Synthetic study of peptidoglycan partial structures. Synthesis of tetrasaccharide and octasaccharide fragments

Partial structures of peptidoglycan, a potent immunostimulating glycoconjugate of bacteria, were synthesized for precise biological studies. A key disaccharide glucosaminyl-β(1–4)-muramic acid was prepared by stereoselective glycosylation of a N-Troc (Troc=2,2,2-trichloroethoxycarbonyl) muramic acid acceptor with a N-Troc-glucosaminyl trichloroacetimidate. The disaccharide was converted to either a disaccharide acceptor or a donor. They were then coupled together by the same glycosylation method to give a tetrasaccharide in a good yield. Octasaccharide was also obtained in a good yield in a similar manner. N-Acetylation and coupling with the dipeptide moiety of l-alanyl-d-isoglutamine followed by deprotection afforded the repeating peptidoglycan tetrasaccharide and octasaccahride peptide conjugates for the first time.