Using tandem mass spectrometry to predict chemical transformations of 2-pyrimidinyloxy-N-arylbenzyl amine derivatives in solution

Tandem mass spectrometry is used to predict the chemical transformations of 2-pyrimidinyloxy-N-arylbenzyl amine derivatives. Compound 1, N-2-2-4,6- dimethoxypyrimidin-2-yloxy benzylamino phenyl benzamide was selected as a model to present our idea. The CID reactions of protonated 1 include an intramolecular S(N)2 reaction and a cyclodehydration reaction. Under in-source CID conditions, deprotonated 1 undergoes a Smiles rearrangement reaction and then dissociates to the ion at m/z 349. Theoretical computations were invoked to shed light on the reaction mechanisms of 1 by the semiempirical PM3 method. These studies of gas-phase reactions show the reactivity of some potential reaction centers in this molecule, which inspired us to explore the solution phase analogous reactions of 1. Further experiments show that 1 has two analogous reactions in acidic solution: the acid-catalyzed cyclodehydration reaction and the acid-catalyzed Smiles rearrangement reaction. Moreover, 1 undergoes the base-catalyzed Smiles rearrangement under basic conditions. The present study demonstrates that mass spectrometry can play an important role in predicting the chemical solution phase transformations of 2-pyrimidinyloxy-N-arylbenzyl amine derivatives.     

土卫六大气中H2和N+反应的动力学研究

依据Titan大气的压强和温度条件计算了N++H2→NH++H反应的热化学函数. 结果发现, 该反应是一个吸热反应, 在Titan的低温环境中不具有反应自发性. 运用量子化学理论计算研究了反应的动力学性质, 发现该反应在300 K温度下的反应速率k=4.16×10−10 cm3•mol−1•s−1, 在实验室温度下(298.15 K)的反应势垒是109.847 kJ•mol−1. 依据Titan电离层气压温度条件计算了90 Pa压强条件下1 K到5000 K温度范围内(极低温度和极高温度)的 反应活化能和反应速率, 研究发现低温下该反应的反应速率非常低, 而且, 随着温度的降低, 反应速率急剧降低. 理论计算值和文献中的实验值也符合得较好, 理论计算数据可以为星际分子的模拟实验提供一定的参考.     

Study on the alkylation reaction of guanine and N-acetylguanine and the synthesis of 1''''-C alkylated carba-DHPG analogues

The alkylation reaction of guanine and N-acetylguanine with model compounds such as isopropyl bromide or 4-heptyl tosylate were studied. The reaction conditions such as temperature, solvent, base, and catalyst were examined for their effects on the reaction rate, and the yield and regioselectivity of the coupling reaction. The highest yield was obtained by using DMSO as the solvent. The reaction proceeded in a homogenous manner to give higher yield of 9-N and 7-N substituted product in a mole ratio of 1:1. The ratio could be raised to 2:1 if dibenzo-18-crown-6 was used as a catalyst. Using the above procedure, three carba-DHPG analogues bearing different 1'-C alkyl side chains were synthesized.     

PHOTOCHROMIC PROPERTIES OF (E)-DICYCLOPROPYLMETHYLENE-(2,5-DIMETHYL-3-FURYLETHYLIDENE)-SUCCINIC ANHYDRIDE DOPED IN POLYSTYRENE THIN FILMS

Fulgide 1-E doped in polystyrene polymer films was heated at various annealing temperatures.Upon irradiation with UV light(366 nm),fulgide 1-E undergoes a conrotatory ring closure to the pink colored closed form 1-C.The later color was switched back to the original color when the films were irradiated with white light.The kinetics of photocoloration and photobleaching processes were followed spectrophotometrically by monitoring the absorbance of the ring closed product 1-C at itsλ_(max) of 525 nm.The fir...     

