(C-13)-SUBSTITUTED ERYTHRONUCLEOSIDES - SYNTHESIS AND CONFORMATIONAL-ANALYSIS BY H-1 AND C-13 NMR-SPECTROSCOPY

The erythronucleosides, 9-beta-D-erythrofuranosyladenine (1b), 1-beta-D-erythrofuranosylcytosine (2b), 9-beta-D-erythrofuranosylguanine (3b), and 1-beta-D-erythrofuranosyluracil (4b), were synthesized with and without C-13-substitution at C1' of the furanose ring. 75-MHz C-13 and 620-MHz H-1 NMR spectra of 1-4b were interpreted, in the latter case with the assistance of spectral simulation, and H-1-H-1, C-13-H-1, and C-13-C-13 spin couplings were used to assess furanose conformation. 3J(HH) data in (H2O)-H-2 were treated by computer to determine the preferred north and south conformers, their puckering amplitudes, and their mole fractions in solution, and J(CH) data were used to complement this analysis. A similar treatment of spin coupling data for the corresponding ribonucleosides 1-4a was also conducted to permit a comparison of furanose conformations in both series of compounds. Results show that the removal of the exocyclic hydroxymethyl group from 1-4a, giving 1-4b, significantly enhances the proportion of south conformers in aqueous ((H2O)-H-2) solution.