Pinometostat, trans- (9H-Purin-6-amine, 9-[5-deoxy-5-[[trans-3-[2-[6-(1,1-dimethylethyl)-1H-benzimidazol-2-yl]ethyl]cyclobutyl](1-methyl ethyl)amino]-β-D-ribofuranosyl]-) is an isomer of Pinometostat, a small molecule inhibitor of histone methyltransferase with potential antineoplastic activity. Pinometostat, trans-specifically blocks the activity of the histone lysine-methyltransferase DOT1L, thereby inhibiting the methylation of nucleosomal histone H3 on lysine 79 (H3K79) that is bound to the mixed lineage leukemia (MLL) fusion protein which targets genes and blocks the expression of leukemogenic genes.