Isonucleosides with Exocyclic Methylene Groups

Abstract

Synthesis of isonucleosides 13, 14, 16, and 17, bearing an exocyclic methylidene group at the sugar moiety, starting from a 3-keto sugar is described. The keto compound was converted to the methylene-sugar 10b (Scheme 1), which was coupled with nucleobases by means of the Mitsunobu reaction. The coupling reaction with adenine and 8-azaadenine produced both the N9- and N3-nucleosides (see 13 and 14, resp.; Scheme 2). The structures of 13a and 14a were confirmed by single-crystal X-ray data. Synthesis of the pyrimidine compounds was also approached from the β-amino sugar 20 that was prepared using a Gabriel-synthesis methodology (Scheme 3).