Analogs of purine nucleosides and purine mono-and polynucleotides

A number of 6-substituted 9-(1,5-dihydroxy-3-pentyl)purines were obtained from 5-amino-4,6-dichloropyrimidine. 5-Amino-4,6-dichloropyrimidine reacts with 2-hydroxymethylpyrrolidine to give 4-chloro-5-amino-6-(2-hydroxymethylpyrrolidino)pyrimidine.See [1] for communication IV.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 552–555, April, 1976.     

Substituent effects on the ring-chain tautomerism of some 1,3-oxazolidine derivatives

The 14 and 70 eV electron ionization mass spectra of five sets (R1 = Me, Et, i-Pr, t-Bu and Ph) of seven 2-aryl-4-R1-substituted (Ar = C6H4X; X = p-NO2, m-Br, p-Cl, H, p-Me, p-OMe and p-NMe2) (1-5) and of seven 2-aryl-5-phenyl-substituted 1,3-oxazolidines (6; for Ar, see above) were recorded to study their ring-chain equilibria in the gas phase. These equilibria were also studied by 1H NMR spectroscopy in CDCl3 for compounds 5 and 6. A few 2,4- and 2,5-dimethyl-2-aryl derivatives (7, 8: Ar = C6H4X; X = m-Br, H and p-OMe) were studied both in CDCl3 and in the gas phase. The main characteristics of the ring-chain equilibria expressed by the variable SigmaRA% of the ring and of the chain form proved to be a strong dependence on the nature of the substituents on C-2 and C-4. The results in the gas phase are compared with those in CDCl3.     

Analogs of purine nucleosides and purine mono- and polynucleotides

Selective protection of the amino and one of the hydroxyl groups of 6-substituted 9-(α,ω-dihydroxy-2-alkyl)purines was realized. A convenient method for the preparation of monophosphates was developed.     

Analogs of purine nucleosides and purine mono- and polynucleotides

On the basis of a comparison of the protolysis constants and vibrational frequencies it is shown that intermolecular interactions are present in 6-substituted 9-(,-dihydroxyalkyl)-purines and the corresponding mono- and diphosphates. In addition, in the case of the phosphates the existence of intramolecular interactions of electrostatic character between the phosphate group and the heteroring is also proposed. A comparison of the protolysis constants provides evidence for the different character of the interaction of the dihydroxyalkyl residue with the heteroring of the base in series of adenine and hypoxanthine derivatives.See [1] for communication II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1684–1689, December, 1974.     

Analogs of purine nucleosides and purine mono- and polynucleotides

Phosphorylation of 6-substituted 9-(1, 5-dihydroxy-3-pentyl)purines with 2-cyanoethyl phosphate in the presence of dicyclohexylcarbodiimide in anhydrous pyridine gave their 1, 5-diphosphates. Oligomers containing pyrophosphate and ester bonds were obtained by polycondensation of 1, 5-diphosphates of 6-dimethylamino- and 6-oxo-9-(1, 5-dihydroxy-3-pentyl)purines with the appropriate 9-(1, 5-dihydroxy-3-pentyl) purines.See [1] for communication V.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 693–696, May, 1976.     

Substituent effects on ionization energies in some 4r-substituted cyclohexanones

A series of 4R-substituted cyclohexanones were investigated by gas-phase UV photoelectron spectroscopy in order to study the influence of the substituent in the ionization energy of the carbonyl non-bonding orbital. A plot of the IE_s vs. the substituent's Taft's σ_I indicated a different behaviour of the alkyl substituted compounds with respect to the others. A sharp linear correlation between IE_s and conformational energies for the former compounds is found and discussed in terms of ring flattening and angle deformation along the series -H, -Me, -Et and -t-Bu. Conjugative interactions between polar substituents and the n_O(C=O) orbital can explain the departure from linearity of the IE_s vs. σ_I's correlation.     

Chemical synthesis of cross-linked purine nucleosides

[reaction: see text] An efficient route to all of the possible cross-linked 2'-deoxypurines 1-3 has been developed by means of the Pd-mediated C-N bond formation in the key step. Utilizing this protocol, the synthesis of the first unnatural protected purine trimeric adduct 4 has been accomplished.     

Voltammetric studies of purine bases and purine nucleosides with copper

Anodic stripping voltammetry with a hanging mercury drop electrode has been used to investigate the interaction of cooper with the purines adenine, hypoxanthine, xanthine and purine nucleosides adenosine, guanosine and inosine at an ionic strength of 0.1 M in KNO₃ and in the pH range 3.5–5.5. In all cases stabilisation of copper(I) occurs suggesting that the oxidation of copper(0) in the presence of excess ligand proceeds in two one-electron steps.Adsorption onto the electrode has been analysed and conditions where this is negligible were chosen for complexation studies. From the shift of the peak potential corresponding to Cu(0)/Cu(I) oxidation with increasing ligand concentration the stoichiometry of the complexes and their formation constants have been determined. The values obtained are discussed in terms of the ligand structure.     

