Regioselectivity in the multicomponent reaction of 5-aminopyrazoles, cyclic 1,3-diketones and dimethylformamide dimethylacetal under controlled microwave heating

MRSA Inhibitory Activity of Some New Pyrazolo[1,5-a]pyrimidines Linked to Arene and/or Furan or Thiophene Units

Methicillin-resistant Staphylococcus aureus (MRSA) is a major contributor to hospital-acquired infections and is highly resistant to treatment. Ongoing research focuses on developing new antimicrobial medications to prevent the spread of resistance. A facile method was employed to efficiently synthesize new pyrazolo[1,5-a]pyrimidines in 84-93 % yields by reacting 4-benzyl-1H-pyrazole-3,5-diamine with the respective α,β-unsaturated ketones. The reaction was carried out in ethanol containing 1.2 equivalents of potassium hydroxide at reflux for 5-6 h. The new products are attached to a para-substituted aryl group with variable electronic properties at pyrazolopyrimidine-C5, in addition to one of three units at C7, namely phenyl, thiophen-2-yl, or furan-2-yl units. A wide spectrum of antibacterial activity was displayed by the new pyrimidines against six different bacterial strains. In general, pyrimidines attached to furan-2-yl units at C7, in addition to another aryl unit at C5, attached to 4-Me or 4-OMe groups, demonstrate significant antibacterial activity, particularly against S. aureus strain. They had MIC/MBC of 2.5/5.1 and 2.4/4.9 μM, respectively, which exceeded that of ciprofloxacin. Moreover, they demonstrate more effective MRSA inhibitory activity than linezolid, with MIC/MBC values up to 4.9/19.7 and 2.4/19.7 μM against MRSA ATCC:33591 and ATCC:43300 strains, respectively.

Controlled microwave-assisted reactions: A facile synthesis of polyfunctionally substituted phthalazines as dual EGFR and PI3K inhibitors in CNS SNB-75 cell line

Brain tumors are stubborn cancers with poor prognosis and disappointing survival rates. Targeted cancer therapeutics with higher efficacy and lower resistance are highly demanded. An efficient one-pot synthesis of polyfunctionalized phthalazines derivatives was developed by reacting ethyl 1-aryl-5-cyano-1,6-dihydro-4-methyl-6-oxo-3-pyridazine-carboxylates with cinnamonitrile derivatives and the cycloaddition reaction of thieno[3,4-d]pyridazines with activated double or triple bond systems under controlled microwave heating with high yields. The resultant synthesized phthalazines (5a-e, 9 and 13) were tested for their in vitro anti-cancer activities by using in vitro one dose assay at National Cancer institute, USA. Only phthalazine (5b) showed broad spectrum anti-tumor activity against most tested cancer cell lines from all subpanels with mean % GI = 22.61. Interestingly, all tested compounds showed varying growth inhibitory activity against a particular cell line, CNS SNB-75 cell line, but (5b) exhibited the highest growth inhibitory activity against CNS-SNB-75 cell line with (GI% = 108.81) and (IC₅₀ = 3.703 ± 0.2) compared to erlotinib; (IC₅₀ = 12.5 ± 0.68). It caused Pre-G1 apoptosis and growth arrest at S phase. It also increased percentage of the total apoptotic cells in CNS-SNB-75 cell line (39.26%) compared to control cells (2.17%) in the annexin V-FITC experiment. It revealed pronounced EGFR inhibitory activity (IC₅₀ = 47.27 ± 2.41 ng/mL) compared to erlotinib (IC₅₀ = 30.7 ± 1.56 ng/mL). It also inhibited the different PI3K isoforms α, β, γ and δ (with IC₅₀ of 4.39, 13.6, 12.5 and 3.11 μg/mL, respectively compared to LY294002 (with IC₅₀ of 12.7, 8.57, 6.89 and 5.7 μg/mL, respectively). It also caused significant lower protein expression levels of pPI3K, AKT, pAKT and Bcl2 and higher protein expression levels of BAX, Casp3 and Casp9 when compared to untreated cells. Conclusion: Phthalazine (5b) may be an effective, convenient and safe anti-cancer agent acting via proapoptotic and dual EGFR and PI3K kinase inhibitory actions in CNS SNB-75 cell line.

