Synthesis of the lipoteichoic acid of the Streptococcus species DSM 8747.

The lipoteichoic acid (LTA) of the Streptococcus species DSM 8747 consists of a beta-d-galactofuranosyl diacylglycerol moiety (with different acyl groups) that is linked via 6-O to a poly(glycerophosphate) backbone; about 30% of the glycerophosphate moieties carry at 2-O hydrolytically labile d-alanyl residues. As typical LTA for this array of compounds LTA 1a was synthesized. To this end, from d-galactose the required galactofuranosyl building block 5 was obtained. The anomeric stereocontrol in the glycosylation step with 1,2-O-cyclohexylidene-sn-glycerol (4) was based on anchimeric assistance, thus finally leading to the unprotected core glycolipid 16. Regioselective protection and deprotection procedures permitted the defined attachment of the pentameric glycerophosphate 3 to the 6-hydroxy group of the galactose residue. Introduction of four d-alanyl residues led after global deprotection and purification to target molecule 1a possessing on average about two d-alanyl residues at 2-O of the pentameric glycerophosphate backbone, thus being in close accordance with the structure of the natural material.