- Label-Free Surface Enhanced Raman Scattering Approach for High-Throughput Screening of Biocatalysts
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Biocatalyst discovery and directed evolution are central to many pharmaceutical research programs, yet the lack of robust high-throughput screening methods for large libraries of enzyme variants generated (typically 106-108) has hampered progress and slowed enzyme optimization. We have developed a label-free generally applicable approach based on Raman spectroscopy which results in significant reductions in acquisition times (>30-fold). Surface enhanced Raman scattering (SERS) is employed to monitor the enzyme-catalyzed conversion by xanthine oxidase of hypoxanthine to xanthine to uric acid. This approach measures the substrates and products directly and does not require chromogenic substrates or lengthy chromatography, was successfully benchmarked against HPLC, and shows high levels of accuracy and reproducibility. Furthermore, we demonstrate that this SERS approach has utility in monitoring enzyme inhibition illustrating additional medical significance to this high-throughput screening method.
- Westley, Chloe,Xu, Yun,Carnell, Andrew J.,Turner, Nicholas J.,Goodacre, Royston
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Read Online
- Identification of function and mechanistic insights of guanine deaminase from Nitrosomonas europaea: Role of the C-terminal loop in catalysis
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NE0047 from Nitrosomonas europaea has been annotated as a zinc-dependent deaminase; however, the substrate specificity is unknown because of the low level of structural similarity and sequence identity compared to other family members. In this study, the function of NE0047 was established as a guanine deaminase (catalytic efficiency of 1.2 × 105 M-1 s-1), exhibiting secondary activity towards ammeline. The structure of NE0047 in the presence of the substrate analogue 8-azaguanine was also determined to a resolution of 1.9 A?. NE0047 crystallized as a homodimer in an asymmetric unit. It was found that the extreme nine-amino acid C-terminal loop forms an active site flap; in one monomer, the flap is in the closed conformation and in the other in the open conformation with this loop region exposed to the solvent. Calorimetric data obtained using the full-length version of the enzyme fit to a sequential binding model, thus supporting a cooperative mode of ligand occupancy. In contrast, the mutant form of the enzyme (ΔC) with the deletion of the extreme nine amino acids follows an independent model of ligand occupancy. In addition, the ΔC mutant also does not exhibit any enzyme activity. Therefore, we propose that the progress of the reaction is communicated via changes in the conformation of the C-terminal flap and the closed form of the enzyme is the catalytically active form, while the open form allows for product release. The catalytic mechanism of deamination was also investigated, and we found that the mutagenesis of the highly conserved active site residues Glu79 and Glu143 resulted in a complete loss of activity and concluded that they facilitate the reaction by serving as proton shuttles.
- Bitra, Aruna,Hussain, Bhukya,Tanwar, Ajay Singh,Anand, Ruchi
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Read Online
- The Influencing of Preanodized Inlaying Ultrathin Carbon Paste Electrode on the Oxidation for the Xanthine and Hypoxanthine by the Hydrogen Bond
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In this paper, a pre-anodized inlaying ultrathin carbon paste electrode (PAIUCPE) with 316L as a matrix was constructed by a simple and fast electrochemical pretreatment. Using xanthine (Xa) and hypoxanthine (HXa) as the target compounds, the pH effects compositions of buffer solution, the accumulation times, hydrogen bond catalysis, degree of auxiliary electrode reaction on the size of peak currents (Ip) of Xa and HXa was discussed in detail. Also, it was proposed that Xa and HXa were respectively absorbed at the surface of PAIUCPE through hydrogen bonding. The influencing mechanisms of the PAIUCEP on electrochemical oxidation of Xa and HXa were explained in detail. Moreover, the linear relationships for the Xa and HXa were obtained in the range of 6×10-8-3×10-5 mol/L and 2×10-7-7×10-5 mol/L, respectively. The detection limits for the Xa and HXa were 1.2×10-8 mol/L and 5.7×10-8 mol/L, respectively. Moreover, this proposed method could be applied to determine the Xa and HXa in human urine simultaneously with satisfactory results.
- Qiao, Yue-Chun,Li, Jing,Li, Yao,Li, Quan-Min
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Read Online
- Real-Time Monitoring of Human Guanine Deaminase Activity by an Emissive Guanine Analog
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Guanine deaminase (GDA) deaminates guanine to xanthine. Despite its significance, the study of human GDA remains limited compared to other metabolic deaminases. As a result, its substrate and inhibitor repertoire are limited, and effective real-time activity, inhibitory, and discovery assays are missing. Herein, we explore two emissive heterocyclic cores, based on thieno[3,4-d]pyrimidine (thN) and isothiazole[4,3-d]pyrimidine (tzN), as surrogate GDA substrates. We demonstrate that, unlike the thieno analog, thGN, the isothiazolo guanine surrogate, tzGN, does undergo effective enzymatic deamination by GDA and yields the spectroscopically distinct xanthine analog, tzXN. Further, we showcase the potential of this fluorescent nucleobase surrogate to provide a visible spectral window for a real-time study of GDA and its inhibition.
