Recent developments in the chemistry of pyrazolo[4,3-c]quinolines

Reaction of 3-Cl/OMe-Substituted 5-Nitrobenzisothiazoles with Hydrazine: Structural and Computational Evidence for Rearrangement Pathways Implicating Intramolecular Formation of Pivotal Meisenheimer Complexes

In projected structure-activity relationship studies of the novel diheteroarylamide-based anti-HIV agent 2 (1C8), one objective was to evaluate the influence of incorporating the central amide motif in 2 into a five-membered pyrazolone ring, as found in 3. It was envisaged that compound 3 could be prepared through reaction of 3-hydrazino-5-nitrobenzisothiazole 5 with the methyl ester of 4-chloropyridine-3-carboxylic acid, followed by N-methylation of the pyridine nitrogen. However, the reaction of 3-methoxyl-5-nitrobenzisothiazole with hydrazine resulted in formation of ring-opened hydrazonate product 18. In the corresponding reaction with 3-chloro-5-nitrobenzisothiazole, a different rearrangement product 19 was formed, in which two 2,1-benzisothiazole units are joined by a sulfur bridge. Meisenheimer complex formation, favored by the presence of the 5-nitro substituent on the benzisothiazole ring, was postulated to be a key feature in the formation of these deep-seated rearrangement products. Support for the proposed formation of the pivotal Meisenheimer complexes and their subsequent evolution to the observed products in which the benzisothiazole sulfur atom is either expelled or maintained in the isomeric 2,1-benzisothiazole system was obtained by density function theory calculations.

Investigations of the Optical and Thermal Properties of the Pyrazoloquinoline Derivatives and Their Application for OLED Design

In this study, the photo-optical properties of the series of new 1H-pyrazolo[3,4-b]quinoline derivatives were investigated. Pyrazoloquinoline studies were conducted to explain the electroluminescent effect in organic LEDs. Absorption and photoluminescence spectra for the materials under consideration were examined, and quantum chemical calculations were made. Differential scanning calorimetric and thermogravimetric measurements were carried out for the manufactured materials. The phase situation of the materials was determined, and glassy transitions were detected for three of the investigated materials. Degradation temperatures were obtained. Single-layer luminescent diodes based on the ITO/PEDOT:PSS/active layer/Al scheme were fabricated. Current-voltage and brightness-voltage characteristics of the diodes were determined, ignition voltage was calculated, and electroluminescence types were determined.

Organocatalyzed Synthesis of Functionalized Quinolines

As one of the most widely investigated compound skeleton, quinolines possess important medicinal and biological activities. As such, a great number of literatures, including reviews, have reported various methodologies to construct quinolines. Recently, organocatalyzed reactions have attracted the attention of organic chemists due to its being "green" because the reactions avoid the use of toxic metals. In this review, various distinctive contributions are surveyed with specific emphasis on organocatalyzed reactions for quinoline core constructions.

Novel Pyrazolo[4, 3-c]Quinolin-3-One Derivatives as PDE5A Inhibitors

BACKGROUND

PDE5A is a phosphodiesterase which specifically hydrolyzes the cGMP to GMP. It takes part in several physiological and pathological pathways and is considered an important drug target. Currently, PDE5 inhibitors (ex; Sildenafil, Tadalafil) available in the market are not only being used for the treatment of erectile dysfunction but at the same time, they are also in clinical trials being investigated as anticancer agents.

MATERIALS & METHODS

In this work, we have examined pyrazolo [4,3-c]quinolin-3-ones as PDE5A inhibitors. Pyrazolo [4,3-c]quinolin-3-ones are the class of tricyclic heterocyclic derivatives having a variety of therapeutically interesting drug candidates known for their anti-inflammatory, anti-viral, anti-anxiety and anti-cancer activity. Therefore, synthetic methods providing access to pyrazolo [4, 3-c] quinolin-3-ones are immensely valuable. Here, we are reporting a simple but efficient route for the synthesis of novel 8-morpholino-2-aryl - 2, 5-dihydro-3H-pyrazolo [4, 3-c] quinolin-3-one derivatives.

RESULTS

Further, molecular docking studies of synthesized compounds with human PDE5A protein showed that all the compounds exhibited good docking score in comparison with known inhibitors. In addition, all the synthesized molecules were evaluated against HCT116 cell lines for their antitumor activity.

CONCLUSION

Among all the synthesized compounds, compound 5a, 5d, and 6e showed better cytotoxicity. Thus, these derivatives can be studied as potential inhibitors of PDE5A.

Exogenous-oxidant- and catalyst-free electrochemical deoxygenative C2 sulfonylation of quinoline N-oxides

By employing quinoline N-oxides as the starting materials, the electrochemical C–H sulfonylation of electron-deficient quinolines was indirectly achieved at room temperature.

Synthesis and preliminary structure-activity relationship study of 2-aryl-2H-pyrazolo[4,3-c]quinolin-3-ones as potential checkpoint kinase 1 (Chk1) inhibitors

The serine-threonine checkpoint kinase 1 (Chk1) plays a critical role in the cell cycle arrest in response to DNA damage. In the last decade, Chk1 inhibitors have emerged as a novel therapeutic strategy to potentiate the anti-tumour efficacy of cytotoxic chemotherapeutic agents. In the search for new Chk1 inhibitors, a congeneric series of 2-aryl-2 H-pyrazolo[4,3-c]quinolin-3-one (PQ) was evaluated by in-vitro and in-silico approaches for the first time. A total of 30 PQ structures were synthesised in good to excellent yields using conventional or microwave heating, highlighting that 14 of them are new chemical entities. Noteworthy, in this preliminary study two compounds 4e₂ and 4h₂ have shown a modest but significant reduction in the basal activity of the Chk1 kinase. Starting from these preliminary results, we have designed the second generation of analogous in this class and further studies are in progress in our laboratories.

