A cell-permeable inhibitor of SIRT1 (IC50 = 56 µM) and SIRT2 (IC50 = 59 µM); less effectively inhibits SIRT5 (IC50 >300 µM) and has no effect on class I and II HDACs; sensitizes H460 lung cancer cells to etoposide and paclitaxel; blocks a SIRT1-dependent hypoxic response in vivo.