A series of novel, potent orthopoxvirus egress inhibitors was identified during high-throughput screening of the ViroPharma small molecule collection. Using structure−activity relationship information inferred from early hits, several compounds were synthesized, and compound 14was identified as a potent, orally bioavailable first-in-class inhibitor of orthopoxvirus egress from infected cells. Compound 14has shown comparable efficaciousness in three murine orthopoxvirus models and has entered Phase I clinical trials. [ABSTRACT FROM AUTHOR]