A potent SIRT1 inhibitor (IC₅₀ = 38 nM). EX-527 is 200-500-fold more selective for SIRT1 than for SIRT2 or SIRT3. Does not inhibit SIRT4-7, does not inhibit class I/II HDAC activity at concentrations up to 100µM. Enhances p53 acetylation in response to DNA damaging agents.