The reaction of C-5 mercurated pyrimidine nucleosides with palladium (II) and olefins is to be investigated. The C-5 substituted derivatives of 2'-deoxyuridine obtained by this method are potential antiviral and antitumor agents. The structure of the C-5 side chain will be varied to obtain derivatives for exploratory studies as inhibitors and reporter molecules for the enzymes thymidine phosphorylase, thymidine kinase, and thymidylate synthetase. 14C-Labeled thymidine analogs are to be synthesized for biosynthetic and nucleic acid incorporation studies. The reaction or organopalladium intermediates, derived from mercurated nucleotides and polynucleotides, with olefins will be explored.