Proton N.M.R. of the muramyl dipeptide adjuvant in dimethyl sulfoxide

Abstract

The active principle of complete Freund's adjuvant, N-acetylmuramyl-L-alanyl-D-isoglutamine, was studied in the α-anomeric form in dimethyl sulfoxide solutions by ¹H n.m.r, at 200 MHz. All resonances except those of the nonanomeric sugar protons were assigned. Temperature dependences of the chemical shifts of the amide protons indicated that the alanyl NH is involved in hydrogen bonding. The isoglutamine β-CH₂ protons showed large chemical-shift nonequivalence, an effect consistent with a hydrogen bond to the side chain carboxyl of this residue.