Thymine-3-propenal

Figure 5.5 Reaction mechanism for the 1,2-addition of 3-substituted acroleins (thymine propenal) with dC. (Figure adapted from [46].)...

This activated iron-oxygen complex then oxidizes the 4 -hydrogen atom of the deoxyribose moiety in the DNA of cancer cells (Grollman and Takeshita, 1980). This attack causes the release of four propenal-base molecules, of which thymine-propenal 4.31) is typical. This scission is an oxidative cleavage of the bond between C-3 and C-4 atoms in the deoxyribose ring (Giloni etal., 1981). 

Thymine-propenal 4.31) is profoundly cytotoxic. It is not yet known whether the anti-cancer effect of bleomycin is largely due to the base-propenals to which it degrades the DNA of tumours. 

Intramolecular photocycloaddition is also reported to occur in the thiothymidine thymidinyl phosphates (80, R = H) and this gives the thietane (81) and the ring-opened thiol (82) (Scheme lO). The importance of this process is related to lesion in DNA. Irradiation of (80, R = Me) gives a new type of photoproduct (83) in the nucleic acid series that involves attack of the thiocarbonyl across the propene moiety of the thymidine ring. Irradiation at 366 nm in aqueous solution of the thiothymine (84) in the presence of adenine derivative (85) results in the formation of the adduct (86) this is formed presumably by way of the (2-l-2)-cycloaddition reaction between the C=S and the C=N bonds. Inter-molecular (2-i-2)-cycloaddition is also reported in the photoreaction of (84) with pyrimidinone derivative. Intramolecular photocycloaddition also occurs between thymine and 6-thioinosine derivatives tethered with ribose-phosphate-ribose and thietanes are obtained. ... 

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