Regioselectivity in the reaction of 5-amino-3-anilino-1H-pyrazole-4-carbonitrile with cinnamonitriles and enaminones: Synthesis of functionally substituted pyrazolo[1,5-a]pyrimidine derivatives

The development of efficient methods for the synthesis of polyfunctional N-heterocycles is an important area of research in organic and medicinal chemistry. Pyrazolo[1,5-a]pyrimidine derivatives are purine analogous of biomedical importance and have been extremely studied for their broad spectrum of biological activities. Recently, they have attracted great interest in materials science owing to their photophysical properties. 3(5)-Aminopyrazoles are extensively utilized in the synthesis of condensed heterocyclic systems, particularly pyrazolo[1,5-a]pyrimidines via the reaction with 1,3-biselectrophilic reagents. However, the information available in the literature provides little in the way of reasoning their cyclization, particularly the initial attack either by the exocyclic amino group or endocyclic nitrogen. Unfortunately, the relative nucleophilicity of exo- and endocyclic nitrogen atoms in 1-unsubstituted 3(5)-aminopyrazoles is not clear and contradicting. It has been found that other factors can modulate the regioselectivity rather than basicity or steric hindrance for both active sites. The reported studies in the structure–activity relationship revealed that pyrazolo[1,5-a]pyrimidines having a substitution at fifth, sixth, and seventh positions possess potent biological activities, especially those with an amino group at the seventh position. We here developed a regioselective, high yield synthesis of 7-amino-5-arylpyrazolo[1,5-a]pyrimidine-3,6-dicarbonitriles by the reaction of N-(5-amino-4-cyano-1H-pyrazole-3-yl)-benzamide with various cinnamonitriles and enaminones in pyridine at 120°C under controlled microwave heating conditions. All structures of newly synthesized compounds were established by analytical and spectral data as well as single-crystal diffraction and rationalized for their formation.

Pyrazolopyrimidines as anticancer agents: A review on structural and target-based approaches

Pyrazolopyrimidine scaffold is one of the privileged heterocycles in drug discovery. This scaffold produced numerous biological activities in which anticancer is important one. Previous studies showed its importance in interactions with various receptors such as growth factor receptor, TGFBR2 gene, CDK2/cyclin E and Abl kinase, adenosine receptor, calcium-dependent Protein Kinase, Pim-1 kinase, Potent Janus kinase 2, BTK kinase, P21-activated kinase 1, extracellular signal-regulated kinase 2, histone lysine demethylase and Human Kinesin-5. However, there is a need of numerous studies for the discovery of target based potential compounds. The structure activity relationship studies may help to explore the generation of potential compounds in short time period. Therefore, in the present review we tried to explore the structural aspects of Pyrazolopyrimidine with their structure activity relationship against various targets for the development of potential compounds. The current review is the compilation of significant advances made on Pyrazolopyrimidines reported between 2015 and 2020.

Synthesis of a new series of pyrazolo[1,5-a]pyrimidines as CDK2 inhibitors and anti-leukemia

