Design and synthesis of 3,5-disubstituted boron-containing 1,2,4-oxadiazoles as potential combretastatin A-4 (CA-4) analogs

New Combretastatin Analogs as Anticancer Agents: Design, Synthesis, Microtubules Polymerization Inhibition, and Molecular Docking Studies

A new series of 4-(4-methoxyphenyl)-5-(3,4,5-trimethoxyphenyl)-4H-1,2,4-triazole-3-thiol derivatives were synthesized as analogs for the anticancer drug combretastatin A-4 (CA-4) and characterized using FT-IR, 1 H-NMR, 13 CNMR, and HR-MS techniques. The new CA-4 analogs were designed to meet the structural requirements of the highest expected anticancer activity of CA-4 analogs by maintaining ring A 3,4,5-trimethoxyphenyl moiety, and at the same time varying the substituents effect of the triazole moiety (ring B). In silico analysis indicated that compound 3 has higher total energy and dipole moment than colchicine and the other analogs, and it has excellent distribution of electron density and is more stable, resulting in an increased binding affinity during tubulin inhibition. Additionally, compound 3 was found to interact with three apoptotic markers, namely p53, Bcl-2, and caspase 3. Compound 3 showed strong similarity to colchicine, and it has excellent pharmacokinetics properties and a good dynamic profile. The in vitro anti-proliferation studies showed that compound 3 is the most cytotoxic CA-4 analog against cancer cells (IC50 of 6.35 μM against Hep G2 hepatocarcinoma cells), and based on its selectivity index (4.7), compound 3 is a cancer cytotoxic-selective agent. As expected and similar to colchicine, compound 3-treated Hep G2 hepatocarcinoma cells were arrested at the G2/M phase resulting in induction of apoptosis. Compound 3 tubulin polymerization IC50 (9.50 μM) and effect on Vmax of tubulin polymerization was comparable to that of colchicine (5.49 μM). Taken together, the findings of the current study suggest that compound 3, through its binding to the colchicine-binding site at β-tubulin, is a promising microtubule-disrupting agent with excellent potential to be used as cancer therapeutic agent.

Synthesis of a boron-containing amidoxime reagent and its application to synthesize functionalized oxadiazole and quinazolinone derivatives

Herein, we report the design, synthesis and application of a borylated amidoxime reagent for the direct synthesis of functionalized oxadiazole and quinazolinone derivatives. This reagent exhibits broad synthetic utility to obtain a variety of biologically relevant drug-like molecules. It can be easily prepared at large scale from relatively inexpensive reagents, and can undergo facile transformations to obtain target compounds. The developed amidoxime reagent was synthesized from 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzonitrile and hydroxyl amine hydrochloride using N,N-diisopropylethylamine as a base in ethanol under reflux conditions. Overall advantages include a metal-free route to boronated oxadiazoles, quinazolinone derivatives, and restriction of the multistep sequences. Importantly, the boron-rich pharmacophore derived compounds were obtained through an efficient and inexpensive strategy.

A novel procedure for the synthesis of borylated quinolines and its application in the development of potential boron-based homeodomain interacting protein kinase 2 (HIPK2) inhibitors

Herein, we demonstrate a Pd catalyzed C-4 borylation of structurally complex chloroquinolines with bis(pinacolato)diboron under relatively simple and efficient conditions. Moreover, the borylated quinolines were converted into oxaborole, trifluoroborate salt and boronic acid and also rendered in the Suzuki reaction successfully. The method was also applied for the synthesis of potential boron-based homeodomain interacting protein kinase 2 (HIPK2) inhibitors. The strategy opens up new avenues for the functionalization of quinolines as potential probes and pharmacological agents for future biomedical research.

This report reveals a Pd catalyzed C-4 borylation of structurally complex chloroquinolines with B₂(pin)₂ without the use of any external ligand for the synthesis of potential boron-based homeodomain interacting protein kinase 2 inhibitors.

Recent Trends in Tubulin-Binding Combretastatin A-4 Analogs for Anticancer Drug Development

Although significant progress over several decades has been evidenced in cancer therapy, there still remains a need for the development of novel and effective therapeutic strategies to treat several relapsed and intractable cancers. In this regard, tubulin protein has become one of the efficient and major targets for anticancer drug discovery. Considering the antimitotic ability, several tubulin inhibitors have been developed to act against various cancers. Among various tubulin inhibitors available, combretastatin-A4 (CA-4), a naturally occurring lead molecule, offers exceptional cytotoxicity (including the drug-resistant cell lines) and antivascular effects. Although CA-4 offers exceptional therapeutic efficacy, several new advancements have been proposed, such as the structural modification via A and B rings, as well as cis-olefinic bridging, which provide highly efficient analogs with improved tubulin-binding efficiency to meet the anticancer drug development requirements. This review systematically emphasizes the recent trends and latest developments in the anticancer drug design & discovery, using CA-4 analogs as the tubulin inhibiting agents, highlighting their structure-activity relationships (SAR) and resultant pharmacological efficacies.

