Synthesis of 2',3'-Didehydro-2',3'-dideoxynucleosides Utilizing Coupling Reactions between Nucleic Bases and Phenylthio-substituted 2,3-Dideoxyribose
摘要:
Stereoselectivities in coupling reactions between silylated pyrimidine bases and 3- or 2-alpha-phenylthio-2,3-dideoxyribose were examined. In the former case, no stereoselectivies were observed when the coupling reactions were performed either with 1-chlorosugar in an S(N)2 mode or in the presence of Lewis acids as catalyst in an S(N)1 mode. Coupling reaction with 2-alpha-phenylthio-2,3-dideoxyribose in the presence of Lewis acids, especially SnCl4, proceeded with good stereoselectivity to give anomeric mixtures of alpha:beta = 1:9. All these nucleosides were converted to 2',3'-didehydro-2',3'-dideoxynucleosides by oxidation to sulfoxides followed by thermal elimination of sulfenic acid.