Non-Alkaloidal Compounds from Tubers of Gloriosa superba and their In vitro and In silico Antibacterial and Antioxidant Activities

Abstract

Background: The tubers of Gloriosa superba L. (Colchicaceae) are previously well known for their alkaloidal constituents. The present work aimed to investigate the non-alkaloidal constituents and evaluate their in vitro and in silico antibacterial and antioxidant activities from the tuber. Methods: The chloroform: methanol (1:1) tuber extract was fractionated over silica gel column chromatography, and isolated compounds were characterized by NMR spectroscopy. Various extracts and isolated compounds were evaluated for their antibacterial and antioxidant activities against certain pathogenic strains and oxidants. The in silico drug-likeness properties of isolated compounds were also studied against 6F86 antibacterial and 1HD2 antioxidant protein models. Results: Three non-alkaloidal compounds, β-sitosterol (1), 3-(cyclopenta-2,4-dienyloxy) β- sitosterol (2) and 1,2-n-dipropyl phthalate (3), were reported herein. The n-hexane and chloroform extracts displayed better antibacterial activity against E. coli (9.83 ± 0.28 mm) and P. aeruginosa (10.65 ± 0.79 mm), and S. aureus (10.33 ± 0.3 mm), respectively, at 100,000 μg/mL concentration. Compound 3 established a better activity against all bacterial strains (9.78 ± 0.63-11.07 ± 0.09 mm) at 1000 μg/mL (IC50 values of 1.5-3.2 μg/mL). All the extracts exhibited a DPPH free radical scavenging activity comparable to ascorbic acid (IC50 value of 1.2 μg/mL), whereas isolated compounds were found with negligible DPPH scavenging activity and weak ferric ion reduction power up to 500 μg/mL dose. The docking study revealed that all the compounds fulfilled Lipinski’s rule of five by contravening no more than one rule with strong binding affinity shown by compound 1 (-8.2 kcal/mol) and compound 3 (-4.5 kcal/mol) to the 6F86 bacterial and 1HD2 antioxidant protein models, respectively, which are comparable to the ciprofloxacin (-7.2 kcal/mol) and ascorbic acid (- 4.5 kcal/mol) drugs. All the compounds also did not show any cytotoxicity properties. Whereas compound 1 showed an immunotoxicity and mutagenicity properties; and compounds 2 and 3 were found as immunotoxic and carcinogenic isolates, respectively. Conclusion: The promising antioxidant activity result of the various tubers extracts may highlight the potential use of Gloriosa superba as a source of foods by conducting further phytochemical investigation and additional bioassay evaluation, including the cytotoxicity effect of the whole part of the plant.