Phytochemical Investigations, Antibacterial and Antioxidant Activities, and In Silico Molecular Docking Studies of Compounds Isolated From The Leaf Extracts of Salvia leucantha CAV.

Abstract

Since ancient times, medicinal plants have been used around the world to treat a wide range of diseases. Traditionally, Salvia leucantha has been used as a remedy to relieve cough, chest, lung, and stomach pains. In this study, we used sequential extraction and silica gel column chromatography method for isolation of compounds. The essential oil obtained by hydro distillation was analyzed using GC-MS. The antibacterial and antioxidant activities were evaluated using the agar disc diffusion method against four strains of bacteria and DPPH methods, respectively. The leaf of Salvia leucantha (450 g) was successively extracted with n hexane, ethylacetate, and methanol to afford 19.4 g (4.3%), 29.1 g (6.4%), and 16.6 g (3.6%) yields, respectively. The GC-MS result revealed that the presence of 50 components, with compound (40), identified as the most abundant constituent (36.3 %) of the oil. The methanol extract affords three compounds, identified as hesperidin (44), urosilic acid (45), and β sitosterol (46). All compounds are reported herein for the first time from the Salvia leucantha. The structures of the isolated compounds were characterized using NMR ( 1H NMR, 13C NMR, and DEPT-135) spectroscopic techniques. The n-hexane and ethylacetate extracts showed the highest antibacterial activity against E. coli (20.5±0.70 mm at 200 mg/mL) and S. aureus (24.5±0.70 mm at 200 mg/mL), respectively. Whereas methanol extract exhibited the highest zone of inhibition (23.0±0.00 mm at 200 mg/mL) against P. aeruginosa. Compounds 44 and 45 showed significant activity against S. aureus (24.50±0.70 mm) and S. pyogenes (24.50±2.12 mm) respectively. Compound 46 also exhibited promising inhibition activity against S. pyogenes (22.50±0.70 mm) each at 2 mg/mL, compared with ciprofloxacin (ranging from 33.20±0.44 34.50±1.06 mm at 30 μg/mL). The highest percent inhibition of the DPPH radical was observed with methanol extract (IC50: 12.17 μg/mL) and compound 44 (IC50: 9.83 μg/mL), compared with ascorbic acid (IC50: 0.681 μg/mL). In a molecular docking study, compound 44 and compound 45 exhibited the highest binding affinity (-9.0 kcal/mol) with the target DNA gyrase B and compound 44 exhibited (-10.3 kcal/mol) with pyruvate kinase as the target. Additionally, compounds 45 and 44 showed higher binding affinity (-10.5 and -9.9 kcal/mol respectively) against human myeloperoxidase. The drug-likeness analysis showed that compounds 45 and 46 satisfy Lipinski’s rule of five with one violation. The current study generally revealed that both the extract and isolated compounds have promising antibacterial and antioxidant activity.