Martin D. Shetlar and Janet Chung Ring-Opening Photoreactions of 5-Methylcytosine with 3-Mercaptopropionic Acid and Other Thiols Photochemistry and Photobiology 89
The photoreactions of 5-methylcytosine (5MeCyt), a minor base contained in eukaryotic DNA, with several cysteine analogs have been studied. The reaction of 5MeCyt with 3-mercaptopropionic acid (3MP) is shown schematically in the accompanying Figure. Irradiation with UVB light produces the opened-ring adduct Ia. Upon standing at ambient temperature in the presence of 3MP, the product IIa appears in solution. The latter reaction proceeds via a closed-ring intermediate that has been characterized using UV spectroscopy, proton NMR spectrometry and mass spectrometry. Either heating or irradiation of purified Ia with UVB light in aqueous solution converts it into 3-amino-2-methylacrylamidine.
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