Search

We evaluate here different analytical strategies for the chromatographic separation and determination of N-acetyl-5-methoxytryptamine (MEL) and its oxidative metabolites N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), N1-acetyl-5-methoxykynuramine (AMK) and cyclic 3-hydroxymelatonin (c3OHM) in cell culture samples. Two dimensional liquid chromatography (2D-LC) in the multiple heart-cutting mode was compared with regular 1D chromatographic separations of MEL and its oxidative metabolites. Our results showed that the use of trifluoroacetic acid (TFA) as mobile phase modifier was required to obtain a satisfactory resolution and peak shapes particularly for c3OHM. As TFA is not compatible with ESI ionization the application of the MHC mode was mandatory for a proper chromatographic separation. We evaluate also different internal standardization approaches based on the combined use of a surrogate standard (5-methoxytryptophol) and an internal standard (6-methoxytryptamine) for MEL quantification in cell culture samples obtaining unsatisfactory results both by 1D- and 2D-LC-ESI-MS/MS (from 9 ± 2 to 186 ± 38%). We demonstrate that only the application of isotope dilution Mass Spectrometry through the use of an in house synthesized

The synthesis of novel l-prolinal dithioacetal and its application as an organocatalyst for the direct Michael addition of cyclic ketones and acetophenone derivatives to trans-β-nitrostyrene and related compounds is described. The prolinal dithioacetal acts as effective catalyst in the case of cyclic ketones of different ring size, in particular five- and six-membered examples, as well as larger and smaller ring systems. High enantioselectivity and diastereoselectivity is observed for different substrates and trans-β-nitrostyrenes. Also, the first asymmetric syntheses of selected 2-methyl-4-nitro-1,3-diphenylbutan-1-one derivatives by application of the obtained organocatalyst is presented.

The Suzuki–Miyaura cross-coupling reactions between 2,3,5-tribromo-4,6-dimethylpyridine and ortho-methoxyphenyl or ortho-chlorophenyl boronic acids were studied. The use of limited amount of the boronic acid resulted in the regioselective formation of biarylated products. In the case of ortho-methoxy- and ortho-chloro substituted series, the complete arylation furnished stable at room temperature atropisomers of different stereochemistry. This result may be attributed to the presence of additional transition state stabilisation caused by the complexation of the palladium atom with ortho-methoxy group and this observation may be helpful in the stereoselective synthesis of analogous compounds. The structure of all obtained pyridine derivatives was unambiguously determined by NMR spectroscopy, as well as the single-crystal X-ray analysis. All compounds described are chiral entities and the presence of individual enantiomers were visualized by the NMR spectra with chiral solvating agent.

Cholinesterase inhibitors are potent therapeutics in the treatment of Alzheimer's disease. Among them, dual binding ligands have recently gained a lot of attention. We discovered novel dual-binding cholinesterase inhibitors, using “clickable” fragments, which bind to either catalytic active site (CAS) or peripheral anionic site (PAS) of the enzyme. Copper(I)-catalyzed azide-alkyne cycloaddition allowed to effectively synthesize a series of final heterodimers, and modeling and kinetic studies confirmed their ability to bind to both CAS and PAS. A potent acetylcholinesterase inhibitor with IC50 = 18 nM (compound 23g) was discovered. A target-guided approach to link fragments by the enzyme itself was tested using butyrylcholinesterase.

Podophyllotoxin (PPT) is an antimitotic drug used topically in the treatment of anogenital warts. Due to its toxicity it cannot be administered systemically as an anticancer agent. However, modified PPT derivatives such as etoposide and teniposide are used clinically as systemic agents. Thus, we invented novel PPT derivative KL3 that was synthesized by photocyclization. Earlier we have shown that KL3 has an anticancer effect in various cell lines. Here we compared the toxicity of KL3 vs PPT on non-cancerous normal human keratinocytes (HaCaT) and peripheral blood mononuclear cells (PBMC) showing that KL3 is less toxic than PPT to non-cancerous cells. At concentrations that neither induced cell death, nor affected cell cycle, KL3 in HaCaT cells evoked transient ultrastructural features of ER stress, swelling of mitochondria and elongation of cytoplasmic processes. Those changes partially reversed with prolonged incubation while features of autophagy were induced. PPT in equivalent concentrations induced HaCaT cell death by cell cycle arrest, intrinsic apoptosis and finally disintegration of cell membranes followed by secondary necrosis. In conclusion, we show that the KL3 derivative of PPT in contrast to PPT allows repair of normal keratinocytes and triggers mechanisms that restore non-tumor cell homeostasis.

