4485-08-9

The ene reaction of singlet oxygen (1O2), triazolinedione (TAD), and nitrosoarene, specifically 4-nitronitrosobenzene (ArNO), with the tetrasubstituted 1,3-allylically strained, chiral allylic alcohol 3,4- dimethylpent-3-en-2-ol (2)

Hydroxamic acids are metal-chelating compounds that show important biological activity including anti-tumor effects. We have recently engineered the transketolase from Geobacillus stearothermopilus (TKgst) to convert benzaldehyde as a non-natur

Azobenzenes are important molecular switches that can still be difficult to functionalize selectively. A high yielding Pd-catalyzed cross-coupling method under mild conditions for the introduction of NHS esters to azobenzenes and diazocines has been established. Yields were consistently high with very few exceptions. The NHS functionalized azobenzenes react with primary amines quantitatively. These amines are ubiquitous in biological systems and in material science.

Imines are photoaddressable motifs useful in the development of new generations of molecular switches, but their operation with low-energy photons and control over isomer stability remain challenging. Based on a computational design, we developed phenylimino indolinone (PIO), a green-light-addressable T-type photoswitch showing negative photochromism. The isomerization behavior of this photoactuator of the iminothioindoxyl (ITI) class was studied using time-resolved spectroscopies on time scales from femtoseconds to the steady state and by quantum-chemical analyses. The understanding of the isomerization properties and substituent effects governing these photoswitches opens new avenues for the development of novel T-type visible-light-addressable photoactuators based on C=N bonds.

The desire to photocontrol molecular properties ranging from materials to pharmacology using light as an external trigger with high spatiotemporal resolution led to the development of a broad range of photochromic scaffolds. Among them, azobenzenes are synthetically well accessible and show excellent fatigue resistance. Their photochromic properties vary with the substitution pattern and for different heteroarenes. However, the photochromism of 3(5)-substituted-1H-pryazoles has not yet been investigated, although this compound class offers interesting possibilities of metal ion coordination and hydrogen bond formation via its NH moiety. Herein, we present the results of an experimental and computational investigation of arylazo-3(5)-arylazo-1H-pyrazoles. To elucidate their properties, solvent and substitution effects on their light absorption, thermal half-lives, photostationary states, fatigue, and quantum yields were determined.

Self-assembly is a fundamental feature of biological systems, and control of such processes offers fascinating opportunities to regulate function. Fragaceatoxin C (FraC) is a toxin that upon binding to the surface of sphingomyelin-rich cells undergoes a s

The histamine H1 G protein-coupled receptor (GPCR) plays an important role in allergy and inflammation. Existing drugs that address the H1 receptor differ in their chemical structure, pharmacology, and side effects. Light-controllable spatial and temporal activity regulation of photochromic H1 ligands may contribute to a better mechanistic understanding and the development of improved correlations between ligand structure and pharmacologic effects. We report photochromic H1 receptor ligands, which were investigated in an organ-pharmacological assay. Initially, five photochromic azobenzene derivatives of reported dual H1–H4 receptor antagonists were designed, synthesized, photochemically characterized, and organ-pharmacologically tested on the isolated guinea pig ileum. Among them, one compound [trans-19: (Z)-1-(4-chlorophenyl)-1-(4-methylpiperazin-1-yl)-N-(4-((E)-phenyldiazenyl)phenyl)methanimine] retained the antagonistic activity of its non-photochromic lead, and trans–cis isomerization by irradiation induced a fourfold difference in the pharmacological response. Further structural optimization resulted in two bathochromically shifted derivatives of 19 [NO2-substituted 35 {(Z)-1-(4-chlorophenyl)-1-(4-methylpiperazin-1-yl)-N-(4-((E)-(4-nitrophenyl)diazenyl)phenyl)methanimine} and SO3?-substituted 41 {4-((E)-(4-(((Z)-(4-chlorophenyl)(4-methylpiperazin-1-yl)methylene)amino)phenyl)diazenyl)benzenesulfonate}], which do not require the use of UV light for photoisomerization and which also have improved solubility and show reduced tissue impairment. The trans isomers of both compounds showed a remarkable increase in antagonistic activity relative to their lead trans-19; furthermore, a 46-fold difference in activity on the isolated guinea pig ileum was observed between trans- and cis-35.

