Hypervalent Iodine Oxidation of 2-Aryl-1,2,3,4-tetrahydro-4-quinolones: An Easy Access to 2-Aryl-4-quinolones

Oxidation of 2-aryl-1,2,3,4-tetrahydro-4-quinolones (1a-e) using iodobenzene diacetate in methanolic potassium hydroxide leads to dehydrogenation of 1 thereby providing an easy access to 2-aryl-4-quinolones (2a-e).     

Iodine Activation of Coordinated White Phosphorus: Formation and Transformation of 1,3-Dihydride-2-iodidecyclotetraphosphane

Double stabilization: Previously unknown polyphosphorus compounds are obtained by activation of white phosphorus (P(4) ) coordinated between two CpRu(PPh(3) )(2) moieties with iodine, and subsequent hydrolysis. The polyphosphorus compounds (P(4) H(2) I, P(4) H(2) , P(3) H(5) ; see scheme, Cp=cyclopentadienyl) are all stabilized by coordination to two ruthenium centers.     

Crystal Structure of Tryptophan Lyase (NosL): Evidence for Radical Formation at the Amino Group of Tryptophan

Streptomyces actuosus tryptophan lyase (NosL) is a radical SAM enzyme which catalyzes the synthesis of 3‐methyl‐2‐indolic acid, a precursor in the synthesis of the promising antibiotic nosiheptide. The reaction involves cleavage of the tryptophan Cα? Cβ bond and recombination of the amino‐acid‐derived ‐COOH fragment at the indole ring. Reported herein is the 1.8 Å resolution crystal structure of NosL complexed with its substrate. Unexpectedly, only one of the tryptophan amino hydrogen atoms is optimally placed for H abstraction by the SAM‐derived 5′‐deoxyadenosyl radical. This orientation, in turn, rules out the previously proposed delocalized indole radical as the species which undergoes Cα? Cβ bond cleavage. Instead, stereochemical considerations indicate that the reactive intermediate is a ^.NH tryptophanyl radical. A structure‐based amino acid sequence comparison of NosL with the tyrosine lyases ThiH and HydG strongly suggests that an equivalent ^.NH radical operates in the latter enzymes.     

Non-Covalent Binding of Tripeptides-Containing Tryptophan to Polynucleotides and Photochemical Deamination of Modified Tyrosine to Quinone Methide Leading to Covalent Attachment

A series of tripeptides TrpTrpPhe (1), TrpTrpTyr (2), and TrpTrpTyr[CH₂N(CH₃)₂] (3) were synthesized, and their photophysical properties and non-covalent binding to polynucleotides were investigated. Fluorescent Trp residues (quantum yield in aqueous solvent Φ_F = 0.03–0.06), allowed for the fluorometric study of non-covalent binding to DNA and RNA. Moreover, high and similar affinities of 2×HCl and 3×HCl to all studied double stranded (ds)-polynucleotides were found (logK_a = 6.0–6.8). However, the fluorescence spectral responses were strongly dependent on base pair composition: the GC-containing polynucleotides efficiently quenched Trp emission, at variance to AT- or AU-polynucleotides, which induced bisignate response. Namely, addition of AT(U) polynucleotides at excess over studied peptide induced the quenching (attributed to aggregation in the grooves of polynucleotides), whereas at excess of DNA/RNA over peptide the fluorescence increase of Trp was observed. The thermal denaturation and circular dichroism (CD) experiments supported peptides binding within the grooves of polynucleotides. The photogenerated quinone methide (QM) reacts with nucleophiles giving adducts, as demonstrated by the photomethanolysis (quantum yield Φ_R = 0.11–0.13). Furthermore, we have demonstrated photoalkylation of AT oligonucleotides by QM, at variance to previous reports describing the highest reactivity of QMs with the GC reach regions of polynucleotides. Our investigations show a proof of principle that QM precursor can be imbedded into a peptide and used as a photochemical switch to enable alkylation of polynucleotides, enabling further applications in chemistry and biology.     

Hypervalent Iodine in Synthesis XXIII: Oxidation with [Hydroxy(tosyloxy)iodo]benzene: Selective Oxidation of Sulfides to Sulfoxides

Alkyl-and aryl-sulfides can be selectively oxidated to their corresponding sulfoxides with excellent yields under mild conditions by [hydroxy (tosyloxy)iodo]benzene. Morever, [hydroxy (((+)-10-camphorosulfonyl)oxy)iodo]benzene as the chiral oxidizer, can be used to oxidate unsymmetric sulfides to sulfoxides with a few %ee to some extent.     

