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ULTRAVIOLET‐AND γ‐RAY‐INDUCED REACTIONS OF NUCLEIC ACID CONSTITUENTS WITH ALCOHOLS. ON THE SELECTIVITY OF THESE REACTIONS FOR PURINES

THE photochemical reactions of nucleic acids and their constituents have been submitted to extensive investigations in recent years (For reviews see Setlow, 1967; Smith and Hanawalt, 1969; Lomant and Fresco, 1972). The photoreactions of the pyrimidine moieties were studied in more detail than those of other constituents, and it has been concluded that the pyrimidines in nucleic acids are the most sensitive targets for ultraviolet-induced lesions, while the purines are relatively stable under these conditions. However, it has been shown recently that purines and purine nucleosides are also reactive in photochemical reactions and give photoproducts with alcohols, amines, or amino acids (Linschitz and Connolly, 1968; Connolly and Linschitz, 1968; Evans and Wolfenden, 1970; Steinmaus et al., 1969, 1971; Yang et al., 1971; Stankunas et al., 1971; Elad and Salomon, 1971; Elad and Rosenthal, 1969). The purines acted both as hydrogen atom abstraction agents in their excited state, and as scavengers for free radicals generated during the ultraviolet( UV)and y-ray-induced reactions (Stermitz et al., 1970; Taylor et al., 1969). Since it has been found that purines and purine moieties in nucleic acids participate in photochemical reactions (Steinmaus et al., 1970) it was felt that the development of irradiation conditions under which one group of the nucleic acid bases would react selectively might be of major importance. We wish to report preliminary results of an investigation regarding UVand yray-induced reactions of alcohols with a variety of purines and pyrimidines. We have studied initially the photochemical reactions of uracil and thymine, as well as those of 1,3-dimethyluracil (DMU) and 1,3-dimethyIthymine (DMT) with 2-propanol in the presence of a variety of photosensitizers. Two types of pyrimidine-alcohol photoproducts were obtained, (Wang, 1961; Wang and Alcantara, 1965; Brown et al., 1966; Wang and Rhoads, 1971), namely I and 11, derived from uracil and thymine, respectively. Results of these reactions are summarized in Table 1.