Advantages of the Ns group in the reactions of N1-SO2R inosines with benzylamine and with 15NH3

The reactivity of N1-alkylsulfonyl- and N1-arylsulfonyl-2′,3′,5′-tri-O-acetylinosine with benzylamine and with 15NH3, regarding the attack on C2, has been shown to be in the order CF3SO2 (Tf) > 2,4-(NO2)2C6H3SO2 (DNs) ⩾ 4-NO2C6H4SO2 (pNs) ≈ C6F5SO2 (PFBs) > 2-NO2C6H4SO2 (Ns) ≫ CH3SO2 (Ms) > 4-CH3C6H4SO2 (Ts) > 2,4,6-(CH3)3C6H2SO2 (Mts). In spite of its intermediate reactivity, the Ns group is the most appropriate, since in this case the formation of by-products is minimised during the ring-opening and ring-closing steps of the process. Another advantage of the Ns group is thus disclosed.

The attack of PhCH2NH2 and of 15NH3 on C2 largely predominates over the attack on the sulfur atom and on Cipso, in the case of the N1-Ns inosine derivative (shown above). The open intermediates arising from the attack on C2 afford the desired N1-benzyl and N1-labelled inosines, respectively, by heating under appropriate conditions.