Search

Employing pure water, the ultimate green source of hydrogen donor to initiate chemical reactions that involve a hydrogen atom transfer (HAT) step is fascinating but challenging due to its large H−O bond dissociation energy (BDEH‐O=5.1 eV). Many approaches have been explored to stimulate water for hydrogenative reactions, but the efficiency and productivity still require significant enhancement. Here, we show that the surface hydroxylated graphitic carbon nitride (gCN−OH) only requires 2.25 eV to activate H−O bonds in water, enabling abstraction of hydrogen atoms via dehydrogenation of pure water into hydrogen peroxide under visible light irradiation. The gCN−OH presents a stable catalytic performance for hydrogenative N−N coupling, pinacol‐type coupling and dehalogenative C−C coupling, all with high yield and efficiency, even under solar radiation, featuring extensive impacts in using renewable energy for a cleaner process in dye, electronic, and pharmaceutical industries. [ABSTRACT FROM AUTHOR]

Employing pure water, the ultimate green source of hydrogen donor to initiate chemical reactions that involve a hydrogen atom transfer (HAT) step is fascinating but challenging due to its large H−O bond dissociation energy (BDEH‐O=5.1 eV). Many approaches have been explored to stimulate water for hydrogenative reactions, but the efficiency and productivity still require significant enhancement. Here, we show that the surface hydroxylated graphitic carbon nitride (gCN−OH) only requires 2.25 eV to activate H−O bonds in water, enabling abstraction of hydrogen atoms via dehydrogenation of pure water into hydrogen peroxide under visible light irradiation. The gCN−OH presents a stable catalytic performance for hydrogenative N−N coupling, pinacol‐type coupling and dehalogenative C−C coupling, all with high yield and efficiency, even under solar radiation, featuring extensive impacts in using renewable energy for a cleaner process in dye, electronic, and pharmaceutical industries. [ABSTRACT FROM AUTHOR]

Non‐heme iron/α‐ketoglutarate dependent halogenases acting on freestanding substrates catalyze the regio‐ and stereoselective halogenation of inactivated C(sp3)‐H bonds. Yet, with only a handful of these halogenases characterized, the biosynthetic potential of enzymatic radical halogenation remains limited. Herein, we describe the remodeling of L‐proline cis‐4‐hydroxylase from Sinorhizobium meliloti into a halogenase by introduction of a single point mutation (D108G) into the enzyme's active site. The re‐programmed halogenase displays a striking regio‐divergent reaction chemistry: While halogenation of L‐proline exclusively occurs at the C3‐position, the retained hydroxylation activity leads to derivatization at the C4‐position, corresponding to the regioselectivity of the wildtype enzyme. By employing several rounds of directed evolution, an optimized halogenase variant with 98‐fold improved apparent kcat/Km for chlorination of L‐proline compared to the parental enzyme SmP4H (D108G) was identified. The development and optimization of this novel halogenation biocatalyst highlights the possibility to rationally harness the chemical versatility of non‐heme Fe/αKG dependent dioxygenases for C−H functionalization. [ABSTRACT FROM AUTHOR]

An efficient, reusable and stable binaphthyl stabilized Pd‐nanoparticles (Pd‐BNP) catalyzed the direct ortho‐C−H hydroxylation of acetophenone oxime ethers under neutral and phosphine ligand‐free condition has been developed. A readily available, economic, safe and greener oxidant oxone has been used in this direct ortho‐hydroxylation. The scope of the reaction has been studied with various acetophenone oxime ethers including electron rich to electron deficient system and the reaction afforded only mono hydroxylated products in a highly regioselective manner. Several control experiment results confirmed that the oxone is the hydroxyl source. The Pd‐BNP catalyst has been reused up to five times. The heterogeneous test confirmed that the reaction is catalyzed by the heterogeneous Pd‐BNP catalyst. [ABSTRACT FROM AUTHOR]

2‐Quinolylzincates were efficiently produced from the regioselective metalation reactions of quinoline with various organozincates as key intermediates. The four different types of title reactions of these intermediates under the presented reaction conditions allowed for the facile formation of the corresponding C‐2 functionalized quinolines, which are not successfully accessed through typical zincation methods. The diverse C‐2 functionalizations of quinoline are successfully achieved via 2‐quinolylzincate intermediates by the four different types of title reactions. [ABSTRACT FROM AUTHOR]

Abstract: A route for directional conversion of bio‐oil into phenol by means of coupling the catalytic cracking of the bio‐oil with the hydroxylation of the bio‐oil‐based benzene‐rich aromatics is proposed. High selectivity for phenol in the resulting organic liquid was achieved, with an almost complete conversion of the bio‐oil. Co‐cracking of the bio‐oil with methanol over a Zn‐modified zeolite significantly enhanced the yields of aromatics and decreased the deactivation of the catalyst during the catalytic cracking of the bio‐oil. The phenol yield depended on the metal oxide catalysts, the temperature, and the reaction time during hydroxylation of the benzene‐rich aromatics. The reaction pathway of converting bio‐oil into phenol was elucidated based on the products identified and the characterization of the catalysts. [ABSTRACT FROM AUTHOR]

