5-Halogenation of Uridine Suppresses Protonation-Induced Tautomerization and Enhances Glycosidic Bond Stability of Protonated Uridine: Investigations via IRMPD Action Spectroscopy, ER-CID Experiments, and Theoretical Calculations

Abstract

Uridine (Urd), a canonical nucleoside of RNA, is the most commonly modified nucleoside among those that occur naturally. Uridine has also been an important target for the development of modified nucleoside analogues for pharmaceutical applications. In this work, the effects of 5-halogenation of uracil on the structures and glycosidic bond stabilities of protonated uridine nucleoside analogues are examined using tandem mass spectrometry and computational methods. Infrared multiple photon dissociation (IRMPD) action spectroscopy experiments and theoretical calculations are performed to probe the structural influences of these modifications. Energy-resolved collision-induced dissociation experiments along with survival yield analyses are performed to probe glycosidic bond stability. The measured IRMPD spectra are compared to linear IR spectra predicted for the stable low-energy conformations of these species computed at the B3LYP/6-311+G(d,p) level of theory to determine the conformations experimentally populated. Spectral signatures in the IR fingerprint and hydrogen-stretching regions allow the 2,4dihydroxy protonated tautomers (T) and O4-and O2-protonated conformers to be readily differentiated. Comparisons between the measured and predicted spectra indicate that parallel to findings for uridine, both T and O4-protonated conformers of the 5halouridine nucleoside analogues are populated, whereas O2-protonated conformers are not. Variations in yields of the spectral signatures characteristic of the T and O4-protonated conformers indicate that the extent of protonation-induced tautomerization is suppressed as the size of the halogen substituent increases. Trends in the energy-dependence of the survival yield curves find that 5halogenation strengthens the glycosidic bond and that the enhancement in stability increases with the size of the halogen substituent.

Exploring Glycosylated Soy Isoflavones Affinities toward G‐tetrads as Studied by Survival Yield Method

“…[17] Rodgers and coworkers have used E com50 in order to evaluate the influence of various substituents on the stability of glycosidic bonds in nucleosides. [18] It is worth adding that Hill et al have compared E com50 values measured by four different mass spectrometers and the values have been found to be well correlated. [19] In this paper we studied the interaction between G-tetrads (Scheme 1), namely [4G + Na] + ions (were G stands for guanosine -G r , or deoxyguanosine -G dr ) and isoflavone glucosides present in the soy based food supplements for menopausal symptoms (their brief characteristics is shown in the supplementary material, Table S1), by using electrospray ionization-collision induced dissociation-mass spectrometry (ESI-CID-MS) and survival yield method.…”