A method of preparing C-5 substituted nucleotides by reacting a C-5 posit mercurated nucleoside with an alkyl or aryl disulfide in the presence of palladium(II) ion. The resulting new method for attaching linker arms to nucleic acids (DNA,RNA) provides a wide ranging reaction far more useful than those heretofore developed, and allows preparation of modified components with linking reactive functionality that allows usefulness as probes, therapeutics, and for DNA sequencing.