Sirtuins are signaling hubs orchestrating the cellular response to various stressors with roles in all major civilization diseases. Sirtuins remove acyl groups from lysine residues of proteins, thereby controlling their activity, turnover, and localization. The seven human sirtuins, SirT1-7, are closely related in structure, hindering the development of specific inhibitors. Screening 170,000 compounds, we identify and optimize SirT1-specific benzoxazine inhibitors, Sosbo, which rival the efficiency and surpass the selectivity of selisistat (EX527). The compounds inhibit the deacetylation of p53 in cultured cells, demonstrating their ability to permeate biological membranes. Kinetic analysis of inhibition and docking studies reveal that the inhibitors bind to a complex of SirT1 and nicotinamide adenine dinucleotide, similar to selisistat. These new SirT1 inhibitors are valuable alternatives to selisistat in biochemical and cell biological studies. Their greater selectivity may allow the development of better targeted drugs to combat SirT1 activity in diseases such as cancer, Huntington's chorea, or anorexia.