Further Insights on Structural Modifications of Muramyl Dipeptides to Study the Human NOD2 Stimulating Activity

Abstract

A series of muramyl dipeptide (MDP) analogues with structural modifications at the C4 position of MurNAc and on the d-iso-glutamine (isoGln) residue of the peptide part were synthesized. The C4-diversification of MurNAc was conveniently achieved by using CuAAC click strategy to conjugate an azido muramyl dipeptide precursor with structurally diverse alkynes. d-Glutamic acid (Glu), replaced with isoGln, was applied for the structural diversity through esterification or amidation of the carboxylic acid. In total, 26 MDP analogues were synthesized and bio-evaluated for the study of human NOD2 stimulation activity in the innate immune response. Interestingly, MDP derivatives with an ester moiety are found to be more potent than reference compound MDP itself or MDP analogues containing an amide moiety. Among the varied lengths of the alkyl chain in ester derivatives, the MDP analogue bearing the d-glutamate dodecyl (C12) ester moiety showed the best NOD2 stimulation potency.

Structural Fine-Tuning of Desmuramylpeptide NOD2 Agonists Defines Their In Vivo Adjuvant Activity

“…When compared to the 2.83-fold and 3.06-fold NOD2 activations of MDP and 1 in a single point assay, with respect to untreated control cells, these compounds showed considerably diminished NOD2 agonistic activity at 2 μM (1.30-fold to 1.45-fold NOD2 activation). These data are in agreement with the previously reported impaired activities of MDP derivatives that have either a diamidated d -isoglutamine moiety or a lipophilic amide attached to the α position of d -isoglutamine . Slightly better activities were expected for the derivatives with hydroxamate, given that hydroxamic acids are readily hydrolyzed to their corresponding carboxylic acids .…”

“…These data are in agreement with the previously reported impaired activities of MDP derivatives that have either a diamidated d -isoglutamine moiety 52 or a lipophilic amide attached to the α position of d -isoglutamine. 71 Slightly better activities were expected for the derivatives with hydroxamate, given that hydroxamic acids are readily hydrolyzed to their corresponding carboxylic acids. 72 However, it is worth noting that HEK293 cells have low hydrolytic activity due to low expression of carboxylesterases, the enzymes involved in the hydrolysis of both hydroxamic acids and amides.…”

Design, Synthesis, and Biological Evaluation of Desmuramyl Dipeptides Modified by Adamantyl-1,2,3-triazole

“…The results show that the adamantyl-triazole DMP derivative induces higher production of anti-OVA IgG than the reference compound, ManAdDMP, which was the most active adjuvant in this class of compounds. This indicates that the introduction of an adamantyl-triazole moiety at α-COOH is preferred for the amplification of immunostimulant activity, while MDP derivatives with a substituted triazole moiety at the C4 position of MurNAc showed lower affinity toward NOD2 [21]. Based on the IgG1/IgG2a ratio (Figure 3c), it is evident that compound 8 shifts the reaction toward a pronounced Th2-type immune response (p < 0.01).…”

“…Natural polymeric peptidoglycans-as well as smaller peptidoglycan fragments, such as MDP and its synthetic derivatives-exhibit immunomodulatory properties. To date, a number of structure-activity studies have been reported, and they have included synthetic modifications at the saccharide and peptide parts of the MDP [7,20,21]. Several synthetically modified MDPs have already been used in clinical settings.…”

Recent Advances in the Synthesis and Biological Applications of Peptidoglycan Fragments

“…Recent research by the Cheng group emphasizes modifications of the 4-OH and the Glu/Gln of MDP. [65] By beginning with D-GalN, the 4-OH could be cleanly converted to a 4-N 3 38 with inversion of configuration via an appropriate S N 2 reaction -the rest of the synthesis with D-GalN generally follows the route to MDP from D-GlcN (Scheme 10). The azide moiety could either participate in a CuAAC reaction or be reduced to generate amine 39 for acyl addition.…”