Highly regioselective synthesis of 1-aryl-3 (or 5)-alkyl/aryl-5 (or 3)-(N-cycloamino)pyrazoles

Selected Electrosynthesis of 3-Aminopyrazoles from α,β-Alkynic Hydrazones and Secondary Amines

An available and simple electromediated cyclization method for 3-amino-substituted pyrazoles by using α,β-alkynic hydrazone and secondary amine is described. The strategy utilizes KI as an electrolyte in an undivided cell with a constant current, generating the desired products in moderate-to-good yield. The method features selective amination at the 3-position of the pyrazole skeleton. The results indicate that α,β-alkynic hydrazones functionalized with aromatic groups and secondary amines functionalized with electron-rich groups were better tolerated in this transformation.

Synthesis, in silico modelling, and in vitro biological evaluation of substituted pyrazole derivatives as potential anti-skin cancer, anti-tyrosinase, and antioxidant agents

Twenty-five azole compounds (P1-P25) were synthesised using regioselective base-metal catalysed and microwave-assisted approaches, fully characterised by high-resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR), and infrared spectra (IR) analyses, and evaluated for anticancer, anti-tyrosinase, and anti-oxidant activities in silico and in vitro. P25 exhibited potent anticancer activity against cells of four skin cancer (SC) lines, with selectivity for melanoma (A375, SK-Mel-28) or non-melanoma (A431, SCC-12) SC cells over non-cancerous HaCaT-keratinocytes. Clonogenic, scratch-wound, and immunoblotting assay data were consistent with anti-proliferative results, expression profiling therewith implicating intrinsic and extrinsic apoptosis activation. In a mushroom tyrosinase inhibition assay, P14 was most potent among the compounds (half-maximal inhibitory concentration where 50% of cells are dead, IC50 15.9 μM), with activity greater than arbutin and kojic acid. Also, P6 exhibited noteworthy free radical-scavenging activity. Furthermore, in silico docking and absorption, distribution, metabolism, excretion, and toxicity (ADMET) simulations predicted prominent-phenotypic actives to engage diverse cancer/hyperpigmentation-related targets with relatively high affinities. Altogether, promising early-stage hits were identified - some with multiple activities - warranting further hit-to-lead optimisation chemistry with further biological evaluations, towards identifying new skin-cancer and skin-pigmentation renormalising agents.

Antitubercular 2-Pyrazolylpyrimidinones: Structure-Activity Relationship and Mode-of-Action Studies

Phenotypic screening of a Medicines for Malaria Venture compound library against Mycobacterium tuberculosis (Mtb) identified a cluster of pan-active 2-pyrazolylpyrimidinones. The biology triage of these actives using various tool strains of Mtb suggested a novel mechanism of action. The compounds were bactericidal against replicating Mtb and retained potency against clinical isolates of Mtb. Although selected MmpL3 mutant strains of Mtb showed resistance to these compounds, there was no shift in the minimum inhibitory concentration (MIC) against a mmpL3 hypomorph, suggesting mutations in MmpL3 as a possible resistance mechanism for the compounds but not necessarily as the target. RNA transcriptional profiling and the checkerboard board 2D-MIC assay in the presence of varying concentrations of ferrous salt indicated perturbation of the Fe-homeostasis by the compounds. Structure-activity relationship studies identified potent compounds with good physicochemical properties and in vitro microsomal metabolic stability with moderate selectivity over cytotoxicity against mammalian cell lines.

