Synthesis of methylene isosteres of α- and β-D-galactopyranosyl-L-serine

Abstract

The BF₃·Et₂O promoted coupling of tetra-O-benzyl-α-D-galactopyranosyl trichloroacetimidate with a silyl enol ether carrying an oxazolidine ring leads to the α-C-glycosylmethyl ketone (32%, 95% ds) that is converted into the title α-C-glycosyl amino acid by carbonyl oxygen removal (Barton–McCombie) and oxidative cleavage (Jones) of the heterocyclic ring, and into the β-isomer by anomerization and the same two-step sequence.