Chemical Synthesis and Biological Activities of Two Disaccharide Dipeptides Corresponding to the Repeating Units of Bacterial Peptidoglycan

Two disaccharide dipeptides, i.e., O-(N-acetyl-β-d-glucosaminyl)-(1→4)-N-acetylmuramyl-l-alanyl-d-isoglutamine (2) and O-(N-acetyl-β-muramyl-l-alanyl-d-isoglutamine)-(1→4)-N-acetyl-d-glucosamine (3), which correspond to partial structures of cell wall peptidoglycan were synthesized via the same glucosamine disaccharide as a common intermediate. Thus, selective introduction of lactic acid moiety on either one of the sugar moieties of the intermediate gave two disaccharides respectively which contain muramic acid on either reducing or nonreducing side. Coupling of the peptide moiety followed by deprotection afforded 2 and 3. The results of biological tests showed that both 2 and 3 have the same magnitude of immunostimulating activities as those of N-acetylmuramyl-l-alanyl-d-isoglutamine which is the minimum structure required for expression of the activities.