Biotransformation of phenolic tetrahydroprotoberberines in plant cell cultures followed by LC-NMR, LC-MS, and LC-CD

NMR-Based Chromatography Readouts: Indispensable Tools to “Translate” Analytical Features into Molecular Structures

Gaining structural information is a must to allow the unequivocal structural characterization of analytes from natural sources. In liquid state, NMR spectroscopy is almost the only possible alternative to HPLC-MS and hyphenating the effluent of an analyte separation device to the probe head of an NMR spectrometer has therefore been pursued for more than three decades. The purpose of this review article was to demonstrate that, while it is possible to use mass spectrometry and similar methods to differentiate, group, and often assign the differentiating variables to entities that can be recognized as single molecules, the structural characterization of these putative biomarkers usually requires the use of NMR spectroscopy.

Significantly different effects of tetrahydroberberrubine enantiomers on dopamine D1/D2 receptors revealed by experimental study and integrated in silico simulation

Tetrahydroberberrubine (TU), an active tetrahydroprotoberberines (THPBs), is gaining increasing popularity as a potential candidate for treatment of anxiety and depression. One of its two enantiomers, l-TU, has been reported to be an antagonist of both D1 and D2 receptors, but the functional activity of the other enantiomer, d-TU, is still unknown. In this study, experiments were combined with in silico molecular simulations to (1) confirm and discover the functional activities of l-TU and d-TU, and (2) systematically evaluate the molecular mechanisms beyond the experimental observations. l-TU proved to be an antagonist of both D1 and D2 receptors (IC50 = 385 nM and 985 nM, respectively), while d-TU shows no affinity against either D1 or D2 receptor, based on the cAMP assay (D1 receptor) and calcium flux assay (D2 receptor). Results from both flexible-ligand docking studies and molecular dynamic (MD) simulations provided insights at the atomic level. The l-TU-bound structures predicted by MD (1) undergo an outward rotation of the extracellular helical bundles; (2) have an enlarged orthosteric binding pocket; and (3) have a central toggle switch that is prevented from rotating freely. These features are unique to the l-TU enantiomer and provide an explanation for its antagonistic behavior toward both D1 and D2 receptors. The present study provides new sight on the structural and functional relationships of l-TU and d-TU binding to dopamine receptors, and provides guidance to the rational design of novel molecules targeting these two dopamine receptors in the future.

Concepts and Methods to Access Novel Antibiotics from Actinomycetes

Actinomycetes have been proven to be an excellent source of secondary metabolites for more than half a century. Exhibiting various bioactivities, they provide valuable approved drugs in clinical use. Most microorganisms are still untapped in terms of their capacity to produce secondary metabolites, since only a small fraction can be cultured in the laboratory. Thus, improving cultivation techniques to extend the range of secondary metabolite producers accessible under laboratory conditions is an important first step in prospecting underexplored sources for the isolation of novel antibiotics. Currently uncultured actinobacteria can be made available by bioprospecting extreme or simply habitats other than soil. Furthermore, bioinformatic analysis of genomes reveals most producers to harbour many more biosynthetic gene clusters than compounds identified from any single strain, which translates into a silent biosynthetic potential of the microbial world for the production of yet unknown natural products. This review covers discovery strategies and innovative methods recently employed to access the untapped reservoir of natural products. The focus is the order of actinomycetes although most approaches are similarly applicable to other microbes. Advanced cultivation methods, genomics- and metagenomics-based approaches, as well as modern metabolomics-inspired methods are highlighted to emphasise the interplay of different disciplines to improve access to novel natural products.