Abstract: A novel hydroperoxoiron(III) species [FeIII(OOH)(MeCN)(PyNMe3)]2+ (3) has been generated by reaction of its ferrous precursor [FeII(CF3SO3)2(PyNMe3)] (1) with hydrogen peroxide at low temperatures. This species has been characterized by several spectroscopic techniques and cryospray mass spectrometry. Similar to most of the previously described low‐spin hydroperoxoiron(III) compounds, 3 behaves as a sluggish oxidant and it is not kinetically competent for breaking weak C−H bonds. However, triflic acid addition to 3 causes its transformation into a much more reactive compound towards organic substrates that is capable of oxidizing unactivated C−H bonds with high stereospecificity. Stopped‐flow kinetic analyses and theoretical studies provide a rationale for the observed chemistry, a triflic‐acid‐assisted heterolytic cleavage of the O−O bond to form a putative strongly oxidizing oxoiron(V) species. This mechanism is reminiscent to that observed in heme systems, where protonation of the hydroperoxo intermediate leads to the formation of the high‐valent [(Porph.)FeIV(O)] (Compound I). [ABSTRACT FROM AUTHOR]

Abstract: Aliphatic C−H oxidation is the most straightforward approach to functionalize hydrocarbon skeletons. The main challenge of this reaction is the control of site selectivity, given the multiple C−H bonds present in any organic molecule. Natural enzymes elegantly solve this problem through the interplay of different interactions that geometrically orient the substrate to expose a single C−H bond to the active unit, thus overriding intrinsic reactivity patterns. A combination of molecular catalysts and supramolecular receptors can be a promising way to replicate such control. This strategy indeed unlocks hydroxylation of C−H bonds that are not accessible with conventional methodologies, in which the selectivity is dictated by the geometry of the substrate–receptor adduct. Herein, we review the reports of recognition‐driven C−H oxidation reactions and highlight the key design principles that inspired these works. [ABSTRACT FROM AUTHOR]

A dicopper(II) complex, stabilized by the bis(tpa) ligand 1,2-bis[2-[bis(2-pyridylmethyl)aminomethyl]-6-pyridyl]ethane (6-hpa), [Cu2(μ-OH)(6-hpa)]3+, was synthesized and structurally characterized. This complex catalyzed selective hydroxylation of benzene to phenol using H2O2, thus attaining large turnover numbers (TONs) and high H2O2 efficiency. The TON after 40 hours for the phenol production exceeded 12000 in MeCN at 50 °C under N2, the highest value reported for benzene hydroxylation with H2O2 catalyzed by homogeneous complexes. At 22 % benzene conversion, phenol (95.2 %) and p-benzoquinone (4.8 %) were produced. The mechanism of H2O2 activation and benzene hydroxylation is proposed. [ABSTRACT FROM AUTHOR]

A dicopper(II) complex, stabilized by the bis(tpa) ligand 1,2-bis[2-[bis(2-pyridylmethyl)aminomethyl]-6-pyridyl]ethane (6-hpa), [Cu2(μ-OH)(6-hpa)]3+, was synthesized and structurally characterized. This complex catalyzed selective hydroxylation of benzene to phenol using H2O2, thus attaining large turnover numbers (TONs) and high H2O2 efficiency. The TON after 40 hours for the phenol production exceeded 12000 in MeCN at 50 °C under N2, the highest value reported for benzene hydroxylation with H2O2 catalyzed by homogeneous complexes. At 22 % benzene conversion, phenol (95.2 %) and p-benzoquinone (4.8 %) were produced. The mechanism of H2O2 activation and benzene hydroxylation is proposed. [ABSTRACT FROM AUTHOR]

A highly efficient and atom-economical route for the synthesis of substituted β-arylethyl ketones was developed by using cheap phosphomolybdic acid (H3PMo12O40) as catalyst and non-volatile propylene carbonate (PC) as green solvent via the carbohydroxylation of terminal alkynes with benzylic alcohols under mild conditions. Various functional groups on the benzylic alcohols and terminal alkynes were tolerated, giving the corresponding substituted β-arylethyl ketones as products in good to excellent yields (up to 95%). It is worth noting that a turnover number (TON) of up to 520 was achieved in the protocol. The mechanism investigation showed that PC might stabilize the heteropoly anion and the carbocation intermediate thus facilitating the carbohydroxylation reaction. [ABSTRACT FROM AUTHOR]

We herein report the first total synthesis of the dibenzocycloheptanoide (±)-dihydroisosubamol. The key step includes a recently developed gold-catalysed hydroarylation reaction for the construction of the dibenzocycloheptene motif. Additional steps are a Suzuki-Miyaura cross coupling, a palladium-catalysed hydroxylation and an allylic oxidation. To access the saturated seven-membered ring system an iridium-catalysed hydrogenation proved to be successful. [ABSTRACT FROM AUTHOR]

