Novel isoxazole polycyclic aromatic hydrocarbons as DNA-intercalating agents

Synthesis of novel spiroisoxazolidino hybrids of alantolactone and isoalantolactone via 1,3 dipolar nitrone cycloaddition and its antimicrobial Evaluation

Alantolactone and isoalantolactone are two isomeric sesquiterpene lactones that were isolated from Innula recemosa. Here, we are used for the semisynthesis of novel isoxazolidine hybrids of alantolactone and isoalantolactone through a two-step process: nitrone synthesis followed by nitrone 1,3-dipolar cycloaddition. The formation of the cycloadduct was well characterized via modern spectroscopic techniques such as HRMS, 1H NMR, 13C NMR, DEPT-90, DEPT-135, and 2D NMR. This study also includes the synthesis of dinitrone with glyoxal and terephthalaldehyde, which is used for the dinitrone cycloadduct of alantolactone and isoalantolactone. Both nitrone cycloaddition and dinitrone cycloaddition proceed with high regio- and diastereoselectivity, resulting in the formation of only one isomer. The formation of the α-cycloadducts and the absolute configuration were established through 2D NMR and single-crystal X-ray diffraction analysis. The antimicrobial activity of all synthesized compounds was evaluated against a panel of Gram-positive and Gram-negative pathogens. Compounds 3f and 4f exhibited potential antimicrobial activity against drug-sensitive and -resistant Staphylococcus aureus strains, with minimum inhibitory concentrations ranging from 6 to 10 µM. A time-kill kinetics assay suggested that compounds 3f and 4f are bacteriostatic. Furthermore, scanning electron microscopy analysis confirmed that compounds 3f and 4f cause significant morphological alternations and exert potent antibacterial effects by causing substantial cellular damage.

Insights into the mechanism of [3+2] cycloaddition reactions between N-benzyl fluoro nitrone and maleimides, its selectivity and solvent effects

We present a theoretical study of the [3+2] cycloaddition (32CA) reactions of N-benzyl fluoro nitrone with a series of maleimides producing isoxazolidines. We use the Molecular Electron Density Theory at the MPWB1K/6-311G(d) level. We focus on the reaction mechanism, selectivity, solvent, and temperature effects. In addition, we perform topological analyses at the minimal and transition states to identify the intermolecular interactions. Electron Localization Function approach classifies the N-benzyl fluoro nitrone as zwitterionic (zw-) three-atom components (TACs), associated with a high energy barrier. The low polar character of the reaction is evaluated using the Conceptual Density Functional Theory analysis of the reactants, confirmed by the low global electron density transfer computed at the transition states. Computations show that these 32CA reactions follow a one-step mechanism under kinetic control, with highly asynchronous bond formation and no new covalent bond is formed at the TS. Besides, the potential energy surfaces along the reaction pathways in gas phase and in solvent are mapped. The corresponding Gibbs free energy profiles reveal that the exo-cycloadducts are kinetically and thermodynamically more favored than endo-cycloadducts, in agreement with the exo-selectivity observed experimentally. In particular, we found that solvent and temperature did not affect this selectivity and mainly influence the activation energies and the exothermic character of these 32CA reactions.

Influence of conventional hydrogen bonds in the intercalation of phenanthroline derivatives with DNA: The important role of the sugar and phosphate backbone

The influence of hydrogen bonds in model intercalated systems between guanine-cytosine and adenine-thymine DNA base pairs (bps) was analyzed with the popular intercalator 1,10-phenanthroline (phen) and derivatives obtained by substitution with OH and NH2 groups in positions 4 and 7. Semiempirical and Density Functional Theory (DFT) methods were used both including dispersion effects: PM6-DH2, M06-2X and B3LYP-D3 along with the recently developed near linear-scaling coupled cluster method DLPNO-CCSD(T) for benchmark calculations. Our results given by QTAIM and non-covalent interaction analysis confirmed the existence of hydrogen bonds created by OH and NH2 . The trends in the energy decomposition analysis for the interaction energy, ΔEint , showed that the ΔEelstat contributions are equal or even a little bit higher than the values for ΔEdisp . Such important ΔEelstat attractive contribution comes mainly from the conventional hydrogen bonds formed by OH and NH2 functional groups with DNA not only with bps but specially with the sugar and phosphate backbone. This behavior is very different from that of phen and other classical intercalators that cannot form conventional hydrogen bonds, where the ΔEdisp is the most important attractive contribution to the ΔEint . The inclusion of explicit water molecules in molecular dynamics simulations showed, as a general trend, that the hydrogen bonds with the bps disappear during the simulations but those with the sugar and phosphate backbone remain in time, which highlights the important role of the sugar and phosphate backbone in the stabilization of these systems.

