Structure activity relationship studies of imidazo[1,2-a]pyrazine derivatives against cancer cell lines

Pharmacological activity and mechanism of pyrazines

Heterocycles are common in the structure of drugs used clinically to deal with diseases. Such drugs usually contain nitrogen, oxygen and sulfur, which possess electron-accepting capacity and can form hydrogen bonds. These properties often bring enhanced target binding ability to these compounds when compared to alkanes. Pyrazine is a nitrogen-containing six-membered heterocyclic ring and many of its derivatives are identified as bioactive molecules. We review here the most active pyrazine compounds in terms of their structure, activity in vitro and in vivo (mainly antitumor activity) and the reported mechanisms of action. References have been downloaded through Web of Science, PubMed, Science Direct, Google Scholar and SciFinder Scholar. Publications reporting only the chemistry of pyrazine derivatives are beyond the scope of this review and have not been included. We found that compounds in which a pyrazine ring was fused into other heterocycles especially pyrrole or imidazole were the highly studied pyrazine derivatives, whose antineoplastic activity had been widely investigated. To the best of our knowledge, this is the first review of pyrazine derivatives and their bioactivity, especially their antitumor activity. This review should be useful for those engaged in development of medications based on heterocyclic compounds especially those based on pyrazine.

Synthesis, cytotoxicity, pharmacokinetic profile, binding with DNA and BSA of new imidazo[1,2-a]pyrazine-benzo[d]imidazol-5-yl hybrids

Novel derivatives possessing imidazo[1,2-a]pyrazine and 1H-benzo[d]imidazole scaffolds were synthesized using Suzuki-Miyaura cross-coupling reactions. In vitro anticancer activities against NCI-60 cancer cell panels were tested at 10 µM concentration. The best results were obtained from substitution of two 1-cyclohexyl-1H-benzo[d]imidazole groups present at C-6 and C-8 positions of imidazo[1,2-a]pyrazine (31). Compound 31 was found to be cytotoxic against 51 cell lines and cytostatic against 8 cell lines with broad range of growth inhibitions (−98.48 to 98.86%). GI₅₀ value of compound 31 was found in the range of 0.80–2.87 µM for 59 human cancer cell lines at five-dose concentration levels. DNA binding study of potent compound 31 was suggested that this compound was intercalated into DNA base pairs with binding constant of 1.25 × 10⁴ M⁻¹. Compound 31 showed effective binding with bovine serum albumin (BSA) and presented binding constant value of 3.79 ×10⁴ M^-1. Pharmacokinetic studies revealed that all compounds are following Lipinski’s rule of five and expected to be orally active.

Mekheimer R, M. Hayallah A, A. Abo Elsoud F, U. Sadek K. Recent Advances in the Utility of Glycerol as a Benign and Biodegradable Medium in Heterocyclic Synthesis

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Glycerol is a non-toxic, recyclable and biodegradable organic waste produced as a byproduct in the production of biodiesel fuel. Currently, glycerol is considered a green solvent and catalyst for a large variety of applications. This work discusses the significance of glycerol for heterocyclic synthesis. All the reported studies consider glycerol as an efficient and sustainable benign medium.

Dispersion-Corrected Density Functional Theory Study of the Noncovalent Complexes Formed with Imidazo[1,2-a]pyrazines Adsorbed onto Silver Clusters

Imidazo[1,2-a]pyrazines are cyclic amidine-type compounds composed of α-amino acid residues. A full structural identification of these molecules constitutes an analytical challenge, especially when imidazo[1,2-a]pyrazines are obtained from physical processes (e.g., sublimation and pyrolysis of amino acids). A valuable source of molecular information can be obtained from absorption spectroscopies and related techniques encompassing the use of metallic substrates. The aim of this study is to provide new knowledge and insights into the noncovalent intermolecular interactions between imidazo[1,2-a]pyrazines and two Ag _n (n = 4 and 20) clusters using density functional theory (DFT) methods. Semiempirical DFT dispersion (DFT-D) corrections were addressed using Grimme's dispersion (GD2) and Austin-Petersson-Frisch (APF) functionals in conjunction with the 6-31+G(d,p) + LANL2DZ mixed basis set. These DFT-D methods describe strong interactions; besides, in all cases, the APF dispersion (APF-D) energies of interaction appear to be consistently overestimated. In comparison with B3LYP calculations, the mean values for the difference in the energies of interaction calculated are 2.25 (GD2) and 6.24 (APF-D) kcal mol^-1 for Ag₄-molecules, and 2.30 (GD2) and 8.53 (APF-D) kcal mol^-1 for Ag₂₀-molecules. The effect of applying GD2 and APF-D corrections to the noncovalent complexes is nuanced in the intermolecular distances calculated, mainly in the Ag···N(amidine) bonding, which appears to play the most important role for the adsorptive process. Selective enhancement and considerable red shifts for Raman vibrations suggest strong interactions, whereas a charge redistribution involving the metallic substrate and the absorbate leads to a significant rearrangement of frontier molecular orbitals mainly in the Ag₂₀-molecule complexes. Finally, time-dependent DFT calculations were carried out to access the orbital contributions to each of the transitions observed in the absorption spectrum. The corresponding UV-vis spectra involve transitions in the visible region at around 400 and 550 nm for the Ag₄-molecule and the Ag₂₀-molecule complexes, respectively.

