muramic acids N-acetylmuramic acid 2-(acetylamino)-3-O-[(1R)-1-carboxyethyl]-2-deoxy-D-glucose 2-acetamido-3-O-[(1R)-1-carboxyethyl]-2-deoxy-D-glucose C11H19NO8 CAS:1856-93-5 CHEBI:47965 acetylmuramic acid chebi_ontology