Limonoids from Nigerian Harrisonia abyssinica and their stimulatory activity against Striga hermonthica seeds

Deoxyobacunone (1), a new limonoid with a double bond in ring D, has been i solated from the root bark of Harrisonia abyssinica collected in Nigeria. A lso, the known limonoids obacunone (2), harrisonin (3), 12 beta -acetoxyhar risonin (4), and pedonin (5) have been isolated. The structure of 1 was ass igned unambiguously by spectral data analysis. Under laboratory conditions, 10(-8)-10(-5) M concentrations of compounds 1-5 exhibited significant stim ulatory activity (12-98%) against conditioned Striga hermonthica seeds. Thi s study provided useful insight regarding the functionalities required for activity of limonoids against Striga seeds. The variation in activity was r ationalized through quantitative structure-activity relationship (QSAR) mod els based on several molecular descriptors including van der Waals volume ( VDWv), molecular polarizability (alpha), dipole moment (mu), log P, and the differences between the highest occupied molecular orbital and lowest unoc cupied molecular orbital (HOMO-LUMO gap).