Synthesis and antibacterial activity of substituted 1,2,3,4-tetrahydropyrazino [1,2-a] indoles

Synthesis and Biological Activities of Pyrazino[1,2-a]indole and Pyrazino[1,2-a]indol-1-one Derivatives

This review concerns the synthesis and biological activities of pyrazino[1,2-a]indoles and pyrazino[1,2-a]indol-1-ones reported since 1997 and the discovery of biological activity of pyrazinoindole derivatives. In the first part, we first presented the synthetic routes that have been reported from a methodological point of view to access the pyrazinoindole unit according to cyclization reactions using or not using metal catalysts. Then, syntheses and neuropsychiatric, auto-immune, anti-infectious and anti-cancer properties of pyrazinoindoles were detailed. In the second part, we first reported the main accesses to pyrazinoindol-1-one substrates according to Michael reactions, metal-catalyzed and metal-free cyclization reactions. The syntheses and anti-cancer, anti-infectious, anti-allergenic and neuropsychiatric properties of pyrazinoindolones were next described and discussed.

A convenient one-pot approach to the synthesis of novel pyrazino[1,2-a]indoles fused to heterocyclic systems and evaluation of their biological activity as acetylcholinesterase inhibitors

Pyrazino[1,2-a]indoles fused with various heterocycles, such as oxazolidine, oxazinane, imidazolidine, hexahydropyrimidine and benzimidazole, were synthesized transition metal-free by domino reactions which involved the condensation of 1-(2-bromoethyl)-3-chloro-1H-indole-2-carbaldehydes 28–31 with various nucleophilic amines, resulting in the formation of two new interesting fused heterocycles. The anticholinesterase, antioxidant and antibacterial activities of the compounds were evaluated. Acetylcholinesterase (AChE) inhibitory activities were tested by Ellman’s assay, antioxidant activities were detected using the 2,2-azinobis[3-ethylbenzthiazoline]-6-sulfonic acid (ABTS•+) free-radical scavenging method and antibacterial activities were determined by agar diffusion tests. The oxazolo-pyrazino[1,2-a]indoles (8, 10), the oxazino-pyrazino[1,2-a]indoles (16, 18, 19), the pyrimido-pyrazino[1,2-a]indole (22), and the benzoimidazo-pyrazino[1,2-a]indole (27) possessed the highest inhibitory activity against AChE with IC50 values in the range 20–40 μg mL−1. The oxazolo-pyrazino[1,2-a]indoles (8, 9), the imidazo-pyrazino[1,2-a]indoles (12, 13), and the benzoimidazo-pyrazino[1,2-a]indole (24) revealed the highest antioxidant values with IC50 values less than 300 μg mL−1. However, the oxazolo-pyrazino[1,2-a]indole (11) and imidazo-pyrazino[1,2-a]indoles (12, 13) exhibited weak to moderate bioactivities against all tested Gram-positive bacteria, namely Staphylococcus aureus, Bacillus subtilis and Bacillus cereus.

Cu(II) complex with auxin (3-indoleacetic acid) and an aromatic planar ligand: synthesis, crystal structure, biomolecular interactions and radical scavenging activity

A novel water soluble ternary copper(II) complex,-[Cu₂(phen)₂(3-IAA)₂(H₂O)](ClO₄)₂·H₂O-(phen: 1,10-phenanthroline, 3-IAA: 3-indoleacetic acid), has been synthesized and characterized by elemental CHN analysis, ESI-TOF, FTIR and single-crystal X-ray diffraction techniques. Interaction of the complex with calf thymus DNA (CT-DNA) has been investigated by absorption spectral titration, ethidium bromide (EB) and Hoechst 33258 displacement assay. The interactions between the complex and bovine serum albumin (BSA) were investigated by electronic absorption and fluorescence spectroscopy methods. The experimental results indicate that the fluorescence quenching mechanism between the complex and BSA is a static quenching process. The Stern-Volmer constants, binding constants, binding sites and the corresponding thermodynamic parameters (ΔG, ΔH, ΔS) of BSA + complex systems were determined at different temperatures. The binding distance between the complex and BSA was calculated according to Förster non-radiation energy transfer theory (FRET). The effect of the complex on the conformation of BSA was also examined using synchronous, two dimensional (2D) and three dimensional (3D) fluorescence spectroscopy. Furthermore, the oxygen radical scavenging activity of the complex was determined in terms of IC₅₀, using the DPPH and H₂O₂ method, to show that it particularly enables electron loss from radical species. This study highlights the importance of indole and moieties in the development of antioxidant agents. A potent drug candidate novel water soluble ternary copper(II) complex,-[Cu₂(phen)₂(3-IAA)₂(H₂O)] (ClO₄)₂·H₂O-(phen: 1,10-phenanthroline, 3-IAA: 3-indoleacetic acid), has been synthesized and characterized by elemental CHN analysis, FTIR, ESI-MS and single-crystal X-ray diffraction techniques. The complex has been tested for in vitro biomacromolecular interactions by spectroscopic methods. Furthermore, radical scavenging activities of the complex were also investigated.

