Synthesis of conformationally constrained γ-D-glutamyl-meso-diaminopimelic acid derivatives as ligands of nucleotide-binding oligomerization domain protein 1 (Nod1)

Abstract

Nod1, an important member of the pattern recognition receptor family, remains a virtually unexploited target. Harnessing its innate immune stimulatory properties still remains an unfulfilled goal of medicinal chemistry. Nucleotide-binding oligomerization domain protein 1 (Nod1) agonists have been shown to boost the inflammatory responses against pathogenic microbes and could thus constitute a new class of broad spectrum antimicrobial agents. To gain additional insight into the structure/activity relationships of Nod1 agonistic compounds, a series of novel, conformationally constrained γ-D-glutamyl-meso-diaminopimelic acid (iE-DAP) analogs have been designed and synthesized. Ramos-Blue cells expressing Nod1 were used to screen and validate our compounds for their Nod1-agonist activity. Their immunomodulatory properties were subsequently determined in vitro, by evaluating their capacity to induce pro-inflammatory cytokine and chemokine production from human peripheral blood mononuclear cells (PBMC), by themselves and in synergy with lipopolysaccharide (LPS), a Toll-like receptor 4 (TLR4) ligand. The synthesized iE-DAP analogs were shown to possess immuno-enhancing properties as a result of their potent and specific Nod1-agonistic effect. The activity of the compound exhibiting the greatest capacity to induce pro-inflammatory cytokine release from PBMC surpassed that of lauroyl-γ-D-glutamyl-meso-diaminopimelic acid (C12-iE-DAP).

Keywords: 1,8-diazabicyclo[5.4.0]undec-7-ene; 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate; C12-iE-DAP; DBU; IL; Immunomodulator; Immunostimulant; Immunotoxicity; LPS; LRR; MAPK; NF-κB; NF-κB activation; NLR; Nod; Nod-like receptor; Nod1; PAMP; PBMC; PRR; RICK; RIG; SAR; SEAP; TBTU; TLR; TNF-α; Toll-like receptor; iE-DAP; interleukin; lauroyl-γ-d-glutamyl-meso-diaminopimelic; leucine rich repeats; lipopolysaccharide; mitogen-activated protein kinase; nuclear factor κB; nucleotide-binding oligomerization domain protein; pathogen-associated molecular pattern; pattern recognition receptors; peripheral blood mononuclear cells; receptor-interacting serine-threonine kinase; retinoic acid inducible gene; secreted embryonic alkaline phosphatase; structure/activity relationship; tumor necrosis factor-α; γ-d-Glutamyl-meso-diaminopimelic acid; γ-d-glutamyl-meso-diaminopimelic acid.