A potent allosteric inhibitor of PRMT3 (IC50 = 50 nM) with >100-fold selectivity over other methyltransferases and other non-epigenetic targets; avidly binds PRMT3 (Kd = 50 nM by isothermal titration calorimetry) and inhibits histone methylation in cells with an IC50 value below 1 µM.