Synthesis of two new heteroaromatic beta-carboline-fused pentacycles. Observation of a new intercalating agent

Base-mediated [3 + 2]-cycloannulation strategy for the synthesis of pyrazolo[1,5-a]pyridine derivatives using (E)-β-iodovinyl sulfones

Pyrazolo[1,5-a]pyridines continue to occupy a special place in medicinal chemistry, but the direct construction of 3-sulfonyl analogues remains unexplored. Under basic conditions, pyridinium-N-amine and the corresponding dipolar aminide played a vibrant role in [3 + 2]-cycloaddition using (E)-β-iodovinyl sulfones. K₂CO₃-mediated tandem cycloannulative-desulfonylation of (E)-β-iodovinyl sulfones with 1-aminopyridinium iodide is realized to access 2-substituted pyrazolo[1,5-a]pyridines in good to high yields. An essential modification of the dipolar N-tosylpyridinium imide allows the first preparative synthesis of 3-sulfonyl-pyrazolo[1,5-a]pyridines in moderate to high yields. Of note, the metal-free protocol features a broad substrate scope with good functional group tolerance and compatibility. The efficacy of the process was proved with gram-scale reactions, and a plausible mechanism is also presented based on concrete results.

A Comprehensive Review on Fused Heterocyclic as DNA Intercalators: Promising Anticancer Agents

Since the discovery of DNA intercalating agents (by Lerman, 1961), a growing number of organic, inorganic, and metallic compounds have been developed to treat life-threatening microbial infections and cancers. Fused-heterocycles are amongst the most important group of compounds that have the ability to interact with DNA. DNA intercalators possess a planar aromatic ring structure that inserts itself between the base pairs of nucleic acids. Once inserted, the aromatic structure makes van der Waals interactions and hydrogen-bonding interactions with the base pairs. The DNA intercalator may also contain an ionizable group that can form ionic interactions with the negatively charged phosphate backbone. After the intercalation, other cellular processes could take place, leading ultimately to cell death. The heterocyclic nucleus present in the DNA intercalators can be considered as a pharmacophore that plays an instrumental role in dictating the affinity and selectivity exhibited by these compounds. In this work, we have carried out a revision of small organic molecules that bind to the DNA molecule via intercalation and cleaving and exert their antitumor activity. A general overview of the most recent results in this area, paying particular attention to compounds that are currently under clinical trials, is provided. Advancement in spectroscopic techniques studying DNA interaction can be examined in-depth, yielding important information on structure-activity relationships. In this comprehensive review, we have focused on the introduction to fused heterocyclic agents with DNA interacting features, from medicinal point of view. The structure-activity relationships points, cytotoxicity data, and binding data and future perspectives of medicinal compounds have been discussed in detail.

Synthesis of 3D-Rich Heterocycles: Hexahydropyrazolo[1,5-a]pyridin-2(1H)-ones and Octahydro-2H-2a,2a1-diazacyclopenta[cd]inden-2-ones

Two cyclic azomethine imines, 7-methyl- and 7-phenyl-2-oxo-Δ⁷-hexahydropyrazolo[1,5-a]pyridin-8-ium-1-ide, were prepared in seven steps from the respective commercially available δ-keto acids. The addition of Grignard reagents followed by N-alkylation at position 1 afforded the 1,7,7-trisubstituted hexahydropyrazolo[1,5-a]pyridin-2(1H)-ones, whereas 1,3-dipolar cycloadditions of these dipoles to typical acetylenic and olefinic dipolarophiles gave 4a-substituted 2a,2a¹-diazacyclopenta[cd]indene derivatives as the first representatives of a novel heterocyclic system. Regio- and stereoselectivity as well as the mechanism of these [3 + 2]-cycloadditions were evaluated using computational and experimental methods. The data obtained were in agreement with the polar concerted cycloaddition mechanism via the energetically favorable syn/endo-transition states.

