The dipeptides Boc-Thr-Lys(Cbz)-OMe and Boc-Lys(Cbz)-Glu(OEt)-OEt were prepared by the classical method of peptide synthesis. The Cbz protecting group was subsequently removed via hydrogenolysis. AMP was then covalently joined to the free lysine epsilon-amine by the carbodiimide (DCC) method. The resulting RNA-ligase active center model compounds, the adenylyl-(5----N epsilon)-lysylpeptides were then used to study the participation of the amino acid residue functional groups in the hydrolysis of the phosphoamide center.