Determination of Eight Coccidiostats in Eggs by Liquid-Liquid Extraction-Solid-Phase Extraction and Liquid Chromatography-Tandem Mass Spectrometry.

A method for the simultaneous determination of robenidine, halofuginone, lasalocid, monensin, nigericin, salinomycin, narasin, and maduramicin residues in eggs by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. The sample preparation method used a combination of liquid-liquid extraction (LLE) and solid-phase extraction (SPE) technology to extract and purify these target compounds from eggs. The target compounds were separated by gradient elution using high-performance liquid chromatography (HPLC) and ultra-performance liquid chromatography (UPLC). Tandem mass spectrometry was used to quantitatively and qualitatively analyze the target compounds via electrospray ionization (ESI+) and multiple reaction monitoring mode. The HPLC-MS/MS and UPLC-MS/MS methods were validated according to the requirements defined by the European Union and the Food and Drug Administration. The limits of detection and limits of quantification of the eight coccidiostats in eggs were 0.23-0.52 µg/kg and 0.82-1.73 µg/kg for HPLC-MS/MS, and 0.16-0.42 µg/kg and 0.81-1.25 µg/kg for UPLC-MS/MS, respectively. The eggs were spiked with four concentrations of the eight coccidiostats, and the HPLC-MS/MS and UPLC-MS/MS average recoveries were all higher than 71.69% and 72.26%, respectively. Compared with the HPLC-MS/MS method, utilizing UPLC-MS/MS had the advantages of low reagent consumption, a short detection time, and high recovery and precision. Finally, the HPLC-MS/MS and UPLC-MS/MS methods were successfully applied to detect eight coccidiostats in 40 eggs.

Nigericin and grisorixin methyl ester from the Algerian soil-living Streptomyces youssoufiensis SF10 strain: a computational study on their epimeric structures and evaluation of glioblastoma stem cells growth inhibition.

The present work describes the metabolites produced by a strain identified as Streptomyces youssoufiensis, whose secondary metabolites profile has not been studied so far. The crude ethyl acetate extract was analyzed by high performance liquid chromatography-electrospray ionization mass spectrometry, leading to the detection of the ionophoric polyethers nigericin, epinigericin, abierixin and the newly isolated grisorixin methyl ester. The presence of epimeric forms of nigericin/epinigericin and grisorixin/epigrisorixin has spurred density functional theory computational calculations. This analysis was able to provide the relative stability of the most favored epimers, setting the basis for general structural considerations applicable to several other polyethers. Both nigericin sodium salt and grisorixin methyl ester showed to affect glioblastoma stem cells proliferation in a dose-dependent manner, with a higher activity for the more lipophilic grisorixin methyl ester (GI50 values of 3.85 and 3.05 µM for VIPI and COMI human glioblastoma stem cells, respectively).

Lonomycins B and C, two new components of polyether antibiotics. Fermentation, isolation and characterization.

Lonomycin B (II), C44H75O14Na, m.p. 181-182 degrees C, and lonomycin C (III), C43H73O14Na, m.p 186-187 degrees C, were isolated as their sodium salts from the fermentation broth of Streptomyces ribosidificus TM-481. Their physicochemical properties demonstrated that II and III are closely related congeners of lonomycin A (I). The identical mass spectra of methyl esters of I and II indicated that II is a stereoisomer of I. On the other hand, the mass spectrum of a methyl ester of III showed a peak at m/e 810 due to M+-H2O which is smaller by 14 mass units than the maximum peak at m/e 824 due to M+-H2O of the methyl esters of I and II. This result together with the elemental analysis strongly suggested that III is a demethyl derivative of I or II. II and III are slightly less active than I in their antimicrobial activities.

Grisorixin, an ionophorous antibiotic of the nigericin group. I. Fermentation, isolation, biological properties and structure.

Grisorixin is an ionophorous antibiotic of the nigericin group isolated from cultures of a strain of Streptomyces griseus. It shows activity against Gram-positive bacteria and fungi but is also very toxic. The isolation and purification procedures are reported. Its structure and physico-chemical properties are also described.