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The monocyclic 1,4-benzoquinone, HU-331, the direct oxidation product of cannabidiol, inhibits the catalytic activity of topoisomerase II but without inducing DNA strand breaks or generating free radicals, and unlike many fused-ring quinones exhibits minimal cardiotoxicity. Thus, monocyclic quinones have potential as anti-cancer agents, and investigation of the structural origins of their biological activity is warranted. New syntheses of cannabidiol and (±)-HU-331 are here reported. Integrated synthetic protocols afforded a wide range of polysubstituted resorcinol derivatives; many of the corresponding novel 2-hydroxy-1,4-benzoquinone derivatives are potent inhibitors of the catalytic activity of topoisomerase II, some more so than HU-331, whose monoterpene unit replaced by a 3-cycloalkyl unit conferred increased anti-proliferative properties in cell lines with IC50 values extending below 1 mM, and greater stability in solution than HU-331. The principal pharmacophore of quinones related to HU-331 was identified. Selected monocyclic quinones show potential for the development of new anticancer agents.

A simple protocol to measure the effective value of the circularly polarized magnetic induction of the microwave field is proposed and demonstrated employing continuous-wave saturation of a standard sample of Fremy’s salt measured under specified conditions. The fact that the doubly integrated intensity of first-derivative spectra is invariant with respect to the line shape is used to take into account the non-Lorentzian line shape to study the peak-to-peak intensity or the line width. Corrections for the use of line- rather than point-samples are developed.

Peptide-based supramolecular gels are an important class of biomaterials that can be used for biomedical applications ranging from drug delivery to tissue engineering. Methodology that allows one to readily modulate the mechanical properties of these gels will allow yet even a broader range of applications. Frémy's salt is an inorganic salt and long-lived free radical that is known to oxidize phenols. Herein, we show that Frémy's salt can be used to dramatically increase the mechanical rigidity of hydrogels formed by tyrosine-containing self-assembling β-hairpin peptides. When Frémy's salt is added to pre-formed gels, it converts tyrosine residues to o-quinones that can subsequently react with amines present within the lysine side chains of the assembled peptide. This results in the installation of chemical crosslinks that reinforce the gel matrix. We characterized the unoxidized and oxidized gel systems using UV-Vis, transmission electron microscopy and rheological measurements and show that Frémy's salt increases the gel rigidity by nearly one order of magnitude, while retaining the gel's shear-thin/recovery behavior. Thus, Frémy's salt represents an on-demand method to modulate the mechanical rigidity of peptide-based self-assembled gels.

A stopped-flow-electron paramagnetic resonance (EPR) method was applied for the detection of short-lived radicals of flavonoids bearing a catechol moiety as the B-ring, such as flavonols (quercetin, fisetin, and rutin), flavanones (eriodictyol and taxifolin), flavanols (catechin and epicatechin), and flavone (luteolin). 15N-labeled sodium salt of nitrosodisulfonate (15NDS) was employed to obtain the highly resolved EPR hyperfine structure (hfs) of flavonoid-derived semiquinone radicals under stoichiometrically regulated reaction conditions in aqueous media (pH 10). The EPR hfs of these flavonoids radicals, except catechin and epicatechin, were recorded. Based on the g value and the proton hyperfine coupling constants (hfcc), these flavonoid-derived radicals were assigned to be semiquinone radicals of the catechol moiety (B-ring). For example, the observed EPR hyperfine structure (hfs) of the luteolin radical (Lut−·) was composed of four sets of doublet splitting, which could be ascribed to the three protons of the B-ring (a2′ = 0.136, a5′ = 0.102, and a6′ = 0.272 mT) and a vinyl proton of the C-ring (a3 = 0.099 mT). In addition, the characteristically small doublet splitting resolved for the fisetin anion radical (Fis−·, 0.028 mT) was assigned to the aromatic proton at the C5 carbon of the A-ring, indicating that the unpaired electron of the radials was partially delocalized onto the A-ring through the π bonds involved in the vinyl-carbonyl moiety of the C-ring. The hfcc of the methine protons at the C2 carbon of taxifolin and eriodictyol-derived radicals (Tax−· and Eri−·) was, respectively, evaluated to be 0.102 and 0.230 mT. The assignment of the proton hfcc of flavonoid-derived semiquinone radicals will be discussed in relation with the molecular structure of the C-ring.

