Aromatic Nitrile Oxides Research Articles

Organo NHC catalyzed aqueous synthesis of 4β-isoxazole-podophyllotoxins: in vitro anticancer, caspase activation, tubulin polymerization inhibition and molecular docking studies.

We present, for the first time, the organo-N-heterocyclic carbene (NHC) catalyzed 1,3-dipolar cycloaddition of 4β-O-propargyl podophyllotoxin (1) with in situ aromatic nitrile oxides to afford regioselective 4β-isoxazolepodophyllotoxin hybrids (6a-n) in benign aqueous-organic media. Preliminary anticancer activity results showed that compound 6e displayed superior activity against MCF-7, HeLa and MIA PaCa2 human cell lines compared with podophyllotoxin. Compounds 6j and 6n showed greater activity against the MCF-7 cell line than the positive control. Caspase activation studies revealed that compound 6e at 20 μg ml-1 concentration had greater caspase 3/7 activation in MCF-7 and MIAPaCa2 cells than podophyllotoxin. Furthermore, in vitro tubulin polymerization inhibition studies revealed that compound 6e showed comparable activity with podophyllotoxin. Finally, in silico molecular docking studies of compounds 6e, 6j, 6n and podophyllotoxin on α,β-tubulin (pdb id 1SA0) revealed that compound 6n showed excellent binding energies and inhibition constants compared with podophyllotoxin.

Studies on the [2+3] cycloaddition reaction of nitrile oxides to abietic acid esters

[2+3] Dipolar cycloadditions of aromatic nitrile oxides to abietic acid esters were investigated. The reactions showed complete site selectivity and regioselectivity, while the stereoselectivity depended on the structures of the dipolarophiles.

Synthesis of 4,5-dihydroisoxazole derivatives of maleopimaric acid by 1,3-dipolar cycloaddition reaction between its allyl derivatives and aromatic nitrile oxides

While searching for pharmacologically active compounds among 4,5-dihydrooxazole derivatives of maleopimaric acid, we studied for the first time the reaction between allyl-substituted maleopimaric acid derivatives and aromatic nitrile oxides that were generated from oximes by oxidation with sodium hypochlorite with or without ultrasonication of the biphasic system. The reaction occurred under mild conditions and regiospecifically provided 4,5-dihydroisoxazol-5-ylmethyl derivatives of maleopimaric acid in 77–99% yields.

Regioselective synthesis of some isoxazolines and isoxazolidines bearing caprolactam moiety

ABSTRACTIsoxazoline and isoxazolidine series were obtained by the reactions of aromatic aldonitrones and nitrile oxides with N-vinyl caprolactam via regioselective 1,3-dipolar cycloadditions that yield only 5-caprolactam-substituted regioisomers in moderate yields. The cycloaddition reactions were optimized using different conditions. The utilized one for the transformation of nitrile oxides to isoxazoles is triethylamine at room temperature and the best protocol have been found for the transformation of nitrones to N-methyl isoxazolidines is silver acetate in refluxing xylene. The structural identification of target compounds was established by IR, nuclear magnetic resonance (NMR), high resolution mass spectrometry (HRMS) spectra, and X-ray diffraction analyses.

Synthesis of carbohydrate-substituted isoxazoles and evaluation of their antitubercular activity

Abstract Eight new sugar-substituted isoxazoles were synthesized by a 1,3-dipolar cycloaddition reaction of aromatic nitrile oxides with carbohydrate-substituted alkynes. Products were screened for antimycobacterial activity against the Mycobacterium tuberculosis H37Rv strain. Four compounds, 5e–h, significantly inhibit growth of the bacterial strain with a minimum inhibitory concentration (MIC) of 3.125 μg/mL.

Isoxazole derivatives as new nitric oxide elicitors in plants.

Several 3,5-disubstituted isoxazoles were obtained in good yields by regiospecific 1,3-dipolar cycloaddition reactions between aromatic nitrile oxides, generated in situ from the corresponding hydroxyimidoyl chlorides, with non-symmetrical activated alkynes in the presence of catalytic amounts of copper(I) iodide. Effects of 3,5-disubstituted isoxazoles on nitric oxide and reactive oxygen species generation in Arabidopsis tissues was studied using specific diaminofluoresceine dyes as fluorescence indicators.

