The two structurally interesting bioorganometallic analogues of muramyldipeptide (MDP) with potential immunomodulatory activity were synthesized starting from the O-protected N-acetylmuramic acid (MurNAc), or El-Ala and 1'-aminoferrocene-1-carboxylic acid (Fca). They were fully characterized by IR, H-1 NMR, C-13 NMR and CD spectroscopy as well as by FD mass spectrometry. (C) 2011 Elsevier Ltd. All rights reserved.