Total Synthesis of the Diglycosidic Tetramic Acid Ancorinoside A.

Ancorinoside A, a metabolite of a sponge Ancorina sp., was prepared in 18 steps as the first derivative of this class of glycosylated 3-acyltetramic acids. It features a β-d-glucopyranosyl-(1→4)-β-d-galacturonic acid linked to a d-aspartic acid derived tetramic acid via a 3-docosanoyl spacer. The diglycoside was built up by connecting the protected monosaccharides d-galactose and d-glucose via a thioglycoside glycosylation. Attachment of the spacer by a subsequent Schmidt glycosylation of this diglycoside, TEMPO oxidation to the uronic acid, functionalisation of the spacer terminus with an N-(β-ketoacyl)aspartate, and a final Dieckmann cyclisation were the key steps leading to ancorinoside A. This approach should also allow access to ancorinoside D.