400-MHz ¹H N.M.R. of adjuvant muramyl dipeptide in dimethyl sulfoxide

Abstract

The minimal active principle, N-acetylmuramyl-L-alanyl-D-isoglutamine* (MDP), of complete Freund's adjuvant was studied in dry dimethyl sulfoxide solutions by ¹H n.m.r. at 400 MHz. All resonances except those of the non-anomeric CH protons of the sugar ring were assigned. The α/β anomeric ratio was found to be the same (2 : 1) as reported for the equilibrated aqueous solutions from which the dimethyl sulfoxide solutions were prepared. The present findings indicate that MDP adopts a substantially structured conformation in dimethyl sulfoxide solutions.