Uncovering the Potent Antiviral Activity of the Sesterterpenoids from the Sponge <i>Ircinia Felix</i> Against Human Adenoviruses: from the Natural Source to the Total Synthesis

Human Adenovirus (HAdV) infections in immunocompromised patients can result in disseminated diseases with high morbidity and mortality rates due to the absence of available treatments for these infections. The sponge Ircinia felix was selected for the significant anti-HAdV activity displayed by its organic extracts. Its chemical analysis yielded three novel sesterterpene lactams, ircinialactams J-L, along with three known sesterterpene furans which structures were established by a deep spectrometric analysis. Ircinialactam J displayed significant antiviral activity against HAdV without significant cytotoxicity, showing an effectiveness 11 times greater than that of the standard treatment, cidofovir®. Comparison of the antiviral evaluation results of the isolated compounds allowed us to deduce some structure-activity relationships. Mechanistic assays suggest that ircinialactam J targets an early step of the HAdV replicative cycle before HAdV genome reaches the nucleus of the host cell. The first total synthesis of ircinialactam J was also accomplished to prove the structure and to provide access to analogues. Key steps are a regio- and stereoselective construction of the trisubstituted Z-olefin at Δ⁷ by iron-catalyzed carbometallation of a homopropargylic alcohol, a stereoselective methylation to generate the stereogenic center at C18, and the formation of the (Z)-Δ²⁰ by stereoselective aldol condensation to introduce the tetronic acid unit. Ircinialactam J is a promising chemical lead to new potent antiviral drugs against HAdV infections.