- Bucardo, Marcela S.,Wu, You,Ludford, Paul T.,Li, Yao,Fin, Andrea,Tor, Yitzhak
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p. 1208 - 1214
(2021/07/26)
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- Inhibition of xanthine oxidase by theaflavin: Possible mechanism for anti-hyperuricaemia effect in mice
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Xanthine oxidase (XO) catalyzes the oxidation of hypoxanthine to xanthine and then to uric acid. Excessive production of uric acid leads to hyperuricaemia. Due to the serious side effects of allopurinol, it is an urgent need to explore new XO inhibitors. Herein, the effects of theaflavin (TF1) on XO and anti-hyperuricaemia effect in hyperuricemic mice were investigated. Kinetic analysis indicate that TF1 is a reversible competitive inhibitor and has a significant inhibitory effect on XO with an IC50 value of 63.17 ± 0.13 μmol/L. Analysis of fluorescence spectra suggests that TF1 causes the obvious fluorescence quenching of XO, which is mainly driven by hydrophobic interactions and hydrogen bonds. Docking studies demonstrate that TF1 interacts with dozens of amino acid residues surrounded in the active cavity of XO, including Glu-879, Pro-1012, Thr-1010, Val-1011, Lys-771, Glu-802, Pro-1076, Leu-873, Leu-1014, Asn-768, Leu-648 and Phe-649. The inhibitory mechanism may be the insertion of TF1 into the active site of XO, which hinders the substrate xanthine to enter into the site. Furthermore, the results from animal experiments demonstrate that TF1 is effective in reducing serum uric acid in mice. These findings suggest that TF1 may be a potential drug candidate for the treatment of hyperuricaemia.
- Chen, Jianmin,Jin, Nan,Li, Qinglian,Ran, Mengnan,Ruan, Zhipeng,Ye, Yaling
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- SUBSTITUTED XANTHINE DERIVATIVES
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The present invention relates to compounds of formula (I) a process for their manufacture, pharmaceutical compositions containing them and their use in therapy, particularly in the treatment of conditions having an association with TRPC5 containing ion channels. R1, R2, R3, R4 and R5 have meanings given in the description.
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Page/Page column 41
(2020/07/07)
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- Preparation method of xanthine
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The invention discloses a preparation method of xanthine. The preparation method comprises the following steps that 1, guanine performs diazo-reaction with sodium nitrite in a dilute acid or diazotized recovered mother solution; 2, after the diazo-reaction is completed, solid-liquid separation is performed, the step 3 is conducted on the obtained solid, and optionally the obtained liquid serves asthe diazotized recovered mother solution is reused in the step 1; 3, the solid obtained in the step 2 is subjected to hydrolysis reaction, and after reaction is completed, the xanthine is obtained posttreatment. The guanine is adopted as an initial raw material, the new preparation method is adopted, prepared diazonium salt is extracted from a system, the side reaction is inhibited, meanwhile reuse of the diazo-reaction mother solution is achieved, and the yield of three wastes is greatly reduced; in addition, a new refining method is adopted, so that the molar yield and product purity are far higher than literature values.
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Paragraph 0052-0061
(2019/02/10)
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- One-Step Synthesis of 2-Fluoroadenine Using Hydrogen Fluoride Pyridine in a Continuous Flow Operation
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We report the development of a one-pot synthesis of 2-fluoroadenine from an inexpensive 2,6-diaminopurine starting material using diazonium chemistry in a continuous fashion. Given the sensitivity of this transformation to temperature, we conducted critical experiments to study the exothermicity of the reaction and the heat removal, which were critical for the development of the process. Our goal was to improve the yield and purity of this pharmaceutical intermediate (2-fluoroadenine) and develop a more robust process.
- Salehi Marzijarani, Nastaran,Snead, David R.,McMullen, Jonathan P.,Lévesque, Fran?ois,Weisel, Mark,Varsolona, Richard J.,Lam, Yu-Hong,Liu, Zhijian,Naber, John R.
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supporting information
p. 1522 - 1528
(2019/07/10)
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- Hydroxyl radical induced oxidation of theophylline in water: A kinetic and mechanistic study
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Oxidative destruction and mineralization of emerging organic pollutants by hydroxyl radicals (OH) is a well established area of research. The possibility of generating hazardous by-products in the case of OH reaction demands extensive investigations on the degradation mechanism. A combination of pulse radiolysis and steady state photolysis (H2O2/UV photolysis) followed by high resolution mass spectrometric (HRMS) analysis have been employed to explicate the kinetic and mechanistic features of the destruction of theophylline, a model pharmaceutical compound and an identified pollutant, by OH in the present study. The oxidative destruction of this molecule, for intermediate product studies, was initially achieved by H2O 2/UV photolysis. The transient absorption spectrum corresponding to the reaction of OH with theophylline at pH 6, primarily caused by the generation of (T8-OH), was characterised by an absorption band at 330 nm (k2 = (8.22 ± 0.03) × 109 dm3 mol-1 s-1). A significantly different spectrum (λmax: 340 nm) was observed at highly alkaline pH (10.2) due to the deprotonation of this radical (pKa ～ 10.0). Specific one electron oxidants such as sulphate radical anions (SO4-) and azide radicals (N 3) produce the deprotonated form (T(-H)) of the radical cation (T+) of theophylline (pKa 3.1) with k2 values of (7.51 ± 0.04) × 109 dm3 mol-1 s-1 and (7.61 ± 0.02) × 109 dm3 mol-1 s-1 respectively. Conversely, oxide radicals (O -) react with theophylline via a hydrogen abstraction protocol with a rather slow k2 value of (1.95 ± 0.02) × 109 dm3 mol-1 s-1. The transient spectral studies were complemented by the end product profile acquired by HRMS analysis. Various transformation products of theophylline induced by OH were identified by this technique which include derivatives of uric acids (i, iv & v) and xanthines (ii, iii & vi). Further breakdown of the early formed product due to OH attack leads to ring opened compounds (ix-xiv). The kinetic and mechanistic data furnished in the present study serve as a basic frame work for the construction of OH induced water treatment systems as well as to understand the biological implications of compounds of this kind. the Partner Organisations 2014.