Discovery of novel quinoline-based analogues of combretastatin A-4 as tubulin polymerisation inhibitors with apoptosis inducing activity and potent anticancer effect

A new series of quinoline derivatives of combretastatin A-4 have been designed, synthesised and demonstrated as tubulin polymerisation inhibitors. These novel compounds showed significant antiproliferative activities, among them, 12c exhibited the most potent inhibitory activity against different cancer cell lines (MCF-7, HL-60, HCT-116 and HeLa) with IC50 ranging from 0.010 to 0.042 µM, and with selectivity profile against MCF-10A non-cancer cells. Further mechanistic studies suggest that 12c can inhibit tubulin polymerisation and cell migration, leading to G2/M phase arrest. Besides, 12c induces apoptosis via a mitochondrial-dependant apoptosis pathway and caused reactive oxygen stress generation in MCF-7 cells. These results provide guidance for further rational development of potent tubulin polymerisation inhibitors for the treatment of cancer.HighlightsA novel series of quinoline derivatives of combretastatin A-4 have been designed and synthesised.Compound 12c showed significant antiproliferative activities against different cancer cell lines.Compound 12c effectively inhibited tubulin polymerisation and competed with [3H] colchicine in binding to tubulin.Compound 12c arrested the cell cycle at G2/M phase, effectively inducing apoptosis and inhibition of cell migration.

Potent Quinoline-Containing Combretastatin A-4 Analogues: Design, Synthesis, Antiproliferative, and Anti-Tubulin Activity

A novel series of quinoline derivatives of combretastatin A-4 incorporating rigid hydrazone and a cyclic oxadiazole linkers were synthesized and have demonstrated potent tubulin polymerization inhibitory properties. Many of these novel derivatives have shown significant antiproliferative activities in the submicromolar range. The most potent compound, 19h, demonstrated superior IC50 values ranging from 0.02 to 0.04 µM against four cancer cell lines while maintaining low cytotoxicity in MCF-10A non-cancer cells, thereby suggesting 19h's selectivity towards proliferating cancer cells. In addition to tubulin polymerization inhibition, 19h caused cell cycle arrest in MCF-7 cells at the G2/M phase and induced apoptosis. Collectively, these findings indicate that 19h holds potential for further investigation as a potent chemotherapeutic agent targeting tubulin.

Synthesis and biological screening of novel 2-morpholinoquinoline nucleus clubbed with 1,2,4-oxadiazole motifs

Novel series of 2-morpholinoquinoline scaffolds (6a-n), containing the 1,2,4-oxadiazole and moiety, was designed and synthesized in good yield (76-86%). The synthesized compounds were screened for their preliminary in vitro antimicrobial activity against a panel of pathogenic strains of bacteria and fungi. Molecular docking and pharmacokinetic study were carried out for the prepared compounds. The cytotoxicity of the synthesized compounds was tested at different concentrations using bioassay of S. pombe cells at the cellular level. The effect of synthesized compounds on the DNA integrity of S. pombe was observed on agarose gel. Compounds 6d, 6e, 6g, 6h, 6j and 6n exhibited excellent antimicrobial potency as compared to the standard drugs (i.e Ampicillin, Norfloxacin, Chloramphenicol, Ciprofloxacin). Compounds 6d, 6e, 6g, 6k and 6n were found to have significant antifungal activity as compared to griseofulvin. Compounds 6f, 6i, 6k, 6l were found very less cytotoxic, while compounds 6d, 6e, 6g, 6h were found to exhibit maximum toxicity. The rest of the synthesized compounds were found to be moderately toxic.

Synthesis of 2-(1,2,4-oxadiazol-3-yl)quinazolin-4(3H)-ones from diaminoglyoxime-based nitrones

Various 2-[5-(aryl)-1,2,4-oxadiazol-3-yl]quinazolin-4(3H)-ones have been synthesized from the reaction of diaminoglyoxime-based nitrones with methyl 2-aminobenzoate or 2-aminobenzamide in the presence of acetic acid at 100 °C. The reaction was extended as a one-pot three-component approach starting from diaminoglyoxime, aldehyde and methyl 2-aminobenzoate.

Boron chemicals in diagnosis and therapeutics

Advances in the field of boron chemistry have expanded the application of boron from material use to medicine. Boron-based drugs represent a new class of molecules that possess several biomedical applications including use as imaging agents for both optical and nuclear imaging as well as therapeutic agents with anticancer, antiviral, antibacterial, antifungal and other disease-specific activities. For example, bortezomib (Velcade(®)), the only drug in clinical use with boron as an active element, was approved in 2003 as a proteasome inhibitor for the treatment of multiple myeloma and non-Hodgkin's lymphoma. Several other boron-based compounds are in various phases of clinical trials, which illustrates the promise of this approach for medicinal chemists working in the area of boron chemistry. It is expected that in the near future, several boron-containing drugs should become available in the market with better efficacy and potency than existing drugs. This article discusses the current status of the development of boron-based compounds as diagnostic and therapeutic agents in humans.

Novel pyrazoline amidoxime and their 1,2,4-oxadiazole analogues: synthesis and pharmacological screening

A novel series of pyrazoline amidoxime (2a-d) and pyrazoly-1,2,4-oxadiazole (3a-p) and (4) of pharmacological significance have been synthesised. Structures of newly synthesised compounds were characterized by spectral studies. New compounds were screened for their in vitro antioxidant, antimicrobial and antiinflammatory activities. Among the synthesized compounds, compound 2a, 3l and 3o were found to be active antimicrobial agents in addition to having potent antioxidant activity, while the compound 3f showed promising antiinflammatory activity in comparison with standard drug.