Theoretical study of 9-beta-D-erythrofuranosyladenine and corresponding carbocyclic analogues. Evidence for a base-activated conformational lock

The conformational surfaces of three nucleoside analogues have been investigated computationally, where an adenine is attached to a diol of tetrahydrofuran, a diol of cyclopentane, and a diol of cyclopentene. In each system, the lowest-energy conformer displays a conformational lock into the south position by an internal hydrogen bond between O2'H of the five-membered ring and the N3 nitrogen of adenine. When aqueous. solvation is accounted for by the PCM method, the preference for the locked conformer is diminished. A pseudorotation angle of 9-(trans-2',trans-3'dihydroxycyclopentyl)adenine has been determined to be 176.8degrees by fitting the measured (3)J(HH) values using PSEUROT which is in good agreement with the calculated value of 169.3degrees