- Sunil Paul,Aravind,Pramod,Saha,Aravindakumar
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p. 5611 - 5620
(2014/07/22)
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- Characterization of inosine-uridine nucleoside hydrolase (RihC) from Escherichia coli
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A non-specific nucleoside hydrolase from Escherichia coli (RihC) has been cloned, overexpressed, and purified to greater than 95% homogeneity. Size exclusion chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis show that the protein exists as a homodimer. The enzyme showed significant activity against the standard ribonucleosides with uridine, xanthosine, and inosine having the greatest activity. The Michaelis constants were relatively constant for uridine, cytidine, inosine, adenosine, xanthosine, and ribothymidine at approximately 480 μM. No activity was exhibited against 2′-OH and 3′-OH deoxynucleosides. Nucleosides in which additional groups have been added to the exocyclic N6 amino group also exhibited no activity. Nucleosides lacking the 5′-OH group or with the 2′-OH group in the arabino configuration exhibited greatly reduced activity. Purine nucleosides and pyrimidine nucleosides in which the N7 or N3 nitrogens respectively were replaced with carbon also had no activity.
- Arivett, Brock,Farone, Mary,Masiragani, Ranjith,Burden, Andrew,Judge, Shelby,Osinloye, Adedoyin,Minici, Claudia,Degano, Massimo,Robinson, Matthew,Kline, Paul
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p. 656 - 662
(2014/03/21)
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- Discovery of a bacterial 5-methylcytosine deaminase
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5-Methylcytosine is found in all domains of life, but the bacterial cytosine deaminase from Escherichia coli (CodA) will not accept 5-methylcytosine as a substrate. Since significant amounts of 5-methylcytosine are produced in both prokaryotes and eukaryotes, this compound must eventually be catabolized and the fragments recycled by enzymes that have yet to be identified. We therefore initiated a comprehensive phylogenetic screen for enzymes that may be capable of deaminating 5-methylcytosine to thymine. From a systematic analysis of sequence homologues of CodA from thousands of bacterial species, we identified putative cytosine deaminases where a "discriminating" residue in the active site, corresponding to Asp-314 in CodA from E. coli, was no longer conserved. Representative examples from Klebsiella pneumoniae (locus tag: Kpn00632), Rhodobacter sphaeroides (locus tag: Rsp0341), and Corynebacterium glutamicum (locus tag: NCgl0075) were demonstrated to efficiently deaminate 5-methylcytosine to thymine with values of kcat/Km of 1.4 × 105, 2.9 × 104, and 1.1 × 103 M-1 s-1, respectively. These three enzymes also catalyze the deamination of 5-fluorocytosine to 5-fluorouracil with values of kcat/Km of 1.2 × 105, 6.8 × 104, and 2.0 × 102 M-1 s-1, respectively. The three-dimensional structure of Kpn00632 was determined by X-ray diffraction methods with 5-methylcytosine (PDB id: 4R85), 5-fluorocytosine (PDB id: 4R88), and phosphonocytosine (PDB id: 4R7W) bound in the active site. When thymine auxotrophs of E. coli express these enzymes, they are capable of growth in media lacking thymine when supplemented with 5-methylcytosine. Expression of these enzymes in E. coli is toxic in the presence of 5-fluorocytosine, due to the efficient transformation to 5-fluorouracil.
- Hitchcock, Daniel S.,Fedorov, Alexander A.,Fedorov, Elena V.,Almo, Steven C.,Raushel, Frank M.
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p. 7426 - 7435
(2015/04/16)
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- Proposed mechanisms for HOOOH formation in two typical enzyme reactions responsible for superoxide anion production in biological systems
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We investigated the hypoxanthine (HPX)-xanthine oxidase (XOD) reaction by examining the chemiluminescence (CL) response mediated by a luminol analog, 8-amino-5-chloro-7-phen-y]pyrido[3,4-d]pyridazine-1,4-(2H, 3H)-dione sodium salt (1-012). It was found th
- Kohno, Masahiro,Sato, Emiko,Yaekashiwa, Noriko,Mokudai, Takayuki,Niwano, Yoshimi
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experimental part
p. 302 - 307
(2010/01/16)
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- HAIR TREATMENT PRODUCTS COMPRISING POLYMERS
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The invention relates to hair treatment products, comprising at least one copolymer made of 0.1 to 50% (in relation to the total number of monomers in the copolymer) monomers of the formula (I), wherein the unknowns are defined as in claim 1, and A2) are monomers from the group of acrylic acid, methacrylic acid and the like, and—optionally non-ionic monomers from the group of acrylamide, vinyl alcohol, and the like, wherein the monomers A2 and A3 together represent 50 to 99.9% (in relation to the total number of monomers in the copolymer) of the copolymer, at least one silicon and at least one selected care product, wherein the products result in advantageous effects for skin and hair.