Palladium-catalyzed oxidative homocoupling and hydroxylation of 3-arylbenzo[ d]isoxazoles have been developed via direct C( sp2)−H bond activation using benzoisoxazoles as a new directing group. The protocols offer a divergent approach to functionalized, synthetically useful benzoisoxazoles in good yields. Critically, 1-iodo-4-methoxybenzene functions as an oxidant to mediate the dehydrogenative homocoupling and minimize the cross-coupling. A dual-core dimeric palladacycle intermediate is confirmed by X-ray crystallography, and serves as an active catalytic species in the catalytic cycles. [ABSTRACT FROM AUTHOR]

A natural quinine-catalyzed, efficient and practical asymmetric α-hydroxylation of 4-substituted pyrazolones has been developed, delivering a broad spectrum of pyrazolones bearing an oxygen-attached carbon stereocenter at C-4 in high yields and excellent enantioselectivities. The broad substrate scope, ready availability of the catalyst, ease of operation, and valuable transformation of the product highlight the practical utility of this process. [ABSTRACT FROM AUTHOR]

Bacterial cytochrome P450s (P450s), which catalyze regio- and stereoselective oxidations of hydrocarbons with high turnover rates, are attractive biocatalysts for fine chemical production. Enzyme immobilization is needed for cost-effective industrial manufacturing. However, immobilization of P450s is difficult because electron-transfer proteins are involved in catalysis and anchoring these can prevent them from functioning as shuttle molecules for carrying electrons. We studied a heterotrimeric protein-mediated co-immobilization of a bacterial P450, and its electron-transfer protein and reductase. Fusion with subunits of a heterotrimeric Sulfolobus solfataricus proliferating cell nuclear antigen (PCNA) enabled immobilization of the three proteins on a solid support. The co-immobilized enzymes catalyzed monooxygenation because the electron-transfer protein fused to PCNA via a single peptide linker retained its electron-transport function. [ABSTRACT FROM AUTHOR]

Hydroxylation of mesitylene by a nonheme manganese(IV)-oxo complex, [(N4Py)MnIV(O)]2+ ( 1), proceeds via one-step hydrogen-atom transfer (HAT) with a large deuterium kinetic isotope effect (KIE) of 3.2(3) at 293 K. In contrast, the same reaction with a triflic acid-bound manganese(IV)-oxo complex, [(N4Py)MnIV(O)]2+-(HOTf)2 ( 2), proceeds via electron transfer (ET) with no KIE at 293 K. Interestingly, when the reaction temperature is lowered to less than 263 K in the reaction of 2, however, the mechanism changes again from ET to HAT with a large KIE of 2.9(3). Such a switchover of the reaction mechanism from ET to HAT is shown to occur by changing only temperature in the boundary region between ET and HAT pathways when the driving force of ET from toluene derivatives to 2 is around −0.5 eV. The present results provide a valuable and general guide to predict a switchover of the reaction mechanism from ET to the others, including HAT. [ABSTRACT FROM AUTHOR]

Two independent synthetic approaches were evaluated for the final phase of the asymmetric total synthesis of propindilactone G ( 1). The key steps that led to the completion of the asymmetric total synthesis included: 1) an intermolecular oxidative heterocoupling reaction of enolsilanes to link the core structure to the side chain; 2) an intermolecular Wittig reaction for the formation of the α,β,γ,δ-unsaturated ester; and 3) a regio- and stereoselective OsO4-catalyzed dihydroxylation of an α,β,γ,δ-unsaturated enone, followed by an intramolecular lactonization reaction to afford the final product. These reactions enabled the synthesis of (+)-propindilactone G in only 20 steps. As a consequence of our synthetic studies, the structure of (+)-propindilactone G has been revised. Furthermore, the direct oxidative coupling strategy for ligation of the core of propindilactone G with its side chain may find application in the syntheses of other natural products and complex molecules. [ABSTRACT FROM AUTHOR]

Influences of high speed jet ( HSJ) at different pressures (0, 80, 160, 250 MPa) on digestibility and hydroxypropylation of rice starch were evaluated. HSJ treatment increased the content of rapidly digestible starch and slowly digestible starch and decreased the content of resistant starch with increasing of the treatment pressure in native starch. The degree and the reaction efficiency of hydroxypropylation of rice starch increased with an increase in treatment pressure. Scanning electron microscopy and X-ray diffraction analysis showed that both the crystalline structure and the overall granular structure were partially destroyed. Meanwhile, HSJ treatment led to degradation of starch molecules. The results suggested that the changes of starch structure resulted in decreasing gelatinisation enthalpy of rice starch and might be response for the changes of reactivity and its digestibility to some extent. [ABSTRACT FROM AUTHOR]

