Synthesis of modified pyrimidine bases and positive impact of chemically reactive substituents on their in vitro antiproliferative activity

The antiproliferative activity screening on human tumor cell lines of a series of modified uracil and cytosine bases as well as some corresponding acyclonucleosides, and comparison of structure–activity relationship revealed the importance of chemical reactivity of the substituent attached to the C5-position of uracil for the activity of studied compounds. Namely, the results obtained for the most active compounds, 5-(chloroacetylamino)uracil (2) and its acyclic sugar analogue 18, suggest that formation of a covalent bond between reactive substituent and several possible targets within the thymidylate synthase mechanism (sulphur of the cysteine residue, basic part of the enzyme, N,N-methylene tetrahydrofolate or its reactive iminium forms) is the most probable mode of action. In addition, novel C5-substituted uracil derivative 6 (5-[bis-(2-p-methoxybenzylthioethyl)amine]acetylaminouracil) exhibited high antiproliferative activity against HeLa and MiaPaCa-2 cell lines, by an as yet unknown mechanism.

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