Hydrazones as Substrates in the Synthesis of Isoxazolidines via a KOH-Promoted One-Pot Three-Component Cycloaddition with Nitroso Compounds and Olefins

Hydrazones have been employed as the starting materials in a KOH-mediated one-pot three-component cycloaddition with readily accessible nitroso compounds and olefins to construct various isoxazolidines. Compared with diazo compounds as starting materials, this methodology could afford a wider range of products in good to excellent yields and diastereoselectivities for most substrates, and hydrazones are cheaper, more accessible, and safer substrates. The experimental study shows that the choice of suitable hydrazones is crucial.

Investigation of 3-sulfamoyl coumarins against cancer-related IX and XII isoforms of human carbonic anhydrase as well as cancer cells leads to the discovery of 2-oxo-2H-benzo[h]chromene-3-sulfonamide - A new caspase-activating proapoptotic agent

Herein we report the synthesis of a set of seventeen 3-sulfonamide substituted coumarin derivatives. Prepared compounds were tested in vitro for inhibition of four physiologically relevant isoforms of the metalloenzyme human carbonic anhydrase (hCA, EC 4.2.1.1). Several coumarin sulfonamides displayed low nanomolar K_I values against therapeutically relevant hCA II, IX, and XII, whereas they did not potently inhibit hCA I. Some of these compounds exerted a concentration-dependent antiproliferative action toward RT4 human bladder cancer and especially A431 human epidermoid carcinoma cell lines. In the meantime, the viability of non-tumorigenic hTERT immortalized human foreskin fibroblast cell line Bj-5ta was not significantly affected by the obtained derivatives. Interestingly, compound 10q (2-oxo-2H-benzo [h]chromene-3-sulfonamide) showed a profound and selective dose-dependent inhibition of A431 cell growth with low nanomolar IC₅₀ values. We demonstrated that 10q possessed a concentration-dependent apoptosis induction activity associated with caspase 3/7 activation in cancer cells. As carbonic anhydrase isoforms in question were not potently inhibited by this compound, its antiproliferative effects likely involve other mechanisms, such as DNA intercalation. Compound 10q clearly represents a viable lead for further development of new-generation anticancer agents.

Synthesis of isoxazolidines via catalyst-free one-pot three-component cycloaddition of sulfoxonium ylides, nitrosoarenes and alkenes

A general and practical strategy for the construction of various keto-substituted isoxazolidines via one-pot three-component reaction of easily accessible, safer and more stable sulfoxonium ylides, nitrosoarenes and olefins is described.

Cucurbit[7]uril as a catalytic nanoreactor for one-pot synthesis of isoxazolidines in water

The main objective of supramolecular chemistry is to mimic the macrosystems present in nature, a goal that fits perfectly with the green chemistry guidelines. The aim of our work is to use the hydrophobic cavity of cucurbit[7]uril (CB[7]) to mimic nature for performing different dehydration and cycloaddition reactions in water. The hydrophobic cavity of CB[7] made it possible to synthesize nitrones and isoxazolidines in a one-pot fashion using water as a reaction solvent. Substituted isoxazolidines were obtained from the cycloaddition of nitrones with various styrenes and cinnamates, under microwave irradiation, with a catalytic amount of CB[7], and a moderate increase in the formation of the trans adduct was observed, compared to the reaction being carried out in toluene. The mechanism of the reaction and the inclusion of reagents and products in the CB[7] cavity have been studied and rationalized by NMR spectroscopy, ESI-MS experiments, and molecular modeling calculations.

Semi-synthesis of a novel hybrid isoxazolidino withaferin via chemoselective and diastereoselective 1,3-dipolar nitrone cycloaddition reaction

A facile, atom-economic synthesis of isoxazilidino withaferin, a novel hybrid of withaferin A, has been accomplished via two-step reaction of nitrone synthesis followed by nitrone 1,3-dipolar cycloaddition. The reaction is highly chemoselective (preferential reaction only on one of the two double bonds present on withaferin A) and diastereoselective affording exclusively the cis-fused products. The structure was determined by detailed analysis of 1D, 2D NMR and mass spectral data.

