Isoglutamine can form the C-terminus of a peptide chain, as in muramyl dipeptide (MDP), a constituent of bacterialcell walls. It can also occur inside a peptide chain, in which case the chain is continued at the carboxyl group and isoglutamine behaves as a γ-amino acid, as in mifamurtide, a synthetic derivative of MDP used to treat osteosarcoma.
Stereochemistry
Substituting l-glutamic acid, the proteinogenic enantiomer, gives l-isoglutamine, which has S configuration. d-Isoglutamine, the derivative of the nonproteinogenic d-glutamic acid, has R configuration.[2] The latter is the form occurring in MDP and mifamurtide.
^Brundish, D. E.; Wade, R. (1985). "Synthesis of N-[2-3H]acetyl-D-muramyl-L-alanyl-D-iso-glutaminyl-L-alanyl-2-(1',2'-dipalmitoyl-sn-glycero-3'-phosphoryl)ethylamide of high specific radioactivity". J Label Compd Radiopharm. 22 (1): 29–35. doi:10.1002/jlcr.2580220105.