Selenoxide elimination for the synthesis of unsaturated-sugar uracil nucleosides
摘要:
Introduction of a phenylseleno group to the sugar portion of uracil nucleosides and selenoxide elimination reactions of the resulting selenium-containing derivatives are described. A phenylselenide anion prepared by reducing (PhSe)2 with LialH4 was found to be highly reactive. By using this selenide as a nucleophile, ring openings of various types of cyclonucleosides and nucleosides having an anhydro structure in the sugar portion were accomplished. The products, which contain a phenylseleno group in the sugar portion, were oxidized with m-CPBA in CH2Cl2, and their susceptibility to the selenoxide elimination and regiochemistry of the reaction was investigated.
Substitution of a p-toluenesulfonyloxy group in the sugar portion of uracilnucleosides by an alkyl group was investigated by using Gilman reagents (R2CuLi). In the cases of 5'-O-tosyl derivatives of 2', 3'-O-isopropylideneuridine, moderate vields of 5'-alkylated products were obtained. In contrast to this, the reactions of the corresponding 2'-deoxyuridine derivatives gave higher yields of products. A similar substitution reaction at the 3'-position of 2'-deoxyuridine derivatives was also examined.