Specific Photoreaction Research Articles

Photochimie des polynucleotides: IV. Photochimie de quelques nucleosides puriques methyles

Photochemistry of polynucleotides. IV. Photochemistry of some methylated purinenucleosides The reduction of a number of nucleoside analogues by sodium borohydride has been studied. The generalisation can be drawn that in many cases reduction is facilitated by the imino form. Ring opening of 7-methylguanosine at slightly alkaline pH or reduction of the 7,8 double bond gives a substituted pyrimidine which is susceptible to photodegradation (loss of a formyl group in the case of 7-methylguanosine at pH 9.3) at wavelengths at which absorption of other bases is negligible. This specific photoreaction has been applied to synthetic and natural polynucleotides containing 7-methylguanine. Reduced 7-methylguanine residues are rapidly reoxidised by atmospheric oxygen to yield the original 7-methylnucleoside.