We describe the total synthesis of murrayafoline-B and seven carbazole-1,4-quinone alkaloids. A palladium(II)-catalyzed oxidative cyclization is used to construct the carbazole skeleton. Pyran annulation and oxidation provide pyrayaquinone-A, -B, and -C. DIBAL-H-promoted reductive ring opening of pyrano[3,2-a]carbazole precursors leads to the prenylated and geranylated carbazole-1,4-quinone alkaloids murrayaquinone-B, -C, -D, and -E and to murrayafoline-B.

The structure of the natural dipyranocoumarin dipetalolactone has been confirmed by an unambiguous synthetic route from resorcinol. This sequence was initiated by a pyran ring formation step which introduced the 3-chloro-3-methylbut-1-yne moiety. Then, the expected product undergoes a Fremy’s salt-meditated oxidative addition followed by ring closure to yield dipetalolactone. Dipetalolactone was also found to have immunological activity in a mouse carcinoma S180-bearing mice cell line.

Literature preparations of 2-amino-6-nitrobenzoic acid are usually based on phthalic anhydride. In order to make [benzene-14C(U)]-2-amino-6-nitrobenzoic acid, [benzene-14C(U)]-phthalic anhydride has to be prepared in multiple steps from [14C(U)]-benzene, resulting in an unacceptably lengthy 14-step synthesis. We have been able to develop a completely different method of synthesis, producing [benzene-14C(U)]-2-amino-6-nitrobenzoic acid from [14C(U)]-benzene in just four steps with an overall radiochemical yield of 32%. Copyright © 2011 John Wiley & Sons, Ltd.

(-)-3-Hydroxy-N-methyl-6-oxomorphinan (6a) and its (-)-2-bromo derivative (6b) were converted into (-)-2,3-dihydroxy-N-methyl-6-oxomorphinan (8a) and its (-)-4-bromo derivative (8b), respectively, by oxidation with Fremy's salt to the ortho-quinones, followed by reduction. Methylation of 8a and 8b gave the corresponding methyl ethers 9a and 9b. Catalytic hydrogenolysis of 8b and 9b gave 8a and 9a, respectively. The structure of (-)-2,3-dimethoxy-N-methyl-6-oxomorphinan (9a) was confirmed by total synthesis, and that of (-)-4-bromo-2,3-dimethoxy-N-methyl-6-oxomorphinan (9b) by single-crystal X-ray analysis. The model compound 2-bromo-4,5-dimethylphenol (15) gave, analogously, 3-bromo-4,5-dimethyl-pyrocatechol (16).

In aqueous alkali, Fremy’s salt (potassium nitrosodisulfonate dimer), homolyses nearly exclusively to the monomer radical anion, nitrosodisulfonate (NDS). In this media, NDS almost quantitatively oxidizes benzyl alcohol (PhCH2OH) to benzaldehyde (PhCHO), itself being reduced to hydroxylamine disulfonate (HNDS). The reaction is very nearly first-order in [NDS], [alkanol] and in [OH−]. However, with progressive addition of HNDS, decay kinetics of NDS gradually deviates from first-order. Ultimately, with sufficient excess of HNDS, the reaction becomes second-order in [NDS]. The consumption ratio, (ΔPhCH2OH]/Δ[NDS]), is ∼2. PhCD2OH manifests a large primary kinetic isotope effect (kH/kD = 11.6). Substituted benzyl alcohols (RBzCH2OH) with R-groups withdrawing electron density from the O–H bond accelerated the reaction; those with R-groups donating electron density to the O–H bond retarded the reaction. The conversion of 2-propanol to 2-propanone is much slower compared to that of benzyl alcohol to benzaldehyde. An alpha-H atom transfer mechanism seems logical.

