Ambient ionization mass spectrometry provides screening of selective androgen receptor modulators

Ambient ionization mass spectrometry allows for analysis of samples in their natural state, i.e., with no sample pre-treatment. It can be viewed as a fast, simple, and economical analysis, but its main disadvantages include a lower analytical performance due to the presence of complex sample matrix and the lack of chromatographic separation prior to the introduction of the sample into the mass spectrometer. Here we present an application of two ambient ionization mass spectrometry techniques, i.e., Desorption Atmospheric Pressure Photoionization and Dielectric Barrier Discharge Ionization, for the analysis of known Selective Androgen Receptor Modulators, which represent common compounds of abuse in professional and semiprofessional sport. Eight real samples of illegal food supplements, seized by the local law enforcement, were used to test the performance of the ambient mass spectrometry and the results were validated against a newly developed targeted LC-UV-MS/MS method performed in multiple reaction monitoring mode with an external calibration for each analyte. In order to decide whether or not the compound can be declared as present, we proposed a system of rules for the interpretation of the obtained spectra. The criteria are based on mass spectrum matching (5-10 ppm accuracy from the theoretical exact mass and a correct isotopic pattern), duration of the mass signal (three or five consecutive scans, depending on the instrumentation used), and intensity above the background noise (threefold increase in intensity and absolute intensity above 5E4 or 1E5, depending on the instrumentation). When applying these criteria, good agreement was found between the tested methods. Ambient ionization techniques were effective at detecting SARMs at pharmacologically relevant doses, i.e., approximately above 1 mg per capsule, although they may fail to detect lower levels or isomeric species. It is demonstrated that when adhering to a set of clear and consistent rules, ambient mass spectrometry can be employed as a qualitative technique for the screening of illegal SARMs with sufficient confidence and without the necessity to perform a regular LC-MS analysis.

Structural characterization of wax esters using ultraviolet photodissociation mass spectrometry

Wax esters play critical roles in biological systems, serving functions from energy storage to chemical signaling. Their diversity is attributed to variations in alcohol and acyl chains, including their length, branching, and the stereochemistry of double bonds. Traditional analysis by mass spectrometry with collisional activations (CID, HCD) offers insights into acyl chain lengths and unsaturation level. Still, it falls short in pinpointing more nuanced structural features like the position of double bonds. As a solution, this study explores the application of 213-nm ultraviolet photodissociation (UVPD) for the detailed structural analysis of wax esters. It is shown that lithium adducts provide unique fragments as a result of Norrish and Norrish-Yang reactions at the ester moieties and photoinduced cleavages of double bonds. The product ions are useful for determining chain lengths and localizing double bonds. UVPD spectra of various wax esters are presented systematically, and the effect of activation time is discussed. The applicability of tandem mass spectrometry with UVPD is demonstrated for wax esters from natural sources. The UHPLC analysis of jojoba oil proves the compatibility of MS2 UVPD with the chromatography time scale, and a direct infusion is used to analyze wax esters from vernix caseosa. Data shows the potential of UVPD and its combination with CID or HCD in advancing our understanding of wax ester structures.

Modified aryldifluorophenylsilicates with improved activity and selectivity in nucleophilic fluorination of secondary substrates

Nucleophilic fluorination of secondary aliphatic substrates, especially of halides, still remains a challenge. Among the available reagents, TBAT belongs to one of the best choices due to its stability, affordable price and low toxicity. With the aim to improve its selectivity, we synthesized three analogues modified in the aryl part of the TBAT reagent with one or two electron donating methoxy groups or with one electron withdrawing trifluoromethyl group. All three reagents are air-stable compounds and their structure was confirmed by a single crystal X-ray analysis. In testing the reactivity and selectivity of the reagents with a library of secondary bromides, as well as of other selected primary and secondary substrates, we found that substitution with methoxy groups mostly improves both reactivity and selectivity compared to TBAT, while the substitution with trifluoromethyl group leads to inferior results. Difluorosilicates modified by more than two electron donating methoxy groups proved to be unstable and decomposed spontaneously to the HF2 - anion. DFT calculations of tetramethylammonium analogues of the studied reagents disclosed that the substitution of the phenyl group with the methoxy substituent lowers the transitions state energy of the decomposition to a fluorosilane-fluoride complex, while the substitution with the trifluoromethyl group has an opposite effect.