A chemo- and regiocontrolled approach to bipyrazoles and pyridones via the reaction of ethyl 5-acyl-4-pyrone-2-carboxylates with hydrazines

Chemo- and regiocontrolled syntheses of pyrazoles and pyridones are presented on the basis of 4-pyrones. A novel approach towards highly functionalized 3,4'-bipyrazoles has been developed by using reactions of ethyl 5-acylcomanoates with hydrazines. The acid-promoted double cyclocondensation allows switching of the structure of the pyrazole rings easily through changing both the nature of hydrazine and the reaction conditions. The transformation of 4-pyrones with phenylhydrazine in EtOH at -20 °C leads to hydroxypyridones as monoaddition products which can be used as precursors for the preparation of pyridone and pyrazole derivatives. A novel rearrangement of 2-hydroxypyridone to pyrazolyl-1,3-diketones in DMSO was found. The structure and regiochemistry of bipyrazoles were confirmed by X-ray analysis and 2D NMR experiments.

Efficient One-Pot, Two-Component Modular Synthesis of 3,5-Disubstituted Pyrazoles

The pyrazole scaffold is one of the most prevalent and important tool in medicinal chemistry. Here, we report a method for preparing 3,5-diarylpyrazoles in good to excellent yield by reacting hydrazones of aryl aldehydes with substituted acetophenones in ethanol in the presence of dimethyl sulfoxide/cat. I₂/cat. HCl. The reverse process, reacting hydrazones of substituted acetophenones with aryl aldehydes under the same conditions, also provides 3,5-diarylpyrazoles in good to excellent yields. Reaction of hydrazones of aldehydes with 2'-aryloxy ketones in the presence of cat. HCl in ethanol and the catalyst-free reaction of phenacyl bromides with hydrazones of aldehydes in ethanol also gave good to excellent yields of 3,5-diarylpyrazoles.

Synthesis of diverse N-acyl-pyrazoles via cyclocondensation of hydrazides with α-oxeketene dithioacetal

An elegant, efficient, and highly regioselective approach for the synthesis of novel methyl 5-amino-3-(methylthio)-1-differently substituted-1H-pyrazole-4-carboxylates is reported. The procedure involves the cyclocondensation of α-oxeketene S, S-dimethyl acetal building blocks with different alkyl, aryl, and heterocyclic acid hydrazides. The novel molecules were obtained in good yields and their identities confirmed by NMR and HRMS spectrometry.

Gold-catalyzed chemo- and diastereoselective C(sp(2))-H functionalization of enaminones for the synthesis of pyrrolo[3,4-c]-quinolin-1-one derivatives

An efficient tandem Au(i)/TsOH-catalyzed reaction of enaminones with diazo compounds for the synthesis of pyrroloquinolinone derivatives under mild reaction conditions has been developed. This methodology was realized by relay actions of Au and TsOH in a one-pot multistep manner. Initially, the Au-catalyzed reaction of enaminones with diazo compounds affords chemo- and diastereoselective C(sp(2))-H functionalized products, which then undergo subsequent intramolecular cyclization/rearrangement to give pyrroloquinolinone derivatives under the catalysis of TsOH.

AIEE phenomenon: tetraaryl vs. triaryl pyrazoles

A library of tetraaryl pyrazole derivatives were synthesized and the AIEE phenomenon was explored.

DMAP-promoted domino annulation of β-ketothioamides with internal alkynes: a highly regioselective access to functionalized 1,3-thiazolidin-4-ones at room temperature

One-pot DMAP-mediated regioselective access to functionalized 1,3-thiazolidin-4-ones has been achieved via annulation of β-ketothioamides with internal alkynes.

ZnCl2-catalyzed chemoselective cascade reactions of enaminones with 2-furylcarbinols: a versatile process for the synthesis of cyclopenta[b]pyrrole derivatives

A ZnCl₂-catalyzed cascade reaction of enaminones with 2-furylcarbinols offers a chemo- and diastereo-selective access to functionalized cyclopenta[b]pyrrole derivatives.

