5-Hydroxytoluene-2,4-disulphonic acid diammonium is an impurity of Policresulen. Policresulen is a potent NS2B NS3 protease inhibitor with an IC50 of 0.48 μg mL. Policresulen effectively inhibits the replication of DENV2 virus in BHK-21 cells with an IC50 of 4.99 μg mL. Policresulen acted as a competitive inhibitor of the protease, and slightly affected the protease stability[1]. [1]. Deng-wei Wu, et al. Policresulen, a novel NS2B NS3 protease inhibitor, effectively inhibits the replication of DENV2 virus in BHK-21 cells. Acta Pharmacol Sin. 2015 Sep;36(9):1126-36.