Mass spectrometry and NMR spectroscopy: modern high-end detectors for high resolution separation techniques--state of the art in natural product HPLC-MS, HPLC-NMR, and CE-MS hyphenations

Current natural product research is unthinkable without the use of high resolution separation techniques as high performance liquid chromatography or capillary electrophoresis (HPLC or CE respectively) combined with mass spectrometers (MS) or nuclear magnetic resonance (NMR) spectrometers. These hyphenated instrumental analysis platforms (CE-MS, HPLC-MS or HPLC-NMR) are valuable tools for natural product de novo identification, as well as the authentication, distribution, and quantification of constituents in biogenic raw materials, natural medicines and biological materials obtained from model organisms, animals and humans. Moreover, metabolic profiling and metabolic fingerprinting applications can be addressed as well as pharmacodynamic and pharmacokinetic issues. This review provides an overview of latest technological developments, discusses the assets and drawbacks of the available hyphenation techniques, and describes typical analytical workflows.

Liquid chromatography-nuclear magnetic resonance coupling as alternative to liquid chromatography-mass spectrometry hyphenations: curious option or powerful and complementary routine tool?

Combining the most powerful separation techniques, i.e. liquid chromatography (LC) or capillary electrophoresis (CE) with a information rich detection system - the mass spectrometer or the nuclear magnetic resonance (NMR) spectrometer - has been pursued for more than three decades. This compilation shall provide an overview of the advantages and limitations of the LC-NMR hyphenation in the light of its most valued application-the unequivocal analyte identification. Especially the post LC trapping of analytes with an in-line solid phase extraction (SPE) device prior to transferring the analyte of interest to the NMR spectrometer (LC-SPE-NMR) proved to be a robust installation allowing a significant cut-down of the amount of analyte needed for the generation of high quality heteronuclear NMR shift correlation data. Different available technical realizations will be discussed and typical application examples from natural product research and from industrial settings will be given.

Transcript and metabolite profiling in cell cultures of 18 plant species that produce benzylisoquinoline alkaloids

Benzylisoquinoline alkaloids (BIAs) are a large and diverse group of ~2500 specialized metabolites found predominantly in plants of the order Ranunculales. Research focused on BIA metabolism in a restricted number of plant species has identified many enzymes and cognate genes involved in the biosynthesis of compounds such as morphine, sanguinarine and berberine. However, the formation of most BIAs remains uncharacterized at the molecular biochemical level. Herein a compendium of sequence- and metabolite-profiling resources from 18 species of BIA-accumulating cell cultures was established, representing four related plant families. Our integrated approach consisted of the construction of EST libraries each containing approximately 3500 unigenes per species for a total of 58,787 unigenes. The EST libraries were manually triaged using known BIA-biosynthetic genes as queries to identify putative homologs with similar or potentially different functions. Sequence resources were analyzed in the context of the targeted metabolite profiles obtained for each cell culture using electrospray-ionization and collision-induced dissociation mass spectrometry. Fragmentation analysis was used for the identification or structural characterization coupled with the relative quantification of 72 BIAs, which establishes a key resource for future work on alkaloid biosynthesis. The metabolite profile obtained for each species provides a rational basis for the prediction of enzyme function in BIA metabolism. The metabolic frameworks assembled through the integration of transcript and metabolite profiles allow a comparison of BIA metabolism across several plant species and families. Taken together, these data represent an important tool for the discovery of BIA biosynthetic genes.

First enantioselective syntheses of the dopamine D1 and D2 receptor modulators, (+)- and (-)-govadine

There is a pressing need to find and develop new antipsychotic agents for the treatment of schizophrenia. Current drugs primarily target dopamine D2 receptors and are only effective in the treatment of the positive symptoms of this indication. The tetrahydroprotoberberine natural product (±)-govadine has shown unique promise for the treatment of both the positive and negative symptoms of schizophrenia as it targets both dopamine D1 and D2 receptors. However, further clinical research has been hindered by the lack of availability of significant quantities of enantioenriched material. A new, enantioselective synthetic route has been developed that affords (-)-govadine in 39% overall yield over 5-steps from commercially available dopamine and homovanillic acid derivatives. Using only minor modifications in the synthetic route, (+)-govadine can be synthesized in comparable yields and enantioselectivities. The route is readily scalable as every intermediate was purified by crystallization and no flash column chromatography was necessary.