A novel protecting/activating strategy for beta-hydroxy acids and its use in convergent peptide synthesis

beta-Hydroxy acids were reacted with hexafluoroacetone and carbodiimides to give carboxy-activated six-membered lactones in good yields. On reaction with amines, the corresponding amides were obtained. We demonstrate the following applications of this protecting/activating strategy: preparation of carboxamides in solution and on solid phase (both normal and reverse mode); recovery and reuse of the excess material in solid-phase synthesis; and convergent solid-phase peptide synthesis (CSPPS) with peptide segments bearing C-terminal Ser or Thr with very low levels of epimerization (<1%, HPLC).     

Accurate mass as a bioinformatic parameter in data-to-knowledge conversion: Fourier transform ion cyclotron resonance mass spectrometry for peptide de novo sequencing

With the availability of ultra-precise mass spectrometric biomolecular data, the accurate mass is becoming a physical quantity of high interest for bioinformatics tools and strategies. Fourier transform ion cyclotron resonance mass spectrometry with electrospray ionization or matrix-assisted laser desorption/ionization sources now allows the easy determination of amino acid composition of medium size, unknown peptides when employing combinatorial calculation of hypothetical parent and fragment ion masses. This new method, which in a second step, allows the reliable de-novo sequencing of completely unknown peptides ["composition-based sequencing (CBS)"(1)] appears to open a wide new field of bioanalytical investigation. It has been shown that even unspecifically cleaved proteins can be identified easily and reliably when accurate mass evaluation is combined with protein database search tools.(2) It is quite clear that, while the nominal mass of a peptide has obviously no useful correlation to biomolecular structure, the accurate mass, instead, has a strong and direct correlation to structure that so far has not been exploited considerably by bioinformatic tools. It has already become obvious that accurate mass evaluation is going to become a central goal for bioinformatics strategies in the near future.(3-11) Strategies for extracting structural, and even functional, information out of accurate mass values of biomolecules still have to be developed. Examples and prospects of accurate mass evaluation in bioinformatics for the field of proteomics are outlined in the following.     

Effective solvation of alkaline earth ions by proline-rich proteolytic peptides of galectin-3 upon electrospray ionisation

In an analysis of a combined chymotrypsin/AspN digest of galectin-3 by positive ion nano-electrospray ionisation mass spectrometry (nanoESI-MS) several peptides were observed which showed metal adduct ions as their most abundant ion signals. The most prominent adduct ions were observed at m/z values corresponding to [M+40]2+, [M+41]3+, and [M+42]4+ ions. Detailed investigation of the [M+40]2+ ion of the peptide GAPAGPLIVPY showed that it was not, as originally expected, a [M+H+39K]2+ adduct ion but had the composition [M+40Ca]2+. This was verified by several approaches: (i) nanoESI-MS/MS of the [M+Ca]2+ adduct ions resulted in the virtually exclusive formation of doubly charged fragment ions; (ii) mass determination by quadrupole time-of-flight (QTOF)-MS provided a preliminary identification; and (iii) accurate mass measurement using nanoESI Fourier transform ion cyclotron resonance (FTICR)-MS at a mass resolving power of 500 000 allowed the specific detection and identification of the isobaric ion pairs [M+40Ca]2+/[M+H+39K]2+ and [M+24Mg]2+/[M+H+23Na]2+. All peptides in the chymotryptic galectin-3 digest without a basic residue (K or R) showed addition of calcium as the most prominent ionisation principle. A further common feature of these nonbasic peptides was the presence of several proline residues, which is assumed to be a factor promoting the intense addition of calcium. It was observed that the common trace levels of sodium and calcium in analytical grade solvents (about 1-10 microM) are sufficient to generate the [M+H+23Na]2+ and [M+40Ca]2+ ions as the most prominent species of the peptide GAPAGPLIVPY. We conclude that the sequence motifs P-XX-P and P-XXX-P favour the solvation of alkaline earth ions in ESI-MS. In view of the successful detection of physiological Ca/protein interactions by ESI-MS, this finding may point to a solvation of Ca2+ by galectin in solution. The findings open new routes of research in the study of metal/protein and metal/peptide interactions     