ChemInform Abstract: Asymmetric Cycloaddition: An Efficient Synthesis of Enantiopure Isoxazolines Substituted with Carbohydrate Analogues.

A simple and convenient method for the synthesis of heterocycles substituted with carbohydrate analogs is described. The chiral optically pure five-membered glycoconjugates containing the isoxazoline unit were obtained by an aromatic nitrile oxides cycloaddition with 1-phenyl-1,2-dihydro-pyridazine-3,6-dionyl N-glycoside derivatives.

Fluorescent Probes from Stable Aromatic Nitrile Oxides

AbstractStable aromatic nitrile oxides underwent a 1,3‐dipolar cycloaddition reaction with 1‐iodo‐4‐(prop‐2‐yn‐1‐yloxy)benzene to afford the expected isoxazoles in very good yields as single regioisomers. The formation of the 5‐substituted isoxazoles is in agreement with frontier orbital theory. The reductive cleavage of the N–O bond followed by complexation with BF3·Et2O afforded the corresponding boron complexes, which were further derivatized with a triple bond for click chemistry applications. The photochemical behavior and the fluorescence properties of the derivatives were investigated and discussed, taking theoretical calculations into consideration.

Asymmetric Cycloaddition: An Efficient Synthesis of Enantiopure Isoxazolines Substituted with Carbohydrate Analogues

A simple and convenient method for the synthesis of heterocycles substituted with carbohydrate analogs is described. The chiral optically pure five‐membered glycoconjugates containing the isoxazoline unit were obtained by an aromatic nitrile oxides cycloaddition with 1‐phenyl‐1,2‐dihydro‐pyridazine‐3,6‐dionyl N‐glycoside derivatives.

Design and synthesis of D-ring steroidal isoxazolines and oxazolines as potential antiproliferative agents against LNCaP, PC-3 and DU-145 cells

Two series of novel steroidal isoxazolines and oxazolines were synthesized through different routes from dehydroepiandrosterone acetate and pregnenolone acetate, respectively. The synthesis of the analogs of both series is multistep and proceeds in good overall yields. While the key step in the synthesis of former is the cycloaddition of aromatic nitrile oxides across α,β-unsaturated olefins, it is the condensation of α,β-azidoalcohols with aromatic aldehydes in the later. Compounds of both the series were tested for their cytotoxic activities against LNCaP, PC-3 and DU-145 prostate cancer cell lines. Amongst all the compounds of both the series screened for their prostate cancer activity, compound 6a, 6e and 12a are the most active especially against LNCaP and DU-145 cancer cell lines.

HNO made-easy from photochemical cycloreversion of novel 3,5-heterocyclic disubstituted 1,2,4-oxadiazole-4-oxides

A variety of symmetric and asymmetric 3,5-heterocyclic disubstituted 1,2,4-oxadiazole-4-oxides have been prepared through cycloaddition of aromatic and heteroaromatic nitrile oxides to heteroaromatic amidoximes. A library of novel, fully characterized, 1,2,4-oxadiazole-4-oxides has been obtained as valuable precursors, upon photochemical activation, of new nitrosocarbonyl intermediates. The photochemical cycloreversion of the 1,2,4-oxadiazole-4-oxides was investigated from the computational point of view and the hydrolysis of the generated nitrosocarbonyl intermediates in water constituted the way for an easy-made HNO generation process because of the photochemical behavior of the parent compounds.

Direct oxidation of Δ2-isoxazolines synthesis by metal ion-mediated diastereoface-selective 1,3-dipolar cycloaddition with “activated” DMSO

A series of 4-hydroxyl-Δ2-isoxazol-6(6aH)-one derivatives was prepared by magnesium ion-mediated diastereoface-selective 1,3-dipolar cycloaddition of aromatic nitrile oxides with pyrrolidinone derivatives. The reaction of 4-hydroxyl-Δ2-isoxazol-6(6aH)-one derivatives with dimethylsulfoxide and oxalyl chloride under Swern conditions led to a Δ2-isoxazole-4,6(5H,6aH)-dione.

An unexpected transformation by reduction of isoxazolines

Abstract Aromatic nitrile oxides undergo regio- and stereo-specific 1,3-dipolar cycloaddition reactions with racemic 5-hydroxy-4-methyl-1,5-dihydropyrrol-2-one derivatives 1 . In each case, a single product 3 results from an anti approach to the hydroxyl group, the oxygen of the 1,3-dipole being attached to C-5 of pyrrolidinones. A detailed study of a procedure for the selective reduction of Δ 2 -isoxazolines to the corresponding vinylogous amide derivatives is reported.

