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Regioselective ferrocenoylation of purines

Nucleoside analogues are compounds which may interfere with the nucleic acid synthesis through the mimicking of endogenous substrates. The sugar unit in these molecules is frequently modified or completely replaced1. Our research group has developed an one-step synthetic route to prepare ferrocenoyl derivatives of pyrimidine nucleobases (uracil, thymine, and 5- fluorouracil) incorporating a carbonyl group as a chemical spacer.2 The ferrocenoyl unit was introduced into the N1-position of the pyrimidine ring systems without protection of the N3-position. The regioselectivity of the substitution was confirmed by NMR spectroscopic analysis and quantum chemical calculations. Here we are focused on synthesis of a series of ferocenoyl-purine conjugates I and II, with special attention being focused on the regioselectivity of the reaction. According to our results, the ferrocenoylation of the N9- position in purines is both kinetically and thermodynamically favored. The ratio of the isomers formed during the reaction has been monitored under different reaction conditions such as solvent, temperature of deprotection and coupling reactions, or base catalyst. The position of the substitution in products and the reaction regioselectivity has been explored by spectroscopy methods (1D and 2D-NMR, FTIR) and quantum chemical calculations (DFT level of theory).

ferocenoyl-purine conjugates, regioselectivity, NMR, DFT

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