Based on the structural study of previously known CDK2 inhibitors, a new series of pyrazolo[1,5-a]pyrimidine derivatives was designed and synthesized. The target compounds were biologically assessed as potent CDK2 inhibitors and promising anti-leukemia hits. The 7-(4-Bromo-phenyl)-3-(3-chloro/2-chloro-phenylazo)-pyrazolo[1,5-a]pyrimidin-2-ylamines 5 h and 5i revealed the best CDK2 inhibitory activity with comparable potency (IC₅₀ = 22 and 24 nM, respectively) to that of dinaciclib (IC₅₀ = 18 nM). Additionally, both analogues showed potent activities against CDK1, CDK5 and CDK9 at nanomolar concentrations (IC₅₀ = 28-80 nM). The anti-leukemia screening of the target compounds showed strong to moderate cytotoxicity against the used leukemia cell lines (MOLT-4 and HL-60). Compound 5 h inhibited MOLT-4 and HL-60 by 1.4 and 2.3 folds (IC₅₀ = 0.93 and 0.80 µM), respectively, compared to dinaciclib (IC₅₀ = 1.30 and 1.84 µM). Furthermore, compound 5i was comparable to dinaciclib against MOLT-4 and exhibited twice its activity against HL-60. Besides, the cytotoxicity of the promising analogues on normal human blood cells indicated the safety of 5h and 5i as compared to the reference dinaciclib. The pharmacokinetic properties of 5h and 5i were predicted using ADME calculations revealing good oral bioavailability and high GI absorption. The molecular docking simulations indicated, as expected, that the dinaciclib analogues can well-accommodate the CDK2 binding site, forming a variety of interactions.

Microwave-assisted reactions: Efficient and versatile one-step synthesis of 8-substituted xanthines and substituted pyrimidopteridine-2,4,6,8-tetraones under controlled microwave heating

We report herein a simple and efficient one-step synthesis of 8-substituted xanthines and substituted pyrimidopteridine-2,4,6,8-tetraones via reaction of 1,3-dimethyl-5,6-diaminouracil 1 with activated double bond systems 2 assisted by controlled microwave irradiation. The obtained heterocycles are privileged biologically relevant scaffolds.

Densely functionalized cinnolines: Controlled microwave-assisted facile one-pot multi-component synthesis and in vitro anticancer activity via apoptosis induction

There is an urging continuous need for novel anti-cancer agents due to persistent chemoresistance. Herein, newly synthesized cinnolines are evaluated for their possible anticancer activities and suggested mechanisms. In the current study, a simple and efficient synthesis of densely functionalized cinnolines has been developed that relied on multi-component reaction of ethyl 5-cyano-4-methyl-1-aryl-6-oxo-1,6-dihydropyridazine-3-carboxylates with aromatic aldehydes and nitromethane in dioxane/pipridine under controlled microwave heating. Selected cinnolines (4a-c, e, h, j-n, q-v) were tested for possible anticancer activity using in vitro one dose assay at National Cancer institute, USA. Only cinnoline 4b stood out as the most potent cinnoline derivative (mean GI%=26.33) with broad-spectrum antitumor activity against the most tested cancer cell lines from all subpanels. The target cinnoline 4b emerged as the most active derivative against both leukemia RPMI-8226 and melanoma LOX IMVI cell lines (GI% = 106.06 and 82.1) respectively, with IC₅₀ values equal to 17.12 ± 1.31 and 12.32 ± 0.75 μg/mL, which are comparable to those of staurosporin; 24.97 ± 1.47 and 8.45 ± 0.42 μg/mL, respectively. Cinnoline 4b influenced cell cycle distribution causing pre-G1 apoptosis and cell growth arrest at G2/M phase. It also induced apoptosis in both cell lines as manifested by significant increase in the percent of annexin V-FITC positive apoptotic cells in leukemia RPMI-8226 cells (from 1.09% to 12.47%) and melanoma LOX IMVI (from 1.32% to 19.05%). In addition, it showed lower expression levels of anti-apoptotic Bcl-2 protein, and higher expression levels of pro-apoptotic proteins; Bax, p53, cytochrome c, caspases 3 and 9. CONCLUSION: Induction of mitochondrial intrinsic pathway of apoptosis is a possible mechanism by which cinnoline 4b may confer its anticancer activity.