An enzymatic approach has been successfully utilized in the total synthesis of (-)-malyngolide and its C(5)-epimer. The required configuration was established by an enzymatic kinetic resolution and Sharpless asymmetric dihydroxylation. [ABSTRACT FROM AUTHOR]

The cytochromes P450 are hemoproteins that catalyze a range of oxidative C−H functionalization reactions, including aliphatic and aromatic hydroxylation. These transformations are important in a range of biological contexts, including biosynthesis and xenobiotic biodegradation. Much work has been carried out on the mechanism of aliphatic hydroxylation, implicating hydrogen atom abstraction, but aromatic hydroxylation is postulated to proceed differently. One mechanism invokes as the key intermediate an arene oxide (and/or its oxepin tautomer). Conclusive isolation of this intermediate has remained elusive and, currently, direct formation of phenols from a Meisenheimer intermediate is believed to be favored. We report here the identification of a P450 [P450cam (CYP101A1) and P450cin (CYP176A1)]-generated arene oxide as a product of in vitro oxidation of tert-butylbenzene. Computations (CBS-QB3) predict that the arene oxide and oxepin have similar stabilities to other arene oxides/oxepins implicated (but not detected) in P450-mediated transformations, suggesting that arene oxides can be unstable terminal products of P450-catalyzed aromatic oxidation that can explain the origin of some observed metabolites. [ABSTRACT FROM AUTHOR]

Peroxygenases catalyze a broad range of (stereo)- selective oxyfunctionalization reactions. However, to access their full catalytic potential, peroxygenases need a balanced provision of hydrogen peroxide to achieve high catalytic activity while minimizing oxidative inactivation. Herein, we report an enzymatic cascade process that employs methanol as a sacrificial electron donor for the reductive activation of molecular oxygen. Full oxidation of methanol is achieved, generating three equivalents of hydrogen peroxide that can be used completely for the stereoselective hydroxylation of ethylbenzene as a model reaction. Overall we propose and demonstrate an atom-efficient and easily applicable alternative to established hydrogen peroxide generation methods, which enables the efficient use of peroxygenases for oxyfunctionalization reactions. [ABSTRACT FROM AUTHOR]

CYP106A1 from Bacillus megaterium DSM319 was recently shown to catalyze steroid and terpene hydroxylations. Besides producing hydroxylated steroid metabolites at positions 6β, 7β, 9α and 15β, the enzyme displayed previously unknown 11-oxidase activity towards 11β-hydroxysteroids. Novel examples for 11-oxidation were identified and confirmed by 1 H and 13 C NMR for prednisolone, dexamethasone and 11β-hydroxyandrostenedione. However, only 11β-hydroxyandrostenedione formed a single 11-keto product. The latter reaction was chosen to investigate the kinetic solvent isotope effect on the steady-state turnover of the CYP106A1-mediated 11-oxidation. Our results reveal a large inverse kinetic isotope effect (∼0.44) suggesting the involvement of the ferric peroxoanion as a reactive intermediate. [ABSTRACT FROM AUTHOR]

Coupling Reaction, Heterogeneous Photocatalysis, Hydrogen Atom Transfer, Surface Hydroxylation, Water Inside Cover: Photocatalytic Abstraction of Hydrogen Atoms from Water Using Hydroxylated Graphitic Carbon Nitride for Hydrogenative Coupling Reactions (Angew. Tingbin Lim, Ren Su, and co-workers show in their Research Article (e202204256) that surface-hydroxylated graphitic carbon nitride only requires 2.25 eV to activate water for reactions involving a hydrogen atom transfer step, allowing solar-driven eco-friendly synthetic chemistry. [Extracted from the article]

A straightforward synthesis of ( S)-gingerols 1- 3 has been described. The requisite stereogenic center in the target molecules was introduced by Sharpless asymmetric dihydroxylation using a chiral complex, AD-mix β. This route is simple and efficient to prepare the products in very good yields. [ABSTRACT FROM AUTHOR]

The asymmetric synthesis of two naturally occurring 5-hydroxy- γ-butyrolactones, (4 R,5 R)-5-hydroxy-4-decanolide ( 1a) and (−)-muricatacin ( 2), is described using a general alkyne-mediated strategy. The key steps involved are Sonogashira coupling for the desired carbon-chain extension followed by Sharpless asymmetric dihydroxylation to construct the hydroxy-lactone framework. [ABSTRACT FROM AUTHOR]

Mild conditions are reported for the hydroxylation of aliphatic CH bonds through radical translocation, oxidation to carbocation, and nucleophilic trapping with H2O. This remote functionalization employs fac-[Ir(ppy)3] together with Tz o sulfonate esters and sulfonamides to facilitate the site-selective replacement of relatively inert CH bonds with the more synthetically useful COH group. The hydroxylation of a range of substrates and the methoxylation of two substrates through 1,6- and 1,7-hydrogen-atom transfer are demonstrated. In addition, a synthesis of the antidepressant fluoxetine using remote hydroxylation as a key step is presented. [ABSTRACT FROM AUTHOR]

