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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
N-Acetylmuramic acid, or MurNAc, is the ether of lactic acid and N-acetylglucosamine with a chemical formula of C11H19NO8. It is part of a biopolymer in the bacterial cell wall, built from alternating units of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc), cross-linked with oligopeptides at the lactic acid residue of MurNAc. This layered structure is called peptidoglycan.
Clinical significance 
Unlike most bacterial cell walls, Chlamydial cell wall lacks muramic acid. For this reason penicillin is not very effective in treating chlamydial infection. Protein synthesis blockers like doxycycline or azithromycin are used instead.
N-Acetylmuramic acid (MURNAc) is part of the peptidoglycan polymer of Gram-positive bacterial cell walls. MURNAc is covalently linked to N-acetylglucosamine and may also be linked through the hyroxyl on carbon number 4 to the carbon of L-alanine (Figure 9.26). A pentapeptide composed of L-alanyl-d--isoglutaminyl-L-lysyl-D-alanine-D-alanine is added to the MURNAc in the process of making the peptidoglycan strands of the cell wall.
See also