Modular synthesis of structurally diverse functionalized azobiphenyls and azoterphenyls for the realization of optically switchable materials has been described. The corresponding synthesis of azobiphenyls and azoterphenyls by stepwise Mills/Suzuki-Miyaura cross-coupling reaction, proceeds with high yields and provides facile access to a library of functionalized building blocks. The synthetic methods described herein allow combining several distinct functional groups within a single unit, each intended for a specific task, such as 1) the ?N=N? azobenzene core as a photoswitchable moiety, 2) aryls and heteroaryls, functionalized with carboxylic acids or pyridine at its peripheries, as coordinating moieties and 3) varying substitution, size and length of the backbone for adaptability to specific applications. These specifically designed azobiphenyls and azoterphenyls provide modular bricks, potentially useful for the assembly of a variety of polymers, molecular containers and coordination networks, offering a high degree of molecular functionality. Once integrated into materials, the azobenzene system, as a side group on the organic linker backbone, can be exploited for remotely controlling the structural, mechanical or physical properties, thus being applicable for a broad variety of ‘smart’ applications.

Tungstate ion was heterogenized on the silica-coated magnetite nanoparticles and applied for the selective oxidation of anilines to nitroso arenes—with hydrogen peroxide/urea as oxidant in dimethyl carbonate as solvent—in moderate–good yields (40–96%). The catalyst was characterized using different techniques including Fourier-transform infrared spectroscopy, X-ray powder diffraction, vibrating sample magnetometry, scanning electron microscopy, energy dispersive X-ray and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The catalyst was easily recovered using an external magnet and reused for six times.

The development of PPARα/γ dual or PPARα/γ/δ pan-agonists could represent an efficacious approach for a simultaneous pharmacological intervention on carbohydrate and lipid metabolism. Two series of new phenyldiazenyl fibrate derivatives of GL479, a previously reported PPARα/γ dual agonist, were synthesized and tested. Compound 12a was identified as a PPAR pan-agonist with moderate and balanced activity on the three PPAR isoforms (α, γ, δ). Moreover, docking experiments showed that 12a adopts a different binding mode in PPARγ compared to PPARα or PPARδ, providing a structural basis for further structure-guided design of PPAR pan-agonists. The beneficial effects of 12a were evaluated both in vitro, on the expression of PPAR target key metabolic genes, and ex vivo in two rat tissue inflammatory models. The obtained results allow considering this compound as an interesting lead for the development of a new class of PPAR pan-agonists endowed with an activation profile exploitable for therapy of metabolic syndrome.

A straightforward indole synthesis via annulation of C-nitrosoaromatics with conjugated terminal alkynones was realised achieving a simple, highly regioselective, atom- and step economical access to 3-aroylindoles in moderate to good yields. Further functionalizations of indole scaffolds were investigated and an easy way to JWH-018, a synthetic cannabinoid, was achieved.

Benzoylphenylureas (BPUs) are used as synthetic insect growth regulators for inhibiting chitin synthesis. Merging insecticidal BPUs with photoswitchable azobenzene generated photoresponsive chitin synthesis inhibitors. A prepared azobenzene-benzoylphenylurea can be activated upon irradiation with UV light, and shows 6-fold and 2-fold activity difference to armyworm (Mythimna separata) and German cockroach (Blattella germanica) sulfonylurea receptors, respectively. This is the first example of a photoswitchable BPU insecticide. The generation of such a photoresponsive BPU insecticide allows for modulation of the insecticidal activity by light, and may facilitate the spatiotemporal control over the sulfonylurea receptor and the mechanistic study of this kind of insecticide.

Nitrosobenzenes have been used as a convenient aminating reagent for the efficient synthesis of 1H-indazoles via rhodium and copper catalyzed C-H activation and C-N/N-N coupling. The reaction occurred under redox-neutral conditions with high efficiency and functional group tolerance. Moreover, a rhodacyclic imidate complex has been identified as a key intermediate.

Azobenzenes reacted with 3-ethoxycyclobutanoes to give 2,3-dihydro-pyridazin-4(1H)-ones by using EtAlCl2as a Lewis acid. Thus, ring cleavage of 3-ethoxycyclobutanones took place to form a zwitterionic intermediate by activation with EtAlCl2, and intermolecular formal [4+2] cycloaddition of the zwitterionic intermediate proceeded with azobenzenes to give 2,3-dihydro-pyridazin-4(1H)-ones after elimination of ethanol. Regioselectivity for cycloaddition of unsymmetrical azobenzenes, ring contraction and chemoselective reduction of 2,3-dihydro-pyridazin-4(1H)-ones, and [4+2] cycloaddition to 4-phenyl-1,2,4-triazolin-3,5-dione are also described.