Hydrothermal Synthesis, Structural Characterization, and Interaction Mechanism with DNA of Copper(II) Complex Containing 2,2'-Bipyridine

A Cu(II) complex [Cu(bipy)(H₂O)₂(SO₄)] _n (bipy = 2,2'-bipyridine) was synthesized by hydrothermal method and characterized structurally by elemental analyses, single crystal X-ray diffraction, infrared spectra, and thermogravimetry and differential scanning calorimetry. The Cu(II) was hexacoordinated by two N atoms from bipy, two O atoms from different sulfate radical anions, and two O atoms from two water molecules, forming a slightly distorted octahedral geometry, and bridged by sulfato groups into polymeric chains. Under the condition of physiological pH, the interaction mechanism between the complex and hsDNA was explored with acridine orange as a fluorescence probe by spectroscopic methods. The binding modes between the complex and hsDNA were the electrostatic and embedded modes.

γ-Cyclodextrin as a Catalyst for the Synthesis of 2-Methyl-3,5-diarylisoxazolidines in Water

A green and efficient 1,3-dipolar cycloaddition of nitrones with different styrenes and cinnamates using a catalytic amount of γ-cyclodextrin (γ-CD) in water has been developed to give substituted isoxazolidines. γ-CD was found to be highly efficacious in carrying out this reaction under an eco-friendly environment, affording moderate to excellent yields and, in some cases, excellent diastereomeric excess (up to >95%) at 100 °C in 8-12 h. The catalyst can be easily recuperated and recycled for several times without loss of activity. Water, an eco-friendly reaction medium, has been utilized for the first time, to the best of our knowledge, in this reaction. The credit of the presented protocol includes high yields and catalyst reusability, and precludes the use of organic solvents. The use of in silico calculations allowed us to rationalize the obtained results and to improve the stereoselectivity.

Effects of oxygenation on the intercalation of 1,10-phenanthroline-5,6/4,7-dione between DNA base pairs: a computational study

The effects of oxygen in positions 4,7 and 5,6 of phenanthroline have been studied computationally when this ligand intercalates between DNA base pairs. Our results indicate that solvation energy could be the driving force of the process and thus, it can be also related with the cytotoxicity of the drug.

Isoxazolidine: A Privileged Scaffold for Organic and Medicinal Chemistry

The isoxazolidine ring represents one of the privileged structures in medicinal chemistry, and there have been an increasing number of studies on isoxazolidine and isoxazolidine-containing compounds. Optimization of the 1,3-dipolar cycloaddition (1,3-DC), original methods including electrophilic or palladium-mediated cyclization of unsaturated hydroxylamine, has been developed to obtain isoxazolidines. Novel reactions involving the isoxazolidine ring have been highlighted to accomplish total synthesis or to obtain bioactive compounds, one of the most significant examples being probably the thermic ring contraction applied to the total synthesis of (±)-Gelsemoxonine. The unique isoxazolidine scaffold also exhibits an impressive potential as a mimic of nucleosides, carbohydrates, PNA, amino acids, and steroid analogs. This review aims to be a comprehensive and general summary of the different isoxazolidine syntheses, their use as starting building blocks for the preparation of natural compounds, and their main biological activities.

Structure-activity relationship (SAR) study and design strategies of nitrogen-containing heterocyclic moieties for their anticancer activities

The present review article offers a detailed account of the design strategies employed for the synthesis of nitrogen-containing anticancer agents. The results of different studies describe the N-heterocyclic ring system is a core structure in many synthetic compounds exhibiting a broad range of biological activities. Benzimidazole, benzothiazole, indole, acridine, oxadiazole, imidazole, isoxazole, pyrazole, triazoles, quinolines and quinazolines including others drugs containing pyridazine, pyridine and pyrimidines are covered. The following studies of these compounds suggested that these compounds showed their antitumor activities through multiple mechanisms including inhibiting protein kinase (CDK, MK-2, PLK1, kinesin-like protein Eg5 and IKK), topoisomerase I and II, microtubule inhibition, and many others. Our concise representation exploits the design and anticancer potency of these compounds. The direct comparison of anticancer activities with the standard enables a systematic analysis of the structure-activity relationship among the series.

