop‐92 and ovarian cancer OVCAR‐4 cell lines (GI values 63.9 and 48.5%, respectively).