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- Photosensitized oxidation of hypoxanthine and xanthine by aluminum phthalocyanine tetrasulfonate. Role of the alkylating quinone 2,5-dichloro-diaziridinyl-1,4-benzoquinone
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Photoirradiation of nitrogen-saturated aqueous solutions containing aluminum phthalocyanine tetrasulfonate (AlPcS4) at 675 nm in the presence of 2,5-dichloro-diaziridinyl-1,4-benzoquinone (AZDClQ) and hypoxanthine (HX) produces the oxidized HX
- Alegria, Antonio E.,Inostroza, Yaritza,Kumar, Ajay
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experimental part
p. 1583 - 1588
(2009/04/06)
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- One-step synthesis of lumazine and xanthine: First co-crystal of lumazine and perchloric acid with a unique monohydrated hydronium ion (H 5O2+) mediated supramolecular assembly of the lumazine dimer
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A perchloric acid mediated one-step synthesis of lumazine derivatives from pterins and xanthine from guanine is reported. However, 2-pivaloylamino derivatives of pterins underwent simple hydrolysis of the pivaloylamino group generating free pterin compounds, but the 2-oxo derivatives, that is, the lumazine compounds, were not obtained. A novel supramolecular assembly is constructed by the unique hydrogen bonding of H5O2 + bridging two hydrogen-bonded dimers of lumazine to form the co-crystal 21 with aqueous perchloric acid. In contrast, N2-pivaloyl- 6-bromo-5-deazapterin was simply hydrolysed to form the protonated deazapterin 22, which forms a unique six-membered cyclic hydrogen-bonded structure leading to the generation of a polymeric supramolecular assembly. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Goswami, Shyamaprosad,Maity, Annada C.,Fun, Hoong-Kun
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p. 4056 - 4064
(2008/02/13)
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- Design of inhibitors against guanase: Synthesis and biochemical evaluation of analogues of azepinomycin
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As part of a program to design rational, mechanism-based inhibitors of guanase, we report here the synthesis and biochemical screening of two analogues of azepinomycin (1 and 2), a naturally occurring inhibitor of guanase, known to mimic the transition-state of the enzyme-catalyzed reaction. Our biochemical results show that compounds 1 and 2 are competitive inhibitors with Ki of 2.01 ± 0.16 × 10-5 and 5.36 ± 0.14 × 10-5 M, respectively.
- Ujjinamatada, Ravi K.,Bhan, Anila,Hosmane, Ramachandra S.
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p. 5551 - 5554
(2007/10/03)
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- Comprehensive study of bioanalytical platforms: Xanthine oxidase
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A comprehensive study of a general bioanalytical platform for biosensor applications is presented using xanthine oxidase (XnOx) as a case study within the framework of developing approaches of broad applicability. In this context, emphasis is placed on amperometric biosensors based on XnOx, which has been immobilized by covalent binding to gold electrodes modified with dithiobis-N-succinimidyl propionate. The immobilized XnOx layers have been characterized using atomic force microscopy under liquid conditions and quartz crystal microbalance techniques. In addition, spatially resolved mapping of enzymatic activity has been carried out using scanning electrochemical microscopy. Redox dyes of phenothiazine derivatives, specifically, thionine and methylene blue, have been found to work well as electron acceptors for reduced XnOx. The kinetic parameters and equilibrium constants of the mediated enzymatic oxidation of xanthine in the presence of the above-mentioned redox dyes have been calculated. The response of the enzymatic electrode to varying xanthine concentrations has been obtained in the presence of thionine or methylene blue as redox mediator in solution. Under these conditions, xanthine could be determined amperometrically at +0.2 V versus SSCE.
- Casero,De Quesada, A. Martinez G.,Jin,Quintana,Pariente,Abruna,Vazquez,Lorenzo
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p. 530 - 537
(2008/02/07)
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- Compositions and methods of use of 8-nitroguanine
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Novel methods for the synthesis of 8-nitroguanine are provided. Compositions comprising 8-nitroguanine, made by the novel synthetic methods are also provided herein. Methods of use of 8-nitroguanine, made by the novel synthetic methods, as a standard for detection of 8-nitroguanine in samples are also encompassed within the scope of the present invention. The present invention further concerns methods of predicting organ transplant rejection and detecting exposure to environmental stressors, such as ionizing radiation, toxic chemicals or infectious agents, by detecting 8-nitroguanine in one or more samples from a transplant recipient or an organism exposed to stress.
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Page column 15-17
(2010/02/08)
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- Amide substituted xanthine derivatives
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The present invention is a 1,3,8 substituted xanthine derivative of formula I or a pharmaceutically acceptable salt thereof, wherein R1, R2 and R3 are as defined in the specification. Compounds of formula I and pharmaceutically acceptable salts or prodrugs thereof show activity as modulators of gluconeogenesis.
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- Nitration of 2′-deoxyguanosine by a NO/O2 gas mixture: Identification and characterization of N2-nitro-2′ -deoxyguanosine
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(Matrix presented) A gas mixture of NO and O2 was bubbled into 2′-deoxyguanosine solution at neutral pH and 37°C. A novel nitrated nucleoside was generated in the reaction mixture in addition to 8-nitroguanine, 8-nitroxanthine, 2′-deoxyxanthosine, xanthine, and guanine. The novel nucleoside was identified as N2-nitro-2′-deoxyguanosine by spectrometric data.
- Yamada, Masaki,Suzuki, Toshinori,Kanaori, Kenji,Tajima, Kunihiko,Sakamoto, Shunji,Kodaki, Tsutomu,Makino, Keisuke
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p. 3173 - 3176
(2007/10/03)
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- Substituted 8-phenylxanthines useful as antagonists of A2B adenosine receptors
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The present invention provides compounds having the formula I: X is (C1-C8)alkylene, (C2-C8)alkenylene, (C2-C8)alkynylene, wherein one of the carbon atoms in the alkylene, alkenylene or alkynylene groups is optionally replaced with a group having the formula —O—, —N(R4)C(O)—, —OC(O—, S—, —S(O)—or —SO2—, or a pharmaceutically acceptable salt thereof and pharmaceutical compositions comprising compounds having the formula I. The compounds of the invention are selective antagonists of A2Badenosine receptors (ARs). These compounds and compositions are useful as pharmaceutical agents for treatment of diseases that are mediated by A2Badenosine receptors.