A stereoselective synthesis of anti-1,2-diols has been developed using a multitasking Ru catalyst in an assisted tandem catalysis protocol. A cyclometalated Ru complex catalyzes first a Z-selective cross-metathesis of two terminal olefins, followed by a stereospecific dihydroxylation. Both steps are catalyzed by Ru, as the Ru complex is converted to a dihydroxylation catalyst upon addition of NaIO4. A variety of olefins were transformed into valuable, highly functionalized, and stereodefined molecules. Mechanistic experiments were performed to probe the nature of the oxidation step and catalyst inhibition pathways. These experiments point the way to more broadly applicable tandem catalytic transformations. [ABSTRACT FROM AUTHOR]

It was found for the first time that Cs2CO3 serves as highly efficient catalyst for the direct hydroxylation reactions of phosphonates under mild conditions. This reaction provides an efficient approach to quaternary α-hydroxy phosphonates, which possess intriguing biological activities and are widely used in many areas. [ABSTRACT FROM AUTHOR]

Determining the absolute chronology of ceramic artifacts has significant implications for archeological and historical research. Wilson, Hall et al. recently suggested a new technique for direct absolute dating of archeological ceramics based on a moisture-induced chemical reaction, called rehydroxylation (RHX) dating. RHX dating proceeds by measuring the mass of chemically combined water in the ceramics in the form of OH hydroxyls, and the mass gain rate at the Effective Lifetime Temperature (ELT) that the ceramics experienced over its lifetime. To date, ELT determinations have been based on estimates of the ceramic's lifetime temperature history; taking into account weather and climate data and the depth at which the artifact was found. The uncertainty in determining the ELT can be a major component of the overall dating uncertainty. Here, we propose an alternative method which relies minimally on weather and climate data, and provides more precise determinations of the ELT and the ceramic age. The proposed method (SAS: Same Age Samples) involves a minimum of four measurements of the RHX mass gain rate constant for two ceramic samples of the same age at two temperatures. We show via simulations that the proposed SAS method can determine the ELT with a precision of 0.2 K which is comparable to the best ELT determination based on lifetime temperature history, and also comparable to available microbalance temperature resolutions of around 0.1 K. The corresponding percent age error is then 1.4%, or 43 yr for a 3000-yr-old ceramic. The proposed SAS method should be tested with ceramic samples of different ages, whose ELT are well-known. [ABSTRACT FROM AUTHOR]

Photoinduced hydroxylation of neat deaerated benzene to phenol occurred under visible-light irradiation of 2,3-dichloro-5,6-dicyano- p-benzoquinone (DDQ), which acts as a super photooxidant in the presence of water. Photocatalytic solvent-free hydroxylation of benzene derivatives with electron-withdrawing substituents such as benzonitrile, nitrobenzene, and trifluoromethylbenzene used as neat solvents has been achieved for the first time by using DDQ as a super photooxidant to yield the corresponding phenol derivatives and 2,3-dichloro-5,6-dicyanohydroquinone (DDQH2) in the presence of water under deaerated conditions. In the presence of dioxygen and tert-butyl nitrite, the photocatalytic hydroxylation of neat benzene occurred with DDQ as a photocatalyst to produce phenol. The photocatalytic reactions are initiated by oxidation of benzene derivatives with the singlet and triplet excited states of DDQ to form the corresponding radical cations, which associate with benzene derivatives to produce the dimer radical cations, which were detected by the femto- and nanosecond laser flash photolysis measurements to clarify the photocatalytic reaction mechanisms. Radical cations of benzene derivatives react with water to yield the OH-adduct radicals. On the other hand, DDQ .− produced by the photoinduced electron transfer from benzene derivatives reacts with the OH-adduct radicals to yield the corresponding phenol derivatives and DDQH2. DDQ is recovered by the reaction of DDQH2 with tert-butyl nitrite when DDQ acts as a photocatalyst for the hydroxylation of benzene derivatives by dioxygen. [ABSTRACT FROM AUTHOR]

Zeolites are highly important heterogeneous catalysts. Besides Brønsted SiOHAl acid sites, also framework AlFR Lewis acid sites are often found in their H-forms. The formation of AlFR Lewis sites in zeolites is a key issue regarding their selectivity in acid-catalyzed reactions. The local structures of AlFR Lewis sites in dehydrated zeolites and their precursors-'perturbed' AlFR atoms in hydrated zeolites-were studied by high-resolution MAS NMR and FTIR spectroscopy and DFT/MM calculations. Perturbed framework Al atoms correspond to (SiO)3AlOH groups and are characterized by a broad 27Al NMR resonance ( δi=59-62 ppm, CQ=5 MHz, and η=0.3-0.4) with a shoulder at 40 ppm in the 27Al MAS NMR spectrum. Dehydroxylation of (SiO)3AlOH occurs at mild temperatures and leads to the formation of AlFR Lewis sites tricoordinated to the zeolite framework. Al atoms of these (SiO)3Al Lewis sites exhibit an extremely broad 27Al NMR resonance ( δi≈67 ppm, CQ≈20 MHz, and η≈0.1). [ABSTRACT FROM AUTHOR]

