Synthesis of a biologically active fluorescent muramyl dipeptide congener

A fluorescent-labeled muramyl dipeptide (MDP) has been prepared to probe immunoadjuvant cellular interactions. N-Acetylmuramyl-L-alanyl-D-isoglutamine (1) was synthesized in improved yield and reacted with 2-(fluoresceinylamino)-4,6-dichloro-s-triazine (DTAF, 2) to give the fluorescent adduct DTAF-MDP (3), attached through the 6-position of the sugar moiety. Adjuvant activity was assessed by using two different in vitro assays, macrophage spreading, and inhibition of macrophage migration. Both assays indicated that the apparent adjuvant activity of 3 is comparable to that of 1.