Pyrazoline Hybrids as Promising Anticancer Agents: An Up-to-Date Overview

Pyrazolines are five-membered heterocycles possessing two adjacent nitrogens. They have attracted significant attention from organic and medicinal chemists due to their potent biological activities and the numerous possibilities for structural diversification. In the last decade, they have been intensively studied as targets for potential anticancer therapeutics, producing a steady yearly rise in the number of published research articles. Many pyrazoline derivatives have shown remarkable cytotoxic activities in the form of heterocyclic or non-heterocyclic based hybrids, such as with coumarins, triazoles, and steroids. The enormous amount of related literature in the last 5 years prompted us to collect all these published data from screening against cancer cell lines, or protein targets like EGFR and structure activity relationship studies. Therefore, in the present review, a comprehensive account of the compounds containing the pyrazoline nucleus will be provided. The chemical groups and the structural modifications responsible for the activity will be highlighted. Moreover, emphasis will be given on recent examples from the literature and on the work of research groups that have played a key role in the development of this field.

Red fluorescent pyrazoline-BODIPY nanoparticles for ultrafast and long-term bioimaging

Fluorescence bioimaging is very significant in studying biological processes. Fluorescent nanoparticles (NPs) manufactured from aggregation-induced emission (AIE) materials, as promising candidates, have attracted more attention. However, it is still a challenge to explore suitable AIE NPs for bioimaging. Herein, we synthesized pyrazoline-BODIPY (PZL-BDP) with a donor and acceptor (D-A) structure by a condensation reaction, cultured its single crystal, and studied its twisted intramolecular charge transfer (TICT) and AIE effects. PZL-BDP could self-assemble to form red fluorescent nanoparticles (PZL-BDP NPs) which showed a good fluorescence quantum yield of 15.8% in water. PZL-BDP NPs with excellent stability and biocompatibility exhibited a large Stokes shift (Δλ = 111 nm) which resulted in the reduction of external interference and enhancement of the fluorescence contrast. Furthermore, these nanoparticles could be readily internalized by HeLa cells and they stain the cells in just five seconds, indicating an ultrafast bioimaging protocol. Moreover, long-term tracking fluorescence signals in vivo for about 12 days were obtained. The bright red fluorescence, ultrafast cell staining ability, and long-term in vivo tracking competence outline the great potential of rational design nanomaterials with AIE characteristics for monitoring biological processes.

Benefits and applications of microwave-assisted synthesis of nitrogen containing heterocycles in medicinal chemistry

Nitrogen containing heterocycles are of immense research interest because they are often found as naturally occurring bioactive compounds.

A Suitable Functionalization of Nitroindazoles with Triazolyl and Pyrazolyl Moieties via Cycloaddition Reactions

The alkylation of a series of nitroindazole derivatives with 1,2-dibromoethane afforded the corresponding N-(2-bromoethyl)- and N-vinyl-nitro-1H-indazoles. The Cu(I)-catalysed azide- alkyne 1,3-dipolar cycloaddition was selected to substitute the nitroindazole core with 1,4-disubstituted triazole units after converting one of the N-(2-bromoethyl)nitroindazoles into the corresponding azide. The reactivity in 1,3-dipolar cycloaddition reactions with nitrile imines generated in situ from ethyl hydrazono-α-bromoglyoxylates was studied with nitroindazoles bearing a vinyl unit. The corresponding nitroindazole-pyrazoline derivatives were obtained in good to excellent yields.

Synthesis, characterization, molecular docking and biological activities of novel pyrazoline derivatives

In this study, synthesis of ethyl 2-((4-bromophenyl)diazenyl)-3-oxo-phenylpropanoate 1 was carried out and a series of new 3H-pyrazol-3-ones (P1-7) were synthesized from 1 as well as various hydrazines. The obtained yields of the synthesized compounds were moderate (40-70%) and these compounds were confirmed by spectral data. These novel pyrazoline derivatives were effective inhibitor compounds of the human carbonic anhydrase I and II isozymes (hCAs I and II) and of the acetylcholinesterase (AChE) enzyme, with K_i values in the range of 17.4-40.7 nM for hCA I, 16.1-55.2 nM for hCA II, and 48.2-84.1 nM for AChE. In silico studies were performed on the compounds inhibiting hCA I, hCA II, and AChE receptors. On the basis of the findings, the inhibition profile of the new pyrazoline compounds at the receptors was determined.

