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Microwave-Assisted Transition Metal-Catalyzed Synthesis of Pharmaceutically Important Heterocycles
Published in Banik Bimal Krishna, Bandyopadhyay Debasish, Advances in Microwave Chemistry, 2018
Dipti Shukla, Priyank Purohit, Asit K. Chakraborti
The fused pyrazole derivatives have been recognized as biologically important scaffold, and among them, the pyrazolo[3,4-b]pyridine, pyrazolo[3,4-b]quinoline, pyrazolo[1,5-a]pyrimidine, and pyrazolo[1,5-a]quinazoline moieties are an integral part of marketed drugs. The pyrazolo[3,4-b]pyridine derivatives 33 were synthesized through Pd-catalyzed microwave-assisted reaction of β-bromovinyl/aryl aldehyde 31 with 5-aminopyrazoles/3-amino pyrazole derivatives 32 and 32a under solvent-free conditions [52]. The use of 2.5 mol% of Pd(OAc)2 in neat condition under microwave (700 W) for 15 min was the optimal condition to provide the fused pyrazolo[3,4-b]pyridine 33 in good to excellent yields. The imine side product, which was formed in conventional heating conditions was not present under microwave heating conditions. The optimized reaction condition was used to investigate the scope of 3-aminopyrazole derivatives 32a to form various substituted pyrazolo[1,5-a]pyrimidines 34 (Scheme 9.14). All synthesized compounds were screened for in vitro activities against cervical HeLa cancer cell line and prostate DU 205 cancer line using MTT assay, and four compounds were found to have anticancer activity comparable to that of the marketed drug doxorubicin.
New potential fungicides pyrazole-based heterocycles derived from 2-cyano-3-(1,3-diphenyl-1H-pyrazol-4-yl) acryloyl isothiocyanate
Published in Journal of Sulfur Chemistry, 2021
Sayed K. Ramadan, Nasser A. Ibrahim, Sarah A. El-Kaed, Eman A. E. El-Helw
Treatment of 2 with 2-aminobenzoic acid afforded a mixture of pyrimidinethione derivative 8 and acylthiourea derivative 9 which were separated by the fractional recrystallization (cf. Experimental). The 1H NMR spectrum of 8 lacked the olefinic singlet which was conserved in compound 9. Refluxing the latter in acetic anhydride failed to produce quinazoline derivative 10 and achieved the pyrimidine derivative 11 (Scheme 2). The IR spectrum of 11 displayed carbonyl functionality at ν 1656 cm−1 which ruled out the structure 10. Ample evidence for structure 11 was acquired from its 1H NMR spectrum as it disclosed one exchangeable singlet signal at δ 11.87 ppm corresponding to the carboxylic proton, in addition to a singlet signal in the upfield region at δ 2.13 ppm integrated for three protons corresponding to the acetyl group. Cyclocondensation of 8 in boiling dioxane including triethylamine afforded pyrimidobenzothiazine derivative 12. The 1H NMR spectrum of 12 was devoid of any labile hydrogen.
Acryloyl isothiocyanate skeleton as a precursor for synthesis of some novel pyrimidine, triazole, triazepine, thiadiazolopyrimidine and acylthiourea derivatives as antioxidant agents
Published in Journal of Sulfur Chemistry, 2021
Azza A. El-Badawy, Amna S. Elgubbi, Eman A. E. El-Helw
Isothiocyantes, a type of hetero-cumulenes including N=C=S functionality, have attracted a great concern as they are useful synthons in the heterocyclic chemistry like thiadiazole, benzimidazole, triazole, triazine, quinazoline, and pyrimidine derivatives [1–9]. The thiourea backbone also is a considerable thematic motif in the pharmaceutical agents [10–12]. Noteworthy, the pyrazole cores are versatile substrates that exhibit various pharmacological properties, e.g. antiviral, anticancer, anti-inflammatory, antioxidant, antimicrobial, and insecticidal [13–23]. Overproduction and accumulation of free radicals within the body lead to a phenomenon known as oxidative stress that triggers many severe diseases, e.g. cancer, cardiovascular, and inflammation. The harmful effects of this phenomenon can be minimized by utilizing antioxidant compounds as free radical scavengers [24,25]. In this work and as an extension of our contribution [26–29], 2-cyano-3-pyrazolyl isothiocyanate derivative 2 was utilized as a key material for the synthesis of pyrimidine, triazole, triazepine, thiadiazolopyrimidine, and acylthiourea derivatives encompassing a pyrazole core aiming to enhance their antioxidant potency.
Therapeutical potential of metal complexes of quinoxaline derivatives: a review
Published in Journal of Coordination Chemistry, 2022
Chrisant William Kayogolo, Maheswara Rao Vegi, Bajarang Bali Lal Srivastava, Mtabazi Geofrey Sahini
Quinoxaline is a nitrogen-containing heterocyclic compound composed of fused benzene and pyrazine rings, and is also known as benzopyrazine [17, 18]. The compound is one of the four isomers of diazonaphthalene. The three other members are cinnoline, quinazoline, and phthalazine (Figure 1) [19].