Click-chemistry approach to isoxazole-containing α-CF3-substituted α-aminocarboxylates and α-aminophosphonates

A convenient strategy for the synthesis of isoxazole-containing α-CF(3)-substituted α-aminocarboxylates and α-aminophosphonates have been developed. The method is based on copper-catalyzed 1,3-dipolar cycloaddition of different aromatic nitrile oxides to functionalized acetylenes.

ChemInform Abstract: Synthesis with Nitrile Oxides. Part 1. Reaction of Aromatic Nitrile Oxides with N-Cyanoimides.

ChemInform Abstract: Synthesis with Nitrile Oxides. Part 1. Reaction of Aromatic Nitrile Oxides with N-Cyanoimides.

ChemInform Abstract: The Reactions of Nitrile Oxide-Quinone Cycloadducts. Part 1. Base- Induced Rearrangement of the 1:1 -C=C- Adducts of Aromatic Nitrile Oxides with Dialkyl-Substituted p-Benzoquinones.

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ChemInform Abstract: Generation of Nitrile Oxides from Oxime Derivatives by the Oxidation with Ammonium Hexanitratocerate(IV).

Aromatic and aliphatic nitrile oxides are generated by the oxidation of α-hydroxyimino carboxylic acid with ammonium hexanitratocerate(IV). They react with olefinic and acetylenic dipolarophiles to give the corresponding cycloaddition products in good yield. The oxidation of α-oxo aldoximes also affords α-oxo carbonitrile oxides.

Glucose-based spiro-isoxazolines: A new family of potent glycogen phosphorylase inhibitors

A series of glucopyranosylidene-spiro-isoxazolines was prepared through regio- and stereoselective [3+2]-cycloaddition between the methylene acetylated exo-glucal and aromatic nitrile oxides. The deprotected cycloadducts were evaluated as inhibitors of muscle glycogen phosphorylase b. The carbohydrate-based family of five inhibitors displays K i values ranging from 0.63 to 92.5 μM. The X-ray structures of the enzyme–ligand complexes show that the inhibitors bind preferentially at the catalytic site of the enzyme retaining the less active T-state conformation. Docking calculations with GLIDE in extra-precision (XP) mode yielded excellent agreement with experiment, as judged by comparison of the predicted binding modes of the five ligands with the crystallographic conformations and the good correlation between the docking scores and the experimental free binding energies. Use of docking constraints on the well-defined positions of the glucopyranose moiety in the catalytic site and redocking of GLIDE-XP poses using electrostatic potential fit-determined ligand partial charges in quantum polarized ligand docking (QPLD) produced the best results in this regard.

An efficient 1,3-dipolar cycloaddition between aromatic selenoaldehydes and nitrile oxides or nitrile imines: an easy access to selenium-containing five-membered heterocyclic ring system

1,3-Dipolar cycloaddition between aromatic selenoaldehydes, generated by thermal retro Diels–Alder reaction of anthracene cycloadducts, and nitrile oxides or nitrile imines proceeded efficiently to give the corresponding [3+2] cycloadducts as a single isomer in good yields, being 1,4,2-oxaselenazoles or 1,3,4-selenadiazoles, respectively.

A Practical Synthesis of Enantiopure 4,5-Dihydroisoxazole-5-carboxylic Acids

The 1,3-dipolar cycloaddition of a variety of aromatic and aliphatic nitrile oxides to 2,5-trans-2,5-diphenylpyrrolidine derived acrylamide and cinnamamide efficiently affords the corresponding 4,5-dihydroisoxazole-5-carboxamides in a highly regio-and stereoselective manner. The cycloaddition of aliphatic nitrile oxides to the analogue methacrylamide proceeds also smoothly to afford the expected cycloadducts in moderate yields and very high regio- and stereoselectivity. In sharp contrast, aromatic nitrile oxides react with the same amide to afford 5-methyl-4,5-dihydroisoxazole-5-carboxamides in higher yields but as near 1:1 mixtures of diastereoisomers. Acid hydrolysis of these products afforded enantiopure 4,5-dihydroisoxazole-5-carboxylic acids.