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

Two unprecedented C,C-linked dimeric indolizidine alkaloids, flueggines A (1) and B (2), were isolated from the twigs and leaves of Flueggea virosa. The structures and absolute configurations were elucidated by means of NMR, single-crystal X-ray diffraction, and CD analyses. Compound 1 is the first example of Securinega alkaloids bearing an isoxazolidine ring, the plausible biogenetic pathway of which is also proposed. Compound 2 exhibited growth inhibitory activity against MCF-7 and MDA-MB-231 human breast cancer cells.

A consecutive synthetic strategy was developed toward the total synthesis of securinega alkaloids. (-)-Norsecurinine was concisely assembled by addition of a methoxyallene to a ketone for efficient side-chain installation. Ring-closing metathesis was also utilized as a key step. The first total synthesis of (-)-niruroidine was achieved from (-)-norsecurinine in three steps, while the route to (-)-flueggine A featured a 1,3-dipolar cycloaddition to forge the core structure.

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