Rapid identification of elaiophylin and geldanamycin in Streptomyces fermentation broths using CPC coupled with a photodiode array detector and LC-MS methodologies

The isolation of water-soluble natural products - challenges, strategies and perspectives

Covering period: up to 2019Water-soluble natural products constitute a relevant group of secondary metabolites notably known for presenting potent biological activities. Examples are aminoglycosides, β-lactam antibiotics, saponins of both terrestrial and marine origin, and marine toxins. Although extensively investigated in the past, particularly during the golden age of antibiotics, hydrophilic fractions have been less scrutinized during the last few decades. This review addresses the possible reasons on why water-soluble metabolites are now under investigated and describes approaches and strategies for the isolation of these natural compounds. It presents examples of several classes of hydrosoluble natural products and how they have been isolated. Novel stationary phases and chromatography techniques are also reviewed, providing a perspective towards a renaissance in the investigation of water-soluble natural products.

GdmRIII, a TetR Family Transcriptional Regulator, Controls Geldanamycin and Elaiophylin Biosynthesis in Streptomyces autolyticus CGMCC0516

Geldanamycin and elaiophylin are co-produced in several Streptomyces strains. However, the regulation of their biosynthesis is not fully understood yet. Herein the function of a TetR family regulator GdmRIII, which is located in the biosynthetic gene cluster of geldanamycin, was studied to understand the regulatory mechanism of geldanamycin biosynthesis in Streptomyces autolyticus CGMCC0516. The production of geldanamycin decreased substantially in a ΔgdmRIII mutant and the yield of three compounds which were thought to be geldanamycin congeners greatly increased. Surprisingly, the structural elucidation of these compounds showed that they were elaiophylin and its analogues, which implied that GdmRIII not only played a positive regulatory role in the biosynthesis of geldanamycin, but also played a negative role in elaiophylin biosynthesis. GdmRIII affected the expression of multiple genes in both gene clusters, and directly regulated the expression of gdmM, gdmN, and elaF by binding to the promoter regions of these three genes. A conserved non-palindromic sequence was found among the binding sites of elaF. Our findings suggested that the biosynthetic pathways of geldanamycin and elaiophylin were connected through GdmRIII, which might provide a way for Streptomyces to coordinate the biosynthesis of these compounds for better adapting to environment changes.

Dereplication of bioactive constituents of the genus hypericum using LC-(+,-)-ESI-MS and LC-PDA techniques: Hypericum triquterifolium as a case study

Utilizing liquid chromatography-electro spray ionization-mass spectrometry (LC-(+,-)-ESI-MS) and liquid chromatography-photodiode array detection (LC-PDA) techniques, a dereplication strategy for the analysis of the secondary metabolites constituents of the genus Hypericum has been developed. From the crude methanolic extract of the aerial parts of H. triquetrifolium (leaves, stems, and flowers) and on the basis of their UV-profiles, chromatographic retention times and (+,-)-ESI-MS (TIC and SIM) mass spectral data, seven known (1-7) compounds were dereplicated fairly rapidly. The compounds were classified into three structural classes: phloroglucinols: hyperfirin and adhyperfirin; naphthodianthrones: hypericin, pseudo-hypericin, proto-hypericin, and protopseudo-hypericin; and the flavonoid rutin.

Phomacins: Three Novel Antitumor Cytochalasan Constituents Produced by a Phoma sp

Three novel cytochalasans, phomacins A, B and C, were isolated from a fermentation broth of the fungus Phoma sp. and purified by HSCCC (high speed countercurrent chromatography) followed by HPLC. The structures were determined by 1D and 2D NMR techniques. All three compounds have shown potent inhibitory activity against the HT29 colonic adenocarcinoma cell line.

Rapid analysis of antibiotic-containing mixtures from fermentation broths by using liquid chromatography-electrospray ionization-mass spectrometry and matrix-assisted laser desorption ionization-time-of-flight-mass spectrometry

A crucial step in the isolation of antibiotic substances is establishing whether or not the isolated material represents a new chemical entity. Because of the importance of molecular weight to this process-known as dereplication-mass spectrometry has traditionally played an active role. In this communication a strategy for utilizing liquid chromatography-mass spectrometry (LC/MS) for novelty assessment is described. Crude extracts (20-50 µg) are chromatographed by conventional bore high-performance liquid chromatography (1 mL/min) after which a postcolumn split to divert roughly one-tenth of the sample to the mass spectrometer for molecular weight determination by electrospray ionization (ESI) mass spectrometry. The majority of the effluent is sent to a UV detector and ultimately collected as 1-min fractions for biological testing. As a secondary confirmation of molecular weight, an aliquot of each fraction (< 5%) is taken for analysis by matrix-assisted laser desorption ionization (MALDI). The improved efficiency of this approach over more traditional schemes utilizing off-line fraction collection and conventional ionization methods can be explained by several factors. First, the superior sensitivity of ESI and MALDI means that less material is required for successful analysis. Second, on-line LC/MS optimizes the efficiency of sample transfer and saves both time and labor. Furthermore, the concentration dependence of ESI allows a majority of the material injected for LC/MS to be recovered for biological testing without compromising the signal available for molecular weight determination. As a validation of the above method, crude extracts containing two well-characterized antibiotics-teicoplanin and phenelfamycin-were examined. Results from these analyses are presented along with data from the analysis of a potent unknown antifungal sample.