Synthetic Study of Lipoteichoic Acid of Gram Positive Bacteria. II. Synthesis of the Proposed Fundamental Structure of Enterococcus hirae Lipoteichoic Acid

The proposed fundamental structure of Enterococcus hirae lipoteichoic acid (LTA) was synthesized in order to elucidate the chemical structure responsible for the cytokine-inducing activity described for the natural LTA fraction of this bacteria. Synthesis was accomplished by coupling of the glycolipid part with the poly(glycerol phosphate) (PGP) part by using a phosphoramidite method. The glycolipid part was constructed by coupling of the phosphatidic acid moiety with a kojibiosyl diacylglycerol which had been prepared by stepwise glycosidation with glycosyl fluorides. α-Selective glucosidations were effected by virtue of the 2,2,2-trichloroethoxycarbonyl (Troc) group introduced at the 6-hydroxyl function. p-Nitrobenzyl (NPM) and p-pivaloylaminobenzyl (PAB) groups were successfully applied to temporary protection of hydroxyl functions.