Isolation of Antimicrobial Compounds From Cnestis ferruginea Vahl ex. DC (Connaraceae) Leaves Through Bioassay-Guided Fractionation.

Koffi Kouakou,Jing-Guang Lu,Zhi-Hong Jiang,Walter Luyten,Sujogya Kumar Panda,Luc Van Puyvelde,Ming-Rong Yang

doi:10.3389/fmicb.2019.00705

Abstract

Different parts of Cnestis ferruginea are used in traditional African medicine for treating infectious diseases such as dysentery, bronchitis, eye troubles, conjunctivitis, sinusitis, gonorrhea, and syphilis. Despite its long traditional use in the treatment of infections, this plant is not well studied for its in vitro antimicrobial properties. Therefore, the present study aims to establish the antimicrobial activity profile of extracts from this plant, as well as to isolate and evaluate the antimicrobial activity of the most abundant bioactive compound in C. ferruginea leaves through bioassay-guided purification, using Staphylococcus aureus as a target organism. Although both methanol and water extracts of the plant leaves proved active against S. aureus, a water extract was pursued, and subjected further to liquid-liquid partitioning (ethyl acetate, butanol, and water). The ethyl acetate fraction was found to be the most potent and was subjected to silica gel chromatography. In total, 250 fractions were obtained, and those with similar TLC profiles were clustered into 22 major groups, of which pooled fraction-F6 (83 mg) was the most potent. Additional purification by HPLC resulted in two active peaks, which were identified, using a combination of NMR and mass spectrometry, as hydroquinone and caffeic acid methyl ester. Their antimicrobial activity was confirmed using a microdilution protocol on S. aureus, where hydroquinone had a stronger activity (MIC50 = 63 μg/mL) compared to caffeic acid methyl ester (>200 μg/mL). Traditionally this plant is used as an aqueous preparation to treat many infections, and the present study also demonstrated antimicrobial activity in the aqueous extract, which appears due mainly to two major water-soluble compounds isolated through bioassay-guided purification. This supports the clinical use of the aqueous extract of C. ferruginea leaves as a phytotherapeutic for bacterial infections.

Highlights

Despite advances in the discovery of natural and synthetic drugs, infectious diseases are still the leading cause of morbidity and death, especially in developing countries (Vargas et al, 2003)
The objective of the present study was to isolate the main antimicrobial constituents from Cnestis ferruginea leaves through bioassay-guided purification
The water fraction was further partitioned with ethyl acetate (EtOAc) and butanol

Summary

Introduction

Despite advances in the discovery of natural and synthetic drugs, infectious diseases are still the leading cause of morbidity and death, especially in developing countries (Vargas et al, 2003). Actions must be taken to reduce antimicrobial resistance and develop new antibiotics. There is renewed interest in natural products for the discovery of new bioactive substances with better pharmacological (including antibacterial) activities. These drug candidates may help to replace synthetic drugs with strong adverse effects (Adisa et al, 2011). It is understood by bioprospectors that tribal people represent a key to finding new and useful plants. The degree to which these indigenous peoples understand and can use the biodiversity that surrounds them (and in a sustainable manner) is remarkable. The essential components of medicine in Africa are plants (Mahomoodally, 2013)

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