Peptide and protein identification by matrix-assisted laser desorption ionization (MALDI) and MALDI-post-source decay time-of-flight mass spectrometry

The potential of matrix-assisted laser desorption ionization (MALDI) and MALDI-post-source decay (PSD) time-of-flight mass spectrometry for the characterization of peptides and proteins is discussed. Recent instrumental developments provide for levels of sensitivity and accuracy that make these techniques major analytical tools for proteome analysis. New software developments employing protein database searches have greatly enhanced the fields of application of MALDI-PSD. Peptides and proteins can be easily identified even if only a partial sequence information is determined. Derivatization procedures have been optimized for MALDI-PSD to increase the structural information and to obtain a complete peptide sequence even in critical cases. They are fast, simple and can be performed on target. MALDI-PSD is also a very powerful tool to characterize or elucidate post-translational or chemically induced modifications. In association with database searches, proteins issued from electrophoretic gels can be identified after specific enzymatic cleavages and peptide mapping.     

Phenolic compounds,essential oil composition,and antioxidant activity of Angelica purpurascens (Avé-Lall.) Gill

In this study, methanol extracts (MEs) and essential oil (EO) of Angelica purpurascens (Avé-Lall.) Gill obtained from different parts (root, stem, leaf, and seed) were evaluated in terms of antioxidant activity, total phenolics, compositions of phenolic compound, and essential oil with the methods of 2,2-azino-bis(3ethylbenzo-thiazoline-6-sulfonic acid (ABTS•⁺), 2,2-diphenyl-1-picrylhydrazil (DPPH•) radical scavenging activities, and ferric reducing/antioxidant power (FRAP), the Folin–Ciocalteu, liquid chromatography−tandem mass spectrometry (LC−MS/MS), and gas chromatography-mass spectrometry (GC−MS), respectively. The root extract of A. purpurascens exhibited the highest ABTS•⁺, DPPH•, and FRAP activities (IC₅₀: 0.05 ± 0.0001 mg/mL, IC₅₀: 0.06 ± 0.002 mg/mL, 821.04 ± 15.96 µM TEAC (Trolox equivalent antioxidant capacity), respectively). Moreover, EO of A. purpurascens root displayed DPPH• scavenging activity (IC₅₀: 2.95 ± 0.084 mg/mL). The root extract had the highest total phenolic content (438.75 ± 16.39 GAE (gallic acid equivalent), µg/mL)). Twenty compounds were identified by LC−MS/MS. The most abundant phenolics were ferulic acid (244.39 ± 15.64 μg/g extract), benzoic acid (138.18 ± 8.84 μg/g extract), oleuropein (78.04 ± 4.99 μg/g extract), and rutin (31.21 ± 2.00 μg/g extract) in seed, stem, root, and leaf extracts, respectively. According to the GC−MS analysis, the major components were determined as α-bisabolol (22.93%), cubebol (14.39%), α-pinene (11.63%), and α-limonene (9.41%) among 29 compounds. Consequently, the MEs and EO of A. purpurascens can be used as a natural antioxidant source.     

Antiproliferative Phenanthrenes from Juncus tenuis: Isolation and Diversity-Oriented Semisynthetic Modification

