Nickel-catalyzed sp2 C-H bonds arylation of N-aromatic heterocycles with Grignard reagents at room temperature

A novel protocol for nickel-catalyzed direct sp(2) C-H bond arylation of purines has been developed. This new reaction proceeded efficiently at room temperature using Grignard reagent as the coupling partner within 5 hours in good to high yields. This approach provides a new access to a variety of C8-arylpurines which are potentially of great importance in medicinal chemistry.     

苯乙烯基-β-萘噻唑染料电子光谱的含时密度泛函研究

对苯乙烯基-β-萘噻唑染料系列用量子化学密度泛函方法(DFT)在B3LYP/6-31g水平上进行了几何构型全优化, 探讨了苯环对位上不同的取代基CH₃, OCH₃, N(CH₃)₂, 3,4-OCH₂O, NO₂等对分子电荷转移、前线轨道能量和电子光谱等性质的影响规律, 在此基础上采用含时密度泛函方法(TD-DFT)计算了分子第一激发态的电子跃迁能, 得到最大吸收波长λ_max. 计算结果表明, 上述5种取代基的引入, 均导致最大吸收波长红移. 与实验λ_max结果相比, 理论计算最大相对偏差为0.0501, 最小相对偏差为0.0085.     

Alignment of liquid crystal and dichroic dye molecules in mixed Langmuir and Langmuir-Blodgett films

A study of dichroic dye-liquid crystal mixtures (guest-host systems) in monolayers formed at a gas-liquid interface (Langmuir films) and at a solid surface (Langmuir-Blodgett films) has been made. As a host 4- n -octyl-4′-cyanobiphenyl (8CB) or 4- n -pentyl-4″-cyano- p -terphenyl (5CT) were chosen, while three dichroic azo dyes with various molecular structures were used as guest species. The dyes were added to the liquid crystal matrices at a concentration corresponding to the whole range of molar fractions and the surface pressure-mean molecular area isotherms for Langmuir films were recorded. On the basis of the isotherms, conclusions about the molecular organization and the miscibility of the components in the ultrathin films were drawn. The Langmuir films were transferred onto the quartz plates at surface pressures below the collapse point. The polarized absorption spectra of the Langmuir-Blodgett films were recorded and information about the alignment and intermolecular interactions in the mixtures of the non-amphiphilic dichroic dyes and the liquid crystals with strongly polar terminal groups were obtained.     

Analysis of mixtures of purines and pyrimidines by first- and second-derivative ultraviolet spectrometry

Zero-order, first-derivative and second-derivative ultraviolet absorption spectra of a series of purines, pyrimidines and their binary mixtures in aqueous solution have been recorded at 298 K. It is shown that second-derivative spectra can be used for the identification of eight mixtures of purines and pyrimidines. Several graphical procedures are tested for evaluating derivative spectra in quantitative measurements of single compounds and mixtures. Linear log-log calibration plots are obtained with correlation coefficients generally larger than 0.99. Second-derivative spectra appear to provide a precise and simple method for determination of purines and pyrimidines, at concentrations ranging between 5 x 10(-6) and 5 x 10(-4)M.     

Massenspektrometrische Untersuchungen an Heterocyclen—V Fragmentierungsverhalten Einiger Purine

The mass spectra of 9 purines are discussed. The xanthine purines eliminate HNCO and CO consecutively, whereas 3-methylhypoxanthine loses HCN and CO. In the case of 3-methylxanthine an ion is formed whose stabilization by rearrangement is discussed. The fragmentation pattern of 3-methyl-2-thioxanthine and 3-methyl-thiohypoxanthine is different from that of the corresponding oxygen analogues. 6-Methyl-mercaptopurine and 6-methoxypurine eliminate HCS· or HCO· respectively. For the latter reaction a mechanism is suggested.     

Infrared optical constants, molar absorption coefficients, dielectric constants, molar polarisabilities, transition moments and dipole moment derivatives of liquid N,N-dimethylacetamide-carbon tetrachloride mixtures

Mid-infrared spectra of the DMA-carbon tetrachloride system by transmission and single- and multiple-reflection ATR technique in the whole composition range (0相似文献   

Utility of 4,6-dichloro-2-(methylthio)-5-nitropyrimidine. Part 3: Regioselective solid-phase synthesis of a 2,6,8,9-tetrasubstituted purine library

The first regiocontrolled solid-phase synthesis of a 2,6,8,9-tetrasubstituted purine library was performed through on-resin elaboration of 4,6-dichloro-2-(methylthio)-5-nitropyrimidine. A series of primary amines were loaded on ArgoGel-MB-CHO resin via reductive amination to yield secondary amines. Subsequent attachment of the starting pyrimidine core unit and C6-chloride substitution by primary amines yielded the resin-bound 4,6-disubstituted-2-methylthio-5-nitropyrimidines. Oxone^® mediated oxidation of the 2-methylthio moiety to the corresponding sulfone allowed facile substitution at the 2-position. CrCl₂ assisted reduction of the nitro group, followed by acid catalyzed orthoester cyclization and finally TFA mediated cleavage provided the tetrasubstituted purine final products. Most of the final purines were cleaved in good to excellent yield and purity, however, it was found that bulky groups at N9 hindered cyclization in C8-substituted derivatives. For these systems, LC purification of the crude cleavage products provided the target purines in high purity.     

