Virosaines A and B, Two New Birdcage-Shaped <i>Securinega</i> Alkaloids with an Unprecedented Skeleton from <i>Flueggea virosa</i>

Two new <i>Securinega</i> alkaloids, virosaines A (<b>1</b>) and B (<b>2</b>), were isolated from the twigs and leaves of <i>Flueggea virosa</i>. The structures and absolute configurations were elucidated by means of NMR, X-ray diffraction, and CD analyses. Compounds <b>1</b> and <b>2</b> represent the first examples of <i>Securinega</i> alkaloids bearing a 7-oxa-1-azabicyclo[3.2.1]octane ring system, whose plausible biogenetic pathways were also proposed