Static magnetic field effect in the framework of the radial pair mechanism (RPM) theory was studied on the biologically significant chemical reaction between ascorbic acid and Fremy's salt. The data indicate that the reaction rate depends on the applied magnetic field strength. The time scale of the studied reaction and the improved continuous-wave electron paramagnetic resonance system allowed for the first time the direct comparison of the amplitude differences between exposed and control samples in the strictly same boundary conditions. Until now the RPM was studied in a different time scale, focusing only on faster reactions by time-resolved techniques or by spectrophotometer measurement. The magnetic field effects presently measured can not be extended tout court to living systems; however the understanding of magnetic field sensitivity in basic chemical reaction in vitro could help clarifying the underlying basic step of interaction between magnetic fields and biological systems.

Our objective was to develop a method mimicking the natural process of coherence in marine mollusks, by direct chemical conversion of protein tyrosine residues to DOPA-o-quinones, which consequently generates polymerization and cross-linking. Fremy's salt, (ON(SO3K)2, was used to convert tyrosine residues in peptides and proteins to reactive o-quinones. The conversion of tyrosines to DOPA-o-quinones, and their ability to polymerize or cross-link, was tested on tyramine, peptides, and proteins. The peptides tested were as follows: biotin-PEG4-tyramine (PEG-BT), and two decapeptides (identical to the repeating units comprising the mussel's adhesive protein). The proteins tested were as follows: bovine pancreatic ribonuclease A (RNase), lysozyme, IgG, avidin, and streptavidin. The oxidized peptides and proteins were all shown to incorporate oxygen atoms and undergo polymerization and cross-linking, depending on the availability of nucleophiles, mostly lysine amino groups of proteins. All the peptides and the noninteracting proteins such as RNase and lysozyme underwent homopolymerization upon Fremy's salt oxidation. When Fremy's salt oxidaized PEG-BT was mixed with the above proteins, it did not react with any of these proteins because PEG-BT underwent fast self-polymerization. Conversely, streptavidin or avidin cross-linked with PEG-BT after preincubation, thus showing that biorecognition is a prerequisite for cross-linking. Polymerization and cross-linking also occurred, following Fremy's salt oxidation of interacting proteins such as avidin and strepavidin with biotinyilated lysozyme or biotinylated RNase. This indicates that only proteins in very close proximity readily cross-link and polymerize via tyrosine residues. Attempts to convert DOPA-quinone to DOPA by reduction with sodium dithionite (Na2S2O4), was successful as far as small peptides were used. Fremy's salt oxidation can serve as an easy and useful tool to polymerize and cross-link proteins, for fabrication of biomaterials and to study protein-protein interactions.

We have previously shown that superoxide radical anion (O2.-) reacts with hydroethidine (HE) to form a product that is distinctly different from ethidium (E+) (Zhao et al., Free Radic. Biol. Med. 34:1359; 2003). The structure of this product was recently determined as the 2-hydroxyethidium cation (2-OH-E+) (Zhao et al., Proc. Natl. Acad. Sci. USA 102:5727; 2005). In this study, using HPLC and mass spectrometry techniques, we show that 2-OH-E+ is formed from the reaction between HE and nitrosodisulfonate radical dianion (NDS) or Fremy's salt. The reaction kinetics and mechanism were determined using steady-state and time-resolved optical and EPR techniques. Within the first 50 ms, an intermediate was detected. Another intermediate absorbing strongly at 460 nm and weakly at 670 nm was detected within a second. The structure of this species was assigned to an imino quinone derivative of HE. The stoichiometry of the reaction indicates that two molecules of NDS were needed to oxidize a molecule of HE. We postulate that the first step of the reaction involves the hydrogen atom abstraction from HE to form an aminyl radical that reacts with another molecule of NDS to form an adduct that decomposes to an imino quinone derivative of HE. A similar mechanism has been proposed for the reaction between HE and O2.-. The reaction between HE and the Fremy's salt should provide a facile route for the synthesis of 2-OH-E+, a diagnostic marker product of the HE/O2.- reaction.