A brief review of the biological potential of indole derivatives

Background

Various bioactive aromatic compounds containing the indole nucleus showed clinical and biological applications. Indole scaffold has been found in many of the important synthetic drug molecules which gave a valuable idea for treatment and binds with high affinity to the multiple receptors helpful in developing new useful derivatives.

Main text

Indole derivatives possess various biological activities, i.e., antiviral, anti-inflammatory, anticancer, anti-HIV, antioxidant, antimicrobial, antitubercular, antidiabetic, antimalarial, anticholinesterase activities, etc. which created interest among researchers to synthesize a variety of indole derivatives.

Conclusion

From the literature, it is revealed that indole derivatives have diverse biological activities and also have an immeasurable potential to be explored for newer therapeutic possibilities.

Regiodivergent synthesis of pyrazino-indolines vs. triazocines via α-imino carbenes addition to imidazolidines

Hexahydropyrazinoindoles were prepared in a single step from N-sulfonyl triazoles and imidazolidines. Under dirhodium catalysis, α-imino carbenes were generated and formed nitrogen ylide intermediates that, after subsequent aminal opening, afforded the pyrazinoindoles predominantly via formal [1,2]-Stevens and tandem Friedel–Crafts cyclizations. Of mechanistic importance, a regiodivergent reactivity was engineered through the use of a specific unsymmetrically substituted imidazolidine that promoted the exclusive formation of 8-membered ring 1,3,6-triazocines. Based on DFT calculations, an original Curtin–Hammett-like situation was demonstrated for the mechanism. Further derivatizations led to functionalized tetrahydropyrazinoindoles in high yields.

Hexahydropyrazinoindoles are prepared in a single step from N-sulfonyl triazoles and imidazolidines. Of mechanistic importance, a regiodivergent reactivity can be engineered towards the exclusive formation of 8-membered ring 1,3,6-triazocines.

Design and synthesis of an indol derivative as antibacterial agent against Staphylococcus aureus

Several indole derivatives with antibacterial activity have been prepared using different protocols; however, some require special reagents and conditions. The aim of this study involved the synthesis of some indole derivatives using estrone and OTBS-estrone as chemical tools. The synthesis of the indole derivatives involves reactions such as follows: (1) synthesis of two indol derivatives (4 or 5) by reaction of estrone or OTBS-estrone with phenylhydrazine in medium acid; (2) reaction of 4 or 5 with 6-cloro-1-hexyne in medium basic to form two hexynyl-indol (7 or 8); (3) preparation of indol-propargylic alcohol derivatives (10 or 11) by reaction of benzaldehyde with 7 or 8 in medium basic; (4) synthesis of indol-aldehydes (12 or 13) via oxidation of 10 or 11 with DMSO; (5) synthesis of indeno-indol-carbaldehyde (15 or 16) via alkynylation/cyclization of 12 or 13 with hexyne in presence of copper(II); (6) preparation indeno-indol-carbaldehyde complex (19 or 20) via alkynylation/cyclization of 12 or 13 with 1-(hex-5-yn-1-yl)-2-phenyl-1H-imidazole. The antibacterial effect exerted by the indol-steroid derivatives against Streptococcus pneumoniae and Staphylococcus aureus bacteria was evaluated using dilution method and the minimum inhibitory concentration (MIC). The results showed that only the compound 19 inhibit the growth bacterial of S. aureus. In conclusion, these data indicate that antibacterial activity of 19 can be due mainly to functional groups involved in the chemical structure in comparison with the compounds studied.

