Photostimulated Degenerate Ring Transformations of Thymines

Interesting examples of degenerate ring transformations have been observed when an aqueous solution of thymine (58, R = H) or thymidine (58, R = desoxyribose) is irradiated ( 254 nm) in the presence of n-butyl- or t-butylamine at ambient temperature (81JA1598 81TL2365). The 1-R-thymines (R = t-C4Hf) are obtained in good yields. Urea deriva- 

A further exploration of these photoconversion reactions has shown that dAdo, dGuo, and dCyt do not give any detectable photoadduct (81MI1). Irradiation of a mixture of thymidine and dAdo in n-butylamine only gave 1-n-butylthymine, suggesting that the photoreaction preferentially occurs with thymidine (thymine). In the light of these results it is not surprising that 

These results seem to suggest that by irradiation in alkylamines DNA (single stranded) can undergo a selective release of thymine, accompanied by strand scission. This has indeed experimentally been verified. Irradiation of calf thymus DNA in 5% aqueous n-butylamine gave a photoproduct that on heating yields 1-n-butylthymine (81MI1). 

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