Limonoids from the stem bark of Khaya senegalensis.

Six new limonoids with modified furan ring, khaysenelide A-F (1-6), together with six known limonoids (7-12) were isolated from the stem bark of Khaya senegalensis. The basic skeletons of these new limonoids belong to mexicanolide (1, 2) and rearrangement phragmalin (3-6), which were elucidated on the basis of spectroscopic methods including high resolution-electrospray ionization (HR-ESI)-MS, one and two dimensional (1D and 2D)-NMR and confirmed by single-crystal X-ray crystallography using CuKα radiation of 1 and 3. Their absolute configurations were determined by the X-ray crystallography data and comparison of their electronic circular dichroism spectra. The inhibitory effect on nitric oxide (NO) production in lipopolysaccaride-activated RAW264.7 macrophages of new compounds was also tested.