Naturally Occurring 8ß,13ß-kaur-15-en-17-al and Anti-Malarial Activity from Podocarpus polystachyus Leaves

Abstract

Despite much interest and studies toward the genus Podocarpus, the anti-malarial evaluation of Podocarpus polystachyus's phytoconstituents remains lacking. Herein, the phytoconstituents of P. polystachyus leaves and their anti-malarial effect against Plasmodium falciparum were investigated for the first time. One new natural product, 8ß,13ß-kaur-15-en-17-al (1), along with three known compounds, 8ß,13ß-kaur-15-en-17-ol (2) and 13ß-kaur-16-ene (3), and α-tocopherol hydroquinone (4) were isolated via HR-ESI-MS and NMR analyses. Compounds 1 and 2 inhibited P. falciparum growth at 12 and 52 µM of IC₅₀, respectively. Their anti-malarial activity was associated with the in silico P. falciparum lactate dehydrogenase (PfLDH) inhibition. Molecular docking of ligands 1 and 2 with the putative target PfLDH revealed ~-2 kcal/mol of binding energies more negative than the control. Molecular dynamic simulations (100 ns) showed equal or smaller deviation values (RMSD, RMSF, Rg) and stronger interactions of PfLDH-1 and PfLDH-2 complexes via at least one consistent H-bond than the control. Additionally, a slightly increased PfLDH H-bond profile in their interactions improved the PfLDH dynamic and structural stabilities. Overall, this study supports the relevance of 1 and 2 as plasmodial growth inhibitors with their putative anti-PfLDH activity, which could be a potential scaffold for developing anti-malarial drugs.

Keywords: PfLDH; Plasmodium falciparum; Podocarpaceae; Podocarpus polystachyus; anti-malarial; isolation; kaurene; molecular docking; molecular dynamics; structure elucidation.

Figure 1

Structures of 1–4.

Figure 2

Two-dimensional interaction analysis of docked models of compounds 1 (a) and 2 (b) with PfLDH binding site.

Figure 3

The root mean square deviation (RMSD) plots of the enzyme and ligand backbone atoms for the selected systems. Apo-PfLDH (black), PfLDH-control (red and orange), PfLDH-1 (Dark green and lime), and PfLDH-2 (blue and cyan).

Figure 4

The RMSF graphs of the PfLDH backbone atoms throughout the 100 ns MD simulation time for all systems. The RMSF values indicate the residual atomic fluctuations of each amino acid residue when they interact with the ligands throughout the trajectory.

Figure 5

Radius of gyration (Rg) plots of the PfLDH backbone atoms of all systems at MD interval time (0–100 ns); Apo-PfLDH (black), PfLDH-control (red), PfLDH-1 (dark green), and PfLDH-2 (blue).

Figure 6

Two-dimensional interaction models show how H-bonds are formed between PfLDH-1 (a) and PfLDH-2 (b) with the amino acid residues in the PfLDH active binding site at 100 ns (last snapshot) of MD time intervals.