Cyclocondensation of arylhydrazines with 1,3-bis(het)arylmonothio-1,3-diketones and 1,3-bis(het)aryl-3-(methylthio)-2-propenones: synthesis of 1-aryl-3,5-bis(het)arylpyrazoles with complementary regioselectivity

Two efficient highly regioselective routes for the synthesis of unsymmetrically substituted 1-aryl-3,5-bis(het)arylpyrazoles with complementary regioselectivity starting from active methylene ketones have been reported. In the first protocol, the newly synthesized 1,3-bis(het)aryl-monothio-1,3-diketone precursors (prepared by condensation of active methylene ketones with het(aryl) dithioesters in the presence of sodium hydride) were reacted with arylhydrazines in refluxing ethanol under neutral conditions, furnishing 1-aryl-3,5-bis(het)arylpyrazoles 7, in which the het(aryl) moiety attached to the thiocarbonyl group of monothio-1,3-diketones is installed at the 3-position. In the second method, the corresponding 3-(methylthio)-1,3-bis(het)aryl-2-propenones (prepared in situ by base-induced alkylation of 1,3-monothiodiketones) were condensed with arylhydrazines in the presence of potassium tert-butoxide in refluxing tert-butyl alcohol, yielding 1-aryl-3,5-bis(het)arylpyrazoles 9 with complementary regioselectivity (method A). The efficiency of this protocol was further improved by developing a one-pot, three-component procedure for the synthesis of pyrazoles 9, directly from active methylene ketones, by reacting in situ generated 3-(methylthio)-1,3-bis(het)aryl-2-propenones with arylhydrazines in the presence of sodium hydride (instead of potassium tert-butoxide as base). The structures and regiochemistry of newly synthesized pyrazoles were confirmed from their spectral and analytical data along with X-ray crystallographic data of three pairs of regioisomers.

(E)-6-(4-Chloro-phen-yl)-4-[(2-cyano-3-phenyl-all-yl)sulfan-yl]-2,2-difluoro-3-phenyl-1,3,2-oxaza-borinin-3-ium-2-uide

In the title compound, C25H18BClF2N2OS, the characteristic B-N and B-O bond lengths are 1.571 (3) and 1.458 (3) Å, respectively. The phenyl rings form dihedral angles of 83.1 (1) and 64.6 (1)° with the chloro-phenyl ring. In the crystal, weak C-H⋯N, C-H⋯F, C-H⋯π and π-π inter-actions [centroid-centroid distances 3.877 (6) Å between the chloro-phenyl rings of neighbouring mol-ecules] held mol-ecules together, forming ladders along the b axis.

Modulating the reactivity of functionalized N,S-ketene acetal in MCR: selective synthesis of tetrahydropyridines and thiochromeno[2,3-b]pyridines via DABCO-catalyzed tandem annulation

An efficient and straightforward three-component synthetic protocol was developed to synthesize 1,2,3,4-tetrahydropyridine derivatives or thiochromeno[2,3-b]pyridine derivatives from β-aroylthioacetanilides or β-(2-haloaroyl)thioacetanilides, aldehydes, and aroyl acetonitriles via DABCO-catalyzed tandem [3 + 2 + 1] annulation and S(N)Ar reaction. This synthetic approach has the prominent features of high chemo-, stereo- (or enantio-), and unusual regioselectivity. In the domino processes, at least seven reactive sites were involved, and up to three covalent bonds and one functionalized pyridine ring were generated. This facile and efficient reaction is a quite general for the preparation of tetrahydropyridine derivatives or thiochromeno[2,3-b]pyridine derivatives.

Studies with beta-oxoalkanonitriles: simple novel synthesis of 3-[2,6-diaryl-4- pyridyl]-3-oxopropanenitriles

Heteroaromatization of ethyl 2-cyano-4-oxo-2-(2-oxo-2-arylethyl)-4-aryl-butanoates 3a,b with ammonium acetate gave ethyl 2,6-diarylisonicotinates 4a,b.Treatment of the latter with acetonitrile afforded novel β-oxoalkanonitriles 6a,b. Reactions of 6a,b with phenyl hydrazine and hydroxylamine gave the corresponding pyridyl aminopyrazoles 8a,b and pyridyl aminoisoxazoles 10a,b, respectively.