Ascorbate reacts with singlet oxygen to produce hydrogen peroxide

Singlet oxygen is a highly reactive electrophilic species that reacts rapidly with electron-rich moieties, such as the double bonds of lipids, thiols, and ascorbate (AscH-). The reaction of ascorbate with singlet oxygen is rapid (k = 3 x 10(8) M(-1) s(-1)). Here we have investigated the stoichiometry of this reaction. Using electrodes to make simultaneous, real-time measurements of oxygen and hydrogen peroxide concentrations, we have investigated the products of this reaction. We have demonstrated that hydrogen peroxide is a product of this reaction. The stoichiometry for the reactants of the reaction (1 1O2 + 1AscH--->1H2O2 + 1dehydroascorbic) is 1:1. The formation of H2O2 results in a very different oxidant that has a longer lifetime and much greater diffusion distance. Thus, locally produced singlet oxygen with a half-life of 1 ns to 1 micros in a biological setting is changed to an oxidant that has a much longer lifetime and thus can diffuse to distant targets to initiate biological oxidations.     

Quantum chemical study of σ-dimerization reaction of 1-silacycloprop-2-enes

The PBE/TZ2P method was used to study a concerted σ-dimerization reaction of 1-silacycloprop-2-enes having substituents with different electron effects. The corresponding reaction channels were founds in all the cases, that indicated a general character of this reaction. The reaction barriers varied from moderately high to extremely low. The suggestions made earlier on a possibility for this process to take place in the course of the reaction of silylenes with alkynes at elevated temperature were quantitatively confirmed for the first time. The influence of substituents on the barrier heights and exothermicity of σ-dimerization of 1-silacycloprop-2-enes was studied. The σ-dimerization reaction of 1-silacycloprop-2-enes is one of a few examples of metathesis of s-bonds in the absence of transition metal complexes.     

维生素K3电化学反应机理的紫外光谱电化学研究

用薄层池循环伏安法和现场薄层池紫外光谱电化学法研究了维生素Ｋ３（ＶＫ３）在铂电极上的电化学反应机理。薄层池循环伏安实验结果表明：ＶＫ３的电化学反应为二步１ｅ准可逆过程，现场薄层池紫外光谱电化学的实验结果和Ｎｅｒｎｓｔ图解分析表明：电解还原反应的最后产物为２－甲基－１，４－萘酚。该反应偶合有前行化学反应；还原产物经电解氧化的产物为２－甲基－１，４－萘酚。该反应偶合有前行化学反应；还原产物经电解氧化的     

Reactions of electron-rich heterocycles with orthocarboxylic acid derivatives. 11. Reactions of carbazole and 4-methoxycarbazole with triethyl orthoformate: Regiospecific functionalization of the carbazole nucleus

Carbazole ( 1a ) and 4-methoxycarbazole ( 1b ) can be regioselectively functionalized by reaction with triethyl orthoformate. Whereas the reaction of 1a with the ortho ester furnishes the amide acetal 2 , the new carbazole derivatives 4–10 are formed, depending on the reaction conditions, in the electrophilic substitution of 1b . The products of this reaction sequence provide a contribution to studies on the mechanism of the transformation of 1b to tris-carbazolylmethane 5 . Compound 5 represents a new, three-bladed propeller in the triheteroarylmethane series.     

Sodium chloride-catalyzed oxidation of multiwalled carbon nanotubes for environmental benefit

A sodium chloride (NaCl) catalyst (0.1 w/w %) lowers the oxidation temperature of graphitized multiwalled carbon nanotubes: MWCNT-20 (diameter: 20-70 nm) and MWCNT-80 (diameter: 80-150 nm). The analysis of the reaction kinetics indicates that the oxidation of MWCNT-20 and MWCNT-80 mixed with no NaCl exhibits single reaction processes with activation energies of E(a) = 159 and 152 kJ mol(-1), respectively. The oxidation reaction in the presence of NaCl is shown to consist of two different reaction processes, that is, a first reaction and a second reaction process. The first reaction process is dominant at a low temperature of around 600 degrees C, while the second reaction process becomes more dominant than the first one in a higher temperature region. The activation energies of the first reaction processes (MWCNT-20: E(a1) = 35.7 kJ mol(-1); MWCNT-80: E(a1) = 43.5 kJ mol(-1)) are much smaller than those of the second reaction processes (MWCNT-20: E(a2) = 170 kJ mol(-1); MWCNT-80: E(a2) = 171 kJ mol(-1)). The comparison of the kinetic parameters and the results of the spectroscopic and microscopic analyses imply that the lowering of the oxidation temperature in the presence of NaCl results from the introduction of disorder into the graphitized MWCNTs (during the first reaction process), thus increasing the facility of the oxidation reaction of the disorder-induced nanotubes (in the second reaction process). It is found that the larger nanopits and cracks on the outer graphitic layers are caused by the catalytic effect of NaCl. Therefore, the NaCl-mixed samples showed more rapid and stronger oxidation compared with that of the nonmixed samples at the same residual quantity.     

