Phthalazin-1(2H)-one as a remarkable scaffold in drug discovery

One-Pot Synthesis of Polycyclic 4,5-Dihydropyridazine-3(2H)-ones by Inverse Electron-Demand Diels-Alder (IEDDA) Reactions from Alkenes

In the classical Inverse Electron-Demand Diels-Alder (IEDDA) reactions between alkenes and tetrazines, 4,5-dihydropyridazines are formed. 4,5-Dihydropyridazines are rapidly converted to the more energetically stable 1,4-dihydropyridazines by 1,3-prototropic isomerization. In this study, instead of 1,4-dihydropyridazines, 4,5-dihydropyridazine-3(2H)-ones were obtained as a result of IEDDA reactions between tetrazines with leaving groups at the 3,6-positions, and norbornene and barrelene-derived polycyclic alkenes in the presence of moisture in air or solvent. To show that this new method works not only on strained polycyclic alkenes but also on monocyclic and linear alkenes, the corresponding 4,5-dihydropyridazine-3(2H)-ones were obtained in high yields from the reactions performed with styrene and cyclopentene as well. The chemical structures of the polycyclic 4,5-dihydropyridazine-3(2H)-ones were determined by NMR and HRMS analyses. In addition, the exact structures of the polycyclic 4,5-dihydropyridazine-3(2H)-ones were also experimentally proven by converting them to pyridazine-3(2H)-ones known in the literature.

Design, synthesis, in vitro, and in vivo evaluation of novel phthalazinone-based derivatives as promising acetylcholinesterase inhibitors for treatment of Alzheimer's disease

Twenty novel phthalazinone-based compounds were designed as acetylcholinesterase (hAChE) inhibitors. Compounds 7e and 17c demonstrated comparable or superior activity compared to donepezil, respectively, in in vitro enzyme assay. Moreover, both compounds 7e and 17c possess minimal toxicity on hepatic and neuroblastoma cell lines. Besides, it was proved that compounds 7e and 17c have percentage alternations and a transfer latency time comparable to donepezil and can alleviate the cognitive impairment caused by the scopolamine-induced model in mice. The kinetic analysis for compound 17c suggested this compound as a mixed-type inhibitor that could bind to both the peripheral (PAS) and the catalytic site (CAS) of the hAChE enzyme. The synthesized molecules were subjected to in silico analyses, including molecular docking studies, and the outcomes were consistent with the in vitro findings.

Synthesis of 5,6-Dihydropyrazolo[5,1-a]isoquinolines through Tandem Reaction of C,N-Cyclic Azomethine Imines with α,β-Unsaturated Ketones

An innovative and efficient approach has been developed for the synthesis of 5,6-dihydropyrazolo[5,1-a]isoquinolines. This one-pot tandem reaction involves the reaction of C,N-cyclic azomethine imines with α,β-unsaturated ketones, using K₂CO₃ as the base and DDQ as the oxidant. The process results in functionalized 5,6-dihydropyrazolo[5,1-a]isoquinolines with good yields. This convenient one-step method encompasses a tandem [3 + 2]-cycloaddition, detosylation, and oxidative aromatization.

Chemodivergent 1,3-Dipolar Cycloadditions of C,N-Cyclic Azomethine Imines with γ-Sulfonamido-α,β-Unsaturated Ketones to Synthesize Tricyclic Dinitrogen-Fused Heterocycles

1,3-Dipolar cycloadditions of C,N-cyclic azomethine imines with γ-NHTs-α,β-unsaturated ketones were developed to synthesize tricyclic dinitrogen-fused heterocycles. Highly functionalized tricyclic tetrahydroisoquinolines were readily obtained in good to high yields in the [3 + 2]-cycloaddition reaction of N-Bz-protected C,N-cyclic azomethine imines with γ-NHTs-α,β-unsaturated ketones under mild reaction conditions. Moreover, DABCO-catalyzed cycloaddition of N-Ts-protected C,N-cyclic azomethine imines with γ-NHTs-α,β-unsaturated ketones followed by cleavage of the tosyl group is a convenient route to synthesize tetrahydropyrazolo [5,1-a]isoquinolines in good yields with excellent diastereoselectivities.