A highly efficient and stereoselective synthetic pathway towards trans-3,4-dihydroxy-2-alkylpyrrolidines and piperidines is described. The nature of the protecting groups on the hydroxyl moieties played a crucial role on the trans selectivity. By using this method, a concise total synthesis of (−)-2-epilentiginosine has been achieved. [ABSTRACT FROM AUTHOR]

An efficient and concise approach to the total syntheses of paecilomycins E ( 1) and F ( 2) is described. A protecting group directed intermolecular diastereoselective Nozaki-Hiyama-Kishi (NHK) reaction, a Julia-Kocienski olefination, a Sharpless asymmetric dihydroxylation, and De Brabander's lactonization protocol are used as the key steps. [ABSTRACT FROM AUTHOR]

To obtain accurate results in the RHX dating of ceramics, it is essential that the RHX measurements are continued until the rate of mass gain is constant with (time)1/4. In this paper, we discuss how the initial stages of mass gain are affected by the specific surface area (SSA) of the ceramic material. The paper provides guidance on experimental protocols to avoid dating results being distorted by relatively early-time mass gain data. [ABSTRACT FROM AUTHOR]

High-spin iron(III) iodosylarene complexes bearing an N-methylated cyclam ligand are synthesized and characterized using various spectroscopic methods. The nonheme high-spin iron(III) iodosylarene intermediates are highly reactive oxidants capable of activating strong CH bonds of alkanes; the reactivity of the iron(III) iodosylarene intermediates is much greater than that of the corresponding iron(IV) oxo complex. The electrophilic character of the iron(III) iodosylarene complexes is demonstrated in sulfoxidation reactions. [ABSTRACT FROM AUTHOR]

Direct ortho-hydroxylation through CH oxygenation and N-trifluoroacylation of anilines was achieved in a single step under metal-free conditions by using a combination of TFA and oxone. The method allowed the formation of functionalised amino phenolic compounds such as ortho-hydroxy- N-trifluoroacetanilides in good yields with broad substrate scope. [ABSTRACT FROM AUTHOR]

The CuI/triethanolamine catalyst system efficiently promotes the direct hydroxylation of aryl iodides and bromides in water to provide the corresponding phenols in good to excellent yields. Moreover, the procedure avoids the use of toxic organic solvents and tolerates many functional groups. [ABSTRACT FROM AUTHOR]

The article presents abstracts on chemistry topics which include the enantioselective synthesis of axially double chiral bisphosphorylimides, the hydroxylation, and metathesis of olefin.

A transition-metal-free Cs2CO3-catalyzed α-hydroxylation of carbonyl compounds with O2 as the oxygen source is described. This reaction provides an efficient approach to tertiary α-hydroxycarbonyl compounds, which are highly valued chemicals and widely used in the chemical and pharmaceutical industry. The simple conditions and the use of molecular oxygen as both the oxidant and the oxygen source make this protocol very environmentally friendly and practical. This transformation is highly efficient and highly selective for tertiary C(sp3)H bond cleavage. [ABSTRACT FROM AUTHOR]

Organic chemistry to the rescue: Two unrelated nonenzymatic chemical reactions can support the growth of auxotrophic E. coli strains by generating essential nutrients in situ. These biocompatible reactions, which take place in the presence of the organisms and are designed to interface with cellular metabolic processes, provide a means of linking the growth of an organism to the success of a nonbiological chemical transformation. [ABSTRACT FROM AUTHOR]

We have reported previously that an iron(III) complex supported by an anionic pentadentate monoamido ligand, dpaqH (dpaqH=2-[bis(pyridin-2-ylmethyl)]amino- N-quinolin-8-yl-acetamido), promotes selective CH hydroxylation with H2O2 with high regioselectivity. Herein, we report on the preparation of FeIII-dpaq derivatives that have a series of substituent groups at the 5-position of a quinoline moiety in the parent ligand dpaqH (dpaqR, R: OMe, H, Cl, and NO2), and examine them with respect to their catalytic activity in CH hydroxylation with H2O2. As the substituent group becomes more electron-withdrawing, both the selectivity and the turnover number increase, but the selectivity of epoxidation shows the opposite trend. [ABSTRACT FROM AUTHOR]

