Synthesis of biologically active biotinylated muramyl dipeptides

Abstract

Muramyl dipeptide (MDP) is believed to interact with an innate immune receptor, Nod2. To identify the cellular receptor for MDP, we have synthesized biotinylated MDP isomers and tested the ability of these compounds to activate Nod2 in a cell-based assay. We found that the modification of MDP does not perturb its ability to activate Nod2. These tagged versions of MDP will be useful to identify the cellular receptor of the immunostimulatory molecules.

Figure 1. Muramyl dipeptide isomers

1 is the proposed ligand for Nod2. The isomer, 2, does not activate Nod2.

Figure 2. Nod2 dependent response to MDP

a: Nod2 DNA was added to the transfection mixture; b: empty vector in place of Nod2 DNA was added to the transfection mixture.

Scheme 1. Synthetic Route of 6-amino MDP isomers

12 and 13: Reagents and Conditions: (a): IRA H⁺ Resin, MeOH, quantitative (b) p-toluene sulfonic acid, methyl sulfonyl chloride, pyridine, 92% (c) sodium azide, DMF, 87% (d) potassium hydroxide (e) i. N-methylmorpholine, isobutyl chloroformate, DMF, ii. 8 or 9, 63%, (f) H₂, Pd-C,, MeOH/AcOH 82%