Preparation of ethylenediaminephosphoramidates of nucleotides and derivatization with fluorescein isothiocyanate.

Fluorescence post-labeling of nucleotides is a potentially useful technique for the detection of trace amounts of damaged DNA (DNA adducts). Towards this goal, we have studied a derivatization procedure starting with the four major 5'-deoxynucleotides as model compounds. The 5'-phosphate group was first labeled with ethylenediamine via a phosphorimidazolide intermediate in methanol with an organic-soluble carbodiimide. The resulting ethylenediaminephosphoramidate products were reacted in turn with fluorescein isothiocyanate. The reaction sequence has been characterised at all stages by high-performance liquid chromatography.