Microwave-Assisted Stereoselective Heterocyclization to Novel Ring d-fused Arylpyrazolines in the Estrone Series

Microwave-assisted syntheses of novel ring d-condensed 2-pyrazolines in the estrone series were efficiently carried out from steroidal α,β-enones and hydrazine derivatives. The ring-closure reaction of 16-benzylidene estrone 3-methyl ether with hydrazine in acetic acid resulted in a 2:1 diastereomeric mixture of two 16,17-cis fused pyrazolines, which is contrary to the former literature data for both stereoselectivity and product structure. However, the cyclization reactions of a mestranol-derived unsaturated ketone with different arylhydrazines in acidic ethanol furnished the heterocyclic products in good to excellent yields independently of the substituents present on the aromatic ring of the reagents applied. The MW conditions also permitted the ring-closure reaction with p-nitrophenylhydrazine which is unfavorable under conventional heating. Moreover, the transformations led to the heterocyclic compounds stereoselectively with a 16α,17α-cis ring junction without being susceptible to spontaneous and promoted oxidation to pyrazoles.

Organic Fluorescent Dye-based Nanomaterials: Advances in the Rational Design for Imaging and Sensing Applications

Self-assembled fluorescent nanomaterials based on small-molecule organic dyes are gaining increasing popularity in imaging and sensing applications over the past decade. This is primarily due to their ability to combine spectral properties tunability and biocompatibility of small molecule organic fluorophores with brightness, chemical and colloidal stability of inorganic materials. Such a unique combination of features comes with rich versatility of dye-based nanomaterials: from aggregates of small molecules to sophisticated core-shell nanoarchitectures involving hyperbranched polymers. Along with the ongoing discovery of new materials and better ways of their synthesis, it is very important to continue systematic studies of fundamental factors that regulate the key properties of fluorescent nanomaterials: their size, polydispersity, colloidal stability, chemical stability, absorption and emission maxima, biocompatibility, and interactions with biological interfaces. In this review, we focus on the systematic description of various types of organic fluorescent nanomaterials, approaches to their synthesis, and ways to optimize and control their characteristics. The discussion is built on examples from reports on recent advances in the design and applications of such materials. Conclusions made from this analysis allow a perspective on future development of fluorescent nanomaterials design for biomedical and related applications.

Unanticipated Cleavage of 2-Nitrophenyl-Substituted N-Formyl Pyrazolines under Bechamp Conditions: Unveiling the Synthesis of 2-Aryl Quinolines and Their Mechanistic Exploration via DFT Studies

We herein report for the first time an unusual decomposition of 2-nitrophenyl-substituted N-formyl pyrazolines under Bechamp reduction condition employed to yield 2-aryl quinolines exclusively instead of pyrazolo[1,5-c]quinazolines. The reaction investigation suggests acid-mediated cleavage of 1 followed by a retro-Michael addition, and a subsequent in situ intramolecular reductive cyclization through a modified Friedlander mechanism afforded 2-aryl quinolines (2) in good yields. The proposed mechanistic pathways were supported via experimental evidence and density functional theory studies. B3LYP/6-31+G(d) analysis indicated the involvement of trans-2-hydroxyaminochalcone as a key intermediate and its isomerization and cyclization, leading to unusual product formation.

Crystal Structures and Optical Properties of Two Novel 1,3,5-Trisubstituted Pyrazoline Derivatives

Two novel 1,3,5-trisubstituted pyrazoline derivatives—1-acetyl-3-(4-methoxyphenyl)-5-(6-methoxy-2-naphthyl)-pyrazoline (2a) and 1-(4-nitrophenyl)-3-(4-methoxyphenyl)-5-(6-methoxy-2-naphtyl)-pyrazoline (2b)—were synthesized and their structures were determined by single crystal X-ray crystallography. Both of the two crystals exhibit twisted structures due to the large dihedral angles between the pyrazolinyl ring and the aromatic ring at the 5-position (88.09° for 2a and 71.26° for 2b). The optical–physical properties of the two compounds were investigated. The fluorescent emission of 2b arises from the 1,3-disubstituted pyrazoline chromophores and exhibits a red shift in polar solvents and solid-state, which could be attributed to photo-induced intramolecular charge transfer (ICT) from N1 to C3 in the pyrazoline moiety and the intermolecular interactions within the crystal. The fluorescent emissions of 2a (λmax 358–364 nm) in solvents and solid-state both come from 6-methoxy-2-naphthyl chromophores, which are fairly insensitive to the solvent polarity.

A G4·K+ hydrogel made from 5′-hydrazinoguanosine for remediation of α,β-unsaturated carbonyls

A G₄·KCl hydrogel with a nucleophilic 5′ sidechain absorbs α,β-unsaturated carbonyls via formation of cyclic adducts.