3-Acetyloxy-2-cyano-2-(alkylaminocarbamoyl)propyl Groups as Biodegradable Protecting Groups of Nucleoside 5´-mono-Phosphates

摘要

Thymidine 5´-bis[3-acetyloxy-2-cyano-2-(2-phenylethylcarbamoyl)propyl]phosphate (>1) has been prepared and the removal of phosphate protecting groups by hog liver carboxyesterase (HLE) at pH 7.5 and 37 °C has been followed by HPLC. The first detectable intermediates are the (RP)- and (SP)-diastereomers of the monodeacetylated triester >14, which subsequently undergo concurrent retro-aldol condensation to diester >4 and enzyme-catalyzed hydrolysis to the fully deacetylated triester >15. The former pathway predominates, representing 90% of the overall breakdown of >14. The diester >4 undergoes the enzymatic deacetylation 700 times less readily than the triester, but gives finally thymidine 5´-monophosphate as the desired main product. To elucidate the potential toxicity of the electrophilic 2-cyano-N-(2-phenylethyl)acrylamideby-product >17 released upon the deprotection, the hydrolysis of >1 has also been studied in the presence of glutathione (GSH).