Synthesis and Antimicrobial Activities of 3-Methyl-β-Carboline Derivatives

The β-carboline alkaloids possess a diverse range of important biochemical effects and pharmacological properties. Sixteen 3-methyl-β-carboline derivatives were synthesized from indole formaldehyde and nitroethane via the Henry reaction, LAH/THF reduction, the Pictet-Spengler reaction and Pd/C/xylene oxidation, including four 1-substituted and twelve 9-substituted 3-methyl- β-carboline derivatives. The structures of all the derivatives were confirmed by 1H NMR, 13C NMR and ESI-MS. Most of these 3-methyl-β-carboline derivatives showed some antibacterial activity.

Substrate selective synthesis of pyrazolo[1,5-a]pyridines through [3 + 2] cycloaddition of N-aminopyridines and β-nitro styrenes

Synthesis of 2 or 3-(hetero)aryl pyrazolo[1,5-a]pyridines through [3 + 2] cycloaddition ofN-aminopyridine with β-nitrostyrenes followed byin situdenitration under metal-free and mild conditions are described.

Copper-mediated synthesis of pyrazolo[1,5-a]pyridines through oxidative linkage of C–C/N–N bonds

Copper-mediated synthesis of pyrazolo[1,5-a]pyridine-3-carboxylates through oxidative linkage of C–C and N–N bonds under mild reaction conditions with broad substrate scope is described.

A transition metal-free tandem process to pyridazinopyrido[3,2-f][1,4]thiazepine-diones via Smiles rearrangement

A transition metal-free methodology for the synthesis of pyridazinopyrido[3,2-f][1,4]thiazepine-diones was studied. The construction of this tricyclic system went through a one-pot coupling/Smiles rearrangement/cyclization process. The high yields of pure products were obtained through simple recrystallization.

Synthesis and Bioactivity of β-Carboline Derivatives

The β-carboline alkaloids possess a wide diversity of important biochemical effects and pharmacological properties. A series of β-carboline derivatives were synthesized from L-tryptophan through the Pictet-Spengler reaction and oxidation of K2Cr2O7 by a sequential one-pot synthesis method. In Vitro antibacterial, insecticidal, and cytotoxic activities of all synthesized compounds were investigated by the tablet diffusion, leaf disc, and MTT methods, respectively. Some of the compounds (1-1, 1-2, 1-3 and 1-12) exhibited obvious antibacterial effects and some (1-3) had significant cytotoxic activities against tumor cells 3LL, MCF-7, BGC-823 and QGY-7701, with IC50 values of 7.79, 5.75, 3.53 and 4.02 μg/mL, respectively. No insecticidal activity against third stage instar larvae of Mythimna separata Walker were observed under the tested concentration.

A class of 3S-2-aminoacyltetrahydro-beta-carboline-3-carboxylic acids: their facile synthesis, inhibition for platelet activation, and high in vivo anti-thrombotic potency

3S-Tetrahydro-beta-carboline-3-carboxylic acid (TCCA) effectively inhibits ADP-induced platelet activation. This paper used TCCA as a lead, modified its 2-position with amino acids, and provided 20 novel 3S-2-aminoacyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acids (5a-t). With the in vitro assay, it was demonstrated that this modification diminished the IC(50) values from 701 nM of TCCA to 10 nM of 5a-t. With the in vivo assay, it was demonstrated that this modification reduced the efficacious dose from 5.0 micromol/kg of TCCA to 0.1 micromol/kg of 5a-t. Comparing the Cerius based conformation of them with that of their analogues, the 3-position modified TCCA, it was suggested that the comparatively unfolded conformation was one of the important factors of enhancing the in vivo antithrombotic potency.

