Description_x000D_ Application_x000D_ SID 852843 may be used in virology studies to inhibit NS3 proteinase of West Nile Virus._x000D_ Packaging_x000D_ 5 mg in glass bottle_x000D_ Biochem/physiol Actions_x000D_ SID 852843 is an inhibitor of West Nile Virus NS2B-NS3 proteinase. Flaviviruses, such as West Nile and Dengue, are a threat to humans from both public health and bioterrorism perspectives. The NS3 proteinase is essential for flaviviral maturation. Inhibitors of NS3 are sought for treatment and prophylactic therapeutics. The NIH molecular library was screened for activity against West Nile Virus NS3, resulting in the discovery of SID 852843. This compound inhibits the NS3 proteinase of West Nile, but not of Dengue type 2 virus. SID 852843 is a reversible, allosteric inhibitor of the formation of the functional conformation of the NS3 proteinase. This is the first flaviviral proteinase inhibitor with the potential to lead to a drug. Aprotinin is an efficient inhibitor of NS3, but it is not selective and has low penetration into cells, limiting its potential for therapeutic use.