Studies on Prototropic Tautomerism in Neutral and Monoanionic Forms of Pyrimidines by Nuclear Magnetic Resonance Spectroscopy

Abstract NMR methods have been applied to evaluation of prototropic tautomerism, N(1)H ⇌ N (3) H, in several selected pyrimidines, viz. the neutral forms of Isocytosine and 2-alkylthiopyrimidone-4, and the monoanionic forms of uracil, 5-fluorouracil and 4-thiouracil. The predominant tautomeric species of the neutral forms could be estimated only qualitatively from 1H chemical shifts. For the monoanionic forms this procedure was not applicable, for reasons which are discussed in detail. For the monoanionic form of uracil, 13C chemical shifts of C(5) provided a suitable criterion for quantitative estimation of the populations of the two known tautomeric species. However, the potential scope of this procedure appears somewhat limited. By contrast, the values of the vicinal proton-proton coupling constants, J (5,6), provided both necessary and adequate criteria for quantitative evaluation of the tautomer populations for all the neutral and monoanionic forms. The results were in satisfactory agreement with those obtained by optical spectroscopic methods. In some instances the results obtained in this way may be more reliable than those derived from optical methods. The range of applicability, and utility, of NMR methods to studies on protropic tautomerism in pyrimidines are critically assessed.

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Structural revision of glabramycins B and C, antibiotics from the fungus Neosartorya glabra by DFT calculations of NMR chemical shifts and coupling constants

RSC Advances ◽

10.1039/c5ra01753j ◽

2015 ◽

Vol 5 (46) ◽

pp. 36858-36864 ◽

Cited By ~ 15

Author(s):

Yang Li

Keyword(s):

Natural Products ◽

Dft Calculations ◽

Nmr Spectra ◽

Chemical Shifts ◽

Coupling Constants ◽

Proton Proton ◽

Structural Revision ◽

Proton Coupling ◽

Vicinal Proton ◽

C Nmr

The 13C NMR spectra and vicinal proton–proton coupling constants of two tricyclic macrolactone natural products were analyzed using computational methods, which resulted in their structural revisions.

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Solution Conformation of Benzimidazole Nucleosides with the Aid of Model Analogues

Zeitschrift für Naturforschung C ◽

10.1515/znc-1981-1-223 ◽

1981 ◽

Vol 36 (1-2) ◽

pp. 126-134 ◽

Cited By ~ 5

Author(s):

Zygmunt Kazimierczuk ◽

Ryszard Stolarski ◽

Lech Dudycz ◽

David Shugar

Keyword(s):

Chemical Shifts ◽

Coupling Constants ◽

Glycosidic Bond ◽

Benzimidazole Ring ◽

Proton Proton ◽

H Nmr ◽

Proton Coupling ◽

Vicinal Proton ◽

Sugar Ring ◽

Derivatives Of

Abstract The 4,6-dibromo-and 5,7-dibromo-derivatives of 1-β-ᴅ-ribofuranosylbenzimidazole, and the 4,6-dibromo-derivative of 1-α-ᴅ-arabinofuranosylbenzimidazole, have been synthesized by condensation of the trimethylsilylated derivative of 4,6-dibromobenzimidazole with the appropriate protected sugar in the presence of SnCl4. Application of the fusion method led to the β-ribofuranoside of 2-methyl-5,6-dichlorobenzimidazole. Two additional analogues of the biologically active ribofuranoside of 5,6-dichlorobenzimidazole, viz. the 2′,3′-O-isopropylidene and the 5′-chloro-5′-deoxy derivatives have been synthesized. Analyses of the 1H NMR spectra of the foregoing, and of previously synthesized 5(6)-mono-halogeno and 5,6-dihalogeno derivatives, were employed to determine solution conformations of these nucleosides. Conformations of the sugar rings and exocyclic groups were evaluated from vicinal proton-proton coupling constants, as for purine nucleosides. The conformation of the benzimidazole ring about the glycosidic bond was determined from the chemical shifts of the sugar protons, principally H(2′), with the aid of model analogues in fixed syn and anti conformations; and, independently, from the chemical shifts of the benzimidazole ring protons, principally H(4) and H(7). The halogenated benzimidazole ribofuranosides exhibit conformations of the sugar ring similar to those for purine β-nucleosides, but differ from the latter in their preference for the conformation syn about the glycosidic bond.

