Structure of wyosine, the condensed tricyclic nucleoside of torula yeast phenylalanine transfer ribonucleic acid

Large-scale isolation of the minor nucleoside wyosine of torula yeast tRNA(Phe) was accomplished by a combination of enzymatic digestion and reversed-phase chromatography: the wyosine-containing nucleotide fraction, which was obtained by partial digestion of unfractionated tRNA (1 g) with nuclease P1, was concentrated by reversed-phase column chromatography followed by complete digestion with nuclease P1/alkaline phosphatase. The nucleoside mixture thus obtained was purified by reversed-phase HPLC, providing wyosine (70 microg). Comparison of this nucleoside with a chemically synthesized authentic sample has unambiguously established that the structure of wyosine is 4,6-dimethyl-3-beta-D-ribofuranosyl-3,4-dihydro-9H-imidazo[1,2-a]purin-9-one (2).     

Electrochemical reduction of 4-aminopyrimidine and cytosine in dimethyl sulfoxide

The electrochemical reduction in dimethyl sulfoxide of cytosine (4-amino-2-hydroxypyrimidine) and one of its model compounds (4-aminopyrimidine) has been examined. Initially, each pyrimidine (RH) undergoes a reversible, diffusion-controlled one-electron reduction of the 3,4 N=C double bond to the radical anion (RH⁻, which can dimerize or can react with the parent compound (father-son reaction) to form the neutral free radical (RH₂) and the pyrimidine anion (R⁻); the radical can dimerize or be further reduced, perhaps after effectve protonation; the anion forms a redox couple with Hg(1)−Hg(0). Other coupled reactions, which may occur under suitable conditions, include reaction between anionic dimer (⁻RH−RH⁻) and RH, proton-assisted decomposition of dimer to form reducible RH₃⁺, and deamination of the two-electron reduction product (RH₃), which is a gem diamine, to generate 2-hydroxypyrimidine or pyrimidine itself. The effects on the electrochemical redox pattern of added water, strong acid (HClO₄), weak acid (chloroacetic and benzoic acids), and strong base (Et₄NOH) are described.     

Diisobutylaluminum borohydride: An efficient reagent for the reduction of tertiary amides to the corresponding amines under ambient conditions

A synthetically simple mixed metal hydride, diisobutylaluminum borohydride [(iBu)₂AlBH₄], is easily generated from a 1:1 mixture of borane-dimethylsulfide (BMS) and diisobutylaluminum hydride (DIBAL). The reduction of tertiary amides using (iBu)₂AlBH₄ is complete within five minutes under ambient conditions and the product tertiary amines were isolated in 70–99% yields by a simple acid-base extraction. This new methodology, reported herein, works well for reduction of tertiary aliphatic and aromatic amides as well as lactams to the corresponding amines and product isolation and purification does not require column chromatography.     

Solution conformation of the two alditols obtained by sodium borohydride reduction of N-acetylneuraminic acid

The stereochemistries and the conformations of the two alditols1 and2 (3:2) obtained upon reduction of N-acetylneuraminic acid were determined in aqueous solution using proton and carbon nuclear magnetic resonance spectroscopy. Molecular mechanics calculation was proved to be not applicable onto alditols, if the balance of the conformational equilibrium is maintained by 1,3-diaxial interactions. No measurable amount of the -N-acetylneuraminic acid like triple bent alditol form, which is believed to be the substrate of theClostridium perfringens lyase, could be detected in solution. In aqueous solution compound2 is present in its extended form. One can expect that the necessary energy contribution of approximately 1 kcal to fold2 into the form which is recognized by the enzyme is easily available.

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Zur Konformation der beiden durch Reduktion von N-Acetyl-Neuraminsäure mit Natriumborhydrid erhaltenen Alditole in wäßriger Lösung

Zusammenfassung Bei der Reduktion von N-Acetyl-Neuraminsäure mit Natriumborhydrid in wäßriger Lösung werden die Alditole1 und2 im Verhältnis 3:2 gebildet. Die stereochemische Zuordnung und die Konformation der beiden Epimere in Lösung wurden mit Hilfe einer NMR-Analyse durchgeführt. In Ergänzung dazu wurde die Anwendbarkeit von Rechnungen des Typus Molekulare Mechanik auf flexible Moleküle dieser Art untersucht und gefunden, daß Populationen von Konformationen, welche primär durch 1,3-diaxiale Wechselwirkungen determiniert sind, durch Rechnungen dieses Typs nicht vorhersagbar sind. In wäßriger Lösung liegt Verbindung2 in gestreckter Form vor. Die aus2 ableitbare -N-Acetylneuraminsäure ähnliche Konformation, welche dem Substrat derClostridium perfringens-Lyase entspricht, ist um 1 kcal energiereicher als die der gestreckten Form und liegt in Lösung nicht in meßbaren Mengen vor. Man kann erwarten, daß dieser Energiebeitrag unschwer bei der Einbettung in die Enzymtasche der Lyase aufgebracht werden kann.

