Nucleoside conformations. 16. Nuclear magnetic resonance and circular dichroism studies on pyrimidine-2'-fluoro-2'-deoxyribonucleosides.

Abstract

Abstract From the proton and fluorine NMR spectra of 3′,5′-di- O -acetyl-2′fluoro-2′-deoxyuridine, its thiouracil analogue and 2′-fluoro-2′-deoxycytidine at 250 MHz, it was concluded that these compounds are preferentially in a 3′-endo—4′-exo conformation (N-form) with only about 10–20% 2′-endo contribution (S-form). Despite the small van der Waals radius of fluorine, the 2′-fluoronu-cleosides studied in solution show the conformation characteristic for ribosides in the crystal structure. The solution data presented here are in good agreement with the crystal data of the first compound presented in the following paper by Suck, D., Saenger, W., Main, P., Germain, G. and Declercq, J.P. (1974) Biochim. Biophys. Acta 361, 257–265.