Leporizines A–C: Epithiodiketopiperazines Isolated from an <i>Aspergillus</i> Species

Three new compounds named leporizines A–C (<b>1</b>–<b>3</b>) have been isolated from an <i>Aspergillus</i> sp. strain. Their structures were elucidated by analysis of 1D and 2D NMR spectra. Leporizines A and B were isolated during dereplication of hits from a high-throughput screening campaign for correctors of the cystic fibrosis transmembrane conductance regulator (CFTR), and leporizine C was isolated while preparing additional material for characterization of leporizines A and B. CFTR activity observed for leporizines A and B was highly correlated with cell toxicity and was determined to be a nonspecific effect. Leporizine C was not cytotoxic to cells and did not elicit a response in the CFTR assays. To the best of our knowledge, leporizines A–C represent the first examples of this unusual epithiodiketopiperazine skeleton

Isolation and Characterization of Antimicrobial Compounds in Plant Extracts against Multidrug-Resistant <i>Acinetobacter baumannii</i>

<div><p>The number of fully active antibiotic options that treat nosocomial infections due to multidrug-resistant <i>Acinetobacter baumannii</i> (<i>A. baumannii</i>) is extremely limited. <i>Magnolia officinalis</i>, <i>Mahonia bealei</i>, <i>Rabdosia rubescens</i>, <i>Rosa rugosa</i>, <i>Rubus chingii</i>, <i>Scutellaria baicalensis</i>, and <i>Terminalia chebula</i> plant extracts were previously shown to have growth inhibitory activity against a multidrug-resistant clinical strain of <i>A. baumannii</i>. In this study, the compounds responsible for their antimicrobial activity were identified by fractionating each plant extract using high performance liquid chromatography, and determining the antimicrobial activity of each fraction against <i>A. baumannii</i>. The chemical structures of the fractions inhibiting >40% of the bacterial growth were elucidated by liquid chromatography/mass spectrometry analysis and nuclear magnetic resonance spectroscopy. The six most active compounds were identified as: ellagic acid in <i>Rosa rugosa</i>; norwogonin in <i>Scutellaria baicalensis</i>; and chebulagic acid, chebulinic acid, corilagin, and terchebulin in <i>Terminalia chebula</i>. The most potent compound was identified as norwogonin with a minimum inhibitory concentration of 128 µg/mL, and minimum bactericidal concentration of 256 µg/mL against clinically relevant strains of <i>A. baumannii</i>. Combination studies of norwogonin with ten anti-Gram negative bacterial agents demonstrated that norwogonin did not enhance the antimicrobial activity of the synthetic antibiotics chosen for this study. In conclusion, of all identified antimicrobial compounds, norwogonin was the most potent against multidrug-resistant <i>A. baumannii</i> strains. Further studies are warranted to ascertain the prophylactic and therapeutic potential of norwogonin for infections due to multidrug-resistant <i>A. baumannii</i>.</p></div

Determination of antimicrobial activity of purified compounds from plant extracts against two <i>A.</i> baumannii<i> </i> strains.

<p>Two-fold serially diluted norwogonin (<b>A</b>), terchebulin (<b>B</b>), chebulagic acid (<b>C</b>) and corilagin (<b>D</b>) suspensions were prepared in cation-adjusted Mueller-Hinton broth and mixed with an equal volume of either strain 31P or BAA-1605 suspension (5×10⁵ CFU/mL final). Bacterial growth was measured after a 16 h incubation at 37°C. The final test concentration for each compound ranged from 0.25 to 128 µg/mL for norwogonin (MIC₉₀ = 128 µg/mL), and 7.8 to 1,000 µg/mL for terchebulin (MIC₉₀ = 500 µg/mL), chebulagic acid and corilagin. • 31P and ▴ BAA-1605.</p

Dose response testing of synthetic anti-Gram negative bacterial agents in combination with norwogonin.

<p>The IC₉₀ (µg/mL) of each antibiotic either alone or in combination with 8 or 16 µg/mL norwogonin against strain 31P were determined. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061594#s3" target="_blank">Results</a> are presented as the average IC₉₀ for two experiments each done in duplicate.</p>*<p>IC₉₀ for trimethoprim/sulfamethoxazole could not be determined as maximum inhibition remained below 90% at all concentrations tested.</p

MIC₉₀ determination of purified norwogonin against three clonally distinct strains of <i>A. baumannii</i>.

<p>MIC₉₀ of norwogonin against 31P, 125P and 152P was determined by measuring OD_{600 nm} (<b>A</b>) and was confirmed by resazurin reduction assay (<b>B</b>).</p

Time-kill kinetic analysis of norwogonin against 31P.

<p>The time-kill kinetics of 31P by norwogonin at 1× and 2× MIC was studied over a 24 h incubation. Aliquots were collected at 0, 4, 8 and 24 h, serially diluted in phosphate buffered saline before plating on Mueller-Hinton agar plates. Surviving colonies were enumerated after an 18 h incubation at 37°C. * Estimate: no colonies were observed at the highest concentration plated.</p