| Abstract
| - A variety of substituted 2‘-deoxyadenosin-5‘-yl radicals 3 were generated under different reactionconditions. Radicals 3 underwent intramolecular cyclization onto the C8−N7 double bond of the adeninemoiety leading to aminyl radicals (5‘S,8R)-4 and (5‘R,8R)-4 and, eventually, to the correspondingcyclonucleosides 5 and 6. The effect of the solvent, the nature of the substituents, and the generationmethod of radicals 3 on the stereoselectivity of the C5‘-radical cyclization have been considered. Theobserved increase of the (5‘S)/(5‘R) ratio by increasing the bulkiness of the R1 group is explained interms of steric repulsion between R1 and the purine moiety which favors the C5‘-endo conformation,whereas the effect of the water solvent in promoting the (5‘R)-stereoselective cyclization is ascribed tointermolecular hydrogen bonding stabilizing the C5‘-exo confomation.
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