Ivorenoids A-F: limonoids from Khaya ivorensis

Six new limonoids, ivorenoids A-F (1-6), along with ten known analogues, were isolated from an ethanolic extract of the stems of Khaya ivorensis. Their structures were elucidated on the basis of spectroscopic analyses. Compounds 1 and 2 possessed a rare rearranged skeleton of khayanolides and a unique γ-lactone (C-16/C-8) replacing the common and characteristic δ-lactone D-ring (C-16/C-17) of limonoids. A mechanism of the interesting deuteration of H-2 and H-15β of 1, and H-15β of the solvent CD3OD due to the keto-enol tautomerism was demonstrated. Compounds 3 and 6 showed moderate activity against HL-60 cell line with IC50 values of 15.3 and 17.5 μM, respectively.