The effects of the mycotoxin austdiol on cell cycle progression, cytotoxicity and genotoxicity in Chinese hamster ovary (CHO-K1) cells

Austdiol is a mycotoxin mainly produced by Aspergillus ustus and Mycoleptodiscus indicus. These fungi are found in rye, oats, barley, corn and feed grains; thus, as a potential contaminant of human food and animal feed, this mycotoxin is of great concern. As such, the elucidation of the cytotoxicity and mutagenicity of austdiol is important. In this study, austdiol was purified from a rice-oat solid medium culture of M. indicus using chromatographic separation techniques. Chinese hamster ovary (CHO-K1) cells were then used to study the effect of austdiol on mammalian cell cycle, clonogenicity and DNA damage. Austdiol induced cell cycle arrest in G2/M phase, with a decreased S phase population and increased sub-G1 population. Austdiol also increased the polyploid population. These events resulted in cell death detected 7 days after treatment by clonogenic assay. DNA damage represents the main mechanism of action of austdiol, which induces DNA breaks and increases the frequency of micronuclei and nucleoplasmic bridges in binucleated cells in a CHO-K1 cell line. Moreover, cells exposed to austdiol and doxorubicin (DXR) combined treatments presented a reduced number of colonies and increased frequencies of micronuclei and nucleoplasmic bridges compared with negative control and cells treated with austdiol or DXR alone.

Substituent effect study on experimental ¹³C NMR chemical shifts of (3-(substituted phenyl)-cis-4,5-dihydroisoxazole-4,5-diyl)bis(methylene)diacetate derivatives

Eleven novel (3-(substituted phenyl)-cis-4,5-dihydroisoxazole-4,5-diyl)bis(methylene) diacetate derivatives were synthesized in the present study. These dihydroisoxazole derivatives were characterized by IR, (1)H NMR, (13)C NMR and elemental analyses. Their (13)C NMR spectra were measured in Deuterochloroform (CDCl3). The correlation analysis for the substituent-induced chemical shift (SCS) with Hammett substituent constant (σ), inductive substituent constant (σI), different of resonance substituent constants (σR, σR(o)) and Swain-Lupton substituent parameters (F, R) were performed using SSP (single substituent parameter), and DSP (dual substituent parameter) methods, as well as single and multiple regression analysis. From the result of regression analysis, the effect of substituent on the (13)C NMR chemical shifts was explained.

Phosphoramides bearing isoxazole derivative: spectroscopic and structural characterization, study of hydrogen-bonding interactions and two lanthanide complexes (LnIII = Ce and Eu)

In this study, the synthesis and spectroscopic characterization of new phosphoramides based on 3-amino-5-methylisoxazole with the formula R2P(O)[NH-C4H4NO], R = C6H5O (1), C6H5 (2), RP(O)[NH-C4H4NO]2, R = C6H5O (3), CH3-C6H4O (4), C6H5NH (5), (C6H5)ClP(O)[NH-C4H4NO] (6) and two lanthanide complexes [Ln(2)2(NO3)3(EtOH)]·EtOH, Ln(III) = Ce (7) and Eu (8), have been reported. The structural study of (3) shows the presence of two conformers (crystallographically independent molecules) in the crystalline lattice, caused by different orientations of the phenyl and isoxazole rings. For (3), the intermolecular interactions have been studied by Hirshfeld surface analysis and fingerprint plots. Furthermore, the electronic and energy aspects of hydrogen bonds between molecules of (3) have been explored by density functional theory (DFT) calculations. X-ray crystallography of complexes (7) and (8) reveals that two phosphoramide ligands take part in coordination to the metal, one as monodentate from O(phosphoryl), and the other one as chelate through O(phosphoryl) and N(ring). The complexes are also composed of two conformers in the solid-state structure. Quantum theory of atoms in molecules (QTAIM) analysis discloses the electrostatic nature of the Ln-ligand interaction.

An α1-adrenergic receptor ligand repurposed as a potent antiproliferative agent for head and neck squamous cell carcinoma

In this study we report the anticancer properties of RN5-Me, an α₁-adrenergic receptor ligand.