Substituent effects on some physicochemical properties of chalcones and their vinylogues

Carbonyl stretching frequencies (ν_CO), dipole moments (μ), longwave maxima (λ_max), half-wave potentials (°_1/2), and relative intensities (Z/Z₀) of benzoyl-ion in mass-spectra oftrans chalcones and their vinylogues of the general type PhCO(CH=CH)_nC₆H₄R-p (I) were measured. Contrary to the previously investigated polyenes of the type R(CH=CH)_nR′ (R′ = CHO or COOEt) variation of the substituent R in compounds I has little influence on properties of I in the ground state and a satisfactory linear relationship between (ν_CO) or μ and σ constants exists only in the case of I (n = 0, 1); the best correlation with σ⁺ indicates that the mesomeric mechanism plays a great part in the transmission of electronic effects. λ_max.,E_1/2, orZ/Z₀ of all series I (n = 0–3) correlate with σ_p or σ⁰ constants, and the separation of mesomeric and inductive effects by multiparametric correlation reveals that in this case inductive effect is of great importance in the transmission of electronic effects. These features were accounted for by the non-planar structure of molecules of I, which was confirmed by X-ray analysis of I (R = Br). The Pariser-Parr-Pople method has also been applied to the calculation of π-electronic density in molecules I and it was found that the introduction of various substituents in para position of I exercises a very little influence on the electronic distribution in compounds I.     

Substituent effects on the electrophilic activity of nitroarenes in reactions with carbanions

The effect on electrophilic activity of substituents located para, ortho, and meta to the nitro group of nitrobenzenes was determined by using vicarious nucleophilic substitution of hydrogen (VNS) with the carbanion of chloromethyl phenyl sulfone (1) as the model process. Values for the relative activities of substituted nitroarenes are given relative to nitrobenzene, which was taken as the standard. This process was chosen as a model reaction because it meets key criteria, such as the wide range of substituents that can be present on the nitrobenzene ring, a low sensitivity to steric hindrance, and in particular the possibility of ensuring conditions in which the overall relative rates of reaction in competitive experiments are equal to the relative rates of nucleophilic addition. The values of relative rates of addition, which were taken to be a measure of electrophilic activity, were determined by competitive experiments in which pairs of nitroarenes competed for the VNS reaction with carbanion of 1. A comprehensive set of data for effects of substituents on the electrophilic activity of nitroarenes is presented for the first time.     

Acyclic analogues of purine and imidazole nucleosides

Hydroxyl-protected derivatives of 1- and 3-(2-hydroxyethoxymethyl)imidazoles ( 4,5,7-10 ) have been prepared from 5-amino-4-carbamoylimidazoles ( 2 ). The protected derivatives were converted to acyclic analogues of imidazole nucleosides ( 6 ) or subjected to various cyclisation reactions leading to 9-(2-hydroxy-ethoxymethyl)-substituted 2-methyl-, 2-phenyl- and 2-azahypoxanthines ( 18,13 and 20 , respectively) and 1-methylguanine ( 28 ). For assignment of structures to isomeric imidazole and purine derivatives, ¹³C chemical shifts have been used.     

Substituent and solvent effects on electronic spectra of some substituted phenoxyacetic acids

The effects of substituents and solvents have been studied through the absorption spectra of nearly 19 para- and ortho-substituted phenoxyacetic acids in the range of 200-400 nm. The effects of substituent on the absorption spectra of compounds under present investigation are interpreted by correlation of absorption frequencies with simple and extended Hammett equations. Effect of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of Kamlet equation and the results are discussed.     

Substituent effects on direct arylation polycondensation and optical properties of alternating fluorene-thiophene copolymers

Four thiophene derivatives were prepared by replacing the 3,4 positions of thiophene by―OCH3, ―CH3―COOCH3 and ―CN, respectively. The polycondensations via direct arylation took place between the four thiophene derivatives and 2,7-dibromo-9,9-dioctylfluorene under six various catalytic conditions to investigate the substituent effects. The substituent can affect the electron cloud density of the active C―H bond, which can be monitored by the NMR chemical shift. The experimental results show that the reactivity decreases with increasing the chemical shift of active C―H bonds in the four thiophene derivatives, and thus can promote the direct arylation polycondensation. This phenomenon is explained by the electrophilic aromatic substitution(SEAr) mechanism. UV-Visible absorption and photoluminescence were studied to investigate the substituent effect on optical properties of the four copolymers. The results show that these alternating fluorene-thiophene copolymers with different substituents are good fluorescent materials and promising in PLED applications.     

Substituent effects on the H abstraction by recoil38Cl in some organic systems

Total organic yield following ³⁷Cl(n, λ) ³⁸Cl reaction in trichloro solids of acetanilides and anilines is in the range 46–49%. Yield for the dichloro systems is lower: 25%. In general, the organic yields are in the order Ar-OH > Ar-NH₂ > Ar-NHCOCH₃. Solution state irradiation in various solvents further lower the yield (∼28%) which remains independent of the polarity of the solvents.