Aryl sulfonamides are a widely used drug class for the inhibition of carbonic anhydrases. In the context of our program of photochromic pharmacophores we were interested in the exploration of azobenzene-containing sulfonamides to block the catalytic activ

Mechanical treatment (milling) of crystals of aromatic nitroso dimers (azodioxides) induces their dissociation and cross-dimerizations. The mechanisms of these processes are discussed on the basis of kinetic studies and the solid-state 15 N kinetic isotope effect, which is measured for the first time. By comparison with analogous processes in cocrystals and in melts, it appears that the reactions follow similar mechanism in which the surface deformations play the crucial role. The system can also be used as a model for a more general conceptual study of solid-state reaction mechanisms. Copyright

Opioid receptors (ORs) are widely distributed in the brain, the spinal cord, and the digestive tract and play an important role in nociception. All known ORs are G-protein-coupled receptors (GPCRs) of family A. Another well-known member of this family, rhodopsin, is activated by light through the cis/trans isomerization of a covalently bound chromophore, retinal. We now show how an OR can be combined with a synthetic azobenzene photoswitch to gain light sensitivity. Our work extends the reach of photopharmacology and outlines a general strategy for converting Family A GPCRs, which account for the majority of drug targets, into photoreceptors. Lighting up the opioid receptor: Photofentanyl-2 is a photochromic version of the well-known analgesic fentanyl. It is a potent agonist in the dark (or when illuminated with blue light) and loses activity when irradiated with UV light. It can be used to optically control the μ-opioid receptor, converting a G-protein-coupled receptor (GPCR) into a photoreceptor.

Nucleophilic substitution of fluoroaromatics with poly(vinyl amine) (PVAm) is a suitable method for producing various azobenzene-functionalized PVAms. The solubility of the fluoroaromatic reagents in water was mediated by complexation with 2,6-O-dimethyl-

Mechanochemical Oxone oxidation of selected para-substituted anilines was used as a rapid and solvent-free route to nitrosobenzenes; besides avoiding bulk solvents and short reaction times, this method exploits high vapour pressures of nitrosobenzenes for the solvent-free separation of the product by sublimation, demonstrating an entirely solvent-free route to chemical synthesis and product isolation. The Royal Society of Chemistry.

Meridianins, marine alkaloids known as kinase inhibitors with an indole skeleton, and meridianin analogues were produced regioselectively and in moderate to good yields by thermal annulation of nitrosoarenes with 2-amino-4-ethynylpyrimidine and 2-chloro-4-ethynylpyrimidine, respectively, through a novel and atom-economical indolization process.

Possibility of nitrosobenzenes to form dimeric molecular structures (azodioxides) is used as a model for intermolecular selectivity investigations in solution as well as in solid state. Cross-dimerization of different combinations of p- and m-substituted nitrosobenzene pairs was studied by variable temperature 1H NMR, solid-state NMR (CP MAS), IR, and ab initio calculations. It is evident that p-nitronitrosobenzene behaves nonselectively because it forms dimers with all the studied nitrosobenzene partners. In contrast, p-methoxynitrosobenzene in most cases does not form dimers. The evidence that ability to form dimers is different in solution than in the solid state can be explained by influence of molecular arrangements in the crystal lattice.

Cross-linking of nitrosobenzenes to heterodimers (azodioxides) when they are not sterically crowded with large groups in ortho-position was studied by NMR and FT-IR spectroscopy, X-ray crystallography as well as by cryogenic photolysis. It was found for the first time that cross-linked dimers (heterodimers) exist both in solution and in solid state and that they appear in the crystal together with homodimers. The system is used as a model for studying organic solid solution formation. The role of molecular packing in formation of a weak chemical bond is also discussed.

The molybdenum acetylide oxo-peroxo complex obtained in situ by the treatment of the corresponding molybdenum acetylide carbonyl complex, CpMo(CO)3(C{triple bond, long}CPh); Cp = η5-C5H5 with H2O2, has been used as an efficient catalyst for selective N-oxidation of primary amines to nitroso derivatives. Excellent amine conversion (up to 100%) and very high selectivity for nitroso compounds (99%) have been obtained using 30% hydrogen peroxide as an oxidant. The oxo peroxo Mo(VI) complex has also been found to be very active for the oxidation of various substituted primary aromatic amines with electron donating as well as electron withdrawing substituents on the aromatic ring.

A highly efficient, selective, fast, and cheap protocol is developed for oxidation of aromatic amines and alcohols utilizing 34% hydrogen peroxide in water catalyzed by some W- and Mo-based heteropolyoxometalates. Findings showed that dodecatungstophosphoric acid, H3PW12O40, was the most efficient catalyst in the examined oxidation reactions. This methodology may prove to be a valuable alternative for eco-friendly green oxidation. Inherent simplicity, easy work up, and using regenerable catalysts were other key aspects of this oxidation protocol.

Recyclable tungsten- and molybdenum-based coordination polymers efficiently catalyzed the oxidation of primary aromatic amines to the corresponding nitroso derivatives with 30% aqueous hydrogen peroxide in high yields at room temperature.