Oxidation of Palladium with Allyl Bromide and Iodine in Dimethylformamide

The kinetic features of palladium oxidation with allyl bromide and iodine in dimethylformamide were determined. The apparent equilibrium constants, enthalpies, and entropies of reactant adsorption on the palladium surface were calculated.     

金刚烷负载高价碘试剂的合成及氧化反应活性

以1,3,5,7-四氨基金刚烷与4-碘苯基酰氯为原料,经酰化、氧化反应,制备了新型金刚烷负载的高价碘试剂(1a-1c)。 酰化反应以CH₂Cl₂为溶剂,首先,0 ℃,反应4 h,然后室温反应2 h,投料比n(1,3,5,7-四氨基金刚烷)∶n(4-碘苯基酰氯)∶n(三乙胺)=1∶4.4∶5.2。 氧化反应以CH₂Cl₂/醋酸(体积比1∶1)为溶剂,间氯过氧苯甲酸(m-CPBA)为氧化剂,室温反应12 h,投料比n(2)∶n(m-CPBA)=1∶12。 化合物1a,1b和1c的总收率分别为86.4%、85.4%和85.3%。 以化合物1a-1c为氧化剂,在四甲基哌啶氮氧化物(TEMPO)催化下各类醇被氧化成相应的醛或酮,产物收率87%~100%。 负载碘苯2a-2c可以被方便地分离和回收,平均回收率98%,可再经氧化,高收率转化成化合物1a-1c,循环利用。     

黄素为辅基的色氨酸卤化酶及其在生物合成色氨酸衍生物中的应用

黄素为辅基的色氨酸卤化酶在催化合成有机氯化物和溴化物过程中的起着非常重要的作用。在这篇论文我们将阐述一种通过在假单胞菌株中表达外源色氨酸卤化酶基因来催化合成3-（2-氨基-4-氯苯基）吡咯的新组合生物合成方法——组合培育法。3-（2-氨基-4-氯苯基）吡咯是分析和诱导性基因突变硝吡咯菌素生物合成途径的重要中间产物。研究表明,这种新的组合培育法可以用于改变和分析一些重要的二级代谢途径。     

Oxidation of BINOLs by Hypervalent Iodine Reagents: Facile Synthesis of Xanthenes and Lactones

Xanthene derivatives have broad applications in medicines, fluorescent probes, dyes, food additives, etc. Therefore, much attention was focused on developing the synthetic methods to prepare these compounds. Binaphthyl-based xanthene derivatives were prepared through the oxidation of BINOLs promoted by the hypervalent iodine reagent iodosylbenzene (PhIO). Nine-membered lactones were obtained through a similar oxidative reaction when iodoxybenzene (PhIO₂) was used. Additionally, one-pot reactions of BINOLs, PhIO and nucleophiles such as alcohols and amines were also investigated to provide alkoxylated products and amides in good to excellent yields.     

Oxidation Mechanism of 1-Methyl-tryptophan and Tryptophan on Glassy Carbon Electrode: A Comparative Study

The anodic behaviour of 1-methyl-tryptophan (1-mTrp) in aqueous electrolytes was investigated on a glassy carbon electrode (GCE), using voltammetric techniques. The oxidation of 1-mTrp was associated with an electrochemical-chemical (EC) mechanism: one electron and one proton were removed of C2 to form an intermediate radical, 1-mTrp⋅. This was followed by a two-way reaction, producing a 1-mTrp dimer and/or reaction with water to form a final hydroxylated product. The oxidation mechanism of 1-mTrp proposed was also compared with the anodic oxidation Trp on GCE. Differential pulse voltammetry was also explored for quantification of Trp and 1-mTrp in neutral medium with low detection limits, on an anodically pre-treated GCE.     

Synthesis of Ruthenium Xanthate Complex and Its Electrocatalytic Activity for Tryptophan Oxidation

A new ruthenium complex containing bidentate xanthate ligands was synthesized in a good yield. This complex was characterized by elemental analysis, proton nuclear magnetic resonance(¹H NMR), Fourier transform infrared(FTIR) and UV-Vis spectroscopies. The cyclic voltammetry of the complex revealed one quasi-redox wave centered at Ru(Ⅲ)/ Ru(Ⅱ) couple, indicating its catalytic potential. So the preparation of a glass carbon electrode modified with ruthenium xanthate complex and its electrocatalytic activity toward the oxidation of tryptophan(Trp) were also studied. The experimental results show that the modified electrode had excellent electrocatalytic activity for the oxidation of tryptophan. Moreover, under the optimized conditions, the oxidation peak current was proportional to tryptophan concentration in a range of 2.5×10^-7 to 5.0×10^-5 mol/L with a correlation coefficient of 0.9928 and a detection limit of 8.3×10^-8 mol/L(S/N=3). Using the proposed method, tryptophan was successfully determined in pharmaceutical samples with standard addition method.     