Emissive EPR spectral lines were observed in experiments dedicated to investigating the efficiency of ascorbic acid in reducing Fremy's salt. The emission was detected by CW spectroscopy and was exceptionally long lasting, being observed as long as 20 minutes. Fremy's salt emission lines were observed at the end of the redox reaction. The Fremy's salt absorption signal was totally quenched, and was replaced by an emission signal. This feature was observed under different experimental conditions. The inversion proceeded simultaneously for the three lines, which keep their relative intensities and hyperfine separation. The emission signal was also detected together with the normal absorption signal of ascorbyl free radical. No emission spectra were observed by using other nitroxides, or by using as reducing agent 1,4-dithio-DL-threitol instead of ascorbic acid. The observed spin polarization is accounted for on the basis of a Radical Pair Mechanism (RPM). The amount of polarization is related to the diffusion constant D, which decreases with increasing viscosity. By adding glycerol to the solution, enhanced polarisation was indeed observed, as expected, which confirms the proposed RPM polarisation mechanism. We report here for the first time, to our knowledge, the phenomenon of long-lasting emissive EPR lines.

From a synthetic perspective, a quinone’s substitution pattern dictates the difficulty surrounding its construction. A lack of symmetry, or an adjoining ring, often increases the synthetic challenge. Para -quinones and ortho -quinones are most often accessed by oxidation of the corresponding hydroquinone or catechol. This work will discuss many of the oxidants that affect this simple transformation, and highlight methods to access their precursors from less oxidized substrates. Throughout this chapter, the authors aim to stimulate the reader's imagination with a toolbox of methods organized by the number of oxidations and the type of synthetic transformation. The authors intend to provide old and new strategic methods for those faced with creating challenging quinone products.

Hydrophobic host–guest complexes of some water soluble stable free radicals – potassium nitrosodisulfonate (Fremy's salt), 2-$p$-phenylsulphonic acid-2-phenyl-1-picrylhydrazyl (KSO3-DPPH.) and 2,2-p-phenylsulphonic acid-1-picrylhydrazyl ((KSO3)2DPPH.), both of them as potassium salts, with 18-C-6, B18-C-6 and DB18-C-6 crown ethers, were obtained and characterised by elemental analysis, IR, ESR and UV-Vis.

Oxidation of an indoline with Fremy's salt (potassium nitrosodisulfonate) led to the formation of an unstable intermediate which isomerized to the desired 5-hydroxyindole upon standing. This intermediate has been isolated and characterized as an iminoquinone derivative. Identification of this intermediate has allowed us to propose a mechanism for the Fremy's salt mediated oxidation of indolines to 5-hydroxyindoles.

Efavirenz (EFV) is a non-nucleoside reverse transcriptase inhibitor administered as first line treatment against HIV-1. The major drawbacks of EFV therapy are neurotoxicity and hepatotoxicity, which may result from bioactivation to reactive metabolites capable of reacting with bionucleophiles. We investigated the in vitro oxidation of the phenolic EFV metabolites, 7-hydroxy-efavirenz (7-OH-EFV) and 8-hydroxy-efavirenz (8-OH-EFV), with Fremy's salt. A quinoline derivative, 6-chloro-2-cyclopropyl-4-(trifluoromethyl)quinolin-7-ol, presumably stemming from a radical rearrangement, was selectively obtained from 7-OH-EFV in 10% yield. In contrast, when subjected to the same oxidation conditions, 8-OH-EFV was considerably more prone to oxidative degradation and yielded multiple products. Among these, a quinone–imine derivative was tentatively identified upon LC–ESI–MS/MS analysis of the reaction mixture. These observations demonstrate a remarkable difference in the reactivities of the two phenolic EFV metabolites under oxidative conditions. Moreover, taking into consideration the toxicological significance of quinone–imine derivatives, these findings may explain earlier reports that 8-OH-EFV is a more potent toxicant than 7-OH-EFV in model test systems.