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- Highly efficient synthesis of 1H-quinazoline-2,4-diones using carbon dioxide in the presence of catalytic amount of DBU
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The first example of chemical fixation of carbon dioxide in the presence of catalytic amount of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) or DBN (1,5-diazabicyclo[4.3.0]non-5-ene) was developed. Carbon dioxide easily reacted with 2-aminobenzonitriles under
- Mizuno, Takumi,Ishino, Yoshio
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p. 3155 - 3158
(2007/10/03)
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- Synthesis of purine antiviral agents, hypoxanthine and 6-mercaptopurine
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Some potentially biologically active 6-substituted purine derivatives have been synthesized from simple organic reagents. The reaction of urea with ethyl cyanoacetate gave 6-aminopyrimidine-2,4-dione which was converted in two steps into purine derivative, xanthine. The latter was treated with formamide at 200°C to obtain hypoxanthine. The chlorination of hypoxanthine with POCl3 gave 6-chloropurine which was converted into 6-mercaptopurine via reaction with thiourea in acetonitrile, followed by treatment with boiling ethanol.
- Sariri,Khalili
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p. 1053 - 1055
(2007/10/03)
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- Analysis of peroxynitrite reactions with guanine, xanthine, and adenine nucleosides by high-pressure liquid chromatography with electrochemical detection: C8-nitration and -oxidation
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Peroxynitrite, the reaction product of nitric oxide and superoxide anion, and a powerful oxidant, was found to nitrate as well as oxidize adenine, guanine, and xanthine nucleosides. A highly sensitive reverse-phase HPLC method with a dual-mode electrochemical detector, which reduces the nitro product at the first electrode and detects the reduced product by oxidation at the second electrode, was applied to detect femtomole levels of 8-nitroguanine and 8-nitroxanthine. This method was used to separate and identify the products of nitration and oxidation from the reactions of nucleosides with peroxynitrite. Peroxynitrite nitrates deoxyguanosine at neutral pH to give the very unstable 8-nitrodeoxyguanosine, in addition to 8-nitroguanine. 8-Nitrodeoxyguanosine, with a half-life of ～10 min at room temperature and ≤3 min at 37 °C, hydrolyzes at pH 7 to 8-nitroguanine. A decrease in the reaction pH resulted in a decrease in the level of C8-nitration. Peroxynitrite also oxidizes deoxyguanosine in a pH-dependent manner, to give 8-oxodeoxyguanosine with a maximum yield (0.5-0.7%) at pH 5. Guanosine and xanthosine exhibit reactivity similar to that of deoxyguanosine toward peroxynitrite at neutral pH, producing only the corresponding 8-nitronucleosides as well as 8-nitroguanine and 8-nitroxanthine, respectively. 8-Nitroguanosine at pH 7, with a half-life of several weeks at 5 °C and 5 h at 37 °C, was much more stable than 8-nitrodeoxyguanosine. C8-nitration was confirmed by dithionite reduction to the corresponding amino nucleosides, which cochromatographed with synthesized 8-amino nucleoside standards. In contrast to guanine nucleosides, adenine nucleosides undergo peroxynitrite-mediated C8 oxidation even at neutral pH to give the corresponding 8-oxoadenine nucleosides in ～0.3% yield. Adenine nitration, though minor compared to C8-oxidation, appears to occur at both C2 and C8 positions of the adenine ring. Lowering the reaction pH from 7 to 5 results in 2.4- and 2.2-fold increases in the yields of 8-oxo-dA and 8-oxo-Ado, respectively, but the level of nitration is not altered.
- Sodum, Rama S.,Fiala, Emerich S.
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p. 438 - 450
(2007/10/03)
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- Formation of 2-chloroinosine from guanosine by treatment of HNO2 in the presence of NaCl
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We investigated the reaction of Guo with nitrous acid in the presence of NaCl. When 1 mM Guo was incubated with 100 mM NaNO2 and 2 M NaCl in sodium acetate buffer at pH 3.2 and 37°C, 2-chloroinosine (2-Cl-Ino) was produced in addition to oxanosine (Oxo) and xanthosine (Xao). The yield of 2-Cl-Ino was 0.033 mM at an incubation time of 2 h. Under the same reaction conditions, GMP and dGuo gave rise to the corresponding 2-chloro derivatives with comparable yields. All the 2-chloro derivatives were fairly stable (t1/2>360 h) at physiological pH and temperature. To elucidate the reaction mechanism of the chlorination, the diazoate derivative of Guo, a reaction intermediate of the Guo-HNO2 system, was employed as a starting compound. When the diazoate was incubated with 2 M NaCl in a neutral solution, 2-Cl-Ino was produced in addition to Oxo and Xao. These results suggest that the 2-chloro derivatives can be produced from foodstuffs in the human stomach and may have potential importance as a carcinogen causing gastric cancer.
- Suzuki, Toshinori,Ide, Hiroshi,Yamada, Masaki,Morii, Takashi,Makino, Keisuke
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p. 2937 - 2941
(2007/10/03)
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- Synthesis of 2,4-dihydroxyquinazolines using carbon dioxide in the presence of DBU under mild conditions
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Chemical fixation of carbon dioxide was performed under mild conditions. Carbon dioxide (1 atm) easily reacted with 2-aminobenzonitriles at 20°C, assisted by DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) to give 2,4- dihydroxyquinazolines in excellent yields.
