Structural, vibrational, UV–vis, quantum-chemical properties, molecular docking and anti-cancer activity study of annomontine and N-hydroxyannomontine β-carboline alkaloids: A combined experimental and DFT approach

Abstract

A theoretical and experimental DFT study of the vibrational, structural and quantum properties of annomontine (1) and N-hydroxyannomontine (2) alkaloids using the B3LYP exchange-correlation functional with 6-311G (2d, p) basis set is presented. The theoretical geometry optimization data of the two structures were compared with the X-ray data of (1) in the associated literature and a conformational study is presented for both molecules, providing a good comprehension of the conformational stability. In addition, natural bond orbitals (NBOs), HOMO-LUMO energy gap and mapped molecular electrostatic potential surface (MEPS) calculations were also performed at the same calculation approach. The calculated UV spectra agreed well with the measured experimental data, with transitions assigned. The comparative IR studies confirmed the intramolecular hydrogen bonds of the conformations and the intermolecular hydrogen bonds of dimeric forms and also revealed several characteristic vibrations for the structures. Molecular docking studies with DNA Topoisomerase II-DNA complex showed binding free energies of −11.5 and −10.6 kcal/mol for 2 and 1 respectively, while for amsacrine, used for the treatment of leukemia, and doxorubicin, used for the treatment of breast cancer, bladder cancer, Kaposi's sarcoma, and acute lymphocytic leukemia, the presented binding free energies values are −10.0 and −9.9 kcal/mol respectively, revealing good bind affinities of the tested alkaloids with the complex. In vitro cytotoxicity assay revealed an expressive antitumor activity of N-hydroxyannomontine against human hepatocellular carcinoma cell line HepG2.