Reaction products from N methyl N nitrosorea and deoxyribonucleic acid containing thymidine residues. Synthesis and identification of a new methylation product, O4 methylthymidine

Abstract

DNA was treated with N methyl N nitrosourea at pH 7-8, 37°C, degraded to yield 3 and 7 methylpurines and deoxyribonucleosides and the reaction products were separated by chromatography on ion exchange resins. The following methods for identification and determination of products were used: with unlabelled N methyl N nitrosourea, u.v. absorption; use of methyl 14C labelled N methyl N nitrosourea and use of [14C]thymine labelled DNA. The synthesis of O4 methylthymidine and its identification by u.v. and mass spectroscopy are reported. 3 Methylthymidine and O4 methylthymidine were found as methylation products from N methyl N nitrosourea with thymidine and with DNA, in relatively small yields. Unidentified products containing thymine were found in enzymic digests of N methyl N nitrosourea treated DNA, which may be phosphotriesters.