Novel Phthalazin-1(2H)-One Derivatives Displaying a Dithiocarbamate Moiety as Potential Anticancer Agents

Nowadays, cancer disease seems to be the second most common cause of death worldwide. Molecular hybridization is a drug design strategy that has provided promising results against multifactorial diseases, including cancer. In this work, two series of phthalazinone-dithiocarbamate hybrids were described, compounds 6-8, which display the dithiocarbamate scaffold at N2, and compounds 9, in which this moiety was placed at C4. The proposed compounds were successfully synthesized via the corresponding aminoalkyl phthalazinone derivatives and using a one-pot reaction with carbon disulfide, anhydrous H₃PO₄, and different benzyl or propargyl bromides. The antiproliferative effects of the titled compounds were explored against three human cancer cell lines (A2780, NCI-H460, and MCF-7). The preliminary results revealed significant differences in activity and selectivity depending on the dithiocarbamate moiety location. Thus, in general terms, compounds 6-8 displayed better activity against the A-2780 and MCF-7 cell lines, while most of the analogues of the 9 group were selective toward the NCI-H460 cell line. Compounds 6e, 8e, 6g, 9a-b, 9d, and 9g with IC₅₀ values less than 10 µM were the most promising. The drug-likeness and toxicity properties of the novel phthalazinone-dithiocarbamate hybrids were predicted using Swiss-ADME and ProTox web servers, respectively.

Recent developments in the green synthesis of biologically relevant cinnolines and phthalazines

Both cinnolines and phthalazines are heterocyclic compounds which have a wide range of biological activities and pharmacological profiles. This work represents the recent advances in the green synthesis of cinnolines and phthalazines as 1,2 and 2,3-diazanaphalenes were cited. The docking studies and mode of action for key scaffolds were also reported.

Transition-Metal-Free Addition of Dialkyl Phosphites to Phthalazin-2-ium Bromide: Synthesis of α-Aminophosphonate Analogues

α-Aminophosphonate analogues containing a phthalazine skeleton were efficiently obtained by a new transition-metal-free addition of dialkyl phosphites to phthalazin-2-ium bromide under mild conditions. A mechanistic study using isotope labeling and radical inhibition experiment revealed that the present transformation passes through a nucleophilic addition of dialkyl phosphates, rather than an insertion of P-H to carbenes.

Selective Galectin-8N Ligands: The Design and Synthesis of Phthalazinone-d-Galactals

Ligand selectivity among the highly conserved galectins has been an ever-challenging objective. For galectin-8, a protein prevalent in both pathology and tissue distribution, we report phthalazinone-galactals that show excellent selectivity for the galectin-8N-terminal domain. A dissection of structure-activity relationships of the phthalazinone and an extensive molecular dynamics meta-analysis accompany the discovery of the selective galectin-8N ligands presented here. These selective compounds will facilitate the study of galectin-8 biology and may have pharmaceutical relevance in the wide range of galectin-8 associated pathologies.

Discovery of Oral Anticancer 1,2-Bis(hydroxymethyl)benzo[g]pyrrolo[2,1-a]phthalazine Hybrids That Inhibit Angiogenesis and Induce DNA Cross-Links

Designing hybrid molecules with dual functions is one approach to improve the therapeutic efficacy of combination treatment. We have previously conjugated phthalazine and bis(hydroxymethyl)pyrrole pharmacophores to form hybrids bearing antiangiogenesis and DNA interstrand cross-linking activities. To improve the bioavailability, we adopted a benzology approach to design and synthesize a new series of 1,2-bis(hydroxymethyl)benzo[g]pyrrolo[2,1-a]phthalazines. These new hybrids retained the dual functions and could be formulated into vehicles for intravenous and oral administration. Among them, we demonstrated that compound 19a with dimethylamine at the C6 position markedly suppressed the tumor growth of human small cell lung cancer cell line H526, squamous lung cancer cell line H520, and renal cancer cell line 786-O in nude mice, implying that compound 19a is a broad-spectrum anticancer agent. Our results implicated that the conjugation of antiangiogenic and DNA cross-linking is likely to be a helpful approach to improving the efficacy of combination therapy.

