尿中烷化核酸碱基的研究进展

本文论述了目前关于尿中烷化核酸碱基的重要研究进展,其中包括烷墓核酸碱参的生成机理,尿中烷化核酸碱荃的分析方法,人类暴露于烷基致癌物所产生的烷基核酸碱墓的水平。同时,还评述了烷化核酸碱莎,特别是3一甲墓腺嗦吟作为生物指标的可能性及其应用前景。     

Development of a novel environmentally friendly electrolytic system by using recyclable solid-supported bases for in situ generation of a supporting electrolyte from methanol as a solvent: application for anodic methoxylation of organic compounds

We have successfully developed a novel environmentally friendly electrolytic system using recyclable solid-supported bases for in situ generation of a supporting electrolyte from methanol as a solvent. It was found that solid-supported bases are electrochemically inactive at an electrode surface. It was also found that solid-supported bases dissociate methanol into methoxide anions and protons. Therefore, in the presence of solid-supported bases, it was clarified that methanol serves as both a solvent and a supporting electrolyte generated in situ. Anodic methoxylation of various compounds with solid-supported bases was carried out to provide the corresponding methoxylated products in good to excellent yields with a few exceptions. The methoxylated products and the solid-supported bases were easily separated by only filtration, and the desired pure methoxylated products were readily isolated simply by concentration of the filtrates. The separated and recovered solid-supported bases were recyclable for several times.     

Polymeric Schiff Bases. III. Some Prototype Exchange Reactions of Schiff Bases

The amine moiety in Schiff bases can be exchanged quantitatively by another amine to yield new Schiff bases if the volatility of the replacing amine is lower than the derived amine, thereby allowing the latter to distilled from the reaction mass. This amine exchange was shown to be quantitative also for diamines and di-Schiff bases. Similarly, quantitative conversions were found for aldehydes and acetal exchanges with Schiff bases for both monofunctional and difunctional reactants. The bis exchange, involving two complementary Schiff bases, was quantitative also when the reactants were so selected that one of the new derived Schiff bases could be removed by distillation. The bis exchange was demonstrated with mono and di-Schiff bases.

Mechanisms are suggested for these Schiff base exchange reactions: attempts to isolate the proposed intermediates physically were unsuccessful; however spectroscopic evidence indicates the formation of intermediate compounds.

The Schiff base exchanges involving polyfunctional reactants are of interest in the synthesis of polymers.     

Reaction of substitution of low-molecular-mass organic bases in ternary interpolymer complexes

The reaction of the substitution of low-molecular-mass bases forming a part of low-ordered and high-ordered ternary interpolymer complexes for low-molecular-mass bases (dipyridyls, aromatic and aliphatic mono- and diamines) from solutions has been studied. It has been shown that, independently of the chemical natures and structures of low-molecular-mass organic bases, the exchange reaction proceeds between all studied organic bases that are constituents of ternary interpolymer complexes or are present in solutions.     

Structural investigation on phenyl‐ and pyridin‐2‐ylamino(methylene)naphthalen‐2(3H)‐one. Substituent effects on the NMR chemical shifts

Schiff bases bearing phenyl and pyridyl groups were synthesized by condensation of appropriate amines with 2‐hydroxynaphthaldehyde. These Schiff bases were obtained as colored crystalline solids. The proton NMR spectra of these compounds showed a doublet for the NH protons indicating a keto tautomer for these Schiff bases. The pyridyl‐substituted Schiff bases containing hydroxyl moiety were found to show the most downfield shift for the NH protons in DMSO solvent, and this was rationalized due to the formation of a six‐ and five‐membered ring using hydrogen bonds for these two compounds. Correspondingly, the olefinic proton of the Schiff bases is also found to be a doublet due to coupling to the amine proton. These Schiff bases exhibited thermochromic properties. Detailed NMR spectral analysis for both the phenyl‐ and pyridyl‐substituted Schiff bases is presented. Copyright © 2010 John Wiley & Sons, Ltd.     

High-resolution liquid chromatographic analysis of methylated purine and pyrimidine bases in transfer RNA.

