Establishment and validation of a 384-well antibacterial assay amenable for high-throughput screening and combination testing.

A 384-well-based antibacterial assay amenable for high-throughput screening and combination testing is described. The assay uses 100-500nL of test compounds and tolerates up to 2.5% dimethyl sulfoxide concentrations. It can be used for screening compound libraries and testing combinatory/synergistic/antagonistic effects of antibiotics, small molecules, and natural product extracts.

Leporizines A-C: epithiodiketopiperazines isolated from an Aspergillus species.

Three new compounds named leporizines A-C have been isolated from an Aspergillus 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 Acinetobacter baumannii.

The number of fully active antibiotic options that treat nosocomial infections due to multidrug-resistant Acinetobacter baumannii (A. baumannii) is extremely limited. Magnolia officinalis, Mahonia bealei, Rabdosia rubescens, Rosa rugosa, Rubus chingii, Scutellaria baicalensis, and Terminalia chebula plant extracts were previously shown to have growth inhibitory activity against a multidrug-resistant clinical strain of A. baumannii. 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 A. baumannii. 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 Rosa rugosa; norwogonin in Scutellaria baicalensis; and chebulagic acid, chebulinic acid, corilagin, and terchebulin in Terminalia chebula. 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 A. baumannii. 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 A. baumannii strains. Further studies are warranted to ascertain the prophylactic and therapeutic potential of norwogonin for infections due to multidrug-resistant A. baumannii.

Neopyrrolomycins with broad spectrum antibacterial activity.

Three new antibiotics, neopyrrolomycins B (1), C (2), and D (3), with potent activity against Gram-positive pathogens were discovered. They exhibited MIC values < 1 microg/mL versus a number of resistant strains. The compounds were obtained from the ethyl acetate extracts of a Streptomyces sp. after purification by column chromatography and RP-HPLC. Their structures were elucidated using X-ray crystallography (1) and NMR spectroscopy (2 and 3).

Citreamicins with potent gram-positive activity.

Two new xanthone antibiotics, citreamicin delta (1) and epsilon (2), with potent activity against Gram-positive pathogens including multidrug-resistant Staphylococcus aureus (MDRSA) were discovered. Compounds 1 and 2 exhibited MIC values < 1 microg/mL versus a number of resistant strains. The compounds were obtained from EtOAc extracts of Streptomyces vinaceus and were purified by countercurrent chromatography and reversed-phase HPLC. Their structures were elucidated using primarily NMR and mass spectroscopy.

Mutactimycin E, a new anthracycline antibiotic with gram-positive activity.

Resistance to currently available antibiotics has become a widely recognized crisis in the medical community. To address this, many companies and researchers are refocusing their attention towards natural products, which have an excellent track record of producing effective antibacterial drugs. The AMRI natural product library was screened for activity against multi-drug resistant Staphylococcus aureus (MDRSA). The active samples were counter screened for cytotoxicity against the human hepatocellular carcinoma HepG2 cell line to determine an in vitro therapeutic index (in vitro TI). Those samples with a high in vitro TI were selected for fractionation and dereplication. This led to the discovery of a new anthracycline structure. This metabolite, named mutactimycin E (1), exhibited moderate activity against several gram positive organisms. Here we report the isolation, structure elucidation and biological activities of this new compound.

Auxarthrol A and auxarthrol B: two new tetrahydoanthraquinones from Auxarthron umbrinum.

Two new 1,2,3,4-tetrahydroanthraquinones, auxarthrol A (compound 1) and auxarthrol B (2), along with three known pyrrolyloctatetraenyl-alpha-pyrone pigments, auxarconjugatin A (3), auxarconjugatin B (4) and rumbrin (5), were isolated from the fungus Auxarthron umbrinum. Structure elucidation of new compounds 1 and 2 was accomplished by spectroscopic data analysis while identification of the known pigments (3-5) was achieved by LC-MS-photodiode array detection.

14'-Hydroxymytoxin B and 16-hydroxyroridin E, two new cytotoxic trichothecenes from Myrothecium roridum.

Two new trichothecenes, 14'-hydroxymytoxin B (1) and 16-hydroxyroridin E (3), were isolated from a fermentation extract of Myrothecium roridum. The structures of 1 and 3 were determined by spectral data interpretation. Both compounds showed potent cytotoxic activity against primary soft-tissue sarcoma cells.