Phytochemical Investigation of Cycas circinalis and Cycas revoluta Leaflets: Moderately Active Antibacterial Biflavonoids

Chemical examination of the methanolic extract of the leaflets of Cycas circinalis L. led to the isolation of one new biflavonoid, (2S, 2 '' S)-2,3,2 '', 3 ''-tetrahydro-4',4'''-di-O-methylamentoflavone (tetrahydroisoginkgetin; 2), and 15 known compounds, 11 of which are reported for the first time from C. circinalis. Chromatographic separation of the chloroform extract of C. revoluta Thunb. leaflets afforded 12 compounds, seven of which are reported for the first time from this species. The isolated compounds from both species include 14 biflavonoids, three lignans, three flavan-3-ols, two flavone-C-glucosides, two nor-isoprenoids, and one flavanone. This is the first report of NMR and CD data of 2,3,2 '',3 ''-tetrahydro-4'-O-methyl-and 2,3-dihydro-4'-O-methylamentoflavone (6) and (7). The effect of O-methylation on the chemical shifts of the neighboring carbons in the C-13 NMR spectra of the dihydro- and tetrahydro-amentoflavone skeletons provides a tool to identify the location of the methoxy groups. Compounds 2, 6, and 18 displayed moderate antibacterial activity against Staphylococcus aureus (IC50 values of 3.9, 9.7, and 8.2 mu M, respectively) and methicillin-resistant S. aureus (MRSA; IC50 values of 5.9, 12.5, and 11.5 mu M, respectively).