Hybrid inhibitors of acetyl- and butyrylcholinesterase are compounds that combine structural motifs of two different classical inhibitors, leading to a dual binding ligand. A rapidly growing collection of those compounds involves a wide diversity of structural motifs, but the way of linking two active fragments and its impact on the affinity toward cholinesterases usually remains beyond the extent of investigation. We present hereby a detailed analysis of this aspect using melatonin-donepezil hybrids. A new series of compounds, in which two fragments are connected using a carbamate linker, exhibits excellent activity and selectivity toward butyrylcholinesterase.

Multiply arylated heterocycles are interesting structures with highly useful functions and fascinating optoelectronic and biological properties. Pyridines are an important class of compounds, playing a role in various fields of chemistry. When the pyridine ring is connected to other aromatic systems, novel stereochemical outcomes may arise. This work summarizes different methodologies applied for the synthesis of substituted arylpyridine derivatives and summarizes stereochemical phenomena resulting from atropisomerism present in certain arylated pyridines.1 Introduction2 Arylpyridines Containing meta- and para-Substituted Phenyl Groups2.1 Arylpyridine Derivatives as Amphetamine Analogues Markers2.2 Site-Selective Synthesis of Arylpyridines3 Atropisomerism in Arylpyridines Containing ortho-Substituted Phenyl Groups3.1 Synthesis of Arylpyridines Containing ortho-Substituted Phenyl Groups3.2 Other Methods for the Preparation of Arylated Pyridines4 Fully Substituted Pyridine Derivatives4.1 Site-Selective Synthesis of Fully Arylated Pyridines4.3 Atropisomerism in Densely Substituted Arylpyridines Containing ortho-Substituted Phenyl Groups5 Enantioselective Synthesis of Arylpyridine Derivatives6 Conclusion

Lignans are a well-known and widely distributed class of natural products with huge structural and biological diversity. They occur in many species of plants, at different levels of content, in eac...

The Stobbe condensation between 3′,4′,5′-trimethoxyacetophenone and a benzylidenesuccinate derived from piperonal gave the Z,E-2,3-bisbenzylidenesuccinate as the only product. Such regioselectivity was explained by considering the Newman’s projections of the transition states of this reaction. Introducing L-prolinol as a chiral auxiliary, macrolactonization and subsequent photocyclization of the atropoisomeric cyclic amide ester led to new cyclolignan analogue. By comparing the regioselectivity observed in this study with our previous results, some general rules regarding the photocyclization of chiral 2,3-bisbenzylidenesuccinates could be established.

The synthesis of new chiral N-monotosylated-1,2-diamines based on the (-)-menthol skeleton is presented. The elimination of HCl from neomenthyl chloride obtained from an Appel reaction led to p-menth-3-ene in excellent yield. Further functionalization of the double bond in p-menth-3-ene with chloramine-T gave the corresponding N-tosylaziridines, which upon reaction with sodium azide and subsequent reduction of the azide functional group, formed the 1,2-diamine system. The synthesized chiral ligands proved effective in the asymmetric transfer hydrogenation of aromatic ketones and an endocyclic imine.

Besides cell death, autophagy and cell senescence are the main outcomes of anticancer treatment. We demonstrate that tacrine-melatonin heterodimer C10, a potent anti-Alzheimer’s disease drug, has an antiproliferative effect on MCF-7 breast cancer cells. The main cell response to a 24 h-treatment with C10 was autophagy enhancement accompanied by inhibition of mTOR and AKT pathways. Significantly increased autophagy markers, such as LC3B- and ATG16L-positive vesicles, confirmed autophagy induction by C10. However, analysis of autophagic flux using mCherry-GFP-LC3B construct revealed inhibition of autophagy by C10 at the late-stage. Moreover, electron microscopy and analysis of colocalization of LC3B and LAMP-1 proteins provided evidence of autophagosome-lysosome fusion with concomitant inhibition of autolysosomal degradation function. After transient treatment with IC50 dose of C10 followed by cell culture without the drug, 20% of MCF-7 cells displayed markers of senescence. On the other hand, permanent cell treatment with C10 resulted in massive cell death on the 5th or 6th day. Recently, an approach whereby autophagy is induced by one compound and simultaneously blocked by the use of another one has been proposed as a novel anticancer strategy. We demonstrate that the same effect may be achieved using a single agent, C10. Our findings offer a new, promising strategy for anticancer treatment.

