The reaction of 2-0-acetylated and 2-0-benzoylated glycosides 3a, b/4a, b with silylated p- acetylguanine 7 selectively gave"'-guanine nucleosides 8a, b/Sa, b under kinetically controlled conditions (SnC14/CH3CN, room temperature), whereas 2-0-benzoylated glycosides 3b/4b selectively gave the isomeric Ns-guanine nucleosides lob/1 lb under thermodynamically controlled conditions (TMSOTf/(CH, Cl),, reflux). Unambiguous ...