Coupled hydrogen-bonding interactions between beta-carboline derivatives and acetic acid

In this work, we have analysed the tendency of two beta-carboline derivatives, harmane and norharmane, in the formation of hydrogen bonds. We obtained the (1)H and (13)C NMR spectra of different mixtures of these derivatives with acetic acid (AcOH) in CDCl(3). A cyclic 1:3 complex is proposed between harmane and AcOH, while a 1:2 complex is proposed for norharmane. Chemical shifts at temperatures between 233 and 323 K were measured: lowering the temperature produces the same effect as increasing the amount of AcOH in solution. The (13)C data confirm a delocalisation of the pi electron density towards the pyridinic ring that occurs when AcOH is added.

Targeting topoisomerase II with the chiral DNA-intercalating ruthenium(II) polypyridyl complexes

Many antitumor drugs act as topoisomerase inhibitors, and the inhibitions are usually related to DNA binding. Here we designed and synthesized DNA-intercalating Ru(II) polypyridyl complexes Delta--[Ru(bpy)(2)(uip)](2+) and Lambda-[Ru(bpy)(2)(uip)](2+) (bpy is 2,2'-bipyridyl, uip is 2-(5-uracil)-1H-imidazo[4,5-f][1,10]phenanthroline). The DNA binding, photocleavage, topoisomerase inhibition, and cytotoxicity of the complexes were studied. As we expected, the synthesized Ru(II) complexes can intercalate into DNA base pairs and cleave the pBR322 DNA with high activity upon irradiation. The mechanism studies reveal that singlet oxygen ((1)O(2)) and superoxide anion radical (O (2) (*-) ) may play an important role in the photocleavage. The inhibition of topoisomerases I and II by the Ru(II) complexes has been studied. The results suggest that both complexes are efficient inhibitors towards topoisomerase II by interference with the DNA religation and direct topoisomerase II binding. Both complexes show antitumor activity towards HELA, hepG2, BEL-7402, and CNE-1 tumor cells.

DNA binding properties of 9-substituted harmine derivatives

The beta-carboline alkaloids have been characterized as a group of potential antitumor agents. The underlying mechanisms of harmine and its derivatives were investigated by DNA binding assay and Topoisomerase (Topo) inhibition assay. Meanwhile, the DNA photocleavage potential of these compounds and their cytotoxicity were also examined by DNA photocleavage assay and cytotoxicity assay in vitro. Harmine and its derivatives exhibited remarkable DNA intercalation capacity and significant Topo I inhibition activity but no effect with Topo II. Introducing an appropriate substituent into position-9 of beta-carboline nucleus enhanced the affinity of the drug to DNA resulting in remarkable Topo I inhibition effects. These results suggested that the ability of these compounds to act as intercalating agents and Topo I inhibitors was related to the antitumor activity. Moreover, these data showing a correlation between cytotoxicity and Topo I inhibition or DNA binding capacity are very important as they strongly suggested that the Topo I-mediated DNA cleavage assay and DNA binding assay could be used as a guide to design and develop superior analogues for antitumor activities.

Design, synthesis and in vitro and in vivo antitumor activities of novel β-carboline derivatives

To further our SAR study on the chemistry and antitumor activity/neurotoxicity of beta-carboline alkaloids, several series of beta-carboline derivatives with various substituents were designed and synthesized from the starting material l-tryptophan on the basis of harmine chemical structure. Cytotoxic activities of these compounds were investigated in vitro. The results showed that some beta-carboline derivatives had significant cytotoxic activities against human tumor cell lines. Among all the synthesized beta-carboline derivatives, the compounds 27, 28 and 32, having a benzyl substituent at both position-2 and 9, respectively, were found to be the most potent compounds with IC50 value lower than 50 microM against all human tumor cell lines examined. Acute toxicities and antitumor activities of the selected beta-carboline derivatives in mice were also evaluated. The results demonstrated that a benzyl substituent at position-2 increased the antitumor activity as well as acute toxicity significantly. However an (ethoxycarbonyl)amino substituent at position-3 reduced the acute toxicity as well as antitumor activity remarkedly. These data suggested that (1) the antitumor potencies of beta-carboline derivatives were enhanced by the introduction of benzyl substituent into the position-2; (2) the acute toxicity of beta-carboline derivatives reduced dramatically by the introduction of an appropriate substituent into the position-3 and 9; (3) the beta-carboline structure might be an important basis for the design and synthesis of new antitumor drugs with significant antitumor activity and low toxicity.

