Carapanins A–C: new limonoids from andiroba (Carapa guianensis) fruit oil

Carapanins A-C (1-3) were isolated from the fruit oil of Carapa guianensis. Compounds 1 and 2 are limonoids with unique structures. Namely, compound 1 is an andirobin-type limonoid with a C-15/C-30 γ-lactone instead of the δ-lactone of the D-ring, and compound 2 is a mexicanolide-type limonoid with a C-16/C-30 δ-lactone ring. The absolute structures of 1 and 2 were determined using X-ray crystallography, whereas the structure of 3 was established mainly via NMR and mass spectroscopy. The inhibitory effects of 1-3 on nitric oxide production were evaluated, and it was revealed that 2 and 3 were potent nitric oxide inhibitors.