A strategy for chemical synthesis of selectively methyl-esterified oligomers of galacturonic acid

The synthesis of monomethyl-esterified trigalacturonans 1-3 is described as part of a general strategy towards pectic oligosaccharides. The necessary monomeric building blocks were all prepared on a large scale from galactose pentaacetate. The glycosylations were carried out between galactose glycos yl donors and acceptors using the n-pentenyl glycosylation technique. Yield s of the desired alpha -anomers were in the 50 to 74% range. The trigalacta ns thus obtained were then subjected to oxidation at C-6. Depending on the protecting group at this position the oxidation either produced the carboxy lic acid or the corresponding methyl ester. Hereby, oligomers of galacturon ic acid can be prepared with methyl esters introduced in a regiocontrolled fashion.