Synthesis and in vitro cytotoxic evaluation of 1,3-bisubstituted and 1,3,9-trisubstituted beta-carboline derivatives

A series of novel 1,3-bisubstituted and 1,3,9-trisubstituted beta-carboline derivatives was synthesized from the starting material l-tryptophan. Cytotoxic activities of these compounds were investigated in vitro. The results showed that 1,3,9-trisubstituted beta-carboline derivatives had higher cytotoxic activities in vitro than the corresponding 1,3-bisubstituted compounds. Among all the synthesized 1,3,9-trisubstituted beta-carboline derivatives, the compounds with a methyl substituent at position-1 displayed more potent cytotoxic activities, furthermore compound 5e having an ethoxycarbonyl substituent at position-3 and a pentafluorobenzyl at position-9, respectively, was found to be the most potent compounds of this series with IC(50) value of 4 uM against BGC-823 cell lines. These data suggested that (1) the cytotoxic potencies of beta-carboline derivatives were enhanced by the introduction of appropriate substituents into position-1 and position-9 in beta-carboline; (2) the beta-carboline structure might be an important basis for the design and synthesis of new antitumor drugs; (3) the methyl substituent at position-1, the pentafluorobenzyl group at position-9 and the ethoxycarbonyl substituent at position-3 were the optimal combination for the improvement of cytotoxic activity of the beta-carboline derivatives.

3-Aryl β-carbolin-1-ones as a new class of potent inhibitors of tumor cell proliferation: synthesis and biological evaluation

A novel three-step synthesis of 3-aryl beta-carbolin-1-ones from non-indole starting materials has been developed. The two nitrogen atoms in beta-carbolin-1-one were introduced efficiently by Michael addition of ethyl acetamidocyanoacetate to chalcone. The desired pyridone and indole rings were assembled by an intramolecular ketone-nitrile annulation mediated by aqueous HCl-HOAc and a Cu(I)-catalyzed intramolecular N-arylation of the amide, respectively. The target compounds were found to possess significant activity against tumor cell proliferation.

Synthesis, acute toxicities, and antitumor effects of novel 9-substituted β-carboline derivatives

A series of novel 9-substituted beta-carboline derivatives was synthesized from harmine and l-tryptophan, respectively. Cytotoxic activities of these compounds in vitro were investigated. The results showed that most compounds of 9-substituted beta-carboline derivatives had more remarkable cytotoxic activities in vitro than their corresponding parent compounds. Acute toxicities and antitumor effects of the selected beta-carboline derivatives in mice were also examined. The results demonstrated that a short alkyl or benzyl substituent at position-9 increased the antitumor activities significantly and a ethoxycarbonyl or carboxyl substituent at position-3 reduced the acute toxicity and neurotoxicity of these beta-carboline derivatives dramatically. Moreover the compounds both with an alkoxycarbonyl or carboxyl substituent at position-3 and a short alkyl or benzyl substituent at positon-9 exhibited more significant antitumor activities and lower acute toxicities and neurotoxicities than the other compounds. The compound 8c, having an n-butyl and a carboxyl substituent at position-9 and 3, respectively, was found to have the highest antitumor effect and the lowest acute toxicity and neurotoxicity. These data suggested that (1) appropriate substituents at both position-9 and 3 of beta-carboline derivatives might play a crucial role in determining their enhanced antitumor activities and decreased acute toxicities and neurotoxic effects; (2) the beta-carboline derivatives have the potential to be used as antitumor drug leads.

Synthesis of New Polyfused Heterocycles of Biological Importance by Means of Pd(0) Catalysis

A general synthetic methodology employing heteroaryl-aryl Suzuki coupling is reviewed, by which 15 heteroaromatic ring systems of biological interest have been prepared.