Synthesis of new C 6 substituted peptidyl nucleosides. A mechanistic study

The synthesis of four new peptidyl nucleosides is reported. The kinetic data obtained for the transesterification of 2'/3'-O-benzyloxycarbonyl-L-p-nitrophenylalanyl 5'-O-trityl ribonucleosides which contain different substituents at C 6 position of the purine residue indicates for different mechanisms of the transesterification reaction. The peptidyl nucleosides with an amino group at C 6 position and those lacking such group at that position have two distinctive mechanisms of transesterification.