Phytoconstituents, In Vitro Anti-Infective Activity of Buddleja indica Lam., and In Silico Evaluation of its SARS-CoV-2 Inhibitory Potential

Phytochemical investigation of Buddleja indica Lam. leaves methanol extract (BIT) resulted in the isolation of six known compounds for the first time from the plant, namely, p-hydroxybenzoic acid 1), caffeic acid 2), quercetin 3-O-β-D glucoside-7-O-α-L-rhamnoside 3), kaempferol 3-O-β-D glucoside-7-O-α-L-rhamnoside 4), quercetin 7-O-β-D glucoside 5) and kaempferol 6). BIT extract showed potent antibacterial activity with MIC values ranging between 0.48 and 1.95 μg/ml with Bacillus subtilis was the most susceptible to the BIT effect. It showed a notable antimycobacterial and anti-Helicobacter pylori activity with MIC values of 100 and 80 μg/ml, respectively. Vesicular stomatitis virus (VSV) was more sensitive to the antiviral activity of BIT comparable to herpes simplex virus type 1 (HSV-1), showing 48.38 and 41.85% inhibition of the viral replication at a dose of 50 μg/ml for VSV and HSV-1, respectively. In silico molecular docking of the isolated compounds revealed that caffeic acid 2) showed the highest fitting within the active sites of DNA-gyrase, topoisomerase IV, and SARS-CoV-2 M(Pro). Quercetin 7-O-β-D glucoside 5) revealed the best fitting in dihydrofolate reductase active site with ∆ G value equals −36.53 Kcal/mol. Kaempferol 6) exhibited the highest fitting towards β-lactamase, SARS-CoV-2PL(pro), and SARS-CoV-2 3CL(pro) active sites. Thus, B. indica Lam. can be considered as a future source of cheap, substantially safe, and credible antibacterial, antifungal, and antiviral candidate of natural origin that could effectively participate in solving the problem of COVID-19 pandemic. These findings provide a scientific consolidation for the ethnomedicinal uses of Buddleja indica Lam. as a topical antiseptic.