Mononuclear metal-dioxygen species are key intermediates that are frequently observed in the catalytic cycles of dioxygen activation by metalloenzymes and their biomimetic compounds. In this work, a side-on cobalt(III)-peroxo complex bearing a macrocyclic N-tetramethylated cyclam (TMC) ligand, [CoIII(15-TMC)(O2)]+, was synthesized and characterized with various spectroscopic methods. Upon protonation, this cobalt(III)-peroxo complex was cleanly converted into an end-on cobalt(III)-hydroperoxo complex, [CoIII(15-TMC)(OOH)]2+. The cobalt(III)-hydroperoxo complex was further converted to [CoIII(15-TMC-CH2-O)]2+ by hydroxylation of a methyl group of the 15-TMC ligand. Kinetic studies and 18O-labeling experiments proposed that the aliphatic hydroxylation occurred via a CoIV-oxo (or CoIII-oxyl) species, which was formed by OO bond homolysis of the cobalt(III)-hydroperoxo complex. In conclusion, we have shown the synthesis, structural and spectroscopic characterization, and reactivities of mononuclear cobalt complexes with peroxo, hydroperoxo, and oxo ligands. [ABSTRACT FROM AUTHOR]

6 in 1: The highly enantioselective title reaction is mediated by a bifunctional catalyst and leads to E‐configured vinylogous aldol products (see scheme). These products are used as common intermediates in the synthesis of six biologically active 3‐hydroxy‐2‐oxindole derivatives (e.g., CPC‐1). Computational studies indicated that the observed stereoselectivity is a result of favorable secondary π–π* and H‐bonding interactions in the transition state. [ABSTRACT FROM AUTHOR]

The biotransformations of hyodeoxycholic acid with various Rhodococcus spp. are reported. Some strains ( i.e., Rhodococcus zopfii, Rhodococcus ruber, and Rhodococcus aetherivorans) are able to partially degrade the side chain at C(17) to afford 6 α-hydroxy-3-oxo-23,24-dinor-5 β-cholan-22-oic acid ( 2; 23%) and 6 α-hydroxy-3-oxo-23,24-dinorchol-1,4-dien-22-oic acid ( 3; 23-30%), together with two new 9,10-secosteroids 4 and 5 (10-45%), still bearing the partial side chain at C(17) and adopting an intramolecular hemiacetal form. In addition, the 9,10-secosteroid 5 showed an unprecedented C(4)-hydroxylation. The new secosteroids were fully characterized by MS, IR, NMR, and 2D-NMR analyses. [ABSTRACT FROM AUTHOR]

A formal synthesis of (−)-cephalotaxine ( 1) by means of a highly stereoselective radical carboazidation process is reported. The synthesis begins with the protected ( S)-cyclopent-2-en-1-ol derivative 10 and uses the concept of self-reproduction of a stereogenic center ( Schemes 5 and 6). For this purpose, the double bond adjacent to the initial chiral center in 10 is converted into an acetonide after stereoselective dihydroxylation. The initial alcohol function is used to build an exocyclic methylene group suitable for the carboazidation process 8→ 7 (Scheme 7). Finally the protected diol moiety is converted back to an alkene ( 14→ 15→ 6) and used for the formation of ring B via a Heck reaction ( 6→(−)- 16; Scheme 8). [ABSTRACT FROM AUTHOR]

The protection of organic and hybrid organic-inorganic materials from X-ray damage is a fundamental technological issue for broadening the range of applications of these materials. In the present article it is shown that doping hybrid films with fullerenes C60 gives a significant reduction of damage upon exposure to hard X-rays generated by a synchrotron source. At low X-ray dose the fullerene molecules act as `radical scavengers', considerably reducing the degradation of organic species triggered by radical formation. At higher doses the gradual hydroxylation of the fullerenes converts C60 into fullerol and a bleaching of the radical sinking properties is observed. [ABSTRACT FROM AUTHOR]

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • The mean catalytic activities of CYP1A2, CYP2A6, CYP2D6, CYP2E1 and CYP3A4 in human liver microsomes (HLM) of Japanese origin were found to be lower than the corresponding mean values of Caucasian HLM, but the distribution patterns of data in these studies were not well addressed. • Interindividual variations in metabolic activities of Chinese HLM samples were reported for CYP1A2, CYP2C9, CYP2D6 and CYP3A4, but little is known about the difference in CYP activities between Chinese and Caucasian HLM samples. • The vast majority of the preceding studies were based on the measurement of metabolite formation rates at a certain fixed substrate concentration, rather than enzyme kinetic analyses. WHAT THIS STUDY ADDS • Significant differences in metabolic capability were observed for CYP1A2, CYP2C9, CYP2C19 and CYP2E1 with the median values lower for the Chinese HLM samples vs. the Caucasian samples, which were associated with differences in Michaelis constant or maximum velocity. • Despite negligible differences in metabolic capability for CYP2A6, CYP2B6, CYP2C8, CYP2D6 and CYP3A, Michaelis constant of CYP2B6 appeared to have a significant ethnic difference. AIM The most common causes of variability in drug response include differences in drug metabolism, especially when the hepatic cytochrome P450 (CYP) enzymes are involved. The current study was conducted to assess the differences in CYP activities in human liver microsomes (HLM) of Chinese or Caucasian origin. METHODS The metabolic capabilities of CYP enzymes in 30 Chinese liver microsomal samples were compared with those of 30 Caucasian samples utilizing enzyme kinetics. Phenacetin O-deethylation, coumarin 7-hydroxylation, bupropion hydroxylation, amodiaquine N-desethylation, diclofenac 4′-hydroxylation ( S)-mephenytoin 4′-hydroxylation, dextromethorphan O-demethylation, chlorzoxazone 6-hydroxylation and midazolam 1′-hydroxylation/testosterone 6β-hydroxylation were used as probes for activities of CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A, respectively. Mann-Whitney U test was used to assess the differences. RESULTS The samples of the two ethnic groups were not significantly different in cytochrome-b5 concentrations but were significantly different in total CYP concentrations and NADPH-P450 reductase activity ( P < 0.05). Significant ethnic differences in intrinsic clearance were observed for CYP1A2, CYP2C9, CYP2C19 and CYP2E1; the median values of the Chinese group were 54, 58, 26, and 35% of the corresponding values of the Caucasian group, respectively. These differences were associated with differences in Michaelis constant or maximum velocity. Despite negligible difference in intrinsic clearance, the Michaelis constant of CYP2B6 appeared to have a significant ethnic difference. No ethnic difference was observed for CYP2A6, CYP2C8, CYP2D6 and CYP3A. CONCLUSIONS These data extend our knowledge on the ethnic differences in CYP enzymes and will have implications for drug discovery and drug therapy for patients from different ethnic origins. [ABSTRACT FROM AUTHOR]

