Proton-Coupled¹⁵N NMR spectra of neutral adn protonated ethenoadenosine and ethenocytidine

Abstract

The 15N chemical shifts and 15N, 1H spin coupling constants were determined in the title compounds using the INEPT pulse sequence and assigned with the aid of selective proton decoupling. The delta/15N/ and J/N, H/ values are discussed in terms of involvement of the imidazole ring created by ethenobridging in the electronic structure of the whole molecule. Both spectral parameters indicate that the diligant nitrogen in this ring is the primary site of protonation in these modified nucleosides. It is concluded that 15N NMR of nucleoside bases can be largely a complementary method to 1H and 13C NMR studies and, in addition, can serve as a direct probe for studies of nitrogen environment in oligomeric fragments of nucleic acids even at moderately strong magnetic fields due to the higher spectral dispersion compared with 1H and 13C NMR spectra.

Transfer RNA contains sites of localized positive charge: carbon NMR studies of [13C]methyl-enriched Escherichia coli and yeast tRNAPhe

“…To confirm that the correspondence of tRNA methyl carbon chemical shifts to that of m'A-HI and m7G plus TFA was truly attributable to the protonated forms of the mononucleosides, we have characterized the neutral and protonated mononucleosides by , 13C, and 15N NMR spectroscopy under physiological conditions comparable to that for tRNA and by IR spectroscopy. This investigation (H. Sierzputowska-Gracz and P. F. Agris, unpublished results) also revealed the sites of protonation and utilized model compounds, ethenoadenosine (Sierzputowska-Gracz et al, 1984) and ethenocytidine (Jaskolski et al, 1981;Kozerski et al, 1984). The hydroiodide of m'A corresponded to the protonated form of the nucleoside.…”

Comparative structural analysis of 1-methyladenosine, 7-methylguanosine, ethenoadenosine and their protonated salts IV:1H,13C, and15N NMR studies at natural isotope abundance

“…Signal assignments for m A were based on published 15N studies of adenosine ( 24) and the proton coupled, nitrogen spectrum of m1A. Published assignments for ethenoadenosine (EA) were also useful (1). Note that the most significant ring nitrogen chemical shift alterations were strong upfield changes occurring with protonation at N-1 in adenosine and NH2-6 in m A, as well as N-6 of EA.…”

“…Previously reported NMR studies of the neutral and protonated forms of the mononucleosides ethenocytidine (EC) and ethenoadenosine (EA), defined their structures, conformations and sites of protonation in solution in comparison to that in the crystal state. (1,2). Carbon NMR chemical shifts were shown to be just as indicative of the site and extent of protonation as were 15N chemical shifts (1), the latter known to ellucidate the chemical environment of nitrogen nuclei.…”

Theoretical and experimental study of 15 N NMR protonation shifts

“…[9] Marked protonation 15 N NMR shifts can also serve as an unambiguous indicators of the binding sites of nucleic acids and nucleosides, as was exemplified for ethenoadenosine and ethenocytidine. [10] It is well known that most inhibitors of enzymes containing azole and/or azine rings undergo protonation when binding to enzyme. Thus, Bevan et al [11] studied the binding of trimethoprim and [1,3,2-amino- 15 N 3 ]-trimethoprim to Lactobacillus casei dihydrofolate reductase by means of 15 N NMR spectroscopy.…”