Methylated and major purine and pyrimidine bases were separated and quantified by high-resolution liquid chromatography after hydrolyzing transfer ribonucleic acids (tRNAs). Separation was accomplished by eluting the hydrolyzed samples from an anion-exchange column with a concentration gradient of ammonium acetate at pH 9.2. Isolated sample of tRNA were hydrolyzed to the free bases with a trifluoroacetic acid-formic acid mixture of 200 degrees. Detection limits of 100-200 ng/ml were measured for the methylated bases; analytical data are reported for ten methylated bases plus the four major bases of calf liver and rat liver tRNA.     

Anhydro bases of the pyridine series (review)

Methods for the preparation of anhydro bases of the pyridine series by deprotonation of the corresponding quaternary salts under the influence of bases, as well as by the direct reaction of quaternary pyridinium or halopyridinium salts with CH acids in the presence of bases, are examined. The reactions of anhydro bases with various reagents (alkyl cations, acylium cations, the proton, aldehydes, isothiocyanates, carbon disulfide, the hydroxide ion, etc.), which constitute evidence for their high reactivities, are examined. The participation of anhydro bases as intermediates in many reactions intended for the preparation of new heterocyclic systems is demonstrated.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.3, pp. 291–311, March, 1982.     

A spectroscopic study of adducts of heterocyclic nitrogen bases with nickel(II) chelates of 2-methyl-5-nitrophenylthiocarbazone

A spectrophotometric method was employed to study the adduct formation constants of a few typical bases with nickel(II) chelates of 2-methyl-5-nitrophenylthiocarbazone. Monobasic bases such as pyridine and methyl-substituted pyridines form pentacoordinated adducts with a stoichiometry of 1:1 for metal chelate-base. The dibasic bases such as 1,10-phenanthroline, 2,2′-bipyridyl, etc. also exhibit 1:1 stoichiometry giving hexacoordinated adducts. The experimental results are discussed in terms of the basicity and steric factors of the various bases.     

Structure and Physicochemical Properties of Substituted Porphyrins

Reactions of substituted porphyrins: 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphine, 2,3,7,8,12,13,17,18-octamethyl-5,10,15,20-tetraphenylporphine, and dodecaphenylporphine with organic bases (pyridine, piperidine, dimethylformamide, dimethyl sulfoxide) and acetic acid were studied by spectrophotometry. Acid-base interaction between porphyrins and organic bases and formation of ionic species in toluene solution containing an organic base were revealed for the first time. The effect of electronic and structural factors on the acid-base interactions of porphyrin ligands with organic bases is discussed. The stability constants were calculated for complexes of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphine with organic bases, and electronic absorption spectra of substituted porphyrins in basic organic solvents were recorded.     

Development of an electrolytic system using solid-supported bases for in situ generation of a supporting electrolyte from methanol as a solvent

We have successfully developed a novel electrolytic system using solid-supported bases for in situ generation of a supporting electrolyte from methanol as a solvent. Anodic methoxylation of phenyl 2,2,2-trifluoroethyl sulfide using solid-supported bases was carried out to provide the alpha-methoxylated product in good to excellent yields. The alpha-methoxylated product and solid-supported bases were easily separated by only filtration, and the separated solid-supported bases were recyclable. Anodic methoxylation of phenyl 2,2,2-trifluoroethyl sulfide was successfully carried out 10 times by the recycling of silica gel-supported piperidine in good yields.     

Stability and selectivity of unnatural DNA with five-membered-ring nucleobase analogues

In an effort to develop an orthogonal third base pair for the storage of genetic information, thiophene and furan heterocycles have been examined as nucleobase analogues. The stability of the unnatural bases was evaluated in duplex DNA paired opposite other unnatural bases as well as opposite the natural bases. Several unnatural base pairs are identified that are both reasonably stable and strongly selective against mispairing with native bases. These results expand the potential nucleobase analogues with which the genetic alphabet may be expanded to include five-membered-ring heterocycles.     

