Analysis of Underivatized Brassinosteroids by HPLC/APCI-MS. Occurrence of 3-Epibrassinolide in Arabidopsis thaliana

Temperature-programmed capillary high-performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometry for analysis of fatty acid methyl esters

A new capillary high-performance liquid chromatography method with atmospheric pressure chemical ionization mass spectrometry was developed for the analysis of fatty acid methyl esters and long-chain alcohols. The chromatographic separation was achieved using a Zorbax SB-C18 HPLC column (0.3 × 150 mm, 3.5 μm) with a mobile phase composed of acetonitrile and formic acid and delivered isocratically at a flow rate of 10 μL/min. The column temperature was programmed simply, using a common column oven. Good reproducibility of the temperature profile and retention times were achieved. The temperature programming during the isocratic high-performance liquid chromatography run had a similar effect as a solvent gradient; it reduced retention times of later eluting analytes and improved their detection limits. Two atmospheric pressure chemical ionization sources of the mass spectrometry detector were compared: an enclosed conventional ion source and an in-house made ion source with a glass microchip nebulizer. The enclosed source provided better detectability of saturated fatty acid methyl esters and made it possible to determine the double bond positions using acetonitrile-related adducts, while the open chip-based source provided better analytical figures of merit for unsaturated fatty acid methyl esters. Temperature-programmed capillary high-performance liquid chromatography is a promising method for analyzing neutral lipids in lipidomics and other applications.

Determination of Propionylbrassinolide and Its Impurities by High-Performance Liquid Chromatography with Evaporative Light Scattering Detection

The discovery of brassinolide in 1979, a milestone in brassinosteroids research, has sparked great interest of brassinolide analogs (BLs) in agricultural applications. Among these BLs, propionylbrassinolide has captured considerable attention because it shows plant growth regulating activity with an excellent durability. Two impurities of propionylbrassinolide were isolated and purified by semi-preparative high-performance liquid chromatography (HPLC), and the chemical structures were confirmed. For simultaneous separation and determination of propionylbrassinolide and impurities, an efficient analytical method based on HPLC with evaporative light scattering detector (HPLC-ELSD) was developed. The optimized analysis was performed on a C18 reversed phase column (250 mm × 4.60 mm, 5 μm) with isocratic elution of acetonitrile and water (90:10, v/v) as the mobile phase. The drift tube temperature of the ELSD system was set to 50 °C and the auxiliary gas pressure was 150 kPa. The regression equations demonstrated a good linear relationship (R² = 0.9989-0.9999) within the test ranges. The limits of detection (LODs) and quantification (LOQs) for propionylbrassinolide, impurity 1 and 2 were 1.3, 1.2, 1,3 and 4.3, 4.0, 4.2 mg/L, respectively. The fully validated HPLC-ELSD method was readily applied to quantify the active ingredient and impurities in propionylbrassinolide technical concentrate. Moreover, the optimized separation conditions with ELSD have been successfully transferred to mass spectrometry (MS) detector for LC-MS determination.

The determination of 22 natural brassinosteroids in a minute sample of plant tissue by UHPLC-ESI-MS/MS

The triterpenoid plant hormones brassinosteroids (BRs) are believed to influence almost every aspect of plant growth and development. We have developed a sensitive mass spectrometry-based method for the simultaneous profiling of twenty-two naturally occurring brassinosteroids including biosynthetic precursors and the majority of biologically active metabolites. Using ultra-high performance liquid chromatographic (UHPLC) analysis, the run time was reduced up to three times (to 9 min) in comparison to standard HPLC BRs analyses, the retention time stability was improved to 0.1-0.2 % RSD and the injection accuracy was increased to 1.1-4.9 % RSD. The procedures for extraction and for two-step purification based on solid-phase extraction (SPE) were optimised in combination with subsequent UHPLC analysis coupled to electrospray ionisation tandem mass spectrometry (ESI-MS/MS) using Brassica flowers and Arabidopsis plant tissue extracts. In multiple reaction monitoring (MRM) mode, the average detection limit for BRs analysed was close to 7 pg, and the linear range covered up to 3 orders of magnitude. The low detection limits for this broad range of BR metabolites enabled as little as 50 mg of plant tissue to be used for quantitative analyses. The results of determinations exploiting internal standards showed that this approach provides a high level of practicality, reproducibility and recovery. The method we have established will enable researchers to gain a better understanding of the dynamics of the biosynthesis and metabolism of brassinosteroids and their modes of action in plant growth and development.