Selected instrumental techniques [dilatometry, thermogravimetry - mass spectrometry ( TG- MS), and variable temperature - diffuse reflectance infrared Fourier transform spectroscopy ( VT- DRIFTS)] have been used to investigate the role of moisture in the rehydroxylation reaction which causes expansion and mass gain in fired clay ceramics. The temperature range over which adsorbed water molecules and structural hydroxyl groups are desorbed from fired clay ceramic as it is reheated, and the nature of the structural hydroxyls that are formed as the ceramic is cooled and then held under controlled conditions have been explored. The mass chromatogram for m/ z = 18, supported by VT- DRIFTS, showed that physisorbed water molecules were removed from the ceramic at about 105°C, whereas strongly bound molecules of water and structural hydroxyls were held to ≤500°C. Dilatometry revealed a marked contraction of the ceramic between 200°C and 330°C which corresponded to loss of strongly bound molecules of water. The VT- DRIFTS also showed that the interaction of water molecules with the ceramic body following reheating occurred in two stages and confirmed the kinetic law previously derived from mass gain and moisture expansion in fired clay ceramics. [ABSTRACT FROM AUTHOR]

The selectivity of hydroxylation of the distal rings of 4-phenylbenzoic acid, 4-phenylsalicylic acid, and 5-phenylsalicylic acid were determined using partial TiO2-mediated photocatalytic degradation and photo-Fenton conditions. This separation of the binding site from the phenyl group being hydroxylated allows a less-biased evaluation. The hydroxylation regiochemistry behaves as qualitatively expected for an electrophilic reaction, given the assumption that 4-carboxyphenyl is a slightly electron-withdrawing substituent. Selectivity for hydroxylation of the distal phenyl in 4- and 5-phenylsalicylic acid is reversed, due to the reversal of the electronic demand, while adsorption to the TiO2 surface is assumed to be analogous for the two structures. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The biosynthesis of the mineralocorticoid hormone aldosterone involves a multistep hydroxylation of 11-deoxycorticosterone at the 11- and 18-positions, resulting in the formation of corticosterone and 18-hydroxycorticosterone, the final precursor of aldosterone. Two members of the cytochrome P450 11B family, CYP11B1 and CYP11B2, are known to catalyze these 11- and 18-hydroxylations, however, only CYP11B2 can oxidize 18-hydroxycorticosterone to aldosterone. It is unknown what sequence of hydroxylations leads to the formation of 18-hydroxycorticosterone. In this study we have investigated which of the possible conversion paths towards formation of 18-hydroxycorticosterone and aldosterone are most likely from the ligand perspective. Therefore, we combined quantum mechanical investigations on the steroid conformations of 11-deoxycorticosterone and its ensuing reaction intermediates with Fukui indices calculations to predict the reactivity of their carbon atoms for an attack by the iron-oxygen species. Both F and F were calculated to account for different mechanisms of substrate conversion. We show which particular initial conformations of 11-deoxycorticosterone and which conversion paths are likely to result in the successful synthesis of aldosterone, and thereby may be representative for the mechanism of aldosterone biosynthesis by CYP11B2. Moreover, we found that the most likely path for aldosterone synthesis coincides with the substrate conformation proposed in an earlier publication (Ref.). To summarize, we show that on a theoretical and strictly ligand-directed basis only a limited number of reaction paths in the conversion of 11-deoxycorticosterone to aldosterone is possible. Despite its theoretical nature, this knowledge may help to understand the catalytic function of CYP11B1 and CYP11B2. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011 [ABSTRACT FROM AUTHOR]