Studies toward the oxidative and reductive activation of C-S bonds in 2'-S-aryl-2'-thiouridine derivatives
Résumé
Studies directed towardthe oxidative and reductive desulfurizationof readily available 2'-S-aryl-2'-thiouridine derivatives were investigated with the prospect to functionalize the C2'-position of nucleosides. Theoxidative desulfurization-difluorination strategy was successful on 2-(arylthio)alkanoate surrogates,while extension of the combination of oxidants and fluoride sourceswas not an efficient fluorination protocol when appliedto 2'-S-aryl-2'-thiouridine derivatives, resulting mainly in C5-halogenation of the pyrimidine ringand C2'-monofluorination without desulfurization.Cyclic voltammetry of 2'-arylsulfonyl-2'-deoxyuridines and their 2'-fluorinated analogues showed that cleavage of the arylsulfone moiety could occur, although at relatively high cathodic potentials.While reductive-desulfonylation of 2'-arylsulfonyl-2'-deoxyuridineswith organic electron donors (OEDs) gave predominantly base-induced furan type products,chemical (OED) and electrochemical reductive-desulfonylationof the α-fluorosulfone derivatives yieldedthe 2'-deoxy-2'-fluorouridine and 2',3'-didehydro-2',3'-dideoxy-2'-fluorouridine derivatives. These results provided good evidence of the generation ofa C2'-anion through carbon-sulfur bondcleavage, opening new horizons for the reductive-functionalization approaches in nucleosides. _______________________
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