Highly Potent 1H-1,2,3-Triazole-Tethered Isatin-Metronidazole Conjugates Against Anaerobic Foodborne, Waterborne, and Sexually-Transmitted Protozoal Parasites

Parasitic infections like amebiasis, trichomoniasis, and giardiasis are major health threats in tropical and subtropical regions of the world. Metronidazole (MTZ) is the current drug of choice for amebiasis, giardiasis, and trichomoniasis but it has several adverse effects and potential resistance is a concern. In order to develop alternative antimicrobials, a library of 1H-1,2,3-triazole-tethered metronidazole-isatin conjugates was synthesized using Huisgen\u27s azide-alkyne cycloaddition reaction and evaluated for their amebicidal, anti-trichomonal, and anti-giardial potential. Most of the synthesized conjugates exhibited activities against Trichomonas vaginalis, Tritrichomonas foetus, Entamoeba histolytica, and Giardia lamblia. While activities against T. vaginalis and T. foetus were comparable to that of the standard drug MTZ, better activities were observed against E. histolytica and G. lamblia. Conjugates 9d and 10a were found to be 2–3-folds more potent than MTZ against E. histolytica and 8–16-folds more potent than MTZ against G. lamblia. Further analysis of these compounds on fungi and bacteria did not show inhibitory activity, demonstrating their specific anti-protozoal properties

Highly Potent 1H-1,2,3-Triazole-Tethered Isatin-Metronidazole Conjugates Against Anaerobic Foodborne, Waterborne, and Sexually-Transmitted Protozoal Parasites

Parasitic infections like amebiasis, trichomoniasis, and giardiasis are major health threats in tropical and subtropical regions of the world. Metronidazole (MTZ) is the current drug of choice for amebiasis, giardiasis, and trichomoniasis but it has several adverse effects and potential resistance is a concern. In order to develop alternative antimicrobials, a library of 1H-1,2,3-triazole-tethered metronidazole-isatin conjugates was synthesized using Huisgen's azide-alkyne cycloaddition reaction and evaluated for their amebicidal, anti-trichomonal, and anti-giardial potential. Most of the synthesized conjugates exhibited activities against Trichomonas vaginalis, Tritrichomonas foetus, Entamoeba histolytica, and Giardia lamblia. While activities against T. vaginalis and T. foetus were comparable to that of the standard drug MTZ, better activities were observed against E. histolytica and G. lamblia. Conjugates 9d and 10a were found to be 2–3-folds more potent than MTZ against E. histolytica and 8–16-folds more potent than MTZ against G. lamblia. Further analysis of these compounds on fungi and bacteria did not show inhibitory activity, demonstrating their specific anti-protozoal properties

Larrea tridentata: A novel source for anti-parasitic agents active against Entamoeba histolytica, Giardia lamblia and Naegleria fowleri.

Protozoan parasites infect and kill millions of people worldwide every year, particularly in developing countries where access to clean fresh water is limited. Among the most common are intestinal parasites, including Giardia lamblia and Entamoeba histolytica. These parasites wreak havoc on the epithelium lining the small intestines (G. lamblia) and colon (E. histolytica) causing giardiasis and amebiasis, respectively. In addition, there are less common but far more deadly pathogens such as Naegleria fowleri that thrive in warm waters and infect the central nervous systems of their victims via the nasal passages. Despite their prevalence and associated high mortality rates, there remains an unmet need to identify more effective therapeutics for people infected with these opportunistic parasites. To address this unmet need, we have surveyed plants and traditional herbal medicines known throughout the world to identify novel antiparasitic agents with activity against G. lamblia, E. histolytica, and N. fowleri. Herein, we report Larrea tridentata, known as creosote bush, as a novel source for secondary metabolites that display antiparasitic activity against all three pathogens. This report also characterizes the lignan compound classes, nordihydroguairetic acid and demethoxyisoguaiacin, as novel antiparasitic lead agents to further develop more effective drug therapy options for millions of people worldwide

Percent inhibition of <i>N</i>. <i>fowleri</i> and human HUVEC cell proliferation by 1 and 2.

