New benzoxanthenone and benzanthrone derivatives from Tricholaena teneriffae L. roots: structure elucidation, α-amylase inhibitory activity and molecular docking studies

Abstract

The ethyl acetate extract of Tricholaena teneriffae L. roots exhibited significant α-amylase inhibitory activity. Phytochemical analysis of this extract led to the isolation of seven natural products: five 12H-benzo[a]xanthen-12-one derivatives (1–5) and two 7H-benzo[de]anthracen-7-one derivatives (6–7). Among them, compounds 1, 3, 4, 5, and 7 are reported here for the first time as new natural derivatives. Structural elucidation was performed via 1D and 2D NMR spectroscopy, allowing for a precise determination of the substitution patterns of both the benzo[a]xanthen-12-one and benzo[de]anthracen-7-one frameworks. Among them, compounds 6 (IC₅₀ = 0.308 ± 0.015 μM) and 4 (IC₅₀ = 0.480 ± 0.024 μM) showed the most potent inhibitory effects. Molecular docking studies revealed that the presence of both hydroxyl and methoxy groups, as in compound 6, enhances inhibition through strong hydrogen bonding and π-type interactions, while methoxy substitution on ring C, as in compound 4, increases binding affinity via interactions with Glu233 and Asp197. The photophysical properties of seven isolated dyes were examined in dichloromethane by UV–visible and fluorescence spectroscopy. Hydroxyl and methoxy substituents enhanced electron donation, leading to red-shifted absorption and emission compared to the unsubstituted analogue 2. The strongest red shift was observed for the dimethoxylated dye 3, while the hydroxylated dye 6 exhibited higher intensities than its methoxy analogue 7. These results highlight the importance of specific position and nature of substituents in modulating α-amylase inhibition and photophysical behavior in root-derived metabolites.

Graphical Abstract