2,4,4-三甲基-2-氯戊烷与1,1一二苯基乙烯的正碳离子反应(Ⅰ)──反应的主要特点

我们曾报道了合成异丁烯（PIB）类的遥爪聚合物及嵌段共聚物的新方法[1]．该方法的关键步骤——活性中心转化实际上是一可逆平衡反应．Faust等[2]以几乎同样的方法合成了异丁烯嵌段共聚物,但他们尚未意识到该反应是一可逆的平衡反应,相当于先增加一个单体单元,然后终止的聚合反应,在阳离子聚合反应中,这种典型、理想的反应极为少见,因此该反应有可能成为研究阳离子聚合的一个极好的模型反应．本文通过分析聚异丁烯端基的2,4,4-三甲基-2-氯戊烷（TMPCl）与DPE的反应产物,研究该反应的规律．1实验1．1试剂的纯化及合成CH2Cl2经…     

Equilibrating C-S bond formation by C-H and S-S bond metathesis. Rhodium-catalyzed alkylthiolation reaction of 1-alkynes with disulfides

In the presence of a catalytic amount of RhH(PPh3)4 (2 mol %) and 1,1'-bis(diphenylphosphino)ferrocene (dppf) (3 mol %), silylacetylenes reacted with dialkyl disulfides giving 1-alkylthio-2-trialkylsilylethynes in high yields. Alkanethiols liberated in this reaction did not interfere with the reaction, and the addition to silylacetylene forming 1-alkylthio-1-alkenes could be minimized under the conditions. Alkylacetylenes and arylacetylenes also reacted with disulfides when the alkyl or aryl groups were bulky. Diaryl disulfides gave arylthio derivatives under slightly modified conditions. The C-S bond-forming reaction is reversible: A reaction of a thiol and a 1-alkylthio-1-alkyne in the presence of the rhodium catalyst gave a 1-alkyne; alkylthio exchange reaction proceeded between a 1-alkylthio-1-alkyne and a disulfide. This is an equilibrating oxidative reaction of organic molecules with C-H and S-S bond metathesis forming C-S and S-H bonds.     

Synthesis of Some Pyrimidine 2-Oxo(Thio)-4,6-Dione Derivatives

5-Arylidenes 1a and 1b, on reaction with ethyl cyanoacetate and diethyl malonate in the presence of ammonium acetate under Michael condensation, yield pyridine derivatives 2 and 3, respectively. Cyclopentapyrimidine derivative 4 can also be obtained by the reaction of 1a with malononitrile in the presence of piperidine. The reaction of 5-arylidene lb with monochloroacetic acid in an alkaline medium gives the thiazol derivative 5. Also, spiro-[3′, 5′]cyclohexenyl pyrimidine derivative 6 could be obtained from the reaction of 1d with maleic anhydride. On the other hand, 5-arylidene 1e reacts with maleic anhydride to give 2-thiobarbituric acid derivative 7. The condensation reaction of 2-thiovioluric acid 8 with some hydrazines affords the triazole derivatives 9a-d. Finally, barbituric acid condenses with isatin to give 5-arylidene 1f, which can be cyclized with phosphorous pentoxide to afford 10.     