A 'Chiron' approach to novel phytosphingosine mimetics based on a cascade [3,3]-sigmatropic rearrangement

Straightforward access to enantiomerically pure 3,4-diamino-3,4-dideoxyphytosphingosines, as novel analogues of natural d-ribo-phytosphingosine was accomplished, starting from two available chirons: dimethyl l-tartrate and d-isoascorbic acid. A sequential Overman rearrangement followed by late-stage introduction of the alkyl side chain moiety via olefin cross-metathesis is the cornerstone of this approach. The preliminary evaluation study of the synthesised sphingomimetics, based on their ability to inhibit a proliferation of human cancer cells, showed promising cytotoxicity against Jurkat and HeLa cells for (2R,3R,4S)-2,3,4-triaminooctadecan-1-ol trihydrochloride.

Thermal evaporation as sample preparation for silver-assisted laser desorption/ionization mass spectrometry imaging of cholesterol in amyloid tissues

Cholesterol plays an important biological role in the body, and its disruption in homeostasis and synthesis has been implicated in several diseases. Mapping the locations of cholesterol is crucial for gaining a better understanding of these conditions. Silver deposition has proven to be an effective method for analyzing cholesterol using mass spectrometry imaging (MSI). We optimized and evaluated thermal evaporation as an alternative deposition technique to sputtering for silver deposition in MSI of cholesterol. A silver layer with a thickness of 6 nm provided an optimal combination of cholesterol signal intensity and mass resolution. The deposition of an ultrathin nanofilm of silver enabled high-resolution MSI with a pixel size of 10 μm. We used this optimized method to visualize the distribution of cholesterol in the senile plaques in the brains of APP/PS1 mice, a model that resembles Alzheimer's disease pathology. We found that cholesterol was evenly distributed across the frontal cortex tissue, with no evidence of plaque-like accumulation. Additionally, we investigated the presence and distribution of cholesterol in myocardial sections of a human heart affected by wild-type ATTR amyloidosis. We identified the presence of cholesterol in areas with amyloid deposition, but complete colocalization was not observed.

Quaternary ammonium fluorides and difluorosilicates as nucleophilic fluorination reagents

TBAT (tetrabutylammonium difluorotriphenylsilicate) is an excellent homogeneous nucleophilic fluorination reagent, but a high excess of the reagent was reported to be essential. We hence optimized the reaction conditions and compared its nucleophilic fluorination reactivity with that of other common commercial nucleophilic fluorination reagents, such as anhydrous TBAF and TASF (tris(dimethylamino)sulfonium difluorotrimethylsilicate). As the substrates, we employed a standard set of primary and secondary octyl substrates under identical conditions. To eliminate the possibility of hydrogen fluoride elimination in the above reagents, we prepared four quaternary ammonium fluorides lacking β-elimination possibility in the hydrocarbon chain, transformed them to the corresponding difluorotriphenylsilicates, and compared their reactivity with that of the commercial reagents. Furthermore, attempts to isolate analogous tetrabutylammonium difluoromethyldiphenylsilicate or difluorodimethylphenylsilicate failed, as was confirmed by comparison of the published experimental data with computed 19F NMR spectra. Finally, we studied the transition states of decomposition of various tetramethylammonium methylphenyldifluorosilicates by DFT methods and found that their relative energies increase with an increasing number of phenyl groups. The formation of difluorosilicates is a nearly barrierless process.