- Mizuno, Takumi,Okamoto, Noriaki,Ito, Takatoshi,Miyata, Toshiyuki
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p. 1051 - 1053
(2007/10/03)
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- Trisubstituted thioxanthines
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PCT No. PCT/US95/16724 Sec. 371 Date Sep. 29, 1997 Sec. 102(e) Date Sep. 29, 1997 PCT Filed Dec. 12, 1995 PCT Pub. No. WO96/18400 PCT Pub. Date Jun. 20, 1996Disclosed are compounds of formula (I), wherein R1, R3 and R8 are independently alkyl, aryl or aralkyl, and R2 is selected from the group consisting of S and O, R6 is selected from the group consisting of S and O, provided that R2 and R6 are not both O. The compounds are effective PDE IV inhibitors and possess improved PDE IV inhibition and improved selectivity with regard to PDE III inhibition. Methods of treatment using the compounds are also disclosed.
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- Inhibition of nitrous acid-dependent tyrosine nitration and DNA base deamination by flavonoids and other phenolic compounds
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Exposure of tyrosine or DNA bases to acidic nitrite at low pH results in the nitration of tyrosine and the formation of base deamination products, respectively. At pH 1, hypoxanthine and xanthine are formed from the deamination of adenine and guanine, respectively, whereas under the same conditions, uracil is not detected. The yield of 3-nitrotyrosine derived from interaction of equimolar nitrite and tyrosine at pHI is approximately 50% of that obtained from equimolar peroxynitrite-tyrosine interactions at pH 7.4. The ability of a range of plant phenolic constituents to prevent damage mediated by acidic nitrite was also examined in comparison with the activity of vitamin C. The epicatechin/gallate family of flavonols, constituents of green tea, red wine, etc., demonstrates the most extensive inhibitory properties against both tyrosine nitration and base deamination. The results also show that ascorbic acid is a poor inhibitor of nitration or deamination under acidic conditions such as those of the stomach. The ability of plant phenolics to scavenge reactive nitrogen species derived from acidic nitrite may contribute to the protective effects of tea polyphenols against gastric cancer.
- Oldreive, Ceri,Zhao, Kaicun,Paganga, George,Halliwell, Barry,Rice-Evans, Catherine
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p. 1574 - 1579
(2007/10/03)
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- Silyl modification of biologically active compounds. 5. Hydrolytic stability and biological activity of the trialkylsilyl derivatives of some heterocyclic bases
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The kinetics of the desilylation of the triorganosilyl derivatives of some biologically active heterocyclic bases and uridine were investigated by 1H NMR spectroscopy. A correlation was established between the relative rates of desilylation and the steric environment of the silicon atom. In trials on locomotor activity and muscular tone, the effect on memory processes, and the Porsolt test it was found that tris(tert-butylmethylsilyl)barbituric acid has higher sedative activity than barbituric acid. In contrast to uridine, 5′-O-tert-butyldimethylsilyluridine exhibits antitumor activity, suppressing the development of fibrosarcoma in human lungs (HT-1080) and fibroblasts in mice. 1999 Kluwer Academic/Plenum Publishers.
- Lukevits,Segal,Birgele,Zablotskaya
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p. 1076 - 1080
(2007/10/03)
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- Base modification and strand breakage in isolated calf thymus DNA and in DNA from human skin epidermal keratinocytes exposed to peroxynitrite or 3- morpholinosydnonimine
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Exposure of isolated calf thymus DNA and human skin epidermal keratinocytes to peroxynitrite or the peroxynitrite generator, 3- morpholinosydnonimine (SIN-1), led to extensive DNA base modification. Large increases in xanthine and hypoxanthine, possible deamination products of guanine and adenine, respectively, and in 8-nitroguanine were observed, but only small changes in some oxidized base products were seen. This pattern of damage suggests that hydroxyl radicals were not major contributors to base modification caused by peroxynitrite, as OH· is known to cause multiple oxidative modifications to all four DNA bases. Instead, it seems that reactive nitrogen species play a much greater role in the mechanism of base damage, producing both nitration and deamination of purine bases when DNA or whole cells are exposed to peroxynitrite. If this pattern of damage is unique to peroxynitrite, it might act as a marker of cellular damage by this species in vivo.
- Spencer, Jeremy P. E.,Wong, Jon,Jenner, Andrew,Aruoma, Okezie I.,Cross, Caroll E.,Halliwell, Barry
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p. 1152 - 1158
(2007/10/03)
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- Reactions of Nitric Oxide with Amines in the Presence of Dioxygen
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Nitric oxide (NO), a multifaceted bioregulatory agent and an environmental pollutant, can effectively convert aromatic amines to the corresponding triazenes under aerobic conditions, but not under anaerobic conditions.Nucleic acid bases and nucleosides are also determinated via hydrolysis of the diazonium ion products with exposure to aerobic NO solution.A peroxynitrite radical or nitrogen dioxide is suggested to be the ultimate reactive species.
- Nagano, Tetsuo,Takizawa, Hiromasa,Hirobe, Masaaki
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p. 8239 - 8242
(2007/10/02)
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- Xanthines, optionally incorporated in liposomes, for promoting skin or hair pigmentation
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A method of treating skin or hair for promoting pigmentation wherein a xanthine component, in an amount effective to promote pigmentation, is incorporated in liposomes or hydrated lipidic lamellar phases.