The hyperfine coupling constant,A0, of peroxylamine disulfonate in aqueous solutions depends upon the temperature and the concentration of added K2CO3buffer. Near room temperature,A0varies from 13.036 to 13.201 G for K2CO3concentrations varying from zero to near saturation. For samples prepared in 50.0 mMK2CO3, the results are independent of Fremy's salt concentration in the range 0.005–2.8 mMas follows:A0(T) = 12.978 + 0.00311 T, where the hyperfine coupling constant at temperatureT, A0(T), is given in gauss when the temperature is given in °C. This temperature dependence is an order of magnitude larger and of opposite sign than that found for doxylstearic acid esters and is proposed as the basis of an internal thermometer for EPR spectroscopy. The variation ofA0with solvent polarity is found to be a factor of about 27–30 less than for the neutral radicals di-tert-butyl nitroxide and doxylstearic acid esters. It is shown that microwave heating of aqueous samples at high microwave powers can be monitored by measuringA0while conventional thermometry can lead to significant errors even for a thermocouple immersed within the sample just above the microwave cavity. The value ofA0(25°C) = 13.056 ± 0.002 G is significantly different than previously used standards; therefore, some previous data may require recalibration. Correction procedures for nonlinearities in the field sweep are presented.

The effectiveness of dynamic nuclear polarization (DNP) as a tool to enhance the sensitivity of liquid state NMR critically depends on the choice of the optimal polarizer molecule. In this study the performance of (15)N labelled Frémy's salt as a polarizing agent in Overhauser DNP is investigated in detail at X-band (0.35 T, 9.7 GHz EPR, 15 MHz (1)H NMR) and compared to that of TEMPONE-D,(15)N employed in previous studies. Both radicals provide similar maximum enhancements of the solvent water protons under similar conditions but a different saturation behaviour. The factors determining the enhancement and effective saturation were measured independently by EPR, ELDOR and NMRD and are shown to fulfil the Overhauser equation. In particular, following the theory of EPR saturation we provide analytical solutions for the dependence of the enhancement on the microwave field strength in terms of saturation transfer between two coupled hyperfine lines undergoing spin exchange. The negative charge of the radical in Frémy's salt solutions can explain the peculiar properties of this polarizing agent and indicates different suitable application areas for the two types of nitroxide radicals.

Nevirapine (NVP) is a non-nucleoside reverse transcriptase inhibitor used against the human immunodeficiency virus type-1 (HIV-1), mostly to prevent mother-to-child HIV transmission in developing countries [1]. One of the limitations of NVP use is severe hepatotoxicity [2], which raises concerns about its chronic administration, particularly in the perinatal and pediatric settings. The reasons for the adverse effects of NVP administration are currently not clear, although there is increasing evidence that metabolic activation to reactive electrophiles capable of reacting with bionucleophiles is likely to be involved in the initiation of toxic responses. Phase I NVP metabolism involves oxidation of the 4-methyl substituent to 12-hydroxy-NVP , and the formation of phenolic derivatives that are conceivably capable of undergoing further metabolic oxidation to electrophilic quinoid species prone to react with bionucleophiles. The covalent adducts thus formed might be at the genesis of toxic responses. As part of a program aimed at evaluating the possible contribution of quinoid derivatives of NVP Phase I phenolic metabolites to the toxic responses elicited by the parent drug, we have investigated the oxidation of 2-hydroxy-NVP with dipotassium nitroso-disulfonate (Fremy\'s salt), mimicking the one-electron oxidation involved in enzyme-mediated metabolic oxidations. We report herein the isolation and full structural characterization (by NMR, MS and X-ray diffraction) of a 1H-pyrrole-2,5-dione derivative as a major product, stemming from an unusual pyridine ring contraction. References: [1] Lockman et al., N. Engl. J. Med. 2007, 356, 135-147. [2] Pollard et al., Clin. Ther 1998, 20, 1071–1092. Acknowledgments: We thank the Portuguese NMR Network (IST-UTL Center) and the Portuguese MS Network (IST-UTL Center) for providing access to the facilities. This work was supported in part by research