<p>(A) The EC₅₀ dose response curves for <b>1</b> and <b>2</b> against <i>N</i>. <i>fowleri</i> trophozoites. (B) The EC₅₀ dose response curves for <b>1</b> and <b>2</b> against HUVEC cells. (C) Compound <b>1</b> and <b>2</b> displayed more potent inhibition of <i>N</i>. <i>fowleri</i> proliferation compared to HUVEC cells, which was statistically significant by Student’s t test analysis.</p

Key HMBC correlations of compound 9.

<p>The 3D energy minimized conformer was generated using BIOVIA Discovery Studio 2017 software.</p

¹H (400 MHz) and ¹³C NMR (100 MHz) data for 9 (CDCl₃ + CD₃OD) compared to the crude reported ¹H NMR data (CD₃OD)^a.

<p>¹H (400 MHz) and ¹³C NMR (100 MHz) data for 9 (CDCl₃ + CD₃OD) compared to the crude reported ¹H NMR data (CD₃OD)<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005832#t002fn001" target="_blank">^a</a>.</p

EC₅₀^a antiparasitic activity of <i>L</i>. <i>tridentata</i> lignans 1–8 and flavonol 9.

<p>EC₅₀<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005832#t003fn001" target="_blank">^a</a> antiparasitic activity of <i>L</i>. <i>tridentata</i> lignans 1–8 and flavonol 9.</p

<i>Larrea tridentata</i>: A novel source for anti-parasitic agents active against <i>Entamoeba histolytica</i>, <i>Giardia lamblia</i> and <i>Naegleria fowleri</i> - Fig 6

<p>Percent Inhibition of cysteine protease activity present in <i>N</i>. <i>fowleri</i> crude extract after treating the cells with different concentrations of compound <b>1</b> (A) and compound <b>2</b> (B). One microgram of lysate protein was used in the cysteine protease assay. Cysteine protease activity was determined as described in Experimental Section and measured as RFU/min/μg protein. The data represent the mean and standard error of mean of three independent experiments. *P < 0.05 by Student’s t test compared to DMSO-treated <i>N</i>. <i>fowleri</i> lysate.</p

<i>Larrea tridentata</i>: A novel source for anti-parasitic agents active against <i>Entamoeba histolytica</i>, <i>Giardia lamblia</i> and <i>Naegleria fowleri</i>

<div><p>Protozoan parasites infect and kill millions of people worldwide every year, particularly in developing countries where access to clean fresh water is limited. Among the most common are intestinal parasites, including <i>Giardia lamblia</i> and <i>Entamoeba histolytica</i>. These parasites wreak havoc on the epithelium lining the small intestines (<i>G</i>. <i>lamblia</i>) and colon (<i>E</i>. <i>histolytica</i>) causing giardiasis and amebiasis, respectively. In addition, there are less common but far more deadly pathogens such as <i>Naegleria fowleri</i> that thrive in warm waters and infect the central nervous systems of their victims via the nasal passages. Despite their prevalence and associated high mortality rates, there remains an unmet need to identify more effective therapeutics for people infected with these opportunistic parasites. To address this unmet need, we have surveyed plants and traditional herbal medicines known throughout the world to identify novel antiparasitic agents with activity against <i>G</i>. <i>lamblia</i>, <i>E</i>. <i>histolytica</i>, and <i>N</i>. <i>fowleri</i>. Herein, we report <i>Larrea tridentata</i>, known as creosote bush, as a novel source for secondary metabolites that display antiparasitic activity against all three pathogens. This report also characterizes the lignan compound classes, nordihydroguairetic acid and demethoxyisoguaiacin, as novel antiparasitic lead agents to further develop more effective drug therapy options for millions of people worldwide.</p></div

¹H (400 MHz) and ¹³C NMR (100 MHz) data for 8 compared to the crude reported ¹H NMR data ((CD₃)₂CO) ^a.

<p>¹H (400 MHz) and ¹³C NMR (100 MHz) data for 8 compared to the crude reported ¹H NMR data ((CD₃)₂CO) <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005832#t001fn001" target="_blank">^a</a>.</p