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- 1-hydroxyalkylxanthines and medicaments containing them
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Compounds, physiologically acceptable salts of the compounds and pharmaceutical compositions containing the compounds or the salts are provided wherein the compounds have a formula of: STR1 in which R1 is a C2 -C5 ω-hydroxy-n-alkyl group or a C3 -C5 (ω-1)-hydroxy-n-alkyl group, R3 is a C1-C4 alkyl group, R8 is H, methyl, or ethyl and the sum of the carbon atoms in R1 and R3 is between 4 and 9 and provide inotropic (cardiotonic) activity.
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- Electron-transfer reactions of alkyl peroxy radicals
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One-electron-transfer reactions of alkyl peroxy radicals were studied by pulse radiolysis of aqueous solutions. At pH 13, the methyl peroxy radical was found to rapidly, k = 1 × 105-4.9 × 107 s-1, and quantitatively oxidize various organic substrates with E13 = 0.13-0.76 V vs NHE. On the other hand, this radical was unreactive with compounds with E13 ≥ 0.85 V. Consequently, E13 of the methyl peroxy radical is higher than 0.76 V and lower than 0.85 V, which means that E7 is in the range 1.02-1.11 V. At pH 8, the rate constants of the oxidation of four ferrocene derivatives by the alkyl peroxy radicals ranged from 7.1 × 104 M-1 s-1 for ferrocenedicarboxylate (E8 = 0.66 V) to 2.3 × 106 M-1 s-1 for (hydroxymethyl)ferrocene (E8 = 0.42 V). These rate constants were used to evaluate the reduction potential and self-exchange rate of alkyl peroxy radicals in neutral media from the Marcus equation. The calculated E7 = 1.05 V is in excellent agreement with the estimated E7 = 1.02-1.11 V and with one of the perviously published values E7 = 1.0 V, but the value is in excellent agreement higher than the other E7 ～ 0.6 V. It is suggested that the high reorganization energy, λ = 72 kcal mol-1 redox couple originates from the requirement for solvent reorganization due to the solvation of hydroperoxide anion in the transition state. In support of this are the activation parameters of the reaction of the methyl peroxy radical with uric acid. The activation entropy is 9 eu lower at pH 7.3 than it is at pH 13.2, whereas the activation enthalpies are unchanged. The importance of entropy control was verified in the reactions of cyclohexyl peroxy radicals with α- and δ-tocopherol in aerated cyclohexane (ΔH+ ≈ 0 kcal/mol, and ΔS+ = -25 and -26 eu). The implications of these findings on the inactivation of alkyl peroxy radicals in general are discussed.
- Jovanovic, Slobodan V.,Jankovic, Ivana,Josimovic, Ljubica
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p. 9018 - 9021
(2007/10/02)
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- Use of 1,3-diisobutyl-8-methylxanthine as a bronchodilator and antiallergy agent
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The invention relates to the use of 1,3-diisobutyl-8--methylxanthine, or its pharmaceutically acceptable salts, for the treatment or prophylaxis of acute or chronic obstructive airways disease and allergic asthma. The invention also relates to a pharmaceutical composition of an aerosol containing 1,3-diisobutyl-8-methylxanthine, ethanol, sorbitan oleate and one or more freons.
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- 3-METHYLXANTHOSINE: SYNTHESIS AND ACIDIC HYDROLYSIS OF THE GLYCOSYL BOND
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An improved synthesis of 3,9-dimethylxanthine (2a) was achieved via the reaction of 1-methyl-5-(methylamino)-imidazole-4-carboxamide (3a) with EtOCOCl in acetate buffer (pH 5) followed by treatment with aqueous NaOH.This method was successfully applied to the synthesis of 3-methylxanthosine (2b), whose N-glycosidic bond proved to be remarkably sensitive to acidic hydrolysis: 2b underwent hydrolysis at a rate more than 1000 times faster than that of xanthosine (10) in 1.0N aqueous HCl at 25 deg C.Keywords: 3-methylxanthosine synthesis; 3,9-disubstituted xanthine; imidazolylcarbamic acid ester; base-catalyzed cyclization; amide carbamate cyclization; N-glycosidic bond hydrolysis; carbamate cis-trans isomerism; NMR; kinetic study
- Itaya, Taisuke,Harada, Tsunehiro
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p. 1235 - 1238
(2007/10/02)
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- Regioselectivite de la reaction des radicaux hydroxyle et hydroxy-2 propyle-2 avec l'hypoxanthine
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The reactivity of OH and (CH3)2COH radicals with hypoxanthine was studied under comparable γ-irradiation conditions.A difference in regioselectivity of attack by the elelctrophilic OH radical and the nucleophilic (CH3)2COH radical is observed, the latter leading in 70percent yield to a C-8 substituted product.The rate constants of the addition of the radical to hypoxanthine were determined by pulse radiolysis to be k = 1.4E8 M-1 s-1 in acid medium, and in neutral medium k = 7E5 M-1 s-1.The much more reactivee OH radical leads essentially to degradation products arising, inter alia, from attack on C-2 (resulting in the formation of xanthine, which disappears rapidly), while attack at C-8, approximately three times less rapid, leads to the 6,8-diketo purine, which does not undergo further reactions and thus accumulates in the medium.
- Zylber, Jean,Zylber, Nicole,Lefort, Daniel,Ferradini, Christiane,Hickel, Bernard
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p. 283 - 287
(2007/10/02)
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- 8-arylxanthines
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1,3-alkylsubstituted-8-(3,4-,3- or 4-substituted phenyl)xanthines and pharmaceutically acceptable salts of such compounds are disclosed. The 3-substituents are hydrogen, dimethylaminomethyl, or 2,3-dihydroxypropyloxy. The 4-substituents are selected from hydroxy, cyano, --NHCON(R 5) 2, --C( NH)N(R 5) 2, --NH--C( NH)N(R 5) 2, with each R 5 independently being hydrogen or an alkyl group of one to three carbons and provided that when the 3-substituent is hydrogen the 4-substituent is not hydroxy or hydrogen.The compounds are potent adenosine receptor antagonists having relatively low lipophilicity. The compounds are intended for use as bronchodilators and cardiotonics.