Structural influences on the activity of bismuth(III) indole-carboxylato complexes towards Helicobacter pylori and Leishmania

Seven new bismuth(III) complexes derived from indole-carboxylic acids have been synthesised: five are homoleptic; [Bi(IAA)₃] B1, [Bi(IPA)₃] B2, [Bi(IBA)₃] B3, [Bi(MICA)₃] B4, [Bi(IGA)₃] B6, and two are heteroleptic [BiPh(MICA)₂] B5 (where IAA-H=2-(1H-indol-3-yl)acetic acid, IPA-H=3-(1H-indol-3-yl)propanoic acid, IBA-H=4-(1H-indol-3-yl)butanoic acid, IGA-H=2-(1H-indol-3-yl)-2-oxoacetic acid, and MICA-H=1-methyl-1H-indole-3-carboxylic acid). All complexes were fully characterised by elemental analysis, infrared and mass-spectroscopy, and nuclear magnetic resonance (¹H, ¹³C) spectroscopy. Complex [BiPh(IGA)₂] B7 is structurally authenticated by X-ray crystallography as a dimer in the solid-state. The in-vitro anti-bacterial activity of the indole-carboxylic acids and their bismuth(III) complexes was assessed against Helicobacter pylori. While the acids were non-toxic at <100μgmL^-1, all the bismuth compounds showed an MIC of 6.25μgmL^-1, indicating that the anti-bacterial activity is insensitive to the degree of substitution at the Bi(III) centre or the composition of the indole-carboxylate ligands. All compounds were further tested for their anti-parasitic activity against Leishmania major and for their toxicity towards mammalian cells. From the anti-parasitic studies, it was found that the heteroleptic bismuth(III) complexes are the most active, with B5 and B7 showing comparable activity to Amphotericin B, without any toxicity towards the mammalian cells at their effective concentration.

Experimental and computational evidence for KOt-Bu-promoted synthesis of oxopyrazino[1,2-a]indoles

Metal-free intramolecular hydroamination of some Ugi adducts in the presence of KOt-Bu in DMF at room temperature led to the formation of novel oxopyrazino[1,2-a]indole derivatives.

Biomedical importance of indoles

The indole nucleus is an important element of many natural and synthetic molecules with significant biological activity. This review covers some of the relevant and recent achievements in the biological, chemical and pharmacological activity of important indole derivatives in the areas of drug discovery and analysis.

Silver triflate catalyzed synthesis of 3-aminoalkylated indoles and evaluation of their antibacterial activities

An efficient, one-pot synthesis was developed for 3-aminoalkylated indoles by three-component coupling reaction of aldehydes, N-methylanilines, and indoles using AgOTf as a catalyst. A series of twenty 3-aminoalkylated indoles was evaluated for their antibacterial activities against both Gram negative and Gram positive bacteria. Compounds 4b and 4r showed good antibacterial activity against both Gram positive and Gram negative strains. However, inversing the property of substituent (from 4r to 4q) resulted in the significant fall in the magnitude of antibacterial activity against Escherichia coli.

Synthesis, spectral, crystal structure and in vitro antimicrobial evaluation of imidazole/benzotriazole substituted piperidin-4-one derivatives

Imidazole/benzotriazole analogues substituted piperidin-4-one derivatives (17-26) have been synthesized. Their chemical structures were characterized by IR, 1H NMR, 13C NMR and mass spectral analysis. In addition, single crystal X-ray diffraction has also been recorded for compounds 21 and 23. The synthesized compounds were subjected to their in vitro antibacterial and antifungal activities against pathogenic microbial strains. The results pointed out that compounds 19 & 24 against B. subtilis and 20 & 24 against E. coli were explored superior inhibition activity.