咪唑与单线态氧(1O2)1,2-环加成反应的理论研究

采用较新的半经验分子轨道方法Austin Model 1(简称AM1方法), 辅以Berny梯度优化方法, 对单线态氧(~1O_2)与咪唑的1,2-环加成反应,进行了理论研究。计算获得实验尚未检测到的4,5-二氧环丁烷(4,5-dioxetane)的结构, 并在反应势能面上找到单重态双自由基中间体及通过该中间体的两步反应的过渡态。通过对过渡态的结构特征、虚振动方向以及对反应过程的电荷分布情况、轨道相互作用等的分析, 说明该反应是经由单重态双自由基中间体的分步反应。两步反应的活化势垒分别为39.2 kJ·mol~(-1)和150.5 kJ·mol~(-1)。     

Ab initio study on the mechanism of forming a silapolycyclic compound between silylidene and formaldehyde

The mechanism of the cycloaddition reaction of forming a silapolycyclic compound between singlet silylidene and formaldehyde has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by CCSD(T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the cycloaddition reaction process of forming the silapolycyclic compound (P₂) for this reaction consists of four steps: (I) the two reactants first form a semi-cyclic intermediate INT1a through a barrier-free exothermic reaction of 32.5 kJ mol⁻¹; (II) this intermediate then isomerizes to an active four-membered ring intermediate INT1 via a transition state TS1a with an energy barrier of 30.8 kJ mol⁻¹; (III) INT1 further reacts with formaldehyde to form an intermediate INT2, which is also a barrier-free exothermic reaction of 30.1 kJ mol⁻¹; (IV) INT2 isomerizes to a silapolycyclic compound P₂ via a transition state TS2 with a barrier of 50.6 kJ mol⁻¹. Comparing this reaction path with other competitive reaction paths, we can see that this cycloaddition reaction has an excellent selectivity.     

The reaction process of firefly bioluminescence triggered by photolysis of caged-ATP

The reaction process of firefly bioluminescence was studied by photolyzing caged-ATP to adenosine triphosphate (ATP) within 100 ms. The intensity of luminescence increases markedly to reach a maximum within 1 s, maintains almost the same intensity up to 5 s and then decays monotonically. The rise γ(1) and decay γ(2) rate constants were determined to be about 5 s(-1) and 1 × 10(-2) s(-1), respectively, so as to phenomenologically fit the time course. A second luminescence peak appears after around 350 s. The dependence of the rate constants on the concentrations of reactants and a viscous reagent revealed that two kinds of reaction contribute the observed time course: (1) an intrinsic reaction by ATP photolyzed from caged-ATP that is already trapped in luciferase; and (2) a diffusion-controlled reaction by free ATP in the buffer solution outside luciferase. Numerical analysis based on reaction kinetics related γ(1) and γ(2) to the rate constants of a three-step reaction model, and accurately described the effects of concentration of reactants and a viscous reagent on the time courses of bioluminescence. Thus, it has been clearly concluded that the binding mode of caged-ATP at the catalytic center of luciferase is very different from that of ATP.     

单电子转移反应 I.单电子转移反应引发的碳一氟键异裂——顺-1,2二苯基六氟环丁烷的烷氧基化脱氟取代反应

A novel reaction involving electron transfer and the breakage of a C-F bond has been investigated. In this reactio, 1, 2-diphenylhexafluorocyclobutane(1)reacts with i-PrONa to yield a substitution product 9. The reaction has to be photostimulated, and O2 and p-dinitrobenzene inhibit the reaction. Interestingly and unexpectedly, other alkoxides, viz. MeO-, EtO-, n-PrO- and t-BuO-, do not react with 1. Thus the reaction does not look like a SRN 1. However, the most amazing fact is: only the cis isomer of 1 reacts, whereas the trans isomer does not. Possibly, simultaneous breakage of α-C-H bond (in the i-PrO-) and formation of a (temporary) H-F bond is involved in a very tight transition state of the (caged?) reaction between the radical anion of 1 and the i-PrO.     

