A comparative 1H-N.M.R. study of MurNAc- l-Ala- d-iGln (MDP) and its analogue murabutide: Evidence for a structure involving two successive β-turns in MDP

The active principle, MurNAc- l-Ala- d-iGln (MDP), of complete Freund's adjuvant and its analogue, MurNAc- l-Ala- d-Gln-O nBu (murabutide), which express immunomodulatory as well as other biological properties, have been studied by 2D- 1H-n.m.r. spectroscopy at 500 MHz. The results suggest the presence in MDP of two successive turns involving the MurNAc- l-Ala and l-Ala- d-iGln moieties, respectively, whereas only the former turn persists in murabutide. This turn mimics the type II β-turn found in l- d depsipeptides, whereas the other is a typical type II β-turn for l- d peptides.