Crystal structure of 1-(4-chlorophenyl)-6,8-diphenyl-1H-pyrazolo[4,3-c]quinoline, C28H18ClN3

C28H18ClN3, monoclinic, P21/c, (no. 14) a = 5.9519(2) Å, b = 8.0511(3) Å, c = 43.4071(14) Å, β = 90.001(2)°, V =2080.04(12) Å3, Z = 4, Rgt(F) = 0.066, wRref(F2) = 0.190, T = 173 K.

Unveiling a versatile heterocycle: pyrazoline – a review

The design and synthesis of novel fluorescent heterocyclic dyes is a “hotspot” research area, due to their favourable photophysical and electronic properties, which could allow huge advances in the fields of physics, chemistry and biology.

Dehydrogenative [2 + 2 + 1] Heteroannulation Using a Methyl Group as a One-Carbon Unit: Access to Pyrazolo[3,4-c]quinolines

A practical and straightforward access to pyrazolo[3,4-c]quinolines by molecular sieve mediated dehydrogenative [2 + 2 + 1] heteroannulation of N-(o-alkenylaryl)imines with aryldiazonium salts is described using a sp(3)-hybrid carbon atom as a one-carbon unit. The reaction enables the formation of three new chemical bonds, a C-C bond and two C-N bonds, in a single reaction and features simple operation and excellent functional group tolerance.

Friedel–Crafts Chemistry. Part 46. Unprecedented Construction of Tricyclic Pyrazolo[3,4-b]quinolines, -[1,8]naphthyridines, -azepines, -azocines, -pyrido[3,2-g]azocines, and pyrazolo[3,4-b]azonines via Friedel–Crafts Ring Closures

A series of keto-substituted pyrazolo[3,4-b]quinolines, pyrazolo[3,4-b][1,8]naphthyridines, benzo[e]pyrazolo[3,4-b]azepines, benzo[g]pyrazolo[3,4-b]azocines, pyrazolo[3,4-b]pyrido[3,2-g]azocines, and benzo[g]pyrazolo[3,4-b]azonines scaffolds were synthesized via a Friedel–Crafts cyclialkylation approach. The precursor acids were obtained by utilizing the modified Ullman coupling reactions of 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid with different aryl amines followed by ring closures in the presence of AlCl3/CH3NO2 or P2O5 or polyphosphoric acid catalysts. Particular attention is given to the novel structures especially in regard to the promising pharmaceutical and therapeutic values associated with their skeletons.

Metal-free domino one-pot protocols for quinoline synthesis

Metal-free domino one-pot protocols for quinoline synthesis have been reviewed.

Novel polycarbo-substituted alkyl (thieno[3,2-c]quinoline)-2-carboxylates: synthesis and cytotoxicity studies

Direct one-pot base-promoted conjugate addition–elimination of 6,8-dibromo-4-chloroquinoline-3-carbaldehyde with methyl mercaptoacetate and subsequent cyclization afforded methyl [(6,8-dibromothieno[3,2-c]quinoline)]-2-carboxylate. The latter undergoes Suzuki-Miyaura cross-coupling with arylboronic acids to yield exclusively the corresponding alkyl [(6,8-diarylthieno[3,2-c]quinoline)]-2-carboxylates,. The cytotoxicity of the prepared compounds was evaluated against the human breast cancer cell line MCF-7 using the MTT assay. The effects of compounds 2, 3c and 4d on cell kinetics were further determined using the xCELLigence Real Time Cell Analysis (RTCA) system. In both the MTT assay and Real Time Cell Analysis, the compounds inhibited cancer cell growth in a dose- and time-dependent manner. Furthermore, on the basis of the calculated LC₅₀ values, the compounds compared favourably with nocodazole, a well-established anticancer drug.

Progress of the synthesis of condensed pyrazole derivatives (from 2010 to mid-2013)

Condensed pyrazole derivatives are important heterocyclic compounds due to their excellent biological activities and have been widely applied in pharmaceutical and agromedical fields. In recent years, numerous condensed pyrazole derivatives have been synthesized and advanced to clinic studies with various biological activities. In this review, we summarized the reported synthesis methods of condensed pyrazole derivatives from 2010 until now. All compounds are divided into three parts according to the rings connected to pyrazole-ring, i.e. [5, 5], [5,F 6], and [5, 7]-condensed pyrazole derivatives. The biological activities and applications in pharmaceutical fields are briefly introduced to offer an orientation for the design and synthesis of condensed pyrazole derivatives with good biological activities.

Dipyrazolo[1,5-a:4',3'-c]pyridines - a new heterocyclic system accessed via multicomponent reaction

The synthesis of dipyrazolo[1,5-a:4',3'-c]pyridines is described. Easily obtainable 5-alkynylpyrazole-4-carbaldehydes, p-toluenesulfonyl hydrazide, and an aldehyde or ketone containing an α-hydrogen atom were reacted in a silver triflate catalyzed multicomponent reaction affording new tricyclic compounds with a dipyrazolo[1,5-a:4',3'-c]pyridine core. Detailed NMR spectroscopic investigations ((1)H, (13)C and (15)N) were undertaken with all obtained compounds.