Multicomponent syntheses of pyrazoles via (3 + 2)-cyclocondensation and (3 + 2)-cycloaddition key steps

Pyrazoles are rarely found in nature but are traditionally used in the agrochemical and pharmaceutical industries, while other areas of use are also actively developing. However, they have also found numerous other applications. The search for new and efficient syntheses of these heterocycles is therefore highly relevant. The modular concept of multicomponent reactions (MCR) has paved a broad alley to heteroaromatics. The advantages over traditional methods are the broader scope and increased efficiency of these reactions. In particular, traditional multistep syntheses of pyrazoles have considerably been extended by MCR. Progress has been made in the cyclocondensation of 1,3-dielectrophiles that are generated in situ. Limitations in the regioselectivity of cyclocondensation with 1,3-dicarbonyls were overcome by the addition-cyclocondensation of α,β-unsaturated ketones. Embedding 1,3-dipolar cycloadditions into a one-pot process has additionally been developed for concise syntheses of pyrazoles. The MCR strategy also allows for concatenating classical condensation-based methodology with modern cross-coupling and radical chemistry, as well as providing versatile synthetic approaches to pyrazoles. This overview summarizes the most important MCR syntheses of pyrazoles based on ring-forming sequences in a flashlight fashion.

Design, Synthesis and In Vitro Evaluation of Novel Anti-HIV 3-Pyrazol-3- yl-Pyridin-2-One Analogs

Background:

Natural products have shown potent anti-HIV activity, but some of these also possess toxicity. The pharmacophoric fragments of these natural products have scope of combination with other pharmacophoric fragment and derivatization to reduce toxicity and increase the potency. Combination of natural product fragments from different classes of anti–HIV compounds may lead to a new class of potent anti–HIV agents.

Objective:

Design, in silico prediction of drug-likeness, ADMET properties and synthesis of pyrazol– pyridones. Evaluation of the anti–HIV–1 activity of synthesized pyrazol–pyridones.

Methods:

Pyrazol–pyridones were designed by combining reported anti–HIV pharmacophoric fragments. Designed molecules were synthesized after in silico prediction of drug-likeness and ADMET properties. Compounds were evaluated for activity against HIV–1VB59 and HIV–1UG070.

Results:

QED value of designed pyrazol–pyridones was greater than the known drug zidovudine. The designed compounds were predicted to be noncarcinogenic and nonmutagenic in nature. Seventeen novel pyrazol–pyridones were synthesized with good yield. Compound 6q and 6l showed activity with IC50 values 6.14 µM and 15.34 µM against HIV–1VB59 and 16.21 µM and 18.21 µM against HIV–1UG070, respectively.

Conclusion:

Compound 6q was found to be most potent among the synthesized compounds with a therapeutic index of 54.31against HIV–1VB59. This is the first report of anti–HIV–1 activity of pyrazol–pyridone class of compounds. Although the anti–HIV–1 activity of these compounds is moderate, this study opens up a new class for exploration of chemical space for anti–HIV–1 activity.

Direct N-heterocyclization of hydrazines to access styrylated pyrazoles: synthesis of 1,3,5-trisubstituted pyrazoles and dihydropyrazoles

A microwave-assisted method has been developed for the synthesis of tri-substituted pyrazoles via direct N-heterocyclization of hydrazines with metal-acetylacetonate and -dibenzylideneacetonate without using any base or additives. Most importantly, the synthesis of 1-aryl-5-phenyl-3-styryl-1H-pyrazoles was achieved in a single step using hydrochloride salt of various phenylhydrazines and this is the first report for direct construction of these molecules. The reaction medium and microwave conditions play a critical role for their selective product formation during the reaction. The present reaction explored the usage of metal-diketonic complexes as reaction substrates providing acetylacetone and dibenzylideneacetone moieties to directly participate in cyclization with hydrazines to form the corresponding pyrazoles in excellent yields. The present protocol introduces the important N-heterocyclic moieties in the final structures, giving the reaction great applications from a medicinal chemistry perspective, particularly in the late stage modification strategies in drug discovery.

Radical Addition of Hydrazones by α-Bromo Ketones To Prepare 1,3,5-Trisubstituted Pyrazoles via Visible Light Catalysis

A novel efficient tandem reaction of hydrazones and α-bromo ketones is reported for the preparation of 1,3,5-trisubstituted pyrazoles by visible light catalysis. In this system, the monosubstituted hydrazones show wonderful reaction activity with alkyl radicals, generated from α-bromo ketones. A radical addition followed by intramolecular cyclization affords the important pyrazole skeleton in good to excellent yields. This efficient strategy under mild conditions with wide group tolerance provides a potential approach to the 1,3,5-trisubstituted pyrazoles.

Brönsted acid-mediated annulations of 1-cyanocyclopropane-1-carboxylates with arylhydrazines: efficient strategy for the synthesis of 1,3,5-trisubstituted pyrazoles

A diversity-oriented synthesis of 1H-pyrazole derivatives via Brönsted acid-promoted annulations of 1-cyanocyclopropane-1-carboxylates with arylhydrazines has been developed.