Synthesis of 8-substituted 5-deazaflavins

To obtain 5-deazaflavins exhibiting red-shifted light absorption spectra, a number of C(8) substituted 5-deazaisoalloxazines were synthesized. This was accomplished a) by the oxidative cyclization of 5,5′-arylmethylenebis(6-methylaminouracil) derivatives and b) by the cyclization of N-methylanilinouracil derivatives with a one-carbon reagent. The latter method led to the formation of impure products. Condensation and oxidation reactions with the π-electron deficient C(8) methyl group in 5-deazalumiflavin did not occur. Introduction of substituents at the C(8) position caused a bathochromic shift that varied between 10 and 40 nm.     

Chiroptical study of α-aliphatic amino acid films in the vacuum ultraviolet region

A series of natural circular dichroism (CD) and absorption spectra for films of α-aliphatic amino acids--such as alanine, aminobutyric acid, norvaline, norleucine, valine, leucine, and isoleucine--in the vacuum ultraviolet (VUV) region were observed with the absolute values of optical constants at the undulator-based CD beamline TERAS BL5. Preliminary predictions of some CD spectra were also performed, based on quantum-chemical calculations using the crystal structure. Although the absorption spectra show similar features to each other, significant differences between the CD spectra were found, especially in the 7-8 eV region. The CD spectra of aliphatic amino acids with branched alkyl groups in the side-chain--such as valine, leucine, and isoleucine--exhibit strong negative CD peaks in this energy region. In contrast, the corresponding CD peaks were weak or absent in the spectra of amino acids with straight alkyl groups. Our simple calculation, and the absorption spectra of alkanes, suggest that this difference partly originates from the contribution of the alkyl group. Clear discrepancies between the CD spectra of these amino acids in solutions and those in the solid state were also observed; this is probably caused by the different molecular structures in each state. Our results clearly indicated that CD spectra in the VUV region were very sensitive to the conformations of chiral molecules.     

Structural features of semi-synthetic galactomannan sulfates

The positions of sulfate groups in two specimens of sulfated galactomannan from Cyamopsis tetragonoloba seeds were established by analysis of ¹H and ¹³C NMR spectra. For the degree of substitution of 0.6, the signals of galactopyranose residues sulfated at position O(6) or simultaneously at positions O(2) and O(3) were the most intense. Minor signals were due to O(2)- or O(3)-monosubstituted and 2,3,4-tri-O-substituted galactose residues. The substitution of mannopyranose residues involved positions O(6) > O(2,3) > O(2) > O(3). At higher degree of substitution (1.0), the pattern of distribution of sulfate groups over various positions in the residues did not change, the molar content of 2,3-di-O-substituted galactopyranose residues being higher than the content of 6-O-monosubstituted residues. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1745–1749, August, 2008.     

微过氧化物酶-8与Eu3+相互作用的机理

用紫外-可见(UV-Vis)吸收光谱和电化学方法研究Eu3+与微过氧化物酶-8(MP-8)相互作用的机理,发现Eu3+优先与MP-8中血红素基团的2个丙酸基的羧基氧发生强的配位作用,导致MP-8分子中血红素基团的非平面性、暴露程度和电化学可逆性的增加.过剩的Eu3+与MP-8分子中肽链上的含氧基团发生弱的相互作用,对血红素基团结构的影响较小.     

Synthesis of 4-(5-Nitrophenylfur-2-yl)-1,2,3-thia- and Selenadiazoles

Arylation of 2-acetylfuran with o-, m-, and p-nitrophenyldiazonium salts under the conditions of the Gomberg-Bachmann reaction has afforded the corresponding 5-(nitrophenyl)-2-acetylfurans. Their carbo-ethoxyhydrazones have undergone the cyclization into stable 4-(5-nitrophenylfur-2-yl)-1,2,3-thiadiazoles under the conditions of the Hurd-Mori reaction. Analogous semicarbazones have afforded the corresponding selenadiazoles upon oxidation with selenium dioxide. The analysis of electronic absorption spectra of the obtained hybrid heterocycles has shown that the conjugation of the phenyl and the furan ring in o-nitrophenyl derivatives is distorted due to steric hindrance, whereas the effect of direct polar conjugation leading to strong bathochromic shift of the absorption band has been observed in the case of the p-nitro derivatives. The position and intensity of the bands in the electronic absorption spectra of the studied compounds are determined by electronic as well as steric factors. The difference in the length of conjugation chain determined by the position of the nitro group in the phenyl fragment also contributes to the observed trend. The introduction of selenadiazole fragment instead of thiadiazole one has caused slight bathochromic shift of the band in the electron absorption spectra.