Green Synthesis and Antimicrobial Activity of Some Novel N-Arylimidazo[1,2-a]pyrazine-2-Carboxamide Derivatives

The article deals with the synthesis of some novel N-arylimidazo[1,2-a]pyrazine-2-carboxamides (7a-l) by condensation reaction of imidazo[1,2-a]pyrazine-2-carboxylic acid (5) with different aliphatic/aromatic amines (6a-l) by using 1-methylimidazole, Mukaiyama’s reagent and 2-chloro-1-methylpyridinium iodide under microwave irradiation conditions. A new series of compounds 7 have been prepared from 2-iodopyrazine (1). Compound 1 on purged with ammonia gas in the presence of Cu2O and K2CO3 furnishes pyrazin-2-amine (2), which is treated with ethyl 3-bromo-2-oxopropanoate (3) to produce ethyl imidazo[1,2-a]pyrazine-2-carboxylate (4), which on hydrolysis with NaOH yields imidazo[1,2-a]pyrazine-2-carboxylic acid (5). The structures of the newly synthesized compounds have been elucidated on the basis of spectral (IR, 1H and 13C NMR and MS) and analytical data. Compounds 7a-l have also been screened for their antimicrobial activity. Some of the compounds exhibit promising antimicrobial activity

Efficient synthesis of novel RGD based peptides and the conjugation of the pyrazine moiety to their N-terminus

Novel RGD based peptides (RGDFAKLF and RGDNGRG) were designed and synthesized and were later coupled to the pyrazine moiety at the N-terminus. The IC₅₀ values from the in vitro study of the target peptides using a cell adhesion assay indicated the essential impact of the existence of the pyrazine moiety. Meanwhile, peptide 4 exhibited the best IC₅₀ value.

Synthesis and Antibacterial Activity of Benzo[4,5]isothiazolo[2,3-a]pyrazine-6,6-dioxide Derivatives

Using a routine procedure, a number of derivatives of the benzo[4,5]isothiazolo[2,3-a]pyrazine-6,6-dioxide ring system have been synthesized from readily available starting materials. A series of chalcones were synthesized, which were subsequently reacted with chlorosulfonic acid to generate chalcone sulfonyl chlorides. The chalcone sulfonyl chlorides were then treated with bromine to generate dibromo chalcone sulfonyl chlorides. These were subsequently reacted with 1,2-diaminopropane and 2-methyl-1,2-diaminopropane in boiling ethanol resulting in compounds 2-10 and 11-19 respectively, in 12-80% yields. The products were characterized by spectral analysis and the definitive structure of compound 11 was determined by X-ray crystallography. The synthesized compounds were screened for potential antibacterial properties against Bacillus subtilis, Escherichia coli, Proteus vulgaris and Staphylococcus aureus.

Coordination chemistry of pyrazine derivatives analogues of PZA: design, synthesis, characterization and biological activity

A novel Ru(iii) complexes were synthesized and characterized. Their stabilities were discussed in terms of aqueous and MeCN solutions. Antimicrobial properties of complexes studied were characterized against reference strains of bacteria and yeast.

Synthesis, in vitro anticancer activity and SAR studies of arylated imidazo[1,2-a]pyrazine–coumarin hybrids

A diverse array of arylated imidazo[1,2-a]pyrazine–coumarin hybrids have been synthesized for in vitro anticancer activities.

Recent advances in development of imidazo[1,2-a]pyrazines: synthesis, reactivity and their biological applications

The synthesis, reactivity and multifarious biological activities at the different positions of imidazo[1,2-a]pyrazines are concisely discussed in this review.

Crystal structure of 2-[12-methyl-14-phenyl-10,13,14,16-tetra-aza-tetra-cyclo[7.7.0.0(2,7).0(11,15)]hexa-deca-1(16),2,4,6,9,11(15),12-heptaen-8-yl-idene]propandi-nitrile

In the title mol-ecule, C22H12N6, the fused tetracyclic core shows a small lengthwise twist as indicated by the dihedral of 2.7 (2)° between the outer rings. In the crystal, mol-ecules stack along the b-axis direction via offset π-stacking [centroid-centroid distances = 3.5282 (13) and 3.5597 (14) Å] with the stacks weakly associated through C-H⋯N hydrogen bonds. The phenyl ring is rotationally disordered over two orientations with an occupancy ratio of 0.516 (4):0.484 (4).