     

Synthesis and structure of the hypermodified nucleoside of rat liver phenylalanine transfer ribonucleic Acid

The first synthesis of (alphaS,betaS)-beta-hydroxy-alpha-[(methoxycarbonyl)amino]-4,6-dimethyl-9-oxo-3-beta-D-ribofuranosyl-4,9-dihydro-3H-imidazo[1,2-a]purine-7-butanoic acid methyl ester [(alphaS,betaS)-11] has been achieved by OsO(4) oxidation of [S-(E)]-4-[4,6-dimethyl-9-oxo-3-[2,3,5-tris-O-(tert-butyldimethylsilyl)-beta-D-ribofuranosyl]-4,9-dihydro-3H-imidazo[1,2-a]purin-7-yl]-2-[(methoxycarbonyl)amino]-3-butenoic acid methyl ester (13) followed by successive gamma-deoxygenation through the cyclocarbonates, separation from the (alphaS,betaR)-isomer by means of flash chromatography, and deprotection. On the other hand, the minor nucleoside of rat liver tRNA(Phe) was isolated on a scale of 100 microg by partial digestion of unfractionated tRNA (1 g) with nuclease P(1), followed by reverse-phase column chromatography, complete digestion with nuclease P(1)/alkaline phosphatase, and reverse-phase HPLC. Comparison of this nucleoside with the synthetic one has unambiguously established its structure to be (alphaS,betaS)-11.     

Fluorescent probe as reporter on the local structure and dynamics in hydrolysis-condensation process of organotrialkoxysilanes

To get some information on the aggregation behaviors of the products derived from different organotrialkoxysilanes, the hydrolysis-condensation processes of some organotrialkoxysilanes have been examined by means of pyrene as fluorescent probe. The organotrialkoxysilanes used in the research were n-octadecyltri-methoxysilane (ODTMS), n-octyltrimethoxysilane (OTMS), 3-glycidoxypropyltrimethoxysilane (GTMS), 3-methacryloxypropyltrimethoxysilane (MAPTMS), and propyltrimethoxy-silane (PTMS). The results show that pyrene as fluorescence probe can respond sensitively not only to the organization state of the hydrolysates but also to the change in the organization state during the condensation process. The organization states during the hydrolysis and condensation can be explained in terms of structures of the products. In the initial stage, the silanols with long organic chains are amphiphilic molecules, and such nature of the silanols can be compared to that of a surfactant. Therefore, the excimer emission of pyrene is extremely obvious because of such silanols being prone to form aggregates. In the case of silanols having short alkyl groups or epoxy groups, these silanols homogenously disperse in solution, which results in the appearance of an only monomer emission of pyrene. In the late stage, the fluorescence behavior of pyrene is also sensitive to structural evolution of the silicates. The fluorescence spectra of pyrene during the condensation of the silanols with short alkyl groups or epoxy groups are almost in silence, indicating that the condensation products, with a low condensation degree, homogeneously disperse in solution. For the silanols with long hydrophobic substituents in different lengths, the changes in fluorescence spectra of pyrene during the condensation are varied. Commonly, the excimer emission is noticeable, implying that the condensation products with high condensation degree inhomogenously disperse in solution. However, the relative excimer/monomer fluorescence intensity is alkyl chain-length dependent. The longer alkyl chains in the condensation products result in the appearance of the obvious excimer emission. These phenomena imply that the condensation degree of the products increases with the length of the alkyl chains. Additionally, the distorted spectrum of pyrene appears in the case of the organotrialkoxysilanes with side chain substituent, illustrating that the steric hindrance between the substituents can be monitored by fluorescence of pyrene. All these results are verified by the fluorescence-quenching measurements. The approach in the present study gives new insights into the local structure and dynamics in hydrolysis-condensation process of organotrialkoxysilanes and emphasizes the influence of the self-assembling behavior.     

Ultrafast room-temperature reduction of graphene oxide by sodium borohydride,sodium molybdate and hydrochloric acid

Since graphene-based materials have shown great potential in many fields,it is important to explore ultrafast and high-efficient methods to synthesize reduced graphene oxide(rGO) using inexpensive reducing agents under mild conditions.Here,we reported a novel method for the ultrafast chemical reduction of graphene oxide(GO) at room temperature using sodium borohydride(NaBH₄),sodium molybdate(Na₂MoO₄) and hydrochloric acid(HCl).The reduction was carried out within 2 min.A series of characterization results revealed that the obtained reduced graphene oxide has higher reduction degree than that synthesized by NaBH₄ alone at high temperature.Moreover,rGO electrode based on the present reducing method exhibited a superior specific capacitance of 139.8 F/g at a current density of1 A/g,indicating that it can be used as electrode materials for supercapacitors.