DNA−Protein Cross-Linking:  Model Systems for Pyrimidine−Aromatic Amino Acid Cross-Linking

We have synthesized simple model systems to explore the possibility of photo-cross-linking between the pyrimidine bases and the side chains of the aromatic amino acids. Thymine/phenylalanine and thymine/tyrosine models gave cross-links, and thymine/tryptophan models gave complex mixtures; the cytosine/phenylalanine model was unreactive. The quantum yields for the model cross-linking reactions were 18−46 times smaller than those for thymine dimer formation. Biphotonic excitation contributes little to the yield of these reactions.