Measurement of Long Range 1H-19F Scalar Coupling Constants and their Glycosidic Torsion Dependence in 5-Fluoropyrimidine Substituted RNA

摘要

Long range scalar ⁵J(H1’,F) couplings were observed in 5-fluoropyrimidine substituted RNA. We developed a novel S³E-¹⁹F-α,β-edited NOESY experiment for quantitation of these long range scalar ⁵J(H1’,F), where the J-couplings can be extracted from inspection of intraresidual (H1’,H6) NOE crosspeaks. Quantum chemical calculations were exploited to investigate the relation between scalar couplings and conformations around the glycosidic bond in oligonucleotides. The theoretical dependence of the observed ⁵J(H1’,F) couplings on the torsion angle χ can be described by a generalized Karplus relationship. The corresponding density functional theory (DFT) analysis is outlined. Additional NMR experiments facilitating the resonance assignments of 5-fluoropyrimidine substituted RNAs are described and chemical shift changes due to altered shielding in the presence of fluorine-19 (¹⁹F) are presented.