Design and Synthesis of Potent N-Acylethanolamine-hydrolyzing Acid Amidase (NAAA) Inhibitor as Anti-Inflammatory Compounds

N-acylethanolamine-hydrolyzing acid amidase (NAAA) is a lysosomal enzyme involved in biological deactivation of N-palmitoylethanolamide (PEA), which exerts anti-inflammatory and analgesic effects through the activation of nuclear receptor peroxisome proliferator-activated receptor-alpha (PPAR-α). To develop selective and potent NAAA inhibitors, we designed and synthesized a series of derivatives of 1-pentadecanyl-carbonyl pyrrolidine (compound 1), a general amidase inhibitor. Structure activity relationship (SAR) studies have identified a compound 16, 1-(2-Biphenyl-4-yl)ethyl-carbonyl pyrrolidine, which has shown the highest inhibition on NAAA activity (IC₅₀ = 2.12±0.41 µM) and is characterized as a reversible and competitive NAAA inhibitor. Computational docking analysis and mutagenesis study revealed that compound 16 interacted with Asparagine 209 (Asn²⁰⁹) residue flanking the catalytic pocket of NAAA so as to block the substrate entrance. In vitro pharmacological studies demonstrated that compound 16 dose-dependently reduced mRNA expression levels of iNOS and IL-6, along with an increase of intracellular PEA levels, in mouse macrophages with lipopolysaccharides (LPS) induced inflammation. Our study discovered a novel NAAA inhibitor, compound 16, that could serve as a potential anti-inflammatory agent.