Solvent-controlled formation of alkali and alkali-earth-secured cucurbituril/guest trimers

Cucurbit[7]uril (CB[7]) encapsulates adamantyl and trimethylsilyl substituents of positively charged guests in dimethyl sulfoxide (DMSO). Unlike in water or deuterium oxide, addition of a selection of alkali and alkali-earth cations with van der Waals radii between 1.0 and 1.4 Å (Na+, K+, Ca2+, Sr2+, Ba2+ and Eu3+) to the CB[7]/guest complexes triggers their cation-mediated trimerization, a process that is very slow on the nuclear magnetic resonance (NMR) time scale. Smaller (Li+, Mg2+) or larger cations (Rb+, Cs+ or NH4+) are inert. The trimers display extensive CH-O interactions between the equatorial and pseudo-equatorial hydrogens of CB[7] and the carbonyl rim of the neighboring CB[7] unit in the trimer, and a deeply nested cation between the three interacting carbonylated CB[7] rims; a counteranion is likely perched in the shallow cavity formed by the three outer walls of CB[7] in the trimer. Remarkably, a guest must occupy the cavity of CB[7] for trimerization to take place. Using a combination of semi-empirical and density functional theory techniques in conjunction with continuum solvation models, we showed that trimerization is favored in DMSO, and not in water, because the penalty for the partial desolvation of three of the six CB[7] portals upon aggregation into a trimer is less unfavorable in DMSO compared to water.

Galectin-targeting glycocalix[4]arenes can enter the cells

Elevated levels of galectin-3 are associated with tumorigenesis. Its inhibition with high-affinity carbohydrate ligands opens new therapeutic routes. Targeting of intracellular galectin-3 is challenging for polar inhibitors like carbohydrates. We demonstrate the potential of novel biomedical research tools, glycocalix[4]arenes, to enter epithelial cells, which may allow their interaction with galectin-3.

Tracking Isomerizations of High-Energy Adenine Cation Radicals by UV-Vis Action Spectroscopy and Cyclic Ion Mobility Mass Spectrometry

We report experimental and computational studies of protonated adenine C-8 σ-radicals that are presumed yet elusive reactive intermediates of oxidative damage to nucleic acids. The radicals were generated in the gas phase by the collision-induced dissociation of C-8-Br and C-8-I bonds in protonated 8-bromo- and 8-iodoadenine as well as by 8-bromo- and 8-iodo-9-methyladenine. Protonation by electrospray of 8-bromo- and 8-iodoadenine was shown by cyclic-ion mobility mass spectrometry (c-IMS) to form the N-1-H, N-9-H and N-3-H, N-7-H protomers in 85:15 and 81:19 ratios, respectively, in accordance with the equilibrium populations of these protomers in water-solvated ions that were calculated by density functional theory (DFT). Protonation of 8-halogenated 9-methyladenines yielded single N-1-H protomers, which was consistent with their thermodynamic stability. The radicals produced from the 8-bromo and 8-iodo adenine cations were characterized by UV-vis photodissociation action spectroscopy (UVPD) and c-IMS. UVPD revealed the formation of C-8 σ-radicals along with N-3-H, N-7-H-adenine π-radicals that arose as secondary products by hydrogen atom migrations. The isomers were identified by matching their action spectra against the calculated vibronic absorption spectra. Deuterium isotope effects were found to slow the isomerization and increase the population of C-8 σ-radicals. The adenine cation radicals were separated by c-IMS and identified by their collision cross sections, which were measured relative to the canonical N-9-H adenine cation radical that was cogenerated in situ as an internal standard. Ab initio CCSD(T)/CBS calculations of isomer energies showed that the adenine C-8 σ-radicals were local energy minima with relative energies at 76-79 kJ mol^-1 above that of the canonical adenine cation radical. Rice-Ramsperger-Kassel-Marcus calculations of unimolecular rate constants for hydrogen and deuterium migrations resulting in exergonic isomerizations showed kinetic shifts of 10-17 kJ mol^-1, stabilizing the C-8 σ-radicals. C-8 σ-radicals derived from N-1-protonated 9-methyladenine were also thermodynamically unstable and readily isomerized upon formation.

