Antisalmonellal Activities of Extracts, Fractions, Compounds and Semi-synthetic Flavonoid Derivatives from &amp;lt;i&amp;gt;Tristemma hirtum&amp;lt;/i&amp;gt; P. Beauv (Melastomataceae)

Joseph Nandjou Kenfack,Borice Tapondjou Tsafack,Rémy Bertrand Teponno,Beaudelaire Kemvoufo Ponou,Jonas Kühlborn,Léon Azefack Tapondjou,Till Opatz,David Tsafack Ngoudjou,Donatien Gatsing,Luciano Barboni

doi:10.11648/j.sjc.20200803.12

Abstract

The development and spread of resistance to currently available antibiotics is a major drawback in the treatment of microbial infections. Salmonellosis for example remains among the most common cause of morbidity and mortality in developing countries. This study aimed to evaluate the antisalmonellal potential of extracts, fractions, isolated compounds and semi-synthetic flavonoids from Tristemma hirtum P. Beauv. Bioguided fractionation by column chromatography of the EtOAc and n -BuOH fractions led to the isolation of eleven compounds including two new esterified glucuronide flavonoids namely: luteolin-3′-O-β-D-glucuronopyranosylbutyl ester (1), a mixture of compound 1 and quercetin-3-O-β-D-glucuronopyranosylbutyl ester (2). Chemical transformation mainly based on the prenylation of 6-hydroxyapigenin-7-O-β-D-glucopyranoside (5) afforded four new semi-synthetic flavonoid derivatives namely: 6, 4'-O-diprenylapigenin-7-O-β-D-glucopyranoside (5a), 8-C-prenyl-6, 4'-O-diprenylapigenin-7-O-β-D-glucopyranoside (5b), 8-C-prenyl-4'-O-prenylapigenin-7-O-β-D-glucopyranoside (5c), 4'-O-prenylapigenin-7-O-β-D-glucopyranoside (5d). The chemical structures of these compounds were assigned using NMR techniques, mass spectrometry and by comparison of their data with reported ones. The antisalmonellal activity was assessed by determining the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) using serial microdilution methods. The results showed that the MeOH extract and EtOAc fraction were active against all the bacteria tested with MICs ranging from 24 to 1536 µg/mL. Seven isolated compounds and three semi-synthetic compounds tested showed MIC values ranging from 16 to 256 µg/mL. Compounds 1, 3, 5a, 5c and 11 displayed the most potent antisalmonellal properties but were generally less potent than those of reference drugs. The activity of extracts and isolated compounds could be used as the starting point for the development of alternative phytodrugs against salmonellosis.

Highlights

According to the World Health Organization, there is an estimated 22 million cases of typhoid fever causing 216 500 deaths each year in the world [1]
Despite the significant activity on just two bacterial strains (Salmonella paratyphi A, Salmonella typhimurium), the n-BuOH fraction was purified according to its abundance of phenolic components which were shown to be active against many bacterial strains [12]
Four new semi synthetic derivatives were obtained from prenylation of 6-hydroxyapigenin-7-O-β-Dglucopyranoside

Summary

Introduction

According to the World Health Organization, there is an estimated 22 million cases of typhoid fever causing 216 500 deaths each year in the world [1]. Despite the multiple use of antibiotics couple to the advanced research and development of new products, typhoid and paratyphoid remain important problems in developing countries, in Asia and in sub-Saharan Africa [2,3,4]. The non-respect of medical prescriptions and the practice of auto medication cause resistance to common antibiotics including third generation quinolones [5]. Salmonella or bacteria causing salmonellosis are intracellular Gram-negative pathogens. These genera include Salmonella typhi, Salmonella paratyphi A, Salmonella paratyphi B and Salmonella typhimurium [6, 7]. The global emergence of multi-drug resistant bacteria invokes a necessity to identify new antibacterial therapy. Secondary metabolites from plant origin appear to be an alternative source of new efficient and active compounds

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