Through-Space 7JHF and 6JCF Spin–Spin Couplings in 2′,3′-Dideoxy-4′-fluoroalkylnucleosides. The Role of Sugar Ring Conformation and Solvent Effect
✍ Scribed by Andrea Mele; Giuliana Salani; Fiorenza Viani; Pierfrancesco Bravo
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 354 KB
- Volume
- 35
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
1H and 13C NMR spectra of seven compounds of a new class of synthetic Ñuorinated nucleosides, 2º,3º-dideoxy-4º-Ñuoroalkylthymidine and 2º,3º-dideoxy-4º-ÑuoroalkylÑuorouridine, showed long-range and couplings 7J HF 6J CF between the F of the Ñuoroalkyl moiety and H-6 (and C-6) of the nucleobase. All the couplings were selectively detected on a anomers only, and 1H{19F} NOE di †erence spectra indicated that the F nucleus and H-6 are also in spatial proximity, supporting the hypothesis of a through-space mechanism for the transmission of the nuclear spin information. Molecular mechanics calculations on a-2º,3º-dideoxy-4º-Ñuoroalkylthymidine as a model compound indicated that FAE AE AEH-6 distance spans the range 2.58-2.73 irrespective of the sugar ring conformation and the A FAE AE AEH-6ÈC-6 angle is within the range 145-159Ä. Calculated data support the view of an attractive interaction between F and H-6 of the base, consistent with an intramolecular hydrogen bond. Experimental evidence to this hypothesis are provided by NMR measurement in di †erent solvents : the observed values of and decrease 7J HF 6J CF with increasing dielectric constant of the solvent and with the increasing capability of the solvent to establish intermolecular hydrogen bonds in competition with the intramolecular ones, i.e. passing from to CDCl 3 acetone-d 6 and to 1997 by John Wiley & Sons, Ltd. DMSO-d 6 . (