Ozone-enabled fatty acid discovery reveals unexpected diversity in the human lipidome

Fatty acid isomers are responsible for an under-reported lipidome diversity across all kingdoms of life. Isomers of unsaturated fatty acids are often masked in contemporary analysis by incomplete separation and the absence of sufficiently diagnostic methods for structure elucidation. Here, we introduce a comprehensive workflow, to discover unsaturated fatty acids through coupling liquid chromatography and mass spectrometry with gas-phase ozonolysis of double bonds. The workflow encompasses semi-automated data analysis and enables de novo identification in complex media including human plasma, cancer cell lines and vernix caseosa. The targeted analysis including ozonolysis enables structural assignment over a dynamic range of five orders of magnitude, even in instances of incomplete chromatographic separation. Thereby we expand the number of identified plasma fatty acids two-fold, including non-methylene-interrupted fatty acids. Detection, without prior knowledge, allows discovery of non-canonical double bond positions. Changes in relative isomer abundances reflect underlying perturbations in lipid metabolism.

Silver Ion High-Performance Liquid Chromatography-Atmospheric Pressure Chemical Ionization Mass Spectrometry: A Tool for Analyzing Cuticular Hydrocarbons

Aliphatic hydrocarbons (HCs) are usually analyzed by gas chromatography (GC) or matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. However, analyzing long-chain HCs by GC is difficult because of their low volatility and the risk of decomposition at high temperatures. MALDI cannot distinguish between isomeric HCs. An alternative approach based on silver ion high-performance liquid chromatography (Ag-HPLC) is shown here. The separation of HC standards and cuticular HCs was accomplished using two ChromSpher Lipids columns connected in series. A gradient elution of the analytes was optimized using mobile phases prepared from hexane (or isooctane) and acetonitrile, 2-propanol, or toluene. HCs were detected by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). Good separation of the analytes according to the number of double bonds, cis/trans geometry, and position of double bonds was achieved. The retention times increased with the number of double bonds, and trans isomers eluted ahead of cis isomers. The mobile phase significantly affected the mass spectra of HCs. Depending on the mobile phase composition, deprotonated molecules, molecular ions, protonated molecules, and various solvent-related adducts of HCs were observed. The optimized Ag-HPLC/APCI-MS was applied for characterizing cuticular HCs from a flesh fly, Neobellieria bullata, and cockroach, Periplaneta americana. The method made it possible to detect a significantly higher number of HCs than previously reported for GC or MALDI-MS. Unsaturated HCs were frequently detected as isomers differing by double-bond position(s). Minor HCs with trans double bonds were found beside the prevailing cis isomers. Ag-HPLC/APCI-MS has great potential to become a new tool in chemical ecology for studying cuticular HCs.

Positive Effect of Acetylation on Proteomic Analysis Based on Liquid Chromatography with Atmospheric Pressure Chemical Ionization and Photoionization Mass Spectrometry

A typical bottom-up proteomic workflow comprises sample digestion with trypsin, separation of the hydrolysate using reversed-phase HPLC, and detection of peptides via electrospray ionization (ESI) tandem mass spectrometry. Despite the advantages and wide usage of protein identification and quantification, the procedure has limitations. Some domains or parts of the proteins may remain inadequately described due to inefficient detection of certain peptides. This study presents an alternative approach based on sample acetylation and mass spectrometry with atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI). These ionizations allowed for improved detection of acetylated peptides obtained via chymotrypsin or glutamyl peptidase I (Glu-C) digestion. APCI and APPI spectra of acetylated peptides often provided sequence information already at the full scan level, while fragmentation spectra of protonated molecules and sodium adducts were easy to interpret. As demonstrated for bovine serum albumin, acetylation improved proteomic analysis. Compared to ESI, gas-phase ionizations APCI and APPI made it possible to detect more peptides and provide better sequence coverages in most cases. Importantly, APCI and APPI detected many peptides which passed unnoticed in the ESI source. Therefore, analytical methods based on chymotrypsin or Glu-C digestion, acetylation, and APPI or APCI provide data complementary to classical bottom-up proteomics.

