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Sugar ring conformations of guanine nucleosides by proton nuclear magnetic resonance.

Proton NMR studies at 250 MHz showed that ribofuranosyl and 2-deoxyribofuranosyl derivatives of N2-(p-n-butylphenyl)guanine (BuPG) favored the C2'-endo (S) sugar pucker and the gg exocyclic group rotamer, although less so than guanosine and 2'-deoxyguanosine themselves. The correlation calculated between C3'-endo (N) and gg conformational states in these compounds may result from destabilization of syn glycosidic bond conformers by the bulky N2 substituent. Results for a bis(ribofuranosyl) derivative of BuPG showed a strong correlation between N and gg states in both sugar rings, suggesting that both rings are anti and are stabilized by intramolecular hydrogen bonding between C3'-O and H8.