Synthesis of pyridine bases: general methods and recent advances in gas phase synthesis over ZSM-5 zeolite

Pyridine bases are widely used in pharmaceuticals, insecticides, and herbicides due to their high bioactivity. In this paper, in addition to the conventional synthesis methods for pyridine bases, recent advances in the gas phase synthesis of pyridine bases over the shape selective catalysts (ZSM-5) are described.     

Thermodynamic study of two different chewing-gum bases by inverse gas chromatography

This work describes the physico-chemical characterisation of two different chewing gum bases and the interactions with the incorporated flavour molecules using inverse gas chromatography as a specific technique. Ethyl butyrate, limonene, 1-octanol and cis-2-hexenal were injected to calculate the partition coefficients, the activity coefficients and the Henry's constants at infinite dilution and 298 K. The partition coefficients, activity coefficients and Henry's constants showed a difference between the two gum bases, but the excess molar heat of mixing (deltaHm) showed an incompatibility for the flavour compounds in both gum bases. Finally, the determination of the solubility parameter of the gum bases by two methods showed that the two gum bases have similar solubility parameters at 298 K.     

Nitrogen bases in the coking products of coal (composition,methods of isolation,and utilization) (Review)

The compositions and yields of nitrogen bases during thermochemical transformations of the organic mass of coals are presented. The dependence of the distribution of nitrogen in the products of thermal refining of coal on the type of field, the degree of metamorphism, and the coking temperature is demonstrated. The percentages of nitrogen bases in the coking products, the composition of the base fractions, and a list of reagents of the pyridine and quinoline series developed in the USSR are presented. The industrial methods for the isolation of the nitrogen bases from coking gas and coal tar in the USSR and abroad and numerous studies on the development of methods for the isolation of the bases and their analysis are described. Possible ways to use the bases and resources for increasing their production are indicated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1587–1600, December, 1976.     

Rationalisation of unusual changes in efficiency and retention with temperature shown for bases in reversed-phase high-performance liquid chromatography at intermediate pH

Despite the possibility of poorer peak shapes, analysis of pharmaceuticals and other bases using reversed-phase high-performance liquid chromatography (RP-HPLC) at intermediate pH gives useful increases in retention, selectivity and column loading capacity compared with low pH. Retention times of some bases showed anomalous increases with column temperature. Peak shapes for bases improved significantly at elevated temperature (up to 70 degrees C), with the weakest bases studied (pKa approximately 8) giving greater improvement than the strongest bases (pKa approximately 10). In contrast, quaternary ammonium compounds showed reduced retention with increasing column temperature (normal behaviour) and only modest improvements in peak shape. Considering these results, and pKa measurements of the bases made using capillary electrophoresis, it appears that increases in retention and improvement in efficiency may be influenced significantly by reduction in the pKa of bases with temperature, leading to reduction in protonation. It is less likely that efficiency improvements are due to the speeding up of the kinetics of silanol ion exchange, at least in the temperature range studied here.     

Synergistic Effects of Lewis Bases and Substituents on the Electronic Structure and Reactivity of Boryl Radicals

Boryl radicals have the potential for the development of new molecular entities and for application in new radical reactions. However, the effects of the substituents and coordinating Lewis bases on the reactivity of boryl radicals are not fully understood. By using first‐principles methods, we investigated the spin‐density distribution and reactivity of a series of boryl radicals with various substituents and Lewis bases. The substituents, along with the Lewis bases, only affect the radical reactivity when an unpaired electron is in the boron p_z orbital, that is, for three‐coordinate radicals. We found evidence of synergistic effects between the substituents and the Lewis bases that can substantially broaden the tunability of the reactivity of the boryl radicals. Among Lewis bases, pyridine and imidazol‐2‐ylidene show a similar capacity for stabilization by delocalizing the spin density. Electron‐donating substituents, such as nitrogen, more efficiently stabilize boryl radicals than oxygen and carbon atoms. The reactivity of a boryl radical is always boron based, irrespective of the spin density on boron.     

