Pyrimidine Series Research Articles

Sigma complexes in the pyrimidine series. 2. σ Complexes of 5-nitropyrimidine and methoxy-substituted 5-nitropyrimidines with the acetone anion

Sigma complexes in the pyrimidine series. 2. σ Complexes of 5-nitropyrimidine and methoxy-substituted 5-nitropyrimidines with the acetone anion

Sigma complexes in the pyrimidine series. 2. σ Complexes of 5-nitropyrimidine and methoxy-substituted 5-nitropyrimidines with the acetone anion

The corresponding σ complexes of the Meisenheimer type, viz., anions of the potassium salts of 6H-5-nitro-6-acetonylpyrimidines, were obtained and isolated in the reaction of 5-nitro-, 5-nitro-4-methoxy-, 5-nitro-2-methoxy-, and 5-nitro-2,4-dimethoxypyrimidines with acetone in the presence of potassium hydroxide. The structures of the complexes were proved by means of the PMR, IR, and UV spectra. It is shown that the acetone anion in all cases adds to the methoxy-unsubstituted position of the pyrimidine ring, whereas nucleophilic attack takes place at the C4 atom when the 2 and 4 positions are free.

Antimicrobial activity of some pyridinium salts and compounds of the pyrimidine series

Antimicrobial activity of some pyridinium salts and compounds of the pyrimidine series

Investigations in the pyrrolo[3,2-d] pyrimidine series

Investigations in the pyrrolo[3,2-d] pyrimidine series

Specificity of nucleoside transport in Neurospora crassa.

The specificity of nucleoside uptake in germinating conidia of Neurospora crassa was investigated by examining the kinetics of [2-14C]uridine and [8-14C]-adenosine uptake in the wild-type, ad-8, and ud-1 pyr-1 strains. The results obtained strongly indicate that nucleoside transport in N. crassa is mediated solely by a general transport system which accepts both purine and pyrimidine nucleosides. Studies directed at characterizing the specificity of the transport system indicate that general structural features of the nucleoside which enhance its efficiency in binding to the transport system include: (i) a purine or pyrimidine as the heterocyclic ring, (ii) an unfunctionalized ribose or 2'-deoxyribose as the sugar unit, (iii) a beta-configuration about the anomeric carbon, (iv) the absence of substituents at C8 in the purine series and at C5 and C6 in the pyrimidine series, (v) the presence of a C5-C6 double bond in the pyrimidine series, and (vi) the absence of a charge on the heterocyclic ring.

Sigma complexes in the pyrimidine series

Sigma complexes in the pyrimidine series

A study of the stability of pyrimidine series cytostatics, Ftorafur and 5-fluorouracil: The effect of oxidation on the stability of Ftorafur and 5-fluorouracil

The stability of 1% solutions of cytostatics Ftorafur and 5-fluorouracil was studied during oxidation with hydrogen peroxide in alkaline (0.1 N NaOH), acidic (0.1 N H 2SO 4), and weakly acidic (pH 5) solutions by thin-layer chromatography. The decrease in the cytostatic content was monitored spectrophotometrically in the uv region. The greatest decrease in the cytostatic content occurred in alkaline solutions, where the pyrimidine ring opened between N3 and C4 and between C6 and N1, with formation of urea.

ESCA spectra and molecular charge distributions for some pyrimidine and purine bases

A series of pyrimidine and purine bases bas been studied experimentally by electron spectroscopy for chemical analysis. Individual component peaks in the spectra were assigned on the basis of known substituent effects on core electron binding energies. Binding energies for all the core levels in the molecules provide sufficient data to determine the molecular charge distributions. The results compare favourably with atomic charges determined theoretically in the CNDO/2 molecular orbital formalism.

NMR spectra of pyrimidines effect of substituents on the chemical shift of the para protons in 2- and 5-substituted pyrimidines

The chemical shifts of the protons of the pyrimidine ring in the 2 position for a series of 5-substituted pyrimidines and in the 5 position for a series of 2-substituted pyrimidines in solutions in dimethyl sulfoxide were determined. The correlation equations that link the relative chemical shifts with the F and R substituent constants were calculated. The correlation equations were analyzed by comparison with the corresponding correlation equation for a series of monosubstituted benzenes. The reasons for the change in the conductivity of the electronic effects of the substituents via inductive and conjugation mechanisms in the pyrimidine ring as compared with the conductivity in the benzene ring are discussed.

Pyridopyrimidines. 9. An unusual rearrangement in the 8-substituted pyrido[2,3-d]pyrimidine series. Application of the selective nuclear Overhauser effect to unambiguous proton chemical shift assignment

Pyridopyrimidines. 9. An unusual rearrangement in the 8-substituted pyrido[2,3-d]pyrimidine series. Application of the selective nuclear Overhauser effect to unambiguous proton chemical shift assignment

Study of the stability of pyrimidine series cytostatics, ftorafur and fluorouracil injections

The stability of the cytostatics, ftorafur and fluorouracil injections, was studied in dependence on irradiation with UV light and on the medium temperature and pH. In the first stage of the thermal and photochemical decomposition of ftorafur, tetrahydrofuran dissociated from position N 1 in the pyrimidine ring and 5-fluorouracil was formed. In the second stage of the thermal and photochemical decomposition of ftorafur, the pyrimidine ring opened between N 3 and C 4 and between C 6 and N 1, with formation of urea. Ftorafur, fluorouracil, and urea were determined using thin-layer chromatography and spectrophotometry in the UV and visible region.

