NNMT-IN-5 (Compound 3-12) is a potent nicotinamide N-methyltransferase ( NNMT ) inhibitor ( IC 50 = 47.9 ± 0.6 nM). NNMT-IN-5 also has an excellent selectivity profile over a panel of human methyltransferases. NNMT-IN-5 can be used for the research of cancer , diabetes, metabolic disorders, and neurodegenerative diseases.