13C-enriched ribonucleosides: Synthesis and application of 13C-1H and 13C-13C spin-coupling constants to assess furanose and N-glycoside bond conformations

Article abstract of DOI:10.1021/ja00176a043

Adenosine (1), cytidine (2), guanosine (3), and uridine (4) have been prepared chemically with ¹³C enrichment (99 atom %) at C1′ and C2′ of the ribose ring. Reliable synthetic protocols have been developed to permit access to millimole quantities of labeled ribonucleosides required for structural studies of stable isotopically labeled oligonucleotides and for in vivo metabolism studies. High-resolution ¹H and ¹³C NMR spectra of the enriched ribonucleosides have been obtained, and ¹³C-¹³C and ¹³C-¹H spin-coupling constants have been measured for pathways within the β-D-ribofuranose ring and across the N-glycoside bond. Related couplings were determined in methyl α- and β-D-ribofuranosides (5, 6), and in two conformationally constrained nucleosides, 2,2′-anhydro-(1-β-D-arabinofuranosyl)uracil (7) and 2′,3′-O-isopropylidene-2,5′-O-cyclouridine (8). The latter data were used to construct a crude Karplus curve for the ¹³C-C-N-¹³C coupling pathway across the N-glycoside bond in 1-4. ¹H-¹H, ¹³C-¹H, and ¹³C-¹³C coupling data are used to evaluate current models describing the conformational dynamics of 1-4 in aqueous solution.