Novel Pyran-Linked Phthalazinone-Pyrazole Hybrids: Synthesis, Cytotoxicity Evaluation, Molecular Modeling, and Descriptor Studies

A series of novel pyran-linked phthalazinone-pyrazole hybrids were designed and synthesized by a facile one-pot three-component reaction employing substituted phthalazinone, 1H-pyrazole-5-carbaldehyde, and active methylene compounds. Optimization studies led to the identification of L-proline and ethanol as efficient catalyst and solvent, respectively. This was followed by evaluation of anticancer activity against solid tumor cell lines of lung and cervical carcinoma that displayed IC₅₀ values in the range of 9.8–41.6 µM. Molecular modeling studies were performed, and crucial interactions with the target protein were identified. The drug likeliness nature of the compounds and molecular descriptors such as molecular flexibility, complexity, and shape index were also calculated to understand the potential of the synthesized molecules to act as lead-like molecule upon further detailed biological investigations as well as 3D-QSAR studies.

Design, synthesis, and in vitro evaluation of 4-aminoalkyl-1(2H)-phthalazinones as potential multifunctional anti-Alzheimer's disease agents

A series of 4-aminoalkyl-1(2H)-phthalazinone derivatives was designed and synthesized as potential multifunctional agents for Alzheimer's disease (AD) treatment. In vitro biological assay results demonstrated that most synthesized compounds exhibited significant AChE inhibition, moderate to high MAOs inhibitory potencies and good anti-platelet aggregation abilities. Among them, compound 15b exhibited the highest inhibitory potencies towards MAO-B and MAO-A (IC₅₀ = 0.7 µM and 6.4 µM respectively), moderate inhibition towards AChE (IC₅₀ = 8.2 µM), and good activities against self- and Cu²⁺-induced Aβ_1-42 aggregation and platelet aggregation. Moreover, 15b also displayed antioxidant capacity, neuroprotective potency, anti-neuroinflammation and BBB permeability. These excellent results indicated that compound 15b could be worthy of further studies to be considered as a promising multifunctional candidate for the treatment of AD.

Amino- and polyaminophthalazin-1(2H)-ones: synthesis, coordination properties, and biological activity

Amino- and polyaminophthalazinones were synthesized by the palladium‐catalyzed amination (alkyl- and arylamines, polyamines) of 4-bromophthalazinones in good yields. The coordinating properties of selected aminophthalazinones towards Cu(II) ions were investigated and the participation of the nitrogen atoms in the complexation of the metal ion was shown. A biological screening of the potential cytotoxicity of selected synthesized compounds on HT-29 and PC-3 cell lines, as well as on the L-929 cell line, proved that some amino derivatives of phthalazinone show interesting anticancer activities. The detailed synthesis, spectroscopic data, and biological assays are reported.

Simple Analogues of Quaternary Benzo[c]phenanthridine Alkaloids: Discovery of a Novel Antifungal 2-Phenylphthalazin-2-ium Scaffold with Excellent Potency against Phytopathogenic Fungi

Inspired by sanguinarine and chelerythrine, a novel antifungal 2-phenylphthalazin-2-ium scaffold as a simple analogue was designed. Most of the 30 compounds showed excellent inhibition activity against almost all eight phytopathogenic fungi, far superior to sanguinarine and chelerythrine. A third of the compounds were more active than azoxystrobin in most cases. Compounds 26 and 27 showed the highest total activity against all the fungi with EC₅₀ means of ca. 4.6 μg/mL. Fusarium solani showed the highest susceptibility with an EC₅₀ mean of 3.62 μg/mL to 19 compounds. A concentration of 25.0 μg/mL 27 can fully control the Colletotrichum gloeosporioides infection in apples over 9 days. Electron microscopic observations showed that 27 was able to damage the structures of the hypha and cell membrane. The structure-activity relationship showed that the presence of electron-withdrawing groups on the C-ring increases the activity against most of the fungi. Thus, 2-phenylphthalazin-2-ium compounds represent promising leads for the development of novel fungicides.