     

Photochromic polypeptides

Two photochromic polypeptides were synthesized by reaction of 1-(4-iodobutyl)-3,3- dimethylindolindolino-6′-nitrobenzospiropyran with poly-L -tyrosine; their molar contents on photochromic units were 27.3 and 44.7%. The spectra of the photo-induced merocyanines and their decoloration kinetics were compared with these of the monomeric model compound, obtained by reaction of the same N-(4-iodobutyl)-indolinospiropyran derivative with N-acetyltyrosine methyl ester. Different types of solvents have been examined, mainly dimethylformamide and pyridine, acetone and tetrahydrofuran, and methanol and ethylene glycol. The polypeptides showed a much less pronounced solvatochromism than their model; on the other hand, their absorption spectra presented two absorption maxima instead of one for the model. These differences in photochromic behavior were interpreted on the basis of the solvatation of the polymeric chain. Inverse photochromism was observed for polypeptide P₂ as well as for the model in ethylene glycol solution; this effect is due to a higher merocyanine content at the thermal equilibrium spiropyran ? merocyanine in high polar solvent.     

Intramolecular interaction in aryldihydrothiophene 1,1-dioxides

The peculiarities of the intramolecular interaction in unsaturated five-membered cyclic sulfones as a function of their structures were studied on the basis of an analysis of the electronic absorption spectra of single crystals of isomeric -aryldihydrothiophene 1,1-dioxides at 4.2°K, the IR spectra of the molecules at 298°K, and the results of x-ray diffraction analysis of 3-phenyl-4,5-dihydrothiophene 1,1-dioxide. In addition to the inductive effect, conjugation of the SO₂ group with the -electron system of 3-phenyl-4,5-dihydrothiophene 1,1-dioxide, which is manifested most appreciably in the excited electronic state, was observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1056–1059, August, 1977.     

Norbornanes. Part 19. The Inductive Model for Norbornyl Cation Formation

Two CH₃ groups at C(6) of 2-exo- ( 10a ) and 2-endo-norbornyl p-toluenesulfonate 11a lower their solvolysis rates in 80% EtOH by factors of 28 and 16, respectively. A spirocyclopropyl group including C(6), as in 21a and 22a , reduces the rate of exo- and endo-ionization by factors of 250 and 8, respectively. The geminally dimethyl-substituted tosylates 10a and 11a yield the 2-exo-alcohol 10b , whereas the spirocyclopropyl-substituted tosylates 21a and 22a furnish rearranged 3-brendanol 23 . These findings are readily rationalized by the inductive model, according to which norbornyl cation formation is controlled by the inductive effect of dorsal substituents.     

Polar Effects in the Solvolysis of 4-Substituted Bicyclo [2.2.2]octyl p-Nitrobenzenesulfonates. Polar effects. VII

Hydrolysis of bicyclo[2.2.2]octylp-nitrobenzenesulfonate ( 14a , X = p-NO₂C₆H₄SO₃), and nineteen 4-R-substituted derivatives 14b–14t in 70% aqueous dioxane yield the corresponding bicyclo[2.2.2]octanols 14 (X = OH), exclusively. The 7-center fragmentation to 1,4-dimethylidene-cyclohexane ( 15 ) is not observed. The logarithms of most of the rate constants, measured in 80% ethanol, correlate well with the corresponding inductive substituent constants σ of R. Hence, in these cases ionization rate is controlled by the inductive effect of R only. Poor correlations result when the substituents are potentially electrofugal groups, such as COO^?, CH₂OH, CH₂NH₂, CONH₂ and H, the deviations from the inductive regression line corresponding to rate enhancements of 1.6 to 8. These exalted substituent effects are tentatively ascribed to extended hyperconjugation involving two σ-bonds. This study corroborates previous evidence that the inductive effect alone does not fully account for the polar effect of some substituents in reactions involving carbocations.     