Non-symmetrical Tetrafluoroalkadienes Synthesized by ROCM of 3,3,4,4-Tetrafluorocyclobutene

As the first known example of ring-opening cross metathesis (ROCM) of polyfluorinated strained cyclobutenes, ROCM of 3,3,4,4-tetrafluorocyclobutene with electronically rich alkenes, catalyzed by Grubbs or Hoveyda-Grubbs 2nd generation precatalysts, gave a small library of non-symmetrical isolated dienes bearing a tetrafluoroethylene spacer between the double bonds. 1-Butoxy-3,3,4,4-tetrafluorohexa-1,5-diene thus formed underwent subsequent regioselective cross metathesis (CM) with a series of styrenes, catalyzed by Hoveyda-Grubbs 2nd generation precatalyst, leading to non-symmetrically substituted dienes. 6,6-Dibutoxy-3,3,4,4-tetrafluorohex-1-ene, formed by regioselective butoxylation of 1-butoxy-3,3,4,4-tetrafluorohexa-1,5-diene, was dihydroxylated and cyclized to the corresponding 3,3,4,4-tetrafluorohexopyranose.

Gas Dynamic Virtual Nozzle Sprayer for an Introduction of Liquid Samples in Atmospheric Pressure Ionization Mass Spectrometry

Electrospray may exhibit inadequate ionization efficiency in some applications. In such cases, atmospheric-pressure chemical ionization (APCI) and photoionization (APPI) can be used. Despite a wide application potential, no APCI and APPI sources dedicated to very low sample flow rates exist on the market. Since the ion source performance depends on the transfer of analytes from the liquid to the gas phase, a nebulizer is a critical component of an ion source. Here, we report on the nebulizer with a gas dynamic virtual nozzle (GDVN) and its applicability in APCI at microliter-per-minute flow rates. Nebulizers differing by geometrical parameters were fabricated and characterized regarding the jet breakup regime, droplet size, droplet velocity, and spray angle for liquid flow rates of 0.75-15.0 μL/min. A micro-APCI source with the GDVN nebulizer behaved as a mass-flow-sensitive detector and provided stable and intense analyte signals. Compared to a classical APCI source, an order of magnitude lower detection limit for verapamil was achieved. Mass spectra recorded with the nebulizer in dripping and jetting modes were almost identical and did not differ from normal APCI spectra. Clogging never occurred during the experiments, indicating the high robustness of the nebulizer. Low-flow-rate APCI and APPI sources with a GDVN sprayer promise new applications for low- and medium-polar analytes.

Glycocalix[4]arenes and their affinity to a library of galectins: the linker matters

Galectins are lectins that bind β-galactosides. They are involved in important extra- and intracellular biological processes such as apoptosis, and regulation of the immune system or the cell cycle. High-affinity ligands of galectins may introduce new therapeutic approaches or become new tools for biomedical research. One way of increasing the low affinity of β-galactoside ligands to galectins is their multivalent presentation, e.g., using calixarenes. We report on the synthesis of glycocalix[4]arenes in cone, partial cone, 1,2-alternate, and 1,3-alternate conformations carrying a lactosyl ligand on three different linkers. The affinity of the prepared compounds to a library of human galectins was determined using competitive ELISA assay and biolayer interferometry. Structure-affinity relationships regarding the influence of the linker and the core structure were formulated. Substantial differences were found between various linker lengths and the position of the triazole unit. The formation of supramolecular clusters was detected by atomic force microscopy. The present work gives a systematic insight into prospective galectin ligands based on the calix[4]arene core.

Advanced high-affinity glycoconjugate ligands of galectins

Galectins are proteins of the family of human lectins. By binding terminal galactose units of cell surface glycans, they moderate biological and pathological processes such as cell signaling, cell adhesion, apoptosis, fibrosis, carcinogenesis, and metabolic disorders. The binding of monovalent glycans to galectins is usually relatively weak. Therefore, the presentation of carbohydrate ligands on multivalent scaffolds can efficiently increase and/or discriminate the affinity of the glycoconjugate to different galectins. A library of glycoclusters and glycodendrimers with various structural presentations of the common functionalized N-acetyllactosamine ligand was prepared to evaluate how the mode of presentation affects the affinity and selectivity to the two most abundant galectins, galectin-1 (Gal-1) and galectin-3 (Gal-3). In addition, the effect of a one- to two-unit carbohydrate spacer on the affinity of the glycoconjugates was determined. A new design of the biolayer interferometry (BLI) method with specific AVI-tagged constructs was used to determine the affinity to galectins, and compared with the gold-standard method of isothermal titration calorimetry (ITC). This study reveals new routes to low nanomolar glycoconjugate inhibitors of galectins of interest for biomedical research.

