Guanine, photooxidation products

Since chemistry of pterines and purines has been already reviewed (42,48,491), only recent studies will be described here. Guanine (93) was prepared by reaction of 4-hydroxy-2,5,6-triaminopyrimidine sulfate (588 see Scheme 73) with HCONH2 with removal of H2O from the reaction system in an excellent yield (492). Also, irradiation of oxygenated aqueous solutions of 6-mercaptopurine with near-UV light gave hypoxanthine (92) as a minor product (< 10%) together with purine-6-sulfinate (589). It also arises from degradation of purine-6-sulfonate obtained from photooxidation of the sulfinate (589) (493). 

Adam W, Arnold MA, Saha-Moller CR (2001) Photooxidative damage of guanine in DG and DNA by the radicals derived from the a cleavage of the electronically excited carbonyl products generated in the thermolysis of alkoxymethyl-substituted dioxetanes and the photolysis of alkoxyac-etones. J Org Chem 66 597-604... 

It is well established that singlet oxygen is able to oxidise DNA with a much higher specificity than hydroxyl radical. The main stable oxidation products of the reaction of O2 with 2-deoxyribose guanine were identified as the and 4S diastereoisomers of 4-hydroxy-8-oxo-4,8-dihydro-2 -deoxy-guanosine on the basis of extensive NMR and mass spectrometry measurements (Ravanat et al. 1992, Ravanat and Cadet 1995). Similar oxidation products were generated by the type II photooxidation reaction of 2 -deoxyguanosylyl -(3 -5 )-thymidine (Buchko et al. 1992). 

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