New non-symmetrical azobenzene derivatives have been synthesized as potential molecular electronic switching device candidates. The Oxone mediated oxidation of anilines provided nitroso-functionalized arenes, which were then condensed with substituted anilines to provide a series of azobenzene derivatives that could be further converted into oligo(phenylene ethynylene)s or diazonium salts. The resulting thiolacetates, thiols, or diazonium salts are capable of forming molecular layers on the surface of gold or silicon, thereby paving the way for molecular electronics testing.

The thermal reaction of (4-nitrophenyl)nitrene with oxygen in low-temperature matrices produced a new molecular species, which was identified as 4-nitrophenylnitroso oxide on the basis of its IR spectrum in combination with isotopic labeling with 18

Nitroso arenes 2a-k are prepared in 53-80% yield from anilines 1a-k by oxidation with H2O2 catalysed with MoO3/KOH, ammonium molybdate or other molybdenum salts. Further oxidation to nitro arenes 3a,d j in 66-90% is also described.

A matrix-bound superoxide radical anion, generated by treating Ti(OR)4 (R =iPr, nBu) with H2O2, is a selective heterogeneous catalyst for the oxidation of anilines to the corresponding nitroarenes with 50 % aqueous H2O2 [Eq. (1)]. Yields of 82-98 % are obtained, even with anilines bearing electron-withdrawing substituents (R = NO2, COOH).

The HOOSO-3 oxidation of eleven meta-and para-substituted anilines to the corresponding nitrosobenzenes at pH ≈ 11 was characterized by the rate equation v = kK[OX][An]/(1 + K[An]). Formation constant of the reactive intermediate and its rate of decomposition were evaluated separately for ascertaining the structure-reactivity relationships. Under the experimental conditions the dianion, -O-O-SO-3 is probably the effective electrophile. Kinetic data can be rationalized by a bimolecular process which involves the attack of nucleophilic nitrogen atom on the peroxidic oxygen. The highlight of the study is the opposite curvatures observed in the nonlinear Hammett plots of first-order rate constant k and the "equilibrium" constant K, being concave downward and upward, respectively.

N-Arylhydroxamic acids (AHAs) are promising novel N-OH mediators for oxidoreductase catalysis. They are electrochemically active compounds with a redox potential of 0.31-0.41 V vs. SCE. Representative oxidoreductases, e.g. fungal peroxidase from Coprinus

Kinetic study of homogeneous catalytic oxidation of substituted anilines with hydrogen peroxide in the presence of H3PW12O40 showed that the reaction involves formation of intermediate substrate-oxidant complex whose decomposition determines the rate of the process. Donor substituents in the benzene ring favor the oxidation process, indicating its electrophilic nature.

-

Treatment of o-nitroanilines and o-aminobenzoic acids with 30 percent hydrogen peroxide in the presence of Na2WO4 and H3PO4 results in selective formation of corresponding nitroso derivatives.In other cases, the products are azoxy compounds.Oxidation of anilines containing alkyl or alkoxy groups in the ortho and para positions with hydrogen peroxide in the presence of Na2WO4 and tetrabutylammonium bromide quantitatively yields corresponding nitrosobenzenes.The H2O2-Na2WO4-H3PO4 system in the presence of tetrabutylammonium bromide is proposed for preparation of nitroso derivatives from anilines containing electron-acceptor meta and para substituents.

1 catalyses the oxidation of primary aromatic amines to the corresponding nitroso derivatives, in the presence of H2O2 as oxidant.

Evidence which supports a stepwise electron transfer process for the reduction of 1 by Fe(2+) and Cu(+) is presented.

-

Irradiation of nitro-substituted aromatic azides initiates a complex series of chemical reactions that lead to different products depending on the details of the experiment.There is evidence that four reactive intermediates participate in product-determining reactions.These are the singlet nitrene, the triplet nitrene, the triplet azide, and the ring-expanded dehydroazepine.The chemical and physical properties of each of these species is modified by the nitro substituent.The reactivity of the singlet nitrene with nucleophilic amines is increased, the lifetime of the dehydroazepine is shortened, and the triplet nitrene becomes a powerful single-electron acceptor.Nitro-substituted aromatic azides are widely used in photolabeling experiments.The findings of this study suggest that they may be inappropriate choices as photolabeling agents in many circumstances.

The 13C NMR spectra of a wide range of monomeric para-substituted nitrosobenzenes have been determined end the results related to a wide range of published data for other para-disubstituted benzenes.It is shown that the nitroso substituent exercises a different pattern of effect for the 13C chemical shifts at the ipso C atom from at least twenty eight other substituents.It is noted that when the para substituent is a ?-donor, the nitroso group functions in a different manner from that operative when the para substituent is a ?-acceptor, a general possibility that has already been suggested in the recent literature.