Alarm communication predates eusociality in termites

Termites (Blattodea: Isoptera) have evolved specialized defensive strategies for colony protection. Alarm communication enables workers to escape threats while soldiers are recruited to the source of disturbance. Here, we study the vibroacoustic and chemical alarm communication in the wood roach Cryptocercus and in 20 termite species including seven of the nine termite families, all life-types, and all feeding and nesting habits. Our multidisciplinary approach shows that vibratory alarm signals represent an ethological synapomorphy of termites and Cryptocercus. In contrast, chemical alarms have evolved independently in several cockroach groups and at least twice in termites. Vibroacoustic alarm signaling patterns are the most complex in Neoisoptera, in which they are often combined with chemical signals. The alarm characters correlate to phylogenetic position, food type and hardness, foraging area size, and nesting habits. Overall, species of Neoisoptera have developed the most sophisticated communication system amongst termites, potentially contributing to their ecological success.

MALDI Mass Spectrometry Imaging of Lipids on Free-Floating Brain Sections and Immunohistochemically Colocalized Markers of Neurodegeneration

In mass spectrometry imaging (MSI), the essential steps in sample preparation include collection and storage. The most widely used preservation procedure for MSI consists in freezing samples and storing them at temperatures below -80 °C. On the other hand, the most common method for preserving biological samples in clinical practice is their fixation in paraformaldehyde. The storage of free-floating sections is a particular type of the preservation of paraformaldehyde-fixed tissues that is used in immunohistochemistry. This chapter describes the approach of the multimodal imaging of free-floating brain sections using the MSI of lipids and the immunohistochemistry of neurodegeneration markers.

A simple and high-yield route to iridium, rhodium, osmium and ruthenium nido-6-metalladecaborane compounds

We report a high-yield heterogeneous solid/liquid phase synthetic method to a series of nido-6-metalladecaboranes. The hydridoirida- and hydridorhoda-decaboranes, [6,6,6-H(PPh₃)₂-nido-6-MB₉H₁₃] [M = Ir (1), Rh (2)] are isolatable in 98% yields from the reaction of the square-planar M(I) complexes, [MCl(PPh₃)₃] (M = Rh, Ir), with K[B₉H₁₄]. The same synthetic procedure, but using [MCl(CO)H(PPh₃)₃] (M = Ru, Os) as metal starting reagents produces the CO-ligated clusters, [6,6,6-(CO)(PPh₃)₂-nido-6-MB₉H₁₃] [M = Ru (3), Os (4)], in yields of 83% and 95%, respectively. These highly convenient syntheses permit the investigation of the reaction chemistry of the new nido-6-metalladecaboranes. Thus, the CO-ligated compounds, 3 and 4, react with the square-planar platinum(II) complex, [PtCl₂(PMe₂Ph)₂], in the presence of potassium triethylborohydride, to give the bimetallic clusters, [1,1,1-(CO)H(PPh₃)-isocloso-1-RuB₉H₈-μ-(1,2)-{Pt(PMe₂Ph)₂}] (5) and [7,7-(PMe₂Ph)₂-9,9,9-(CO)(PPh₃)₂-nido-7,9-PtOsB₉H₁₁] (6), and the monometallic nido-5-osamadecaborane, [5,5,5-(PPh₃)₂(CO)-nido-5-OsB₉H₁₃] (7). This reactivity illustrates the potential of polyhedral boron-based clusters as molecular scaffolds ("B-frames") for the construction of multimetallic species. Single-crystal X-ray diffraction analyses have revealed the molecular structures of 3, 5, 6 and 7; the compounds are also studied by multielement NMR spectroscopy, mass spectrometry, IR spectroscopy, and in some cases computationally. Futhermore, the rotation of the {M(X)(PR₃)₂} moiety (X = H, CO), as PH₃-ligated models, is studied by means of DFT-calculated relaxed potential energy surface scans, giving some insight into the lability of the metal-to-borane fragment interaction and of the exo-polyhedral ligands.

