Oxidative synthesis of ortho-quinones from hydroxy-PAHs by stabilized formulation of 2-iodoxybenzoic acid (SIBX)

Polycyclic aromatic phenols (PAPs or hydroxy-PAHs) are conveniently converted into their corresponding ortho-quinones using commercially available stabilized iodoxybenzoic acid (SIBX). SIBX provides a safer and commercially available alternative to IBX and displays the same selectivity with comparable or better yields in the oxidative dearomatization of phenols to ortho-quinone, including examples where formation of para-quinones is feasible. This ortho-selectivity from all positions of a hydroxy-group allowed for simple synthesis of the prerequisite hydroxy-PAHs by either photochemical cyclization of stilbenes or Pt-catalyzed cycloisomerization. The later synthesis involved a four-step sequence where suitably substituted biphenyls were prepared by Suzuki-Miyaura cross-coupling, followed by the Corey–Fuchs protocol and cycloisomerization by a catalytic amount of PtCl2. 2- and 4-methylphenanthene were also prepared for the first time using this method.publishedVersio

Total synthesis of tubastrine and 3-dehydroxy tubastrine by microwave-assisted cross-coupling reactions

The first syntheses of tubastrine and 3-dehydroxy tubastrine are described. The target compounds were prepared in four consecutive steps from commercially available starting materials. The central scaffold was formed by a microwave-assisted C–N cross-coupling reaction between 1,3-bis(tert-butoxycarbonyl)-guanidine and (E)-((4-(2-iodovinyl)-1,2-phenylene)bis(oxy))bis(tert-butyldimethylsilane) and (E)-tert-butyl(4-(2-iodovinyl)phenoxy)–dimethylsilane, respectively. The aryl vinyl iodides were obtained by a Hunsdiecker–Borodin-type reaction of aryl acrylic acids, which were easily available from trans-caffeic acid or trans-p-coumaric acid.acceptedVersio

Substituted Two- To Five-Ring Polycyclic Aromatic Compounds Are Potent Agonists of Atlantic Cod (Gadus morhua) Aryl Hydrocarbon Receptors Ahr1a and Ahr2a

Polycyclic aromatic hydrocarbons (PAHs) are among the most toxic and bioavailable components found in petroleum and represent a high risk to aquatic organisms. The aryl hydrocarbon receptor (Ahr) is a ligand-activated transcription factor that mediates the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other planar aromatic hydrocarbons, including certain PAHs. Ahr acts as a xenosensor and modulates the transcription of biotransformation genes in vertebrates, such as cytochrome P450 1A (cyp1a). Atlantic cod (Gadus morhua) possesses two Ahr proteins, Ahr1a and Ahr2a, which diverge in their primary structure, tissue-specific expression, ligand affinities, and transactivation profiles. Here, a luciferase reporter gene assay was used to assess the sensitivity of the Atlantic cod Ahrs to 31 polycyclic aromatic compounds (PACs), including two- to five-ring native PAHs, a sulfur-containing heterocyclic PAC, as well as several methylated, methoxylated, and hydroxylated congeners. Notably, most parent compounds, including naphthalene, phenanthrene, and partly, chrysene, did not act as agonists for the Ahrs, while hydroxylated and/or alkylated versions of these PAHs were potent agonists. Importantly, the greater potencies of substituted PAH derivatives and their ubiquitous occurrence in nature emphasize that more knowledge on the toxicity of these environmentally and toxicologically relevant compounds is imperative.publishedVersio

Regiospecific Photochemical Synthesis of Methylchrysenes

Methylated polycyclic aromatic hydrocarbons (PAHs) are suspected to be some of the toxic compounds in crude oil towards marine life and are needed as single compounds for environmental studies. 1-, 3- and 6-methylchrysene (3a,b,c) were prepared as single isomers by photochemical cyclization of the corresponding stilbenoids in the Mallory reaction using stoichiometric amounts of iodine in 82-88% yield. 2-methylchrysene (3d) was prepared by photochemical cyclization where the regioselectivity was controlled by elimination of an ortho-methoxy group under acidic oxygen free conditions in 72% yield. These conditions failed to form 4-methylchrysene from the corresponding stilbenoid. All stilbenoids were made from a common naphthyl Wittig salt and suitably substituted benzaldehydes. We have also demonstrated that methylchrysenes can be oxidized to the corresponding chrysenecarboxylic acids by KMnO4 in modest yields.publishedVersio

Relationships between Isomeric Metabolism and Regioselective Toxicity of Hydroxychrysenes in Embryos of Japanese Medaka (Oryzias latipes)

Oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) are ubiquitous contaminants that can be formed through oxidation of parent PAHs. Our previous studies found 2-hydroxychrysene (2-OHCHR) to be significantly more toxic to Japanese medaka embryos than 6-hydroxychrysene (6-OHCHR), an example of regioselective toxicity. We have also previously identified a sensitive developmental window to 2-OHCHR toxicity that closely coincided with liver development, leading us to hypothesize that differences in metabolism may play a role in the regioselective toxicity. To test this hypothesis, Japanese medaka embryos were treated with each isomer for 24 h during liver development (52–76 hpf). Although 6-OHCHR was absorbed 97.2 ± 0.18% faster than 2-OHCHR, it was eliminated 57.7 ± 0.36% faster as a glucuronide conjugate. Pretreatment with cytochrome P450 inhibitor, ketoconazole, reduced anemia by 96.8 ± 3.19% and mortality by 95.2 ± 4.76% in 2-OHCHR treatments. Formation of chrysene-1,2-diol (1,2-CAT) was also reduced by 64.4 ± 2.14% by ketoconazole pretreatment. While pretreatment with UDP-glucuronosyltransferase inhibitor, nilotinib, reduced glucuronidation of 2-OHCHR by 52.4 ± 2.55% and of 6-OHCHR by 63.7 ± 3.19%, it did not alter toxicity for either compound. These results indicate that CYP-mediated activation, potentially to 1,2-CAT, may explain the isomeric differences in developmental toxicity of 2-OHCHR.publishedVersio

Synthesis of Phenacene−Helicene Hybrids by Directed Remote Metalation

Polycyclic aromatic hydrocarbons (PAHs) with six and seven rings were synthesized via directed metalation and cross-coupling of chrysenyl N,N-diethyl carboxamides with o-tolyl and methylnaphthalenyl derivatives. In the presence of competing ortho sites, the site selectivity in iodination of chrysenyl amides by directed ortho metalation (DoM) was influenced by the lithium base. The catalyst ligand bite angle was presumably important in the cross-coupling of sterically hindered bulky PAHs. Subsequent directed remote metalation of biaryls under standard conditions and at elevated temperatures afforded various fused six- and seven-ring PAHs, all in good yields and with fluorescent properties.publishedVersio

Regiospesific synthesis of dimethylphenanthrenes

The dimethylated phenanthrenes 2,3-dimethylphenanthrene (4a), 2,7-dimethylphenanthrene (4b), 2,6-dimethylphenanthrene (4c) and 1,7-dimethylphenanthrene (4d) have been prepared in gram-quantities by a short sequence of directed ortho metalation (DoM) of N,N-diethylbenzamides followed by Suzuki–Miyaura cross-coupling reaction and directed remote metalation (DreM) to form 9-phenanthrols. The final phenanthrenes were obtained through protection/deprotection as triflates

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The dimethylated phenanthrenes 2,3-dimethylphenanthrene (4a), 2,7-dimethylphenanthrene (4b), 2,6-dimethylphenanthrene (4c) and 1,7-dimethylphenanthrene (4d) have been prepared in gram-quantities by a short sequence of directed ortho metalation (DoM) of N,N-diethylbenzamides followed by Suzuki–Miyaura cross-coupling reaction and directed remote metalation (DreM) to form 9-phenanthrols. The final phenanthrenes were obtained through protection/deprotection as triflates

Optimization of acid catalyzed transesterification of jatropha and rapeseed oil with 1-butanol

The acid catalyzed transesterification of rapeseed and jatropha oil with 1-butanol was studied by varying temperature, reaction time, butanol/triglyceride ratio and the amount of sulfuric acid. A full factorial design supporting non-linear regression models was used to combine the four design parameters. The measured yield, viscosity and acid number were quantitatively described by PLS-regression as functions of the four design variables for each vegetable oil. Product purity was controlled by 1H NMR. The PLS-regression model was used for optimizing the three response parameters. High (100%) yield is easily obtained within the experimental domain, whereas viscosity and acid number, with different optimum conditions, have to be compromised in order to keep both as low as possible. While rapeseed reached optimum within the experimental limits, the results indicate that for jatropha further reduction in viscosity and acid number requires increasing temperature and/or the butanol/triglyceride ratio beyond the upper limits of the design.acceptedVersio

Enantioselective synthesis of (-)-(1R,2R)-1,2-dihydrochrysene-1,2-diol

A general chiral building block containing the 1R,2R-trans-diol moiety was constructed utilizing the stereoselective Shi-epoxidation reaction on a tetralone scaffold assembled by a Negishi cross-coupling on N,N-diethylbenzamide. Further elaboration of this chiral building block into polycyclic aromatic compounds was demonstrated with the total synthesis of the precursor for the most carcinogenic metabolite of chrysene, (−)-(1R,2R)-1,2-dihydrochrysene-1,2-diol in 87% ee.acceptedVersio