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Proton magnetic resonance study of the conformation of the pyrrolidine ring in some proline-thiohydantoins

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19882503 ◽

1988 ◽

Vol 53 (11) ◽

pp. 2503-2510 ◽

Cited By ~ 3

Author(s):

Jef J. M. Sleeckx ◽

Marc J. O. Anteunis ◽

Frans A. M. Borremans

Keyword(s):

Present Model ◽

Coupling Constants ◽

Proton Proton ◽

Proton Coupling ◽

Proton Magnetic Resonance Study ◽

Vicinal Proton ◽

Different Temperatures ◽

Experimental Justification ◽

State Assumption ◽

Methyl Phenyl

The conformational behaviour of a series of N-substituted thiohydantoins of proline was studied by proton NMR. The pseudorotational parameters of the proline moiety were calculated from the ten vicinal proton-proton coupling constants assuming a two state equilibrium (N ⇋ S). The effect of the different substituents (methyl, phenyl, para-nitrophenyl) at the thiohydantoin nitrogen on the conformation of the pyrrolidine rings is discussed. The spectra of proline-N-methylthiohydantoin were recorded at different temperatures in octadeuterotoluene solution. The conformational analysis of these spectra showed that the ratio of the populations of the N and S forms changes considerably with temperature, while the conformational identity of both the N and S forms remains strictly preserved. These facts provide an additional experimental justification of the two-state assumption, at least so for the present model compounds.

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Vicinal proton—proton coupling constants. Basis set dependence in SCF ab initio calculations

Chemical Physics Letters ◽

10.1016/0009-2614(93)85549-4 ◽

1993 ◽

Vol 206 (1-4) ◽

pp. 253-259 ◽

Cited By ~ 14

Author(s):

Jesús San-Fabián ◽

Joaquín Guilleme ◽

Ernesto Díez ◽

Paolo Lazzeretti ◽

Massimo Malagoli ◽

...

Keyword(s):

Ab Initio Calculations ◽

Ab Initio ◽

Coupling Constants ◽

Basis Set ◽

Proton Proton ◽

Proton Coupling ◽

Vicinal Proton

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Vicinal proton–proton coupling constants: MCSCF ab initio calculations of ethane

Chemical Physics Letters ◽

10.1016/s0009-2614(99)01099-4 ◽

1999 ◽

Vol 314 (1-2) ◽

pp. 168-175 ◽

Cited By ~ 15

Author(s):

J. Guilleme ◽

J. San Fabián ◽

J. Casanueva ◽

E. Dı́ez

Keyword(s):

Ab Initio Calculations ◽

Ab Initio ◽

Coupling Constants ◽

Proton Proton ◽

Proton Coupling ◽

Vicinal Proton

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Vicinal proton-proton coupling constants

Molecular Physics ◽

10.1080/00268979400100664 ◽

1994 ◽

Vol 82 (5) ◽

pp. 913-928 ◽

Cited By ~ 27

Author(s):

Jesús San-Fabián ◽

Joaquín Guilleme ◽

Ernesto Díez ◽

Paolo Lazzeretti ◽

Massimo Malagoli ◽

...

Keyword(s):

Coupling Constants ◽

Proton Proton ◽

Proton Coupling ◽

Vicinal Proton

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Analysis of vicinal proton-proton coupling constants in polypropylene chains

Macromolecules ◽

10.1021/ma50007a044 ◽

1981 ◽

Vol 14 (6) ◽

pp. 1830-1831 ◽

Cited By ~ 1

Author(s):

Dino R. Ferro ◽

Massimo Ragazzi

Keyword(s):

Coupling Constants ◽

Proton Proton ◽

Proton Coupling ◽

Vicinal Proton

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An Investigation of Long-range Proton–Proton Coupling Constants in Phenylacetylene Derivatives