Synthesis and biological activity of some new 1-benzyl and 1-benzoyl-3-heterocyclic indole derivatives

Starting from 1-benzyl- (2a) and 1-benzoyl-3-bromoacetyl indoles (2b) new heterocyclic, 2-thioxoimidazolidine (4a, b), imidazolidine-2,4-dione (5a, b), pyrano(2,3-d)imida-zole (8a, b and 9a, b), 2-substituted quinoxaline (11a, b-17a, b) and triazolo(4,3-a)quinoxaline derivatives (18a, b and 19a, b) were synthesized and evaluated for their antimicrobial and anticancer activities. Antimicrobial activity screening performed with concentrations of 0.88, 0.44 and 0.22 microg mm(-2) showed that 3-(1-substituted indol-3-yl)quinoxalin-2(1H)ones (11a, b) and 2-(4-methyl piperazin-1-yl)-3-(1-substituted indol-3-yl) quinoxalines (15a, b) were the most active of all the tested compounds towards P. aeruginosa, B. cereus and S. aureus compared to the reference drugs cefotaxime and piperacillin, while 2-chloro-3-(1-substituted indol-3-yl)quinoxalines (12a, b) were the most active against C. albicans compared to the reference drug nystatin. On the other hand, 2-chloro-3-(1-benzyl indol-3-yl) quinoxaline 12a display potent efficacy against ovarian cancer xenografts in nude mice with tumor growth suppression of 100.0 +/- 0.3 %.

Synthesis, anti-inflammatory, analgesic and anticonvulsant activities of 1,8-dihydro-1-ary1-8-alkyl pyrazolo(3,4-b)indoles

A series of 1,8-dihydro-1-aryl-8-alkyl pyrazolo(3,4-b)indoles 4a-j, 5a-j and 6a-j has been synthesized and tested for their anti-inflammatory and anticonvulsant activities. Formation of the pyrazoloindole derivatives was achieved by treating arylhydrazones of N-alkyl indole-3-carbox-aldehydes 1a-j, 2a-j and 3a-j with ten times their mass of polyphosphoric acid as a condensing agent. The newly synthesized compounds were evaluated for their anti-inflammatory, analgesic and anticonvulsant activities compared to indomethacin, flufenamic acid and diazepam as positive controls. Detailed synthesis, spectroscopic and toxicity data are reported.

An efficient synthesis of bis(indolyl)methanes and evaluation of their antimicrobial activities

A versatile and efficient method has been developed for the synthesis of bis(indolyl)methanes by using aluminium triflate (0.5 mol%) as a novel catalyst. Further, some of the synthesized compounds were evaluated for their efficacy as antibacterial and antifungal activities. Most of the compounds have shown moderate to good inhibitory activity.

Nickel(II) thiohydrazide and thiodiamine complexes: synthesis, characterization, antibacterial, antifungal and thermal studies

Nickel(II) complexes of type [Ni(L)(2)Cl(2)] and [Ni(L)(2)(OCOCH(3))(2)], where L=N,N-diphenyl-N-thiohydrazide (L(1)) and (N,N-diphenyl-N-thio)-1,3-propanediamine (L(2)), have been synthesized. The thiodiamines coordinate as a bidentate N-S ligand. The synthesized nickel(II) complexes of the thiodiamines were characterized by elemental analysis, IR, mass, electronic and (1)H NMR spectroscopic and TG/DTA studies. Various kinetic and thermodynamic parameters like order of reaction (n), activation energy (E(a)), apparent activation entropy (S(#)) and heat of reaction (DeltaH) have also been carried out for one complex. These complexes were also screened for in vitro antifungal and in vitro antibacterial activities and significant activity have been found.

Synthesis, characterization, cytotoxicity, antibacterial and antifungal evaluation of some new platinum (IV) and palladium (II) complexes of thiodiamines

Some new platinum (IV) and palladium (II) thiodiamine complexes of type [Pt(L)2Cl2] and [Pd(L)Cl2], [where, L=(cyclohexyl-N-thio)-1,2-ethylenediamine (L(1)) and (cyclohexyl-N-thio)-1,3-propanediamine (L(2))] have been synthesized. The thiodiamines coordinate as a bidentate N-S ligand. The synthesized platinum (IV) and palladium (II) complexes of the thiodiamines were characterized by elemental analysis, IR, mass, electronic and (1)H NMR spectroscopic studies. These complexes were also screened for cytotoxicity, in vitro antifungal and in vitro antibacterial activities. Thermodynamic parameters such as activation energy (Ea), apparent activation entropy (S(#)) and enthalpy change (DeltaH) for the dehydration and decomposition reactions of one complex has also been evaluated.