Isolation and structure elucidation of anti-malarial principles from Terminalia mantaly H. Perrier stem bark

Abstract

Emergence of malaria parasite resistance to drugs has raised global public health concerns for a compelling need to develop improved malaria therapy. This study is a bio-guided isolation of triterpenoid antimalarial compounds from Terminalia mantaly. Methanol extract of the plant was subjected to column chromatography, and eluted with a ternary solvent system gradient-wise. Two compounds, 1 and 2, were isolated and characterised by spectroscopic data (IR, 1H and 13C NMR, COSY, HMQC, HMBC) and by comparison with literature. Isolated compounds were investigated for antimalarial property by spectrophotometric determination of inhibition of β-Hematin formation, absorbance taken at 405 nm. Results were analysed using Graghpad Prism® (6.0) and presented as mean IC50±SEM. Statistical significance, determined using Student’s t-test and one-way ANOVA, set at p-value of 0.05. Quantitative β-Hematin formation inhibitory activities gave IC50±SEM values of (compound 1; 4.434±0.47), (compound 2; 5.140±4.2) with (chloroquine; 0.335±0.1 mg/ml). Compound 1 was identified as 2,3,19,23-tetrahydroxyolean-12-en-28-oic acid glucopyranoside (arjunglucoside I), and compound
2 as its aglycone, 2,3,19,23-tetrahydroxyolean-12-en-28-oic acid (arjungenin). This study provided credence for folkloric use of Terminalia mantaly to treat malaria, and this observed activity was probably due to these isolated triterpenoids.

Keywords: β-Hematin, triterpenoids, nuclear magnetic resonance spectroscopy