Screening of promising chemotherapeutic candidates from plants against human adult T-cell leukemia/lymphoma (V): coumarins and alkaloids from Boenninghausenia japonica and Ruta graveolens

During the course of our studies towards the identification of promising chemotherapeutic candidates from plants against two human T-cell lymphotropic virus type I-infected T-cell lines (MT-1 and MT-2), we screened 17 extracts from 9 rutaceous plants against MT-1 and MT-2 cells. The extracts from the aerial parts and roots of Boenninghausenia japonica, as well as the leaves and roots of Ruta graveolens showed potent antiproliferative effects. After activity-guided fractionation, we isolated 44 compounds from two rutaceous plants, including three new compounds (1–3), which were classified into 26 coumarin analogs (13 coumarins, 8 furanocoumarins, 4 dihydrofuranocoumarins and one dihydropyranocoumarin), 15 alkaloid analogs (7 quinolone alkaloids, 4 acridone alkaloids, 3 furanoquinoline alkaloids and one tetrahydroacridone alkaloid) and 3 flavonoid glycosides. Structure–activity relationship studies were also evaluated. The coumarin compounds (2, 3 and 7–9) bearing a 3-dimethylallyl moiety showed potent activity. Similarly, of all the furanocoumarins evaluated in the current study, compound 17 bearing a 3-dimethylallyl group also showed potent activity. A dihydrofuranocoumarin (27) bearing a 3-dimethylallyl moiety showed the most potent activity. Following 27, compound 28 showed potent activity. These results therefore suggested that the presence of a 3-dimethylallyl moiety was important to the antiproliferative activity of these coumarin analogs.