Inhibiting Activities of the Secondary Metabolites of Phlomis brunneogaleata against Parasitic Protozoa and Plasmodial Enoyl-ACP Reductase, a Crucial Enzyme in Fatty Acid Biosynthesis

Abstract

Anti-plasmodial activity-guided fractionation of Phlomis brunneogaleata (Lamiaceae) led to the isolation of two new metabolites, the iridoid glycoside, brunneogaleatoside and a new pyrrolidinium derivative (2S,4R)-2-carboxy-4-(E)-p-coumaroyloxy-1,1-dimethylpyrrolidinium inner salt [(2S,4R)-1,1-dimethyl-4-(E)-p-coumaroyloxyproline inner salt]. Moreover, a known iridoid glycoside, ipolamiide, six known phenylethanoid glycosides, verbascoside, isoverbascoside, forsythoside B, echinacoside, glucopyranosyl-(1→G_i-6)-martynoside and integrifolioside B, two flavone glycosides, luteolin 7-O-β-D-glucopyranoside (10) and chrysoeriol 7-O-β-D-glucopyranoside (11), a lignan glycoside liriodendrin, an acetophenone glycoside 4-hydroxyacetophenone 4-O-(6′-O-β-D-apiofuranosyl)-β-D-glucopyranoside and three caffeic acid esters, chlorogenic acid, 3-O-caffeoylquinic acid methyl ester and 5-O-caffeoylshikimic acid were isolated. The structures of the pure compounds were elucidated by means of spectroscopic methods (UV, IR, MS, 1D and 2D NMR, [α]_D) and X-ray crystallography. Compounds 10 and 11 were determined to be the major anti-malarial principles of the crude extract (IC₅₀ values of 2.4 and 5.9 μg/mL, respectively). They also exhibited significant leishmanicidal activity (IC₅₀ = 1.1 and 4.1 μg/mL, respectively). The inhibitory potential of the pure metabolites against plasmodial enoyl-ACP reductase (FabI), which is the key regulator of type II fatty acid synthases (FAS-II) in P. falciparum, was also assessed. Compound 10 showed promising FabI inhibiting effect (IC₅₀ = 10 μg/mL) and appears to be the first anti-malarial natural product targeting FabI of P. falciparum.

Abbreviations

ACP:Acyl Carrier Protein

CC:Column Chromatography

FabI:Enoyl-Acyl Carrier Protein Reductase

FAS-I:Type I Fatty Acid Synthase System

FAS-II:Type II Fatty Acid Synthase System

MPLC:Medium Pressure Liquid Chromatography

Key words

Phlomis brunneogaleata - Lamiaceae - iridoid - pyrrolidinium derivative - betonicine - luteolin 7-O-β-D-glucopyranoside - Plasmodium falciparum enoyl-acyl carrier protein reductase (FabI) - type II fatty acid synthase (FAS-II)

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