The reaction of anilines 1, 3, and 5 with 4.4 equivalents of Fremy's salt affords ortho-quinones in good yields via a one-pot five-step sequence.

By Sephadex LH-20 gel chromatography of an extract from Gingko biloba leaves, polymeric proanthocyanidins were eluted after the fractions of flavonol glycosides and biflavone glycosides. A purified proanthocyanidin polymer accounted for 86.6% of the total proanthocyanidins, and for 37.7% of the total antioxidant activity of this leaf extract. For structure elucidation, the polymer was submitted to acidic depolymerization in the presence of phloroglucinol. The structures of the resulting flavan-3-ols and phloroglucinol adducts were determined on the basis of 1D-and reverse 2D-NMR (HSQC, HMBC) spectra of their peracetylated derivatives, MALDI-TOF-MS and CD-spectroscopy. The observations resulting from the degradation with phloroglucinol were confirmed by 13C-NMR spectroscopy of the polymer. The mean molecular weight of the polymeric fraction was estimated to be 9–10 flavan-3-ol-units.

The aim of this study was to explore the antiradical activity of Met I (an active metabolite of erdosteine) containing a pharmacologically active sulphydryl group, by means of electron paramagnetic resonance (EPR) spectroscopy which has not previously been used to characterize the antiradical activity of Met I. The effects of concentrations of 20, 10, 5, 2.5, 1.25 and 0.625 µg/ml of Met I were tested against: (a) the Fenton reaction model system with EPR detection of HO·; (b) the KO2-crown ether system with EPR detection of O2–·; (c) the EPR assay based on the reduction of the Tempol radical, and (d) the EPR assay based on the reduction of Fremy’s salt radical. Our findings show that the intensity of 4 different free radicals was significantly reduced in the presence of Met I, thus indicating the presence of a termination reaction between the free radicals and Met I.

The reaction between Fremy's salt and α-tocopherol (VE), ascorbic acid (VC) and its lipophilic derivatives ascorbyl-6-caprylate (VC-8), 6-laurate (VC-12) and 6-palmitate (VC-16) were studied by stopped-flow ESR spectroscopy in cetyl trimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) micelles, as a model reaction of these antioxidants with alkyl peroxy radicals in biological systems. The second order rate constants for the reaction of Fremy's salt with VE in CTAB and SDS micelles were found to be 7.9 × 103 and 2.2 M−1 s−1, respectively, with as high as a 3600-fold variation. Rate constants for VC, VC-8, VC-12 and VC-16 are 4.3, 35, 53 and 56 × 103 M−1 s−1 and 3.3, 2.7, 1.2 and 0.86 × 103 M−1 s−1 in CTAB and SDS micelles, respectively. The results demonstrate remarkable effects of the charge type of the micelles and the side-chain of the antioxidants on the antioxidation reactivity in the micelles. It reveals that the inter-micellar diffusion may be the rate-limiting step for antioxidation carried out in micelles.

The absorption spectrum of Fremy's salt, K 2 [ON(SO 3 ) 2 ] in water shows two bands at λ max = 545 and 248 nm which are assigned to σ b → π b and π b → σ * transitions, respectively. The photolysis of Fremy's salt leads to a decomposition. It is assumed that a homolytic cleavage of a N&-S bond is the primary photochemical step.