A Simple Synthetic Access to Differently 4-Substituted Neu5Ac2en Glycals Combining Elements of Molecules with Anti-Neuraminidase Activity

A protocol for direct access to C-4-functionalized Neu5Ac2en derivatives by allylic substitution of an α-acetoxy group with various nucleophiles is reported. The DANA acetamido group is exchanged for a trifluoroacetylamido group (as in FANA) to avoid the formation of a stable 4,5-oxazoline. With thiols, the reaction involves an initial attack at the anomeric carbon (Ferrier reaction) under kinetic control, followed by an equilibration of the nucleophile to the thermodynamically more stable 4-position.