Histone deacetylases (HDACs) are the group of enzymes that remove the acetyl group from lysine residue. To date, 18 mammalian HDACs have been identified and are characterized into four classes: class I HDACs (HDACs 1, 2, 3, and 8), class II HDACs (HDACs 4, 5, 6, 7, 9, and 1, class IV (HDAC 11) and class III (sirtuin family: sirt1-sirt7).http://www.medchemhub.com/mtor-inhibitors/