Mechanism of and Products from the Oxidation of Phenols by Hypervalent Iodine Compounds

Iodobenzene dichloride or diacetate initiates the polymerization of 2,6-dimethylphenolate anion to poly [oxy(2,5-dimethyl)-l, 4-phenylene]. Electron spin resonance spectroscopy was used to identify the polymeric radical that is the growing chain. Infrared and NMR spectroscopy identified the final polymer. The mechanism proposed is probably applicable also to other phenol oxidation processes yielding substituted poly(oxyphenylenes).

The anomalous chemistry of those compounds of xenon, iodine, and tellurium in which the number of bonding electrons exceeds that given by Lewis valence theory has been considered in general terms by Musher [1] who coined the term “hypervalent” to describe these substances. The oxidizing properties of these compounds is in a general way similar to that of peroxides and other strong oxidizing agents, but has not been characterized in any exact fashion. We have observed [2] that the iodobenzene esters have polymeric analogs of the formula, [-I(R)OOCXCOO-], and these compounds are stable oxidizing agents (R = aryl; X = alkylene or arylene). We have been interested in determining if -I(R)OXO- compounds can be formed.

The first question to consider is the stability of bonds in -OI(R)O- compounds. Only acyl derivatives are known [3]. However, the possibility     

Partial Oxidation of Alcohols to Aldehydes and Ketones Under Mild Conditions

Abstract

A number of aldehydes and ketones were prepared by partial oxidation of alcohols in air catalyzed by RuO₂/ZSM‐5 which can be easily prepared with the industrial grade ZSM‐5 and RuCl₃ · xH₂O.     

Kinetic Features of Aerosol Formation in the Branched Chain Process of Dichlorosilane Oxidation under Static Conditions: I. Initiated Ignition

It is found experimentally that the initial pressure of aerosol formation progressively decreases with an increase in the initial concentration of dichlorosilane in the initiated ignition of dichlorosilane mixtures with oxygen at 293 K. The dependence of the maximal aerosol concentration on the total pressure is S-shaped. A generalized kinetic scheme is proposed that qualitatively describes the regularities observed in the experiments. The most important calculated parameters are the heat evolved in the chain process and the dependence of the pressure of the saturated vapor of a new phase on temperature. It is shown that the specific features of branched-chain processes under nonisothermic conditions determine the kinetic regularities of new phase formation. The optimal range of pressures is recommended for obtaining particles with as low dispersivity as possible.     

气敏材料Cd2V2O7的制备和性能

用水热氧化法制备出γＭｎ２Ｏ３粉末,并在不同温度下进行烧结．采用ＸＲＤ,ＴＥＭ,ＸＰＳ,ＩＲ及紫外分光光度法等表征产物．结果表明,未烧结产物即为单相纳米晶,大部分近似球形,有轻微团聚．产物于空气中１００～５５０℃范围内烧结时热稳定性好．随烧结温度的升高粉末的平均粒子尺寸增大,产物中锰以Ｍｎ（Ⅲ）状态存在．     

Studies on the Interaction of Poly(I:C) with Heterocyclic Compounds Containing Iodine

The iodine heterocvclic compound with trivalent-iodine as the cation has a specially remarkable antitumor activityii^[1]. Although 3, 6-bis (dimethylamino)-dibenzopyriodonium formate([I⁺]) inhibits DNA biosynthesis of cancer cells in vitro, the way of [I⁺] depressing DNA synthesis has not been studied. It is significant to investigate the mechanism of the interaction of [I⁺] with nucleic acids.     

科学补碘:消除碘缺乏病的成败关键

碘对甲状腺功能具有双向作用,在消除碘缺乏病的同时,切不可忽略全民食盐加碘后高碘甲状腺病的防治。分别从水碘和尿碘两个方面论述了碘与甲状腺病之间的双向关系,并根据流行病学调查数据和全国碘缺乏病监测数据确定了盐碘与尿碘之间的数学关系,计算了食盐碘含量的最适宜范围,提出了下调食盐碘含量、设计区域化碘盐和补碘个性化的科学补碘新策略。     

Kinetic Study on the Selective Oxidation of H2S Containing Excess Water and Ammonia

The selective oxidation of hydrogen sulfide containing excess water and ammonia was studied over V₂O₅/SiO₂ catalysts. H₂S was successfully converted to elemental sulfur and ammonium thiosulfate (ATS) without considerable emission of sulfur dioxide. Kinetic studies were carried out to describe the complex reaction paths. This revised version was published online in June 2006 with corrections to the Cover Date.