Nucleosides. XLIX. Nuclear magnetic resonance studies of 2′-and 3′-halogeno nucleosides. The conformations of 2′-deoxy-2′-fluorouridine and 3′-deoxy-3′-fluoro-β-D-arabinofuranosyluracil

Nuclear magnetic resonance data for a series of 2′-halogeno and 3′-halogeno pyrimidine nucleosides are presented. Using a combination of proton–proton and proton–fluorine couplings vs. dihedral angle values 2′-deoxy-2′-fluorouridine is proposed to have an envelope conformation with C–3′ endo, and 1-(3-deoxy-3-fluoro-β-D-arabinofuranosyl)uracil proposed to have a twist conformation with O-ring endo and C–1′ exo. Correlations between substituent electronegativity and both vicinal coupling constants and internal chemical shifts are discussed.Syntheses of several new 2′-halogeno and 3′-halogeno nucleosides are described.