Synthesis, and the Adjuvant and Tumor-Suppressive Activities of Quinonyl Muramyl Dipeptides

Abstract ω-(1,4-Benzoquinon-2-yl)alkanoic acids, 2-[10-(5,6-dimethoxy-3-methyl-1,4-benzoquinon-2-yl)decyl]-3-hydroxytetracosanoic acid, all-trans-5,9,13,17-tetramethyl-4,8,12,16-octadecatetraenoic acid, and stearic acid were coupled to the 6-O-position of the carbohydrate moiety of muramyl dipeptide alkyl esters, and 6-O-aminoacylmuramyl dipeptide methyl esters. The aminoacyl residues used were Gly, Leu, Ahx, and Aud. New synthetic methods were developed for ω-(1,4-benzoquinon-2-yl)alkanoic acids such as 22-(5,6-dimethoxy-3-methyl-1,4-benzoquinon-2-yl)docosanoic acid, and the α-branched ω-(1,4-benzoquinone-2-yl) β-hydroxy acid, 2-[10-(5,6-dimethoxy-3-methyl-1,4-benzoquinon-2-yl)decyl]-3-hydroxytetracosanoic acid. The effects of the resulting quinonyl, multiprenylacetyl, and stearoylmuramyl dipetides on the induction of delayed-type hypersensitivity to ABA-Tyr in guinea pigs and the tumor(meth-A)-suppressive activity in syngeneic BALB/c female mice were measured. The results revealed that all these muramyl-dipeptide derivatives retained the adjuvant activity whereas the potent tumor-suppressive activity was observed only in quinonylmuramyl dipeptides, indicating that the 5,6-dimethoxy-3-methyl-1,4-benzoquinone ring is a requisite for the manifestation of the tumor-suppressive activity. The lipophilicity-hydrophilicity balance of the molecule was also important. Among the compounds tested, N-acetyl-6-O-[10-(5,6-dimethoxy-3-methyl-1,4-benzoquinon-2-yl)decanoyl]muramyl-l-valyl-d-isoglutamine methyl ester showed the most potent tumor-suppressive activity. This compound also showed tumor-regressive activity in guinea pigs, and hence is a good candidate for further studies.