Donor‐Acceptor‐Functionalized Tetraethynylethenes with Nitrothienyl Substituents: Structure‐Property Relationships

Tetraethynylethenes (TEEs) functionalized with donor (4‐(dimethylamino)phenyl) and acceptor (5‐nitro‐2‐thienyl) groups were prepared by Pd⁰‐catalyzed Sonogashira cross‐coupling reactions (Schemes 1 – 6). The physical properties of these novel chromophores were examined and compared with those of analogous systems containing 4‐nitrophenyl instead of 5‐nitro‐2‐thienyl acceptor groups. X‐Ray crystal‐structure analyses showed the π‐conjugated frameworks of 2 , 11 , and 13 , including the TEE core and all aryl moieties, to be nearly perfectly planar (Figs. 1, 3, and 4). In contrast, one 4‐(dimethylamino)phenyl group in 10 is rotated almost 90° out of the molecular plane, presumably due to crystal‐packing effects (Fig. 2). The analysis of bond lengths and bond angles revealed little, if any, evidence of intramolecular ground‐state donor‐acceptor interactions. The electrochemical behavior of nitrothienyl‐substituted TEEs is similar to that of the corresponding nitrophenyl‐functionalized derivatives (Table 3). The nitrothienyl groups were reduced at −1.23 V (vs. the ferrocene/ferricinium couple, Fc/Fc⁺), regardless of the degree or pattern of other substitutions. For nonsymmetrical TEE 13 , the reduction of the nitrothienyl group at −1.23 V is followed by a reduction of the nitrophenyl group at −1.40 V, a potential typical for the reduction of other nitrophenyl‐substituted TEEs, such as 17 – 20 . UV/VIS Spectroscopy showed a consistently lower‐energy absorption cutoff for nitrothienyl derivatives compared with the analogous nitrophenyl‐substituted TEEs that confirms a lowering of the HOMO‐LUMO gap as a result of nitrothiophene substitution (Figs. 5 and 6). A comparison of the tetrakis‐arylated TEEs 11 , 13 , and 20 clearly showed a steady bathochromic shift of the longest‐wavelength absorption maximum and the end‐absorption upon sequential replacement of nitrophenyl by nitrothienyl groups. Quantum‐chemical computations were performed to explain a number of complex features of the electronic absorption spectra. All empirical features of relevance in the experimental UV/VIS spectra for 2 , 5 , 6 , and 17 – 19 were correctly reproduced by computation (Tables 4 and 5). The combination of theory and experiment was found to be very useful to explain the particular acceptor properties of the 5‐nitro‐2‐thienyl group.     

Cocyclotrimerization of 6-alkynylpurines with alpha,omega-diynes as a novel approach to biologically active 6-arylpurines

Transition metal complex catalyzed cocyclotrimerization of 6-alkynylpurines 1 with various diynes enables the preparation of a plethora of substituted 6-arylpurines 3 in good yields. The most general catalyst for the reaction is a user-friendly system based on a nickel-phosphine complex and reductant (NiBr(2)(dppe)/Zn) in MeCN. The reaction conditions are compatible with various protective groups on the purine moiety (Bn, THP). As far as other potential catalysts were concerned, only CoBr(PPh(3))(3) showed reasonable activity in cocyclotrimerization of alkynylpurines with dipropargyl ether. A comparison of catalytic with stoichiometric approaches and the ligand effect in the catalyst is also given. Cytostatic activity screening of title 6-arylpurines was performed and several moderately active compounds were found.     

A Photophysical Study of Purines and Theophylline by Using Laser-Induced Optoacoustic Spectroscopy

Abstract— The photophysics of purinic compounds (purine, 6-meth-ylpurine, 6-aminopurine [adenine], 6-chloropurine, 6-methoxypurine) and theophylline in acetonitrile solution were studied by pulsed laser-induced optoacoustic spectroscopy (LIOAS) exciting at 266 nm. The effect of O₂, Xe and MnCl₂ on the photophysical behavior of these compounds was studied; as well, the formation quantum yield of purine and 6-methylpurine triplet states were determined, with φ_T= 0.88 ± 0.03 for both compounds. Multiphotonic and depletion processes were observed at high laser fluences. In order to explain this behavior, theoretical UV-visible absorption electronic spectra from both the S₀ and S₁ state have been calculated for purines and theophylline by using the semiempirical PM3 and ZINDO/S methods.     

矿物药金礞石的红外光谱分析

采用傅立叶红外光谱法分析了金礞石试样,对所得图谱进行解析,发现试样的红外光谱具备层状硅酸盐矿物的吸收特征.其吸收带主要分为4个区域:3 700～3 000 cm-1区间的OH伸缩振动吸收,1 620 cm-1左右处的H2O弯曲振动吸收,1 000 cm-1左右处的Si-O伸缩振动吸收和550～400 cm-1区间的Si...