Nmr spectra of pyrimidines

The NMR spectra of pyrimidines bearing tautomeric groups (NH2, OH, SH) in the 2-, 4- or 6-position are discussed in connexion with the tautomerism of such pyrimidines (Section 2.13.1.8). 

In the study on tetrasubstituted [l,2,4]triazolo[l,5- ]pyrimidines 45, H and 13C NMR spectra of 35 different compounds have been recorded <1995JHC407>. Substituents in position 2 were various amines and sulfano groups, whereas the other substituents (Rs, R6, and R7) were alkyl, phenyl, and acetyl groups. 

Attempts to detect the uncharged intermediates 6-amino-4-phenyl-l,6-dihydro-4-phenylpyrimidine (66), 2-amino-4-phenyl-l, 2-dihydropyrimidine (68), and the aminodiazahexatriene 67, by recording the NMR spectra of the solution during the stepwise addition of the ammonium chloride were not successful. The facile ring opening of the pyrimidine ring in 66 is not unexpected. It has also been observed in the reaction of A-methylpyrimi-dinium salts with liquid ammonia, which also involves as neutral covalent... 

Even though at present various obstacles prevent a more extensive application of NMR spectroscopy to the study of 77-electron distribution, it seems that it will be possible to make use of the interrelation between the magnitude of the chemical shift of a proton attached at a certain position and the 77-electron density at that position. Among the studies so far published attention should be drawn to the papers dealing with pyridine,111-112 substituted pyridines,113 and pyrimidine and its derivatives.114 Table VII presents data (taken from ref. 112) on experimental and theoretical 77-electron densities in pyridine and the pyridinium cation. The NMR spectra of some azines are briefly discussed by White.114"... 

The H NMR spectra of several thieno[2,3-d]pyrimidines (Figure 6) have been reported (76BSF761). Compared with thieno[3,2-d]pyrimidine (Figure 7) there is obviously no long-range coupling between the protons of the thiophene and pyrimidine rings. 

H NMR and IR data have been reported for 3,6-disubstituted 4-aminopyrimido-[5,4-cf]pyrimidine-2,8-diones. The NMR spectra of these compounds exhibit the presence of three NH protons which are exchangeable with deuterium oxide. One of these arises from the external nitrogen ca. S 11.3), and two result from the NH groups in the ring (ca. S 8.0 and 7.8) (78JOC3231). 

The H-NMR spectra of the isomeric 2-oxo-2H- and 4-oxo-4//-pyrido-[l,2-fl]pyrimidines exhibit some characteristic differences. In the spectra of 4-oxo-4//-pyrido[l,2-a] pyrimidines, which are unsubstituted at position 6, the anisotropic effect of the adjacent carbonyl group causes the signal of the H-6 to be shifted downfield by about 1 ppm as compared with the corresponding signal for the 2-oxo-2H isomer.2 19,24 86... 

Urban et al.u2 compared the UV, IR, and H-NMR spectra of the pyrido[l,2-a]pyrimidines (63) with those of their 1-alkyl and 2-alkoxy derivatives. 

NMR spectra have been used frequently to elucidate and/or confirm the structures of these heterocycles, but little or no systematic study had been done. A detailed study of l3C NMR spectra by distortionless enhancement by polarization transfer (DEPT), inverse H-I3C coherence transfer experiments (HMQC and HMBC) and by INADEQUATE of factor F0 has been reported <91JBC9622>. The 13C NMR spectra of a series of pyrido[4,3-J]pyrimidines were interpreted on the basis of a detailed study of other analogues <91JCS(P2)1559>. Carbon-13 NMR spectroscopy has been used to indicate the site of alkylation of pyrido[2,3-c]pyridazin-4-ones <90CPB3359>. 

The existence of metal intermediate complexes with deoxynucleotides has been elucidated by Eichhorn et al. (26). Proton NMR spectra of dAMP, dCMP, dGMP and dTMP show, especially for dAMP and dGMP, a strong reaction of Cu2+, although the interaction with the pyrimidines was markedly reduced. Further experiments employing 31P NMR spectroscopy show the broadening of the phosphate resonance of the deoxyribonucleotides of adenine and thymine (26). 

Direct evidence for the existence of anionic a-adducts for pyrazine, pyrimidine, and pyridazine (155-157) was first presented by Zoltewicz and Helmick (72JA682). They obtained H-NMR spectra of the adducts formed by mixing the diazine in liquid ammonia with sodium or potassium amide. Upheld shifts (2.2-4.5 ppm) were typical indicators of adduct formation. In an excess of diazine, both free and complexed diazine were evident in the spectrum, while in an excess of amide, the spectrum did not indicate the presence of free diazine. 

The IR and H NMR spectra of a series of 2-aminoethyl derivatives have been briefly discussed <85FES695>. High-resolution mass spectral and C NMR data as well have been reported for l,8-dioxopyrazino[l,2-c]pyrimidine-6-thiones <89H(29)i60i>. The UV data of a perhydro derivative... 

C-, N-, CP MAS- and high resolution multinuclear-NMR methods have been applied to a study of ureido sugars 39. The O-NMR spectra of l-ascorbic acid recorded in aqueous solution as a function of pH have been presented under the title New spectroscopy of an old molecule , and the N- and 0-NMR spectra of doubly labelled pyrimidine nucleosides have been recorded for use as references in NMR analyses of labelled RNA fragments. Information on the hydration behaviour of several monosaccharides (Glc, Gal, Man, All, and Tag) has been obtained by measurements of water O-relaxation times. ... 

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