Purity >98%. DOT1L is a protein methyltransferase (PMT). It is the only enzyme known to methylate histone 3 at lysine 79 (H3K79), where it catalyzes mono-, di-, and trimethylation. Proper DOT1L function is necessary for transcriptional activation of many genes, DNA damage repair, and cell cycle regulation. SGC0946 is a potent inhibitor of DOT1L (IC50 = 0.3 nM) developed by the Structural Genomics Consortium (SGC) . It is over 100-fold selective over other PMTs. It is active in cells, reducing H3K79 dimethylation in A431 and MCF10A cells (IC50 s = 2.6 and 8.8 nM, respectively). SGC0946 is a brominated analog of EPZ004777, an S-adenosylmethionine-competitive inhibitor of DOT1L. Both SGC0946 and EPZ004777 selectively kill mixed lineage leukemia (MLL) cells, in which DOT1L is aberrantly localized via interaction with an oncogenic MLL fusion protein.