Diversity oriented efficient access of trisubstituted purines via sequential regioselective Mitsunobu coupling and SNAr based C6 functionalizations

An efficient protocol for the syntheses of diverse 2,6,7- and 2,6,9-trisubstituted purines is reported starting from the guanine precursor, 2-amino-6-chloropurine nucleoside through subsequent regioselective, high yielding Mitsunobu coupling and nucleophilic substitutions at C6 with versatile primary and secondary amines. A wide range of 2,6,7- and 2,6,9-trisubstituted purines were accessible in good to excellent yields with remarkable functional group tolerance. Moreover, solvent-free, large scale synthesis of precursors 2 & 3 and facile preparation of organophosphorus side chains 4 & 5 were also accomplished with excellent yields.