Structural Characterization of Unusual Fatty Acid Methyl Esters with Double and Triple Bonds Using HPLC/APCI-MS2 with Acetonitrile In-Source Derivatization

Double and triple bonds have significant effects on the biological activities of lipids. Determining multiple bond positions in their molecules by mass spectrometry usually requires chemical derivatization. This work presents an HPLC/MS method for pinpointing the double and triple bonds in fatty acids. Fatty acid methyl esters were separated by reversed-phase HPLC with an acetonitrile mobile phase. In the APCI source, acetonitrile formed reactive species, which added to double and triple bonds to form [M + C₃H₅N]^+• ions. Their collisional activation in an ion trap provided fragments helpful in localizing the multiple bond positions. This approach was applied to fatty acids with isolated, cumulated, and conjugated double bonds and triple bonds. The fatty acids were isolated from the fat body of early-nesting bumblebee Bombus pratorum and seeds or seed oils of Punicum granatum, Marrubium vulgare, and Santalum album. Using the method, the presence of the known fatty acids was confirmed, and new ones were discovered.

Access to cationic polyhedral carboranes via dynamic cage surgery with N-heterocyclic carbenes

Polyhedral boranes and heteroboranes appear almost exclusively as neutral or anionic species, while the cationic ones are protonated at exoskeletal heteroatoms or they are instable. Here we report the reactivity of 10-vertex closo-dicarbadecaboranes with one or two equivalents of N-heterocyclic carbene to 10-vertex nido mono- and/or bis-carbene adducts, respectively. These complexes easily undergo a reaction with HCl to give cages of stable and water soluble 10-vertex nido-type cations with protonation in the form of a BHB bridge or 10-vertex closo-type cations containing one carbene ligand when originating from closo-1,10-dicarbadecaborane. The reaction of a 10-vertex nido mono-carbene adduct with phosphorus trichloride gives nido-11-vertex 2-phospha-7,8-dicarbaundecaborane, which undergoes an oxidation of the phosphorus atom to P = O, while the product of a bis-carbene adduct reaction is best described as a distorted C₂B₆H₈ fragment bridged by the (BH)₂PCl₂⁺ moiety.

In comparison to their neutral or anionic counterparts, examples of cationic boron clusters remain scarce. Here, the authors prepare a variety of cationic polyhedral boranes by reacting closo-10-vertex carboranes with N-heterocyclic carbenes; the resulting open-cage cationic nido- arachno- or closo- derivatives are water soluble, which may enable unprecedented applications.

First Total Synthesis of Phytoprostanes with Prostaglandin-Like Configuration, Evidence for Their Formation in Edible Vegetable Oils and Orienting Study of Their Biological Activity

Phytoprostanes (PhytoP) are natural products, which form in plants under oxidative stress conditions from α-linolenic acid. However, their epimers with relative prostaglandin configuration termed phytoglandins (PhytoG) have never been detected in Nature, likely because of the lack of synthetic reference material. Here, the first asymmetric total synthesis of such compounds, namely of PhytoGF_1α (9-epi-16-F_1t -PhytoP) and its diastereomer ent-16-epi-PhytoGF_1α (ent-9,16-diepi-16-F_1t -PhytoP), has been accomplished. The synthetic strategy is based on radical anion oxidative cyclization, copper(I)-mediated alkyl-alkyl coupling and enantioselective reduction reactions. A UHPLC-MS/MS study using the synthesized compounds as standards indicates PhytoG formation at significant levels during autoxidation of α-linolenic acid in edible vegetable oils. Initial testing of synthetic PhytoGs together with F₁ -PhytoP and 15-F_2t -IsoP derivatives for potential interactions with the PGF_2α (FP) receptor did not reveal significant activity. The notion that PUFA-derived oxidatively formed cyclic metabolites with prostaglandin configuration do not form to a significant extent in biological or food matrices has to be corrected. Strong evidence is provided that oxidatively formed PhytoG metabolites may be ingested with plant-derived food, which necessitates further investigation of their biological profile.