Synthesis and evaluation of novel isoxazolyl chalcones as potential anticancer agents

A series of novel isoxazolyl chalcones were synthesized and evaluated for their activities in vitro against four types of human non-small cell lung cancer cells, including H1792, H157, A549 and Calu-1 cells. The preliminary biological screening showed that compounds 5d and 5f-i exhibited significant cytotoxicity, particularly, compounds 5f and 5h were identified as the most potent anticancer agents with IC50 values 1.35-2.07 μM and 7.27-11.07 μM against H175, A549 and Calu-1 cell lines, respectively. Compounds 5f-i could induce apoptosis in A549 cells by death receptor 5 (DR5) mediated extrinsicpathways. The preliminary structure-activity relationship study showed that compounds bearing electron withdrawing groups (EWG) at the 2-position of the phenyl ring in Ar group were more effective than those with EWG at 4-position. These results further demonstrated that the scaffolds designed in this work might lead to the discovery of novel anti-lung cancer agents.

Recent advances in small organic molecules as DNA intercalating agents: synthesis, activity, and modeling

The interaction of small molecules with DNA plays an essential role in many biological processes. As DNA is often the target for majority of anticancer and antibiotic drugs, study about the interaction of drug and DNA has a key role in pharmacology. Moreover, understanding the interactions of small molecules with DNA is of prime significance in the rational design of more powerful and selective anticancer agents. Two of the most important and promising targets in cancer chemotherapy include DNA alkylating agents and DNA intercalators. For these last the DNA recognition is a critical step in their anti-tumor action and the intercalation is not only one kind of the interactions in DNA recognition but also a pivotal step of several clinically used anti-tumor drugs such as anthracyclines, acridines and anthraquinones. To push clinical cancer therapy, the discovery of new DNA intercalators has been considered a practical approach and a number of intercalators have been recently reported. The intercalative binding properties of such molecules can also be harnessed as diagnostic probes for DNA structure in addition to DNA-directed therapeutics. Moreover, the problem of intercalation site formation in the undistorted B-DNA of different length and sequence is matter of tremendous importance in molecular modeling studies and, nowadays, three models of DNA intercalation targets have been proposed that account for the binding features of intercalators. Finally, despite DNA being an important target for several drugs, most of the docking programs are validated only for proteins and their ligands. Therefore, a default protocol to identify DNA binding modes which uses a modified canonical DNA as receptor is needed.

Synthesis and biological evaluation of 1,7,8,8a-tetrahydro-3H-oxazolo[3,4-a]pyrazin-6(5H)-ones as antitumoral agents

A series of 1,7,8,8a-tetrahydro-3H-oxazolo[3,4-a]pyrazin-6(5H)-ones has been synthesized by an intramolecular, palladium(II) catalyzed, aminooxygenation of alkenyl ureas, readily available from glycine allylamides as starting materials. Biological tests showed that the obtained compounds are endowed with an interesting antitumoral activity against two human thyroid cancer cell lines, namely FTC-133 and 8305C, by promoting the apoptotic pathway and DNA fragmentation.

Self-catalyzed Mannich-type reaction of enolizable cyclic 1,3-dicarbonyls to acyclic nitrones: an entry to functionalized β-enamino diones

A new method for the preparation of highly functionalized β-enamino diones has been developed. The protocol involves an initial self-catalyzed Mannich-type reaction of enolizable cyclic 1,3-dicarbonyls to nitrones, followed by a spontaneous intramolecular reorganization of the resulting nonisolated hydroxylamine to enamino derivatives. These compounds retain the features of unnatural α-amino acids. The ease of preparation makes them attractive intermediates for the synthesis of peptidomimetics, polyheterocycles, and other multifunctional compounds. All experimental results have been efficiently rationalized by in silico studies at the M06-2X level of theory, and a valid mechanistic pathway has been proposed.

New PAH derivatives functionalized by cyclic nitrone framework: synthetic design, anti-proliferative activity and interaction with DNA

Novel approach to functionalized polycyclic aromatic hydrocarbons (PAHs) is presented. Incorporation of cyclic nitrone framework into the structure of PAHs was studied with respect to their anti-proliferative activities and interaction with double stranded DNA. Theoretical docking studies and UV titration methods were used for preliminary evaluation of binding of new PAH derivatives to DNA structure.