Polyphenols based on isoflavones as inhibitors of Helicobacter pylori urease

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Abstract

Twenty polyphenols were synthesized and evaluated for their effect on Helicobacter pylori urease. Among these compounds, 4-(p-hydroxyphenethyl)pyrogallol (15) (IC50 = 0.03 mM) and 7,8,4′-trihydroxyisoflavone (19) (IC50 = 0.14 mM) showed potent inhibitory activities, and inhibited Helicobacter pylori urease in a time-dependent manner. The structure–activity relationship of these polyphenols revealed: the two ortho hydroxyl groups were essential for inhibitory activity of polyphenol. When the C-ring of isoflavone was broken, the inhibitory activity markedly decreased. As for deoxybenzoin, the carboxyl group was clearly detrimental.

Graphical abstract

A series of polyphenols were synthesized and evaluated for inhibitory activity against Helicobacter pylori urease. Compounds 15 and 17 were the potent inhibitors with IC50 = 0.03 and 0.14 mM, respectively.

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Introduction

Urease (urea amidohydrolase; E.C.3.5.1.5) is widely distributed in a variety of bacteria, fungi, algae, and plants. People infected by these bacteria characterized by urease activity such as Helicobacter pylori (H. pylori)and Proteus mirabilis are exposed to a high risk for chronic atrophic gastritis, peptic ulcer1, and urolithiasis.2 Structural studies of the enzymes from Klebsiella aerogenes, Bacillus pasteurii, and H. pylori have revealed a dinuclear Ni active site with a carbamylated lysine residue that bridges the deeply buried metal atoms.3, 4, 5 Urease catalyzes the hydrolysis of urea to produce ammonia and carbon dioxide, and to protect the bacteria in the acidic environment through the elevation in pH.6 Many urease inhibitors have been described in the past decades, like fluorofamide, hydroxyureas, and hydroxamic acids, but part of them were prevented from using in vivo because of their toxicity or instability. For instance, acetohydroxamic acid was demonstrated to be teratogenic in rats.7 Thus, current efforts are focused on seeking novel urease inhibitors with good bioavailability and low toxicity.

Polyphenols, such as flavones and isoflavones, constitute one of the most represented classes of compounds in higher plants including medicinal and edible plants. Extensive epidemiological and animal studies and in vitro experiments with polyphenols have indicated their broad variety of biological activities, including anticancer,8 anti-inflammatory,9 antibacterial,10 cardioprotective,11 anti-osteoporotic12, and enzyme-inhibitory13 activities. More attention has been focused on exploring novel biological properties of polyphenols. As an example, tea polyphenols and flavones as urease inhibitors were reported by Wotherspoon et al.14 and Tamura,15 respectively. In general, isoflavones exhibited similar biological activities as flavones,10, 12, 16, 17, 18, 19 which inspired us to screen isoflavones and their bioisosteres for urease inhibitors. Twenty compounds were designed to test for urease inhibitory activities against H. pylori urease. To our knowledge, this is the first report on the screening of isoflavone-based compounds for their urease inhibitory activities.

Section snippets

Chemistry

A series of isoflavone-based polyphenols with structural diversity were designed for urease inhibitors. Inspection of the chemical structure of isoflavone suggested that the compound could be divided into three subunits: A-, B-, and C-rings (Fig. 3). Initial structure–activity relationship (SAR) studies were performed by modification of the parent compound to determine if any of the subunits displayed urease inhibitory activity. Based on this consideration, we further designed some

Conclusion

Twenty polyphenols were prepared and evaluated for their activity against H. pylori urease. Among these compounds, 15 (IC50 = 0.03 mM) and 17 (IC50 = 0.14 mM) showed potent inhibitory activities. The SAR of these polyphenols disclosed: the two ortho hydroxyl groups were essential for inhibitory activity of polyphenol. When the C-ring of isoflavone was broken, the inhibitory activity markedly decreased. As for deoxybenzoin, the carboxyl group was clearly detrimental. Further efforts to modify the

Materials

Protease inhibitors (Complete mini EDTA-free) were purchased from Roche Diagnostics GmbH (Mannheim, Germany) and brucella broth was from Becton–Dickinson (Cockeysville, MD). Horse serum was from Hyclone (Utah, America).

Bacteria

Helicobacter pylori (ATCC 43504; American Type Culture Collection, Manassas, VA) was grown in brucella broth supplemented with 10% heat-inactivated horse serum for 24 h at 37 °C under microaerobic conditions (5% O2, 10% CO2, and 85% N2), as previously described.27

Preparation of H. pylori urease

For urease

Acknowledgment

The work was financed by Grant (Project 30672516) from National Natural Science Foundation of China.

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