Structure–Activity Relationship Studies of Pyrimidine-4-Carboxamides as Inhibitors of N-Acylphosphatidylethanolamine Phospholipase D

N -Acylphosphatidylethanolamine phospholipase D (NAPE-PLD) is regarded as the main enzyme responsible for the biosynthesis of N -acylethanolamines (NAEs), a family of bioactive lipid mediators. Previously, we reported N -(cyclopropylmethyl)-6-(( S )-3-hydroxypyrrolidin-1-yl)-2-(( S )-3-phenylpiperidin-1-yl)pyrimidine-4-carboxamide ( 1 , LEI-401 ) as the first potent and selective NAPE-PLD inhibitor that decreased NAEs in the brains of freely moving mice and modulated emotional behavior [Mock Nat Chem. Biol. , 2020, 16, 667-675]. Here, we describe the structure-activity relationship (SAR) of a library of pyrimidine-4-carboxamides as inhibitors of NAPE-PLD that led to the identification of LEI-401 . A high-throughput screening hit was modified at three different substituents to optimize its potency and lipophilicity. Conformational restriction of an N -methylphenethylamine group by replacement with an ( S )-3-phenylpiperidine increased the inhibitory potency 3-fold. Exchange of a morpholine substituent for an ( S )-3-hydroxypyrrolidine reduced the lipophilicity and further increased activity by 10-fold, affording LEI-401 as a nanomolar potent inhibitor with drug-like properties. LEI-401 is a suitable pharmacological tool compound to investigate NAPE-PLD function in vitro and in vivo .