Azolo[d]pyridazinones in medicinal chemistry

Azolo[d]pyridazinone is a privileged structure and versatile pharmacophore whose derivatives are associated with diverse biological activities, in particular antidiabetic, antiasthmatic, anticancer, analgesic, anti-inflammatory, antithrombotic, antidepressant and antimicrobial activities. The importance of this scaffold against some targets like PDE, COX and DPP-4 has been reviewed in detail previously. In the present review, we have summarized comprehensive information on azolo[d]pyridazinone derivatives investigated by many researchers for their diverse pharmacological activities, structure-activity relationship and molecular modeling studies since 2000. The review may lead scientists in the research fields of organic synthesis, medicinal chemistry and pharmacology to the strategic design and development of azolo[d]pyridazinone-based drug candidates in the future.

Synthetic and medicinal chemistry of phthalazines: Recent developments, opportunities and challenges

Fused diaza-heterocycles constitute the core structure of numerous bioactive natural products and effective therapeutic drugs. Among them, phthalazines have been recognized as remarkable structural leads in medicinal chemistry due to their wide application in pharmaceutical and agrochemical industries. Accessing such challenging pharmaceutical agents/drug candidates with high chemical complexity through synthetically efficient approaches remains an attractive goal in the contemporary medicinal chemistry and drug discovery arena. In this review, we focus on the recent developments in the synthetic routes towards the generation of phthalazine-based active pharmaceutical ingredients and their biological potential against various targets. The general reaction scope of these innovative and easily accessible strategies was emphasized focusing on the functional group tolerance, substrate and coupling partner compatibility/limitation, the choice of catalyst, and product diversification. These processes were also accompanied by the mechanistic insights where deemed appropriate to demonstrate meaningful information. Moreover, the rapid examination of the structure-activity relationship analyses around the phthalazine core enabled by the pharmacophore replacement/integration revealed the generation of robust, efficient, and more selective compounds with pronounced biological effects. A large variety of in silico methods and ADME profiling tools were also employed to provide a global appraisal of the pharmacokinetics profile of diaza-heterocycles. Thus, the discovery of new structural leads offers the promise of improving treatments for various tropical diseases such as tuberculosis, leishmaniasis, malaria, Chagas disease, among many others including various cancers, atherosclerosis, HIV, inflammatory, and cardiovascular diseases. We hope this review would serve as an informative collection of structurally diverse molecules enabling the generation of mature, high-quality, and innovative routes to support the drug discovery endeavors.

Phthalazinone Scaffold: Emerging Tool in the Development of Target Based Novel Anticancer Agents

Phthalazinones are important nitrogen-rich heterocyclic compounds which have been a topic of considerable medicinal interest because of their diversified pharmacological activities. This versatile scaffold forms a common structural feature for many bioactive compounds, which leads to the design and development of novel anticancer drugs with fruitful results. The current review article discusses the progressive development of novel phthalazinone analogues that are targets for various receptors such as PARP, EGFR, VEGFR-2, Aurora kinase, Proteasome, Hedgehog pathway, DNA topoisomerase and P-glycoprotein. It describes mechanistic insights into the anticancer properties of phthalazinone derivatives and also highlights various simple and economical techniques for the synthesis of phthalazinones.

The crystal structure of phthalazin-1(2H)-one, C8H6N2O1

C8H6N2O1, monoclinic, P21/c (no. 14), a = 8.6277(17) Å, b = 13.134(3) Å, c = 13.062(5) Å, β = 110.54(3)°, V = 1386.0(7) Å3, Z = 8, R gt(F) = 0.0512, wR ref(F 2) = 0.1581, T = 293(2) K.

Synthesis of 1,2-dihydro-1-oxophthalazin-4-yl trifluoromethanesulfonate and its application in the synthesis of 4-(aryl/heteroaryl/alkynyl)phthalazin-1(2H)-one

Biologically significant 4-aryl/heteroaryl/alkynyl phthalazinones have been reported via the Suzuki and Sonogashira coupling reactions.