Interaction of low-energy electrons with the pyrimidine bases and nucleosides of DNA

We report computed cross sections for the elastic scattering of slow electrons by the pyrimidine bases of DNA, thymine and cytosine, and by the associated nucleosides, deoxythymidine and deoxycytidine. For the isolated bases, we carried out calculations both with and without the inclusion of polarization effects. For the nucleosides, we neglect polarization effects but estimate their influence on resonance positions by comparison with the results for the corresponding bases. Where possible, we compare our results with experiment and previous calculations.     

The analysis of pharmaceutical bases on a silica stationary phase by capillary electrochromatography using aqueous mobile phases

Summary The capillary electrochromatographic (CEC) separation of a range of pharmaceutical bases was investigated on a commercially available silica stationary phase using aqueous mobile phases. The effects of mobile phase composition, buffer pH, applied voltage, and buffer anion on the retention behaviour of these bases were studied. Promising chromatography was obtained at pH 7.8 but was later found to be irreproducible. However, successful and reproducible chromatography of the bases was achieved at pH 2.3. We have previously demonstrated that the addition of mobile phase additives such as TEA-phosphate at low pH values has resulted in excellent CEC analysis of bases on reversed-phase packing materials. The same approach was applied to the analysis of bases on the silica phase in order to improve peak shape. Excellent chromatography was obtained for the analysis of strong pharmaceutical bases such as benzylamine, nortriptyline and diphenhydramine. The experimental investigations have shown that the CEC separation of a range of pharmaceutical bases can routinely be achieved with excellent peak shapes and peak efficiencies as high as 320,000 plates m⁻¹.     

Measurement by NMR spectrometry of hydrogen bonding to bases having more than one equivalent electron donor site

The hydrogen bonding parameters for the interaction of chloroform with several Lewis bases having one or two equivalent electron donor sites are obtained on the basis of the formation of a simple 1:1 complex. The twin-site bases have similar structure and are considered to have nearly the same site strength and about the same steric requirements as the corresponding single-site bases. There are large differences in the equilibrium constant K and the change in enthalpy between the single-site and the corresponding twin-site bases. In the twin-site base the number of donor sites exceeds the number of molecules, and the observed chloroform proton shift is much larger than that in the single-site base of the same concentration. An important question therefore concerns the significance of the K obtained by using the actual concentration (in terms of molecules) in the case of the twin-site base. Relative to the single-site bases the temperature dependence of K is enhanced in the open chain twin-site bases, whereas the opposite is found in the cyclic twin-site bases. The reasons for such a behaviour of the measured K are postulated.     

Computational design of ring-expanded pyrimidine-based DNA motifs with improved conductivity

Motivated by a promising expansion of the genetic alphabet and a successful design of conductive DNA bases justified from the hetero-ring-expanded purine base (G and A) analogs, we extend our hetero-ring expansion scheme to the pyrimidine bases (C and T) to examine the ring-expansion effects on various properties of these single-ring bases with a comparison with those in the double-ring purine case. Four kinds of the hetero-rings are considered to expand C and T, forming the C and T analogs (nC and nT), respectively. The relevant structures and properties were investigated by means of quantum calculations and molecular dynamics simulations. The results reveal that all the modified bases can form base pairs specifically with their natural counterparts and assemble duplex helices which have comparable stability to native ones. The HOMO-LUMO gaps of G-nC and A-nT are smaller than those of the natural pairs, and the assembled duplex helices ((G-nC)(12) and (A-nT)(12)) are diameter-enlarged but with smaller rise and twist, both of which favor DNA-conduction, as confirmed by ionization potentials and spin density distributions. In addition, the hetero-ring expansion can lower the activation barriers and reduce the reaction heats of the inter-base double proton transfers. In particular, as evidenced by NMR parameters and the excited states, the hetero-ring expansion leads to an enhancement of the transverse electronic communication between two pairing bases, clearly facilitating the conduction along the helices. Furthermore, the hetero-ring expansion effect on the pyrimidine bases is larger than that on the purine bases. In summary, this work presents clear theoretical evidence for the possibility of hetero-ring expanded pyrimidine bases as promising candidates for the motifs of the genetic alphabet and DNA nanowires.