Mesoionic Nucleosides 3: Studies on Mesoionic Imidazo [2,1-b]-1/3-thiazine Derivatives

Abstract

Anhydro 1- (2', 3', 5’ -tri-Oacetyl-β-D-ribofuranosyl) -5-hydroxy-7-oxoimidazo[2, 1-b]-1, 3-thiazinium hydroxide, a mesoionic imidazothiazine nucleoside, was prepared by the condensation of the appropriately acetylated ribofuranosyl imidazoline-2-thione with carbon suboxide. Although stable at or below O° C, the product rapidly underwent ring-opening at room temperature to afford the precursor nucleoside. A possible scheme for this ring-opening reaction is proposed based on the results of a model study employing anhydro 1-methyl-5-hydrcxy-7-oxoimidazo[2, 1-b]-1, 3-thiazinium hydroxide.