A New Type of Modified Brassinosteroids for Enzyme-linked Immunosorbent Assay

New modified brassinosteroids (BS) with a full set of specific functional groups and with an additional one at C-26 have been synthesized and used as haptens for enzyme-linked immunosorbent assay. The haptens were conjugated to bovine serum albumin (BSA) and the obtained immunoconjugates were applied for production of polyclonal antibodies. A conjugation of the haptens to horseradish peroxidase (HRP) gave the corresponding enzyme-labeled BS – another principal component for immuno-competitive analysis. The steroids were linked to proteins through spacers at the terminal side chain carbon atom (C-26) that made both the cyclic part and the side chain exposed for recognition by antibodies. It allowed maximization of their sensitivity and for the first time made possible immunochemical distinguishing of the most important group of natural BS, B-lactones, from B-ketones and 6-deoxo derivatives. The synthesis of haptens based on a sequence of transformations starting from stigmasterol included Claisen rearrangement of 22-allylic ethers as a key reaction in the side chain construction.

Labeled brassinosteroids for biochemical studies

The present paper describes the results of our studies on the synthesis of brassinolide biosynthetic precursors as tools for investigations of new biosynthetic routes leading to brassinosteroids. The corresponding labeled compounds containing three or six deuterium atoms at terminal methyl group(s) of the side chain (in a position ensuring lack of isotopic exchange) were prepared starting from stigmasterol or bisnorcholenic acid. Two strategies for the construction of the carbon skeleton of the side chain were applied in this study: Claisen rearrangement of allylic alcohols and convergent synthesis based on the coupling of 22-aldehydes with appropriate chiral sulfone. More than 20 brassinolide precursors (actual or suspected) have been prepared for metabolic studies that enabled identification of new brassinosteroids and biosynthetic subpathways to brassinolide in Secale cereale and Arabidopsis thaliana.

Measuring the metabolome: current analytical technologies

The post-genomics era has brought with it ever increasing demands to observe and characterise variation within biological systems. This variation has been studied at the genomic (gene function), proteomic (protein regulation) and the metabolomic (small molecular weight metabolite) levels. Whilst genomics and proteomics are generally studied using microarrays (genomics) and 2D-gels or mass spectrometry (proteomics), the technique of choice is less obvious in the area of metabolomics. Much work has been published employing mass spectrometry, NMR spectroscopy and vibrational spectroscopic techniques, amongst others, for the study of variations within the metabolome in many animal, plant and microbial systems. This review discusses the advantages and disadvantages of each technique, putting the current status of the field of metabolomics in context, and providing examples of applications for each technique employed.

Synthesis of [26,27-2H6]brassinosteroids from 23,24-bisnorcholenic acid methyl ester

A number of hexadeuterated brassinosteroids (BS) containing a hydroxy group at C-22 or a 22R,23R-diol function were prepared starting from 23,24-bisnorcholenic acid methyl ester for biosynthetic studies. Synthesis of the cyclic part was accomplished via the initial hydroboration-oxidation of Delta(5)-double bond. The key step in the synthesis of the side chain involved addition of (2S)-[3,4-(2)H(6)]2,3-dimethylbutylphenyl sulfone to the corresponding C-22 aldehydes.

The chemical characteristic and distribution of brassinosteroids in plants

Brassinosteroids represent a class of plant hormones with high-growth promoting activity. They are found at low levels in pollen, anthers, seeds, leaves, stems, roots, flowers, grain, and young vegetative tissues throughout the plant kingdom. Brassinosteroids are a family of about 60 phytosteroids. The article gives a comprehensive survey on the hitherto known brassinosteroids isolated from plants. The chemical characteristic of brassinosteroids is also presented.