Microwave-assisted efficient one-pot synthesis of N 2-(tetrazol-5-yl)-6-aryl/heteroaryl-5,6-dihydro-1,3,5-triazine-2,4-diamines

An efficient one-pot synthesis of N 2-(tetrazol-5-yl)-6-aryl/heteroaryl-1,3,5-triazine-2,4-diamine derivatives was developed by reacting 5-amino-1,2,3,4-tetrazole with aromatic aldehydes and cyanamide in pyridine under controlled microwave heating with high yields. X-ray crystallography confirmed the structure of the obtained products.

5-Amino-pyrazoles: potent reagents in organic and medicinal synthesis

5-Amino-pyrazoles have proven to be a class of fascinating and privileged organic tools for the construction of diverse heterocyclic or fused heterocyclic scaffolds. This review presents comprehensively the applications of 5-amino-pyrazoles as versatile synthetic building blocks in the synthesis of remarkable organic molecules with an emphasis on versatile functionalities. Following a brief introduction of synthesis methods, planning strategies to construct organic compounds, particularly diverse heterocyclic scaffolds, such as poly-substituted heterocyclic compounds and fused heterocyclic compounds via 5-amino-pyrazoles, have been summarized. Fused heterocycles are classified as bicyclic, tricyclic, tetracyclic, and spiro-fused pyrazole derivatives. These outstanding compounds synthesized via wide variety of approaches include conventional reactions, one-pot multi-component reactions, cyclocondensation, cascade/tandem protocols, and coupling reactions. 5-Amino-pyrazoles represent a class of promising functional reagents, similar to the biologically active compounds, highlighted with diverse applications especially in the field of pharmaceutics and medicinal chemistry. Notably, this critical review covers the articles published from 1981 to 2018.

Design, Synthesis and Antitumor Evaluation of Novel Pyrazolopyrimidines and Pyrazoloquinazolines

A series of N-aryl-7-aryl-pyrazolo[1,5-a]pyrimidines 18a⁻u and N-aryl-pyrazolo[1,5-a]quinazolines 25a⁻c were designed and synthesized via the reaction of 5-aminopyrazoles 11a⁻c with enaminones 12a⁻g or 19, respectively. The new compounds were screened for their in vitro antitumor activity toward liver (HepG-2) and breast (MCF-7) human cancer cells using 3-[4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide MTT assay. From the results, it was found that all compounds showed dose-dependent cytotoxic activities against both HepG-2 and MCF-7 cells. Two compounds 18o and 18a were selected for further investigations. Cell cycle analysis of liver (HepG-2) cells treated with 18o and breast (MCF-7) cells treated with 18a showed cell cycle arrest at G2/M phase and pro-apoptotic activity as indicated by annexin V-FITC staining.

A Novel Synthesis of Highly Functionalized Pyridines by a One-Pot, Three-Component Tandem Reaction of Aldehydes, Malononitrile and N-Alkyl-2-cyanoacetamides under Microwave Irradiation

A convenient, fast and environmentally benign procedure for the synthesis of a new series of highly functionalized N-alkylated pyridines as privileged medicinal scaffolds was developed via a unique three-component reaction of easily available aromatic as well as heteroaromatic aldehydes, N-alkyl-2-cyanoacetamides and malononitrile in EtOH in the presence of K₂CO₃ as a base promoter under microwave irradiation. The presented tandem process is presumed to proceed via Knoevenagel condensation, Michael addition, intramolecular cyclization, autoxidation and subsequent aromatization. Particularly valuable features of this protocol, including high product yields, mild conditions, atom-efficiency, simple execution, short reaction times and easy purification make it a highly efficient and promising synthetic strategy to prepare substituted pyridine nuclei. The proposed mechanism of this novel one-pot reaction and structure elucidation of the products are discussed.

