(-)-Tubifolidine as strychnos indole alkaloid: Spectroscopic charactarization (FT-IR, NMR, UV-Vis), antioxidant activity, molecular docking, and DFT studies

Abstract Strychnos indole alkaloids, which include tubifolidine (2) and are an important group of complex and interesting natural compounds as bio-actives, antioxidants as well as ABCDE ring system. Four different procedures have been employed for the tubifolidine: (i) spectroscopic characterization; (ii) antioxidant activity; (iii) molecular docking, and (iv) DFT studies. The spectroscopic characterization of tubifolidine was performed by FT-IR, NMR, and UV-Vis techniques, and elemental analysis. The antioxidant activity was explored by the DPPH method and molecular docking was used to enlighten the possible interaction of the tubifolidine with the topoisomerase receptor. The DFT/B3LYP/6–311++G(df,pd) level was used for geometry optimization, structure verification and to calculate the reactivity descriptors of tubifolidine. Besides, TD-DFT/B3LYP level was used to evaluate the electronic spectra and main excitations: the results revealed that the observed peak at 292 and 254 nm were mainly associated with n→ Π* and Π→ Π* transitions, and a bit σ → Π*. Besides, the n→ Π* and Π→ Π* transitions in the ground state contributed to the lowering stability of tubifolidine. FMO analysis displayed that the electro-donating power was dominant over the electroaccepting capability of tubifolidine.