Canadian Journal of Chemistry ◽

10.1139/v72-328 ◽

1972 ◽

Vol 50 (13) ◽

pp. 2035-2040 ◽

Cited By ~ 4

Author(s):

C. J. MacDonald ◽

G. K. Hamer ◽

I. R. Peat ◽

W. F. Reynolds

Keyword(s):

Hyperfine Interaction ◽

Long Range ◽

Excellent Agreement ◽

Quantitative Estimation ◽

Theoretical Calculations ◽

Experimental Results ◽

Coupling Constants ◽

Proton Proton ◽

Proton Coupling

Signs and magnitudes of long-range coupling constants in three phenylacetylene derivatives have been determined. Values of the coupling constants are discussed in terms of the McConnell formulation and compared with results of MO–INDO–FPT calculations. Coupling constants are dominated by π contributions. Estimated values of hyperfine interaction constants for acetylene and methylacetylene groups are respectively QCC≡CH = −12 and QCC≡CCH = +12 G. The theoretical calculations are in excellent agreement with experimental results. Both approaches allow quantitative estimation of nine bond couplings in 4-vinylphenylacetylene.

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Studies on the PMR Spectra of Oxetanes. VI 2-(3-Chlorophenyl)oxetane and 2-(2-Chlorophenyl)oxetane at 60 and 100 MHz

Zeitschrift für Naturforschung A ◽

10.1515/zna-1974-1229 ◽

1974 ◽

Vol 29 (12) ◽

pp. 1902-1906 ◽

Cited By ~ 2

Author(s):

Jukka Jokisaari

Keyword(s):

Long Range ◽

Chemical Shifts ◽

Methine Proton ◽

Coupling Constants ◽

Coupling Constant ◽

Proton Proton ◽

Temperature Range ◽

Proton Coupling ◽

Phenyl Proton ◽

Pmr Spectra

The 100 MHz spectra of the phenyl protons in 2-(3-chlorophenyl) oxetane and 2-(2-chlorophenyl) oxetane have been analysed. The 60 MHz PMR chemical shifts and proton-proton coupling constants have been studied in the temperature range from -20 C to +80 °C. The chemical shifts were sensitive to temperature, while the coupling constants were not, except the long range 5Jm coupling constant between the methine proton and the meta positioned phenyl proton in 2-(2-chlorophenyl) oxetane.

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Conformation of purine mononucleotides by H{H} and P{H} nuclear Overhauser effects

Canadian Journal of Chemistry ◽

10.1139/v83-255 ◽

1983 ◽

Vol 61 (7) ◽

pp. 1456-1464 ◽

Cited By ~ 2

Author(s):

H. Santos ◽

A. V. Xavier ◽

C.F.G.C. Geraldes

Keyword(s):

Aqueous Solution ◽

Nuclear Overhauser Effect ◽

Coupling Constants ◽

Glycosidic Bond ◽

Proton Proton ◽

Proton Coupling ◽

Vicinal Proton ◽

Group A ◽

Nuclear Overhauser ◽

Nuclear Overhauser Effects

The proton–proton and phosphorus–proton nuclear Overhauser effect (nOe) of guanosine 5′-monophosphate (5′-GMP) was measured in aqueous solution at different pH values and in the presence of excess LaIII at acid pH. These data and nOe data from the literature for other mononucleotides were used together with vicinal proton–proton coupling constants to investigate the conformations of mononucleotides in aqueous solution, especially their rotational state about the glycosidic bond. Comparison of observed and calculated enhancements using various conformational models for the glycosidic bond gave predominantly anti conformations for 5′-AMP and 5′-GMP and a mixture of syn and anti conformations for 2′-AMP, 2′-GMP, 3′-AMP, and 3′-GMP. Protonation of 5′-GMP at N-7 of the guanine base alters the amplitude of its torsion angle within the anti range. The agreement between the glycosidic nucleotide conformations defined by nOe and by the lanthanide probe method is good but not perfect. As complexation of 5′-GMP with LaIII through the phosphate group has only a small effect on the conformation of its exocyclic group, a comparison of the two methods is justified.

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