An Efficient Synthesis of Pyrazolo[3,4-b]Pyridine Derivatives in Aqueous Media

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 and Synthesis of Imidazopyrazolopyridines as Novel Selective COX-2 Inhibitors

The usefulness of non-steroidal anti-inflammatory drugs (NSAIDs) is hampered by their gastrointestinal side effects. Non-selective cyclooxygenases inhibitors interfere with both COX-1 and COX-2 isozymes. Since COX-1 mediates cytoprotection of gastric mucosa, its inhibition leads to the undesirable side effects. On the other hand, COX-2 is undetectable in normal tissues and selectively induced by inflammatory stimuli. Therefore, it is strongly believed that the therapeutic benefits derive from inhibition of COX-2 only. The presence of a strong connection between reported COX-2 inhibitors and cardiac toxicity encourages medicinal chemists to explore new scaffolds. In the present study, we introduced imidazopyrazolopyridines as new potent and selective COX-2 inhibitors that lack the standard pharmacophoric binding features to hERG. Starting from our lead compound 5a, structure-based drug-design was conducted and more potent analogues were obtained with high COX-2 selectivity and almost full edema protection, in carrageenan-induced edema assay, in case of compound 5e. Increased bulkiness around imidazopyrazolopyridines by adding a substituted phenyl ring(s) afforded less active compounds.

Microwave-assisted synthesis of some new pyrazolopyridines and their antioxidant, antitumor and antimicrobial activities

The chemical behavior of 4-(dimethylaminomethylene)-1-phenyl-3-(pyridin-3-yl)-1H-pyrazol-5(4H)-one (enaminone) (2) toward some active methylene reagents has been reported to give pyrazolopyridine derivatives. All the reactions were carried out by conventional heating and microwave irradiation technique. The antioxidant activity of the prepared compounds was studied using 1,1-phenyl-2-picrylhydrazyl (DPPH) assay. Compounds (4c) and (4d) showed the highest activity. The antitumor activity against liver and breast cell lines was tested. Compounds (6), (9) and (11) showed the highest activity for liver cell line while compounds (6) and (9) showed the highest activity for breast cell line. Compounds (4a-d) were screened for their antibacterial activity against Gram-positive, Gram-negative bacteria and antifungal activity.

Acylation of heteroaromatic amines: facile and efficient synthesis of a new class of 1,2,3-triazolo[4,5-b]pyridine and pyrazolo[4,3-b]pyridine derivatives

1,2,3-Triazolo[4,5-b]pyridines and pyrazolo[4,3-b]pyridines can be readily prepared via cyanoacetylation reactions of 5-amino-1,2,3-triazoles 1a,b and 4-amino- pyrazole 2 followed by subsequent cyclization of the formed cyanoacetamides. Reactions of amines 1a,b with a mixture of p-nitrophenylacetic acid and acetic anhydride under microwave irradiation conditions afforded the corresponding amides 15a,b that underwent cyclization to form 1,2,3-triazolo[4,5-b]pyridines 16a,b upon heating in DMF solutions containing sodium acetate. Reactions of 1a,b with active methylene compounds, including 17a-c, in the presence of zeolites as catalyst also afforded 1,2,3-triazolo[4,5-b]pyridine derivatives 20a-f via the intermediacy of triazole derivatives 19 and not 18.

Efficient one-pot synthesis of spirooxindole derivatives catalyzed by L-proline in aqueous medium

An efficient one-pot synthesis of spirooxindole derivatives by three-component reaction of isatins, malononitrile (cyanoacetic ester) and 1,3-dicarbonyl compounds in water in the presence of l-proline is reported. This new protocol has the advantages of environmental friendliness, higher yields, shorter reaction times, low cost, and convenient operation.