- Common and Potentially Prebiotic Origin for Precursors of Nucleotide Synthesis and Activation
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We have recently shown that 2-aminoimidazole is a superior nucleotide activating group for nonenzymatic RNA copying. Here we describe a prebiotic synthesis of 2-aminoimidazole that shares a common mechanistic pathway with that of 2-aminooxazole, a previously described key intermediate in prebiotic nucleotide synthesis. In the presence of glycolaldehyde, cyanamide, phosphate and ammonium ion, both 2-aminoimidazole and 2-aminooxazole are produced, with higher concentrations of ammonium ion and acidic pH favoring the former. Given a 1:1 mixture of 2-aminoimidazole and 2-aminooxazole, glyceraldehyde preferentially reacts and cyclizes with the latter, forming a mixture of pentose aminooxazolines, and leaving free 2-aminoimidazole available for nucleotide activation. The common synthetic origin of 2-aminoimidazole and 2-aminooxazole and their distinct reactivities are suggestive of a reaction network that could lead to both the synthesis of RNA monomers and to their subsequent chemical activation.
- Fahrenbach, Albert C.,Giurgiu, Constantin,Tam, Chun Pong,Li, Li,Hongo, Yayoi,Aono, Masashi,Szostak, Jack W.
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supporting information
p. 8780 - 8783
(2017/07/12)
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- Kinetics and mechanism of the nucleophilic cleavage of disulfide bond in 2,2′-dithio-diimidazoles with hydroxide ions
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Kinetics of the cleavage of disulfide bond of dithiobisdisulfides of diimidazoles to their parent imidazoles by hydroxide ion have been investigated spectrophotometrically. Rate equation and other observations suggest that the nucleophilic attack of hydroxide ion on one of the sulfur atoms of disulfide bond is a rate limiting step. This process is accompanied by much slower, parallel reaction with water as a nucleophile. Hence the full kinetic equation for nucleophilic cleavage of 2,2′-dithio-diimidazoles in aqueous alkaline solutions is a two-term equation: -(d[RSSR]/dt) = k1 [RSSR][OHl + k2[RSSR][H2O], where k1 > k2. The mechanism of the reaction is proposed.
- Kurzawa,Suszka
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p. 1487 - 1494
(2008/09/18)
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- Kinetics and mechanism of the formation and reactions of S-nitroso derivatives of some heterocyclic thiones
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Rate and equilibrium measurements have been obtained for the nitrosation (using nitrous acid in dilute acid aqueous solution) of the following thione-thiol nitrogen heterocyclic species and for the decomposition reactions of the formed S-NO- io
- Amado,Blakelock,Holmes,Williams
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p. 441 - 447
(2007/10/03)
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- Energy transfer, electron transfer, and addition reactions of triplet state of 1,3-dihydroimidazole-2-thiones investigated by laser flash photolysis
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The transient absorption bands observed at ca. 400 and 550 nm for 1,3- dihydro-2H-imidazole-2-thione (IT), 1,3-dihydro-1-methyl-2H-imidazole-2- thione (MIT), and 1,3-dihydro-2H-benzimidazole-2-thione (BIT) have been assigned to their triplet states (3IT* 's) by the quenching and sensitizing experiments using laser flash photolysis technique. Short intrinsic triplet lifetimes and relatively high triplet energies have been evaluated as characteristics of 3IT* 's. For electron acceptors, photoinduced electron- transfer reaction occurs via 3IT* 's in the diffusion controlled limit. The nucleophilic character of 3IT* 's was confirmed by changing the substituents of alkenes on the addition reactions. MO calculations indicate that the lowest electronic configurations of both 3IT* and 3MIT* have 3(n,π*) character, while 3BIT* has 3(π,π*) character. The addition reactivity of 3BIT* is slightly higher than those of 3IT* and 3MIT*, which is opposite to the general tendency.
- Alam, Maksudul M.,Ito, Osamu
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p. 339 - 345
(2007/10/03)
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- Equilibrium Studies on the Cleavage of Disulfide Bond in 2,2'-Dithio-Diimidazoles with Iodide Ion in Aqueous Solutions
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The equilibrium of the reaction between 2,2'-dithio-diimidazoles and iodide ion in acidic aqueous solutions was studied spectrophotometrically.Cleavage of -S-S- bond and formation of imidazole-2-thiones and iodine, as reaction products, was observed.Factor analysis and spectra's deconvolution were used for estimation of equilibrium system composition and for determination of equilibrium constants.Occurrence of an additional band (with maximum at 30.000 cm-1) in equilibrium spectra was ascribed to the formation of imidazolethione-I2-charge-transfer complex. Key words: charge transfer, complex compounds, equilibrium constants
- Suszka, A.
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p. 565 - 576
(2007/10/02)
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- Fission of 1,2,4-Thiadiazol-3-ones by Triphenylphosphane: Triphenylphosphonio Thioimidazolates and Their Consecutive Reactions
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Treatment of benzimidazothiadiazol-3(2H)-ones (1) and imidazothiadiazol-3(2H)-ones (17) with triphenylphosphan leads to the liberation of isocyanate and the formation of triphenylphosphonio-thiobenzimidazolat (4) and triphenylphosphonio-thioimidazolat (18), respectively. 2,4-Diphenyl-5-phenylimino-1,2,4-thiadiazol-3-one (23) is desulfurized with Ph3P and decomposed into phenyl isocyanate and diphenylcarbodiimide whereas the N-unsubstituted imino-thiadiazol-3-one (25) is attacked at the exocyclic imino group by Ph3P to give the N-phosphoranylidene thiourea (26).The structure of 4 can be rationalized as a dynamic system between polar and apolar valence isomeres.Reactions of 1 and 17 with cyanates, isocyanates, carbon disulfide, acetic anhydride, amines, benzyl chloride, grignard compounds, and CH acidic compounds are described.
- Tittelbach, Franz,Martin, Dieter
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p. 338 - 348
(2007/10/02)
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- 5(1-Piperazinyl(imidazo[2,1-b][1,3,5]benzothiadiazepines
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5-Diazacycloalkyl-imidazo[2,1-b][1,3,5]benzothiadiazepines, e.g. those of the formula STR1 the N-oxides and salts thereof are neuroleptic agents, lacking extrapyramidal side-effects.
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- Cephalosporin displacement reaction
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The present invention is directed to a process for the displacement of the acetoxy group of a cephalosporanic acid by a sulfur nucleophile, in an organic solvent and under essentially anhydrous conditions.
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