PHOTOOXIDATION OF D(TPG) BY RIBOFLAVIN AND METHYLENE-BLUE - ISOLATIONAND CHARACTERIZATION OF -D-ERYTHRO-PENTOFURANOSYL)AMINO]-4H-IMIDAZOL-4-ONE AND ITS PRIMARY DECOMPOSITION PRODUCT TA-D-ERYTHRO-PENTOFURANOSYL)AMINO]-5(2H)-OXAZOLONE

The major initial product of riboflavin- and methylene blue-mediated p hotosensitization of 2'-deoxyguanosine (dG) in oxygen-saturated aqueou s solution has previously been identified as -D-erythro-pentofuranosyl )amino]-4H-imidazol-4-one (diz). At room temperature in aqueous soluti on diz decomposes quantitatively to eta-D-erythropentofuranosyl)amino] -5(2H)-oxazolone (dZ). The data presented here show that the same guan ine photooxidation products are generated following riboflavin- and me thylene blue-mediated photosensitization of thymidylyl-(3',5')-2'-deox yguanosine [d(TpG)]. As observed for the monomers, the initial product , -D-erythro-pentofuranosyl)amino]-4H-imidazol-4-one [d(Tplz)], decomp oses in aqueous solution at room temperature to ta-D-erythro-pentofura nosyl)amino]-5(2H)-oxazolone [d(TpZ)]. Both modified dinucleoside mono phosphates have been isolated by HPLC and characterized by proton NMR spectrometry, fast atom bombardment mass spectrometry, chemical analys es and enzymatic digestions, Among the chemical and enzymatic properti es of these modified dinucleoside monophosphates are: (i) d(Tplz) and d(TpZ) are alkalilabile; (ii) d(Tplz) reacts with methoxyamine, while d(TpZ) is unreactive; (iii) d(Tplz) is digested by snake venom phospho diesterase, while d(TpZ) is unaffected; (iv) relative to d(TpG), d(TpZ ) and d(Tplz) are slowly digested by spleen phosphodiesterase; (v) d(T plz) and d(TpZ) can be 5'-phosphorylated by T4 polynucleotide kinase, The first observation suggests that dlz and dZ may be responsible for some of the strand breaks detected following hot piperidine treatment of DNA exposed to photosensitizers.