Chemical constituents of the roots of Kniphofia schimperi and evaluation of their antimicrobial activity

Kniphofia schimperi is one of the endemic plants of Ethiopia and is widely used for the treatment of microbial infections. However, the biological and phytochemical information pertaining to this plant has not been reported so far. Anticipated by these claims, the chromatographic isolation of the CHCl3/CH3OH (1:1 v/v) extract of the roots of K. schimperi afforded five compounds, viz., knipholone (1), asphodeline (2), β-sitosterol (3), 9-pentacosenoic acid (4), and nonacosanoic acid (5). The structures of the isolated compounds were identified based on their NMR (1D and 2D) spectral data analysis and comparison with reported literature data. The crude extract and isolated compounds were evaluated for their in vitro antimicrobial activity against four bacterial strains (Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, and Bacillus cereus) and a fungal strain (Candida albicans) using the agar disk diffusion method. The test samples showed moderate antimicrobial activity, with the highest activity observed for compound 3 (with a zone of growth inhibition of 15.5 ± 0.71 mm) against S. typhimurium.

Synthesis and antimicrobial activity of knipholone analogs

In the present study, we use knipholone as a prototype molecule to identify new anti-infective agents. Since knipholone is insoluble in water, which would have a detrimental effect on its bioavailability and efficacy, we synthesized knipholone Mannich base derivatives (2-4) that have better predicted solubility and investigated their in vitro antimicrobial activity against eight pathogenic bacterial and fungal strains. The chemical structures of compounds 1-4 were elucidated from their 1H and 13C NMR data, and their antimicrobial activity evaluation was carried out by a broth microdilution MTT assay. Compound 3 exhibited the strongest efficacy against Staphylococcus epidermidis, with MIC value of 9.7 µg/mL. While 4 exhibited the best activity against Staphylococcus aureus, with an MIC value of 19.5 µg/mL, and was the only one to significantly inhibit the fungus Trichophyton mentagrophytes (MIC = 78.2 µg/mL). The study provides evidence for the antibacterial activity of aminoalkyl derivatives of knipholone.

Multi-target molecular dynamic simulations reveal glutathione-S-transferase as the most favorable drug target of knipholone in Plasmodium falciparum

Knipholone is an antiplasmodial phytocompound obtained from the roots of Kniphofia foliosa. Despite several available studies, the molecular drug targets of knipholone in P. falciparum remained unknown. Nowadays, in silico techniques are widely used to study the molecular interactions between compounds and proteins as they provide results quickly with high precision and accuracy. In this study, we aim to identify the potential molecular drug targets of knipholone in P. falciparum. We selected 10 proteins of P. falciparum with unique metabolic functions and we found that knipholone showed better binding affinity than the native ligands of 6 proteins. Out of the 6 proteins, knipholone showed better enzyme inhibitory potential than the native ligands of 4 proteins. We carried out a 100 ns MD simulations for knipholone and the native ligands of four proteins and this was followed by binding free energy calculations. In each step, the performance of knipholone was compared to the native ligands of the proteins. Knipholone outperformed the native ligand of Glutathione-S-Transferase (1OKT) at crucial computational studies as evidence from the lower protein-ligand root mean square deviation value, protein root mean square fluctuation value, and protein-ligand binding free energies. The ligand properties of knipholone provide additional evidence for its stability and it maintains adequate protein-ligand contacts during the entire simulation. The density functional theory study also supported the stability of knipholone at the active binding site of 1OKT. From the studied proteins, we conclude that Glutathione-S-Transferase is the most favorable drug target for knipholone in P. falciparum.Communicated by Ramaswamy H. Sarma.