-Escherichia coli purine nucleoside phosphorylase (PNP) is used as a model enzyme to investigate metabolism and stability of biologically active nucleosides in the cell. The substrate specificity of E. coli PNP was studied in the reactions of phosphorolytic cleavage of the glycoside bond in adenosine derivatives containing a cyclic terpene moiety as precursors of biologically active purine derivatives. A number of N⁶-ter- pene-substituted adenosine derivatives were obtained, differing in hydrocarbon substituent structure. Kinetic parameters of the phosphorolysis reaction were measured, and adenosine derivatives with a bicyclic hydrocarbon moiety were found to bind to the enzyme more efficiently than monocyclic derivatives. The results make it possible to produce new purine derivatives containing a lipophilic terpene moiety in mild reaction conditions.