Kinetic study of Berthelot reaction steps in the absence and presence of coupling reagents

Several reaction steps in the Berthelot reaction for the determination of ammonia have been separately studied. A reaction order of two has been confirmed for the reaction between HOCl and NH(3). The rate constant for this reaction has been determined to be 3.2 x 10(6)l.mole(-1).sec(-1). The first evidence for the formation of benzoquinonechlorimine is presented. Pentacyanoferrate coupling reagents which accelerate the production of indophenol have been found to operate on the reaction between NH(2)Cl and phenol. The rate constant for the final step of the reaction sequence has been determined to be 5.3 x 10(-3)l.mole(-1).sec(-1). A reaction between chlorimine and pentacyanoferrate compounds has been found to be responsible for the formation of a green product in the presence of excess of coupling reagent.     

Dakin反应的研究

本文对九个酚醛及酚酮类化合物的Dakin反应进行了研究。由于避免了过度的氧化和副反应,所以产率较文献报道的60～80％要高,可达81～96％。其中,2-甲酰基雌酚酮和4-甲酰基雌酚酮的Dakin反应尚未见报道,产率几乎是计算量的。采用本文的方法,可将Dakin反应由通常的甲酰基或乙酰基成功地扩展应用到含丙酰基的酚酮。     

2-位氧化糖羰基转位反应的研究

α-甲基－D－葡萄糖苷的2－位羰基衍生物（简称为2－位氧化糖）,不仅在生物体糖代谢过程中起着关键作用,而且由于其自身多个手性中心及高活性羰基的存在,使之成为有机合成中的一种重要手性源,我们在前期的研究中发现,2－位氧化糖的羰基比其它位置氧化的葡萄糖苷具有更高的活性：在D2O中,2－位氧化糖的羰基100％以事形式存在,而3－位氧化糖则100％地以羰基形式存在,4－位氧化糖仅有25％以水合形式存在。因此,2－位氧化糖羰基反应活性的研究在不对称合成中有着重要意义。长期以来此方面的研究主要集中的2－位羰基及其邻位的烷基化,关于其氨基化反应鲜有报道。Tsuda等在合成Nojirimicin的过程中报道了羟胺与2－位氧化糖缩合成肟的反应,我们选择了芳胺与2－位氧化糖的反应进行研究,通过对邻苯二胺与2－位氧化糖反应所形成中间产物的^1H NMR谱变化的跟踪,并选用其它芳胺进行验证,发现芳胺类化合物在与2－位氧化糖反应时,并未生成C＝N双键,而是生成了羰基转化到3－位的加成产物。2－位氧化糖芳胺亲核加成引起羰基转位反应式如Scheme 1所示。     

Kinetics and mechanism of the oxidation of amaranth with hypochlorite

The reaction mechanism of the oxidation of Amaranth dye (2-hydroxy-1-(4-sulfonato-1-naphthylazo) naphthalene-3,6-disulfonate) with hypochlorite under varied pH conditions was elucidated by a kinetic approach. Under excess concentration of oxidant, the reaction followed pseudo-first-order kinetics with respect to Amaranth, and the oxidation was found to occur through two competitive reactions, initiated by hypochlorite and hypochlorous acid. The reaction order with respect to both OCl(-) ion and HOCl was unity. While the latter reaction was fast, the significance of the oxidation paths depended on the relative concentration of the two oxidizing species, which was dictated by the reaction pH. The role of the H(+) ion in the reaction was established. For the hypochlorite ion and hypochlorous acid facilitated reactions, the second-order rate coefficients were 1.9 and 23.2 M(-1) s(-1), respectively. The energy parameters were E(a) = 33.7 kJ mol(-1), ΔH(?) = 31.2 kJ mol(-1) and ΔS(?) = -190.6 J K(-1) mol(-1) for the OCl(-) ion-driven oxidation, and E(a) = 26.9 kJ mol(-1), ΔH(?) = 24.3 kJ mol(-1) and ΔS(?) = -222.8 J K(-1) mol(-1) for the reaction with HOCl-initiated oxidation. The major oxidation products for both the pathways were 3,4-dihydroxy naphthalene-2,7-disulfonic sodium salt (P(1)), dichloro-1,4-naphthoquione (P(2)) and naphtha(2,3)oxirene-2, 3-dione (P(3)). On the basis of the primary salt effect and other kinetic data, the rate law for the overall reaction and probable reaction mechanism was elucidated. The proposed mechanism was validated by simulations using Simkine-2.