Abstract
The flavone C-glycosides namely apigenin 7-O-beta-D glucopyranosyl-8-C-beta-n-glucopyranoside (1) and apigenin-8-C-alpha-L-rhamnopyranosyl-(1 -> 2)-O-beta-D glucopyranoside (2), along with p-methoxycinnamic acid (3), vaccaroside A (4), vaccaroside D (5), vaccaroside E (6) and abscisic acid glucose ester (7) were isolated from the methanol extract of the aerial parts of Vaccaria pyramidata. Structure elucidation of compounds 1-7 was accomplished by the extensive use of 1D- and 2D NMR experiments along with HR-ESI-MS. The structures of 1-2 have been confirmed by theoretical study of the H-1,C- 13 chemical shifts and UV data. In addition, Ionization Potential (IP) and Bond Dissociation Enthalpy (BDE) were used to evaluate the theoretical antioxidant activity of compounds 1 and 2. TD-DFT method (time-dependent density functional) was used to calculate the electronic absorption spectra of compounds 1 and 2 from optimized structures in methanol and the orbitals involved in the electronic transition were elucidated.