13C n.m.r. spectra of 2‐substituted pyrimidines

Abstract13C n.m.r. chemical shifts and carbon‐proton coupling constants of 2‐substituted pyrimidines are reported. The carbon chemical shifts are correlated with π‐electron densities. Substituents which cause deshielding at the directly bound carbon (e.g. NH2, OCH3 and F) exert a more powerful effect in the benzene series than in the pyridine or pyrimidine series. The carbon‐proton coupling constants do not correlate with the electronegativity of the substituents. Carbon‐proton coupling constants and proton‐proton coupling constants over the same number of bonds do not obey the Karabatsos relationship. The changes in the carbon‐proton coupling constants in 2(1H)‐pyrimidinone and 2(1H)‐pyrimidinethione which accompany anion and cation formation are reported.

A proton-relaxation-time study of the conformation of some purine and pyrimidine 5'-nucleotides in aqueous solution.

The measurement of proton relaxation time T1 in a series of purine and pyrimidine 5'-nucleotides has been carried out to investigate their conformation in dilute neutral aqueous solutions. The interpretation of relaxation data has been performed with the help of computer calculations taking into account the different conformers of the ribose ring and of the exocyclic group. It has been found that all nucleotides under study show nearly the same preferential orientations of the base defined by gamma0 = 70 degrees +/- 10 degrees in the syn range. A more elaborate treatment, using an angular distribution derived from calculated potentials on 5" -GMP gives theoretical relaxation times in close agreement with experimental ones.

Formazans of the pyrimidine series

A series of 1-(2′-pyrimidyl)-3,5-diarylformazans was synthesized. Their structures were studied by means of IR and electronic spectroscopy, and assumptions regarding the most probable tautomeric forms of the investigated compounds were made. The ionization constants of the formazans were measured. It was found that 2,5-diphenyltetrazoles are formed instead of the expected tetrazolium salts in the reaction of 1-(2′-pyrimidyl)-3,5-diphenylformazans with N-bromosuccinimide.

Research in the pyrimidine series XXVI. Calculation of the in-plane normal vibrations of the ?enol? forms of barbituric acids

The frequencies and forms of the in-plane normal vibrations of the “enol” forms of barbituric and 5-chloro- and 2-thiobarbituric acids and their deutero derivatives were calculated for the Cs symmetry point group. On the basis of an analysis of the forms of the normal vibrations, the principal frequencies observed in the IR spectra of 5-substituted (methyl, chloro, and bromo) and 2-thiobarbituric acids were assigned with respect to the types of vibrations. The force constants were also determined. The results of the calculations also confirm and refine the previously proposed interpretation of the IR spectra of crystalline samples of the investigated compounds and make it possible to form a judgment regarding the presence of tautomers in the crystalline state and in solutions from the IR spectra.

Research in the pyrimidine series XXV. Calculation of the normal vibrations of barbituric and 2-thiobarbituric acids

The frequencies and forms of the in-plane normal vibrations of the tricarbonyl forms of barbituric and 2-thiobarbituric acids and their tetradeutero derivatives were calculated. The calculations were made for the Czv (or C2v and Cs for barbituric acid) symmetry point group. The principal frequencies observed in the IR spectra of these compounds were assigned with respect to the types of vibrations on the basis of an analysis of the forms of the normal vibrations.

Use of Raman spectroscopy for the establishment of the structure of pyrimidine derivatives

Intense bands of stretching vibrations are characteristic for the ER spectra of compounds of the pyrimidine series, whereas strong polarized bands of the radially symmetrical vibrations of the pyrimidine skeleton are characteristic for the Raman spectra. The band of the radially symmetrical vibration at ∼1000 cm−1 is not observed in the Raman spectra of pyrimidines having a substituent in the 5 position.

Conversion of 2,4,6-triphenylpyrylium perchlorate to a compound of the pyrimidine series

Conversion of 2,4,6-triphenylpyrylium perchlorate to a compound of the pyrimidine series

Research in the pyrimidine series

The frequencies and forms of the normal vibrations of thymine, 5-amino-, 5-fluoro-, 5- and 6-chloro-, 5-bromo-, and 5-nitrouracils and their 1,3-dideutero analogs were calculated, and their force constants were determined. The calculated and observed frequencies were assigned with respect to the types of vibrations. The introduction of substituents into the 5 and 6 positions of the uracil ring leads to a change in a whole series of force constants and to redistribution of the forms of the normal vibrations with respect to natural coordinates. Despite this, one can isolate those structural fragments of the investigated molecules whose normal vibrations remain characteristic in form. A linear dependence of theνN(1)H andνN(3)H frequencies on the force constants of the corresponding bonds was observed.

Research in the pyrimidine series

Research in the pyrimidine series