Isolation, characterization and biological activities of terpenoids from Gunnera perpensa

Abstract

Five pentacyclic triterpenes were identified from the leaves and stalks of Gunnera perpensa. These were ursolic acid (I), 3-β-hydroxyolean-12-en-27-oic acid (II) (β-peltoboykinolic acid), 3- β-hydroxyurs-12-en-27-oic acid (III) (α-peltoboykinolic acid), 3-α-hydroxyolean-12-en-27-oic acid (IV), and 3α-3, 19-dihydroxyurs-12-en-28-oic acid (V) (pomolic acid). These compounds were extracted using ethyl acetate and separated by silica gel column chromatography by the aid of TLC. Their structures were elucidated by 1H and 13C NMR spectroscopy and identified by comparing their spectral data with those reported in the literature. High-Performance Liquid Chromatography (HPLC) was used to identify those compounds that were difficult to separate using CC.

Disc diffusion assay was used to evaluate the antimicrobial potentials of the crude extracts and the isolated compounds against bacterial and fungal species. The sickle-cell normalisation and free radical scavenging potentials of the crude extracts and the isolated compounds were done using Emmel’s test and DPPH (2, 2 dyphenyl-2-picryl hydrate) photometric assay, respectively. The anticancer potential of the isolated compounds was performed using the 3-(4,5- Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

The antimicrobial results showed that the crude extracts GP/A3 and GP/C4 were highly active against S. aureus, B. cereus, E. coli and P. aeruginosa with MIC values ranging from 0.75 to 1.5 µg/ml. Significant antibacterial activity was observed with compound X against S. aureus, S. epidermidis and E. faecalis. Neither of the crude extracts nor the isolates showed antifungal activity.The partial fraction (compound Y) showed the highest normalisation rate to the sickle- cells with 82.135 % standardisation at 144.93 µg/ml. The crude extracts GP/A2, GP/B3, GP/A3, and GP/B2 exhibited the highest radical scavenging capacity against the free radical 2,2- diphenyl-1-picrylhydrazyl with 96, 95, 94.8, and 94.3 percentage values, respectively.While the free radical scavenging potentials of the isolates were found to be less. The highest cytotoxicity activity was recorded by the compounds X and Y followed by the moderate activity of

compounds I, II, III and IV with equal percentage death values of, 54.58. The tested compounds were found to be more toxic to the MCF-7 than HEK293 cell line.

In conclusion, this is the first study to discover pentacyclic triterpenes from the leaves and stalks of G. perpensa. The crude extracts and their isolates together with the two partial fractions (compounds X and Y) were found to be responsible and add value to the existing known potential of G. perpensa. These compounds have shown antimicrobial, anti-sickling, anti-oxidant and anticancer properties. The probability of getting a cure for Sickle Cell Anemia patients from G. perpensa is possible through direct use or after chemical modification of the compounds. The high anti-oxidant potential of the crude extracts will serve as a starting point for further studies to identify and characterise undiscovered secondary metabolites. The anticancer properties of the isolated compounds encourage future studies against different cancer cell lines. Moreover, none of the crude extracts and isolated compounds were found to be toxic to brine shrimp larvae which indicate its safety in any human health related applications. It is highly recommended to further purify the partially purified compounds (X and Y) as they showed high biological activities that can add value to new drug development.