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- One-Electron Redox Potentials of Purines and Pyrimidines
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One-electron redox potentials of some purine and pyrimidine derivatives were determined by pulse radiolysis from electron transfer equilibria involving their and other free radicals.The redox potentials were determined at pH 13 by using p-methoxyphenol (E=0.4 V), Trolox C (E=0.19 V), and tryptophan (E=0.56 V) as references.The lowest oxidation potential measured for DNA bases was guanosine (E=0.72 V vs.NHE), and the highest was for 1-methylpyrimidines (E ca. 1.6 V) Uric acid (E=0.26 V) and isobarbituric acid (E=0.13 V) were found to have the lowest potentials.
- Jovanovic, Slobodan V.,Simic, Michael G.
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p. 974 - 978
(2007/10/02)
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- SYNTHESIS AND PROPERTIES OF ANALOGS OF 5(4)-AMINOIMIDAZOLE-4(5)-CARBOXAMIDE AND PURINES. ACYLATION OF 5(4)-AMINOIMIDAZOLE DERIVATIVES.
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The acylation of 5(4)-aminoimidazole derivatives was studied.It is shown that acylation by means of carboxylic acid anhydrides and chlorides takes place at the amino group, whereas acylation by means of chlorocarbonic acid esters takes place at the nitrogen atoms of the imidazole ring.Methods for the selective introduction of a carbomethoxy group in the 1, 3, and 5 positions of the 5(4)-aminoimidazole-4(5)-carboxamide molecule were developed.
- Mokrushin, V. S.,Pospelova, T. A.,Bakulev, V. A.,Golovina, E. F.,Nikolaeva, S. L.,Pushkareva, Z. V.
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p. 204 - 209
(2007/10/02)
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- PHOTOCHEMISTRY OF PURINE 3-OXIDES IN HYDROXYLIC SOLVENTS
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UV irradiation of the potent oncogen hypoxanthine 3-oxide in aqueoous solution induces elimination of and rearrangement of the nitrogen-bound oxygen.The extent of each reaction shows a complex variation over the pH range 0-7.The variations in quantum yield for product formation are shown to result from the presence in the neutral molecule of tautomeric species with differing photochemistries that ionize in the excited state (pKa* ca. 3.5) just above the protonation pKa (1.2).The photochemical reactivity of each ionic and each tautomeric form was assigned by comparing the effect of pH changes between 0 and 11 on the quantum yields for formation of each photoproduct from hypoxanthine 3-oxide with those of two model compounds, 1-hydroxyhypoxanthine and 6-methoxypurine 3-oxide.Photoreduction of the 3-oxides occurs via the triplet state.This process has a relatively consistent low quantum yield (Φ=0.005 to 0.04) for most ionic and tautomeric forms of both purine 1-oxides and purine 3-oxides.Photorearrangement is a much more efficient process for purine 3-oxides (Φ=0.3) than for purine 1-oxides (Φ=0.04).
- Lam, Fuk L.,Parham, James C.
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p. 2371 - 2376
(2007/10/02)
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- Competitive Reactivity of Nitrenium and Carbenium Ion Contributors of Purinium Cations with "Soft" Bases
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Delocalized cations formed by ionization of "activated" esters of carcinogenic purine N-oxides react with many nucleophiles to yield C-substitution products but afford oxidation-reduction products with others.The present study provides experimental support for the proposals (1) that these two reactivities result from nucleophilic substitutions at different sites of the delocalized cations and (2) that HSAB "hard" bases react only at carbenium ion sites to form C-substitution products, while "soft" bases react preferentially at nitrenium ion contributors to afford adducts that ultimately yield redox products. "Soft" bases showed the following order of reactivity at a purine nitrenium ion: iodide ca. selenourea >> thio amides ca. thio acids ca. biselenide > bisulfide ca. thiols ca. disulfides > thiosulfate.This order differs significantly from that observed for the double SN2 displacement reaction of nucleophiles with compounds of the type NH2-X.This appears to be the first report of differing orders of nucleophilicities of bases involved in SN1 and SN2 reactions at electron-deficient nitrogen centers.No evidence was found for radical intermediates formed by electron transfer.
- Parham, James C.,Templeton, Mary Agnes
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p. 652 - 657
(2007/10/02)
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- On the mechanism of reactions of oncogenic n-acyloxypurines-III. Extent of radical participation1 1 This investigation was supported in part by Grants Number CA-08748 and CA-23622, awarded by the National Cancer Institute, DHEW. Ref. 20 is now designated as II in the series and Ref. 16 is designated as I.
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UV irradiation of a model "activated ester" of the oncogen 3-hydroxyxanthine induced homolytic cleavage of the N-O bond and gave products arising by reduction of as well as by recombination of the solvent caged amidyl radical intermediate. Identification of the latter product constitutes the first evidence that a distinct product associated specifically with a radical from an acyloxypurine can be formed. The absence of this product among those formed spontaneously from 3-acetoxyxanthine provides the first indication that an amidyl radical is not an intermediate in the spontaneous reactions of N-acyloxy purines.
- Parham, James C.,Templeton, Mary Agnes
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p. 709 - 713
(2007/10/02)
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