The First Limonoid Peroxide in the Meliaceae Family: Walsuronoid A from Walsura robusta

Walsuronoid A (1), a limonoid featuring an unprecedented 3,4-peroxide-bridged A-seco skeleton, together with walsuronoids B (2) and C (3) possessing a rare 18(13→14)-abeo-limonoid skeleton, was isolated from Walsura robusta. The structures were elucidated by spectroscopic analysis and chemical correlation, and that of 1 was confirmed by single-crystal X-ray diffraction. Biosynthetic pathway of 2 and 3 was proposed and was chemically mimicked. Compounds 1 and 2 showed weak antimalarial activity.