An efficient and catalyst-free synthesis of N-arylidene-2-arylimidazo[1,2-a]pyridine-3-ylamine derivatives via Strecker reaction under controlled microwave heating

An efficient one-pot multicomponent reaction of 2-aminopyridine with aromatic aldehydes and either benzoyl cyanide or cyanamide in pyridine under controlled microwave heating afforded N-aryldene-2-arylimidazo[1,2-a]-pyridine-3-ylamine derivatives. The reaction is catalyst free and is of high atom economy.

An insight on synthetic and medicinal aspects of pyrazolo[1,5-a]pyrimidine scaffold

Pyrazolo[1,5-a]pyrimidine scaffold is one of the privileged hetrocycles in drug discovery. Its application as a buliding block for developing drug-like candidates has displayed broad range of medicinal properties such as anticancer, CNS agents, anti-infectious, anti-inflammatory, CRF₁ antagonists and radio diagnostics. The structure-activity relationship (SAR) studies have acquired greater attention amid medicinal chemists, and many of the lead compounds were derived for various disease targets. However, there is plenty of room for the medicinal chemists to further exploit this privileged scaffold in developing potential drug candidates. The present review briefly outlines relevant synthetic strategies employed for pyrazolo[1,5-a]pyrimidine derivatives. It also extensively reveals significant biological properties along with SAR studies. To the best of our understanding current review is the first attempt made towards the compilation of significant advances made on pyrazolo[1,5-a]pyrimidines reported since 1980s.

A facile, regioselective synthesis of novel 3-(N-phenylcarboxamide)pyrazolo[1,5-a]pyrimidine analogs in the presence of KHSO4 in aqueous media assisted by ultrasound and their antibacterial activities

An environmentally benign, simple, efficient, and convenient route is described for the synthesis of novel pyrazolo[1,5-a]pyrimidine derivatives under ultrasound irradiation. Condensation of aminopyrazole 5 with formylated active proton compounds (6, 8, E-G, 12, and 15) furnished pyrazolopyrimidine (7, 9, 10, 13, and 16) in high-to-excellent yields. In comparison with conventional methods, ultrasound irradiation offers several advantages, such as shorter reaction time, higher yields, milder conditions, and environmental friendliness. The reaction is clean with excellent yields and reduces the use of solvents. X-ray crystallographic study of compound 7c confirmed the regioselectivity of the reaction. The antibacterial profile of the newly synthesized compounds was evaluated by cup and saucer method.

A facile environment-friendly one-pot two-step regioselective synthetic strategy for 3,7-diarylpyrazolo[1,5-a]pyrimidines related to zaleplon and 3,6-diarylpyrazolo[1,5-a]pyrimidine-7-amines assisted by KHSO₄ in aqueous media

3-Aminopyrazoles required for the synthesis of pyrazolo[1,5-a]pyrimidines were obtained by the reaction of enaminonitriles with hydrazine hydrate. The resulting aminopyrazoles are reacted with formylated acetophenones under reflux at [Formula: see text] assisted by KHSO[Formula: see text] in aqueous media to form regioselectively 3,7-diarylpyrazolo[1,5-a]pyrimidines and 3,6-diarylpyrazolo[1,5-a]pyrimidine-7-amines. X-ray crystallography of selected compounds 5b and 7i further confirmed the regioselective formation of these products.

L-proline catalyzed multicomponent reactions: facile access to 2H-benzo[g]pyrazolo[3,4-b]quinoline-5,10(4H,11H)-dione derivatives

Three component reaction of 2-hydroxy 1,4-naphthoquinones, aldehydes, and aminopyrazoles in the presence of a catalytic amount ofl-proline has been described for the synthesis of a series of 2H-benzo[g]pyrazolo[3,4-b]quinoline-5,10(4H,11H)-dione derivatives.

Green and highly efficient synthesis of 2-arylbenzothiazoles using glycerol without catalyst at ambient temperature

A one-pot and clean synthesis of 2-arylbenzothiazoles via the ambient temperature reaction of 2-aminothiophenols and aromatic aldehydes without catalyst in glycerol as a green solvent has been reported.