Immunoprotective neo-glycoproteins: Chemoenzymatic synthesis of multivalent glycomimetics for inhibition of cancer-related galectin-3

Galectin-3 plays a crucial role in cancerogenesis; its targeting is a prospective pathway in cancer diagnostics and therapy. Multivalent presentation of glycans was shown to strongly increase the affinity of glycoconjugates to galectin-3. Further strengthening of interaction with galectin-3 may be accomplished using artificial glycomimetics with apt aryl substitutions. We established a new, as yet undescribed chemoenzymatic method to produce selective C-3-substituted N,N'-diacetyllactosamine glycomimetics and coupled them to human serum albumin. From a library of enzymes, only β-N-acetylhexosaminidase from Talaromyces flavus was able to efficiently synthesize the C-3-propargylated disaccharide. Various aryl residues were attached to the functionalized N,N'-diacetyllactosamine via click chemistry to assess the impact of the aromatic substitution. In ELISA-type assays with galectin-3, free glycomimetics exhibited up to 43-fold stronger inhibitory potency to Gal-3 than the lactose standard. Coupling to human serum albumin afforded multivalent neo-glycoproteins with up to 4209-fold increased inhibitory potency per glycan compared to the monovalent lactose standard. Surface plasmon resonance brought further information on the kinetics of galectin-3 inhibition. The potential of prepared neo-glycoproteins to target galectin-3 was demonstrated on colorectal adenocarcinoma DLD-1 cells. We investigated the uptake of neo-glycoproteins into cells and observed limited non-specific transport into the cytoplasm. Therefore, neo-glycoproteins primarily act as efficient scavengers of exogenous galectin-3 of cancer cells, inhibiting its interaction with the cell surface, and protecting T-lymphocytes against galectin-3-induced apoptosis. The present neo-glycoproteins combine the advantage of a straightforward synthesis, selectivity, non-toxicity, and high efficiency for targeting exogenous galectin-3, with possible application in the immunomodulatory treatment of galectin-3-overexpressing cancers.

One-Pot Synthesis of 2,5-Dihydrosiloles and Their Silole-Annulated Analogs Starting from Alkynylsilanes with a Terminal Alkynyl Group

In contrast to the reaction of vinyl(alkynyl)silanes with 9-BBN-H, leading to the quantitative formation of 5-R-4-(9-BBN)-2,3-dihydro-1H-siloles, treatment of bis(alkynyl)silanes bearing one terminal alkynyl group with 2 equiv of 9-BBN-H followed by methanolysis afforded 5-R-4-(9-BBN)-2,5-dihydro-1H-siloles with yields of 85-90% (by NMR integration). The reaction proceeds via a double 1,2-hydroboration of the terminal triple bond with the formation of the geminal diborane followed by ring closure via intramolecular 1,1-carboboration of the remaining alkynyl fragment. Depending on the nature of the substituent R in position 5, the allylic BBN group locates in position 3 (R = Ph) or position 5 (R = SiHMe₂, SiMe₃) to give 2,3- or 2,5-dihydrosiloles, respectively. The protodeborylation of the allylic BBN group with MeOH of both 3,4-(9-BBN)₂-2,3-dihydro- and 4,5-(9-BBN)₂-2,5-dihydrosiloles results in the exclusive formation of 4-(9-BBN)-2,5-dihydrosiloles. In all cases, the formation of 10-12% of 2-R-2,4-(9-BBN)₂-2,3-dihydrosilole minor isomers has been observed, which occurs from vicinal diboranes formed as side products by a second hydroboration of the terminal triple bond. Similarly, treatment of the tri- and tetraalkynes containing a terminal triple bond with 2 equiv of 9-BBN-H followed by treatment with methanol resulted in the high-yield formation of 1,2,6,6a-tetrahydro-1,6-disilapentalenes and 2,6,7,7a-tetrahydro-1,6,7-trisila-1H-cyclopenta[a]pentalenes, respectively.