Synthetic approaches, functionalization and therapeutic potential of quinazoline and quinazolinone skeletons: the advances continue

The presence of N-heterocycles as an essential structural motif in a variety of biologically active substances has stimulated the development of new strategies and technologies for their synthesis. Among the various N-heterocyclic scaffolds, quinazolines and quinazolinones form a privileged class of compounds with their diverse spectrum of therapeutic potential. The easy generation of complex molecular diversity through broadly applicable, cost-effective, practical and sustainable synthetic methods in a straightforward fashion along with the importance of these motifs in medicinal chemistry, received significant attention from researchers engaged in drug design and heterocyclic methodology development. In this perspective, the current review article is an effort to recapitulate recent developments in the eco-friendly and green procedures for the construction of highly challenging and potentially bioactive quinazoline and quinazolinone compounds in order to help medicinal chemists in designing and synthesizing novel and potent compounds for the treatment of different disorders. The key mechanistic insights for the synthesis of these heterocycles along with potential applications and manipulations of the products have also been conferred. This article also aims to highlight the promising future directions for the easy access to these frameworks in addition to the identification of more potent and specific products for numerous biological targets.

Discovery of Tröger's base analogues as selective inhibitors against human breast cancer cell line: design, synthesis and cytotoxic evaluation

A library of structurally diverse Tröger's base analogues has been constructed via unusual amination of methylene bridge employing Vilsmeier-Haack conditions as well as by the incorporation of five and six membered heterocycles on the aromatic core of Tröger's base framework. The constructed structurally diverse frameworks were evaluated for their cytotoxic activities against a panel of three human cancer lines A549 (lung adenocarcinoma), MDAMB-231 (breast) and SK-N-SH (neuroblastoma). From the activity profile obtained, a redesign of Tröger's base analogues led to the construction of more potent molecular entities. The study led to development of a series of compounds with MDAMB-231 cell line specific cytotoxicity. Of the 30 compounds synthesized and evaluated, 7 compounds were found to possess cytotoxicity that is equivalent or better than standard drug doxorubicin against MDAMB-231 cell line while only one compound was found to be active against SK-N-SH cell line.

Indolylmethylene benzo[h]thiazolo[2,3-b]quinazolinones: synthesis, characterization and evaluation of anticancer and antimicrobial activities

A series of novel 10-((1H-indol-3-yl)methylene)-7-aryl-7,10-dihydro-5H-benzo[h]thiazolo[2,3-b]quinazolin-9(6H)-ones (8a-t) have been synthesized in good yields by the reaction of benzo[h]quinazoline-2(1H)-thiones (4a-f) with 2-chloro-N-phenylacetamide (5) followed by Knoevenagel condensation with various indole-3-carbaldehydes (7a-d) under conventional method. All the synthesized compounds were characterized by spectral studies and screened for their in vitro anticancer and antimicrobial activities. Compound 8c has exhibited excellent activity against MCF-7 (breast cancer cell line) than the standard drug Doxorubicin. Compound 8d against both the cancer cell lines, 8q against MCF-7 and 8c, 8h against HepG2 have also shown good activity. Remaining compounds have shown moderate activity against both the cell lines. Antimicrobial activity revealed that, the compound 8q and 8t against Staphylococcus aureus and 8i, 8k, 8l, 8q &8t against Klebsiella pneumoniae have shown equipotent activity on comparing with the standard drug Streptomycin. Remaining compounds have shown significant antibacterial and comparable antifungal activities against all the tested microorganisms.

Microwave-assisted palladium mediated efficient synthesis of pyrazolo[3,4-b]pyridines, pyrazolo[3,4-b]quinolines, pyrazolo[1,5-a]pyrimidines and pyrazolo[1,5-a]quinazolines

An efficient method was developed for the synthesis of pyrazole fused heterocycles via the palladium-catalyzed solvent free reaction of β-halovinyl/aryl aldehydes and 3-aminopyrazoles/5-aminopyrazoles under microwave irradiation in good yields.

Design, diversity-oriented synthesis and structure activity relationship studies of quinolinyl heterocycles as antimycobacterial agents

The current study reports design and diversity oriented synthesis of novel bis heterocycles with a common 2-methyl, C-4 unsubstituted quinoline moiety as the central key heterocycle. Employing reagent based skeletal diversity approach; a facile synthesis of bis heterocycles with different heterocyclic rings at C-3 position of the quinoline moiety has been accomplished. A broad range of heterocyclic frameworks thus obtained were evaluated for their antimycobacterial activity. The active scaffolds were further explored by a parallel library generation in order to establish SAR. Further, low cytotoxicity against A549 cell line enhances the potential of the synthesized molecules as promising antimycobacterial agents.

Synthesis, X-ray crystal structure and fluorescent spectra of novel pyrazolo[1,5-a]pyrazin-4(5H)-one derivatives

A series of fluorescent compounds, containing pyrazolo[1,5-a]pyrazin-4(5H)-one moiety, were designed and synthesized from ethyl 1-(2-oxo-2-phenylethyl)-3-phenyl-1H-pyrazole-5-carboxylates. The structures of the compounds have been confirmed by IR, (1)H NMR, HRMS and X-ray crystal diffraction. The optical properties of the compounds were investigated by UV-vis absorption and fluorescence spectroscopy. The effect of pH on the UV-vis absorption of compound 2a in methanol-H(2)O solutions was studied and interpreted by theory calculation. The pK(a) value of compound 2a was determined by the absorption spectra.