The occurrence of phenanthrenes is limited in nature, with such compounds identified only in some plant families. Phenanthrenes were described to have a wide range of pharmacological activities, and numerous research programs have targeted semisynthetic derivatives of the phenanthrene skeleton. The aims of this study were the phytochemical investigation of Juncus tenuis, focusing on the isolation of phenanthrenes, and the preparation of semisynthetic derivatives of the isolated compounds. From the methanolic extract of J. tenuis, three phenanthrenes (juncusol, effusol, and 2,7-dihydroxy-1,8-dimethyl-5-vinyl-9,10-dihydrophenanthrene) were isolated. Juncusol and effusol were transformed by hypervalent iodine(III) reagent, using a diversity-oriented approach. Four racemic semisynthetic compounds possessing an alkyl-substituted p-quinol ring (1–4) were produced. Isolation and purification of the compounds were carried out by different chromatographic techniques, and their structures were elucidated by means of 1D and 2D NMR, and HRMS spectroscopic methods. The isolated secondary metabolites and their semisynthetic analogues were tested on seven human tumor cell lines (A2780, A2780cis, KCR, MCF-7, HeLa, HTB-26, and T47D) and on one normal cell line (MRC-5), using the MTT assay. The effusol derivative 3, substituted with two methoxy groups, showed promising antiproliferative activity on MCF-7, T47D, and A2780 cell lines with IC₅₀ values of 5.8, 7.0, and 8.6 µM, respectively.     

Dimeric Cyclodextrin Carriers with High Binding Affinity to Porphyrinoid Photosensitizers

The aim of our investigation was to develop carrier systems for an application of inert drugs in photodynamic cancer therapy. -Cyclodextrin dimers linked at their primary and secondary faces by spacers of varying lengths were synthesized as carrier systems. The binding constants of the inclusion complexes of these cyclodextrin dimers and porphyrinoid photosensitizers were determined by competitive spectrofluorometry. Particularly the secondary face linked dimers exhibited extremely high binding constants with values of 106-107 L/mol. Theoretical studies were carried out on these inclusion complexes to confirm the influence of spacer length and connecting side on complex stability.     

Analysis of ketone‐based neurosteroids by reactive low‐temperature plasma mass spectrometry

Rationale

Neurosteroids are important signalling molecules that modulate neuronal activity. Their low concentrations and low volatility make neurosteroid detection and quantification by ambient mass spectrometry challenging. Here we develop a reactive low‐temperature plasma mass spectrometry (LTP‐MS) method and demonstrate its potential for fast screening and quantification of neurosteroids in mouse brain.

Methods

Ketone‐based neurosteroids were analysed with the LTP‐MS method. The plasma of the LTP was heated in order to improve the desorption efficiency of low‐volatility neurosteroids. Methylamine with a concentration of 500 ppbv was employed as the reactive reagent. Neurosteroids in mouse brain tissue extracts were detected in 70 s with mass errors less than ±3 ppm due to coupling of the ion source with a high‐performance mass spectrometer.

Results

Reaction between neurosteroids and methylamine, seeded into the LTP gas stream, resulted in the formation of protonated methylamine–neurosteroid adducts with 5‐ to 100‐fold abundances, compared to [M + H]⁺ ions detected in non‐reactive LTP‐MS. The lowest detectable concentrations of neurosteroid standards were in the range of ng/mL. Concentrations of neurosteroids in male and female mouse brain extracts as determined with reactive LTP‐MS were on the level of ng/g, comparable to results obtained with high‐performance liquid chromatography–tandem mass spectrometry.

Conclusions

The developed reactive LTP‐MS is capable of providing sensitive identification and quantification of ketone‐based neurosteroids in mouse brain extracts with minimal sample treatment, and showcases the potential of reactive LTP‐MS as a tool for fast screening of neurosteroid levels in brain.

     

Hexafluoroacetone as Protecting and Activating Reagent. Glycosylated Malic, Citramalic, and Thiomalic Acid Derivatives, New Glycosylated Building Blocks for Drug Design [1]

Summary. Glycosylated -hydroxy and -mercapto acids have been synthesized starting from malic/citramalic/thiomalic acid and Ac₄--D-Glc-NH₂/Bzl₄--D-Glc-NH₂ using hexafluoroacetone as protecting and activating reagent.Dedicated to Prof. Dr. Horst Wilde on the occasion of his 65^th birthday