During the attempted photochemical cyclization of 2,3-bisbenzylidene-γ-hydroxybutyric acid cyclic amide ester, it was observed that a γ-butyrolactone ring was formed, which was concurrent with the release of the amine fragment from the amide. The process occurs with high yield giving rise to the formation of β-apopicropodophyllin and its regioisomer. Additional experiments confirmed the photochemical nature of this transformation, and that it is independent from the photocyclization of the benzylidene groups – a typical reactivity for the members of the fulgide family. In contrast to the latter UV-driven cyclization, the photochemical cleavage of the amide was proven to proceed under irradiation with visible light.

Natural (−)-menthol was applied to construction of mono-N-tosylated-1,2-diamine derivatives. The O-tosylation and elimination of the tosylate of the menthol intermediate led to trans-p-menth-2-ene. The unsaturated menth-2-ene was next transformed into a mixture of N-tosylaziridines, which upon reaction with sodium azide gave four isomeric azides. The reduction of the formed tosylazides on Pd/C gave new chiral mono-N-tosylated-1,2-diamines, which were used as ligands in the asymmetric transfer hydrogenation protocol on aromatic ketones and endocyclic imine.

The first synthesis of sterically demanding, stable at room temperature atropisomeric derivatives of penta-(ortho-substituted phenyl)pyridines is described. The Suzuki-Miyaura cross-coupling reaction of pentabromopyridine and selected meta- and ortho-tolylboronic acids afforded a series of pentaarylpyridine derivatives. The structures of two room temperature stable atropisomeric derivatives of penta-(o-tolyl)pyridines were confirmed by single-crystal X-ray analysis. Racemic atropisomers were examined by 1H NMR spectroscopy with a chiral solvating agent in order to visualize the presence of individual enantiomers.

The Suzuki–Miyaura cross-coupling reaction of 3,5-dibromo-2,4,6-collidine and bromo derivatives of 2,6- and 2,4-lutidine with several ortho-substituted boronic acids produced a library of arylated pyridines. The reaction conditions were carefully optimized to allow high yield of the desired products. In several cases the presence of stable atropisomers were detected, even at elevated temperature during GC–MS analysis. Some of the diastereomers were isolated and characterized by spectroscopic methods and X-ray crystallography. Racemic forms of selected samples were tested by 1H NMR spectroscopy in the presence of chiral solvating agents in order to visualize the presence of individual enantiomers.

Melatonin is metabolized in animals to cyclic 3-hydroxymelatonin (3-OHM) not by an enzymatic pathway, but by interaction with hydroxyl radicals. The production of 3-OHM in animals suggests the possible presence of 3-OHM in plants. Prior to the identification of 3-OHM in plants, we directly cloned the corresponding gene(s) responsible for 3-OHM synthesis using Escherichia coli library strains expressing genes belonging to the 2-oxoglutarate-dependent dioxygenase (2-ODD) superfamily from rice. Three of 35 E. coli library strains supplemented with 1 mmol/L melatonin were found to produce 3-OHM in their extracellular medium, suggestive of three 2-ODD genes involved in 3-OHM production. The purified recombinant 2-ODD 11, 2-ODD 26, and 2-ODD 33 proteins were shown to catalyze the metabolism of melatonin to 3-OHM, with 2-ODD 11 showing the highest melatonin 3-hydroxylase (M3H) catalytic activity. Consistent with the presence of M3H genes, rice leaves supplemented with 5 mmol/L melatonin produced 3-OHM [233 μg/g fresh weight (FW)], 2-hydroxymelatonin (21 μg/g FW), and N1 -acetyl-N2 -formyl-5-methoxykynuramine (5 μg/g FW). Three M3H transcripts were induced upon the treatment of rice leaves with cadmium followed by an increase in M3H enzyme activity. Cloning of M3H genes in plants has paved the way for the studies of melatonin in plants in terms of its multiple physiological roles.

The Suzuki–Miyaura reaction of 4-amino-3,5-dibromo-2,6-lutidine with various ortho-substituted phenylboronic acids resulted in the formation of a series of mono- and diarylated lutidines in the form of atropisomers. The absolute stereochemistry of the chiral compounds was established, in some cases, by X-ray crystal structure analysis and HPLC-ECD (ECD = electronic circular dichroism) in combination with time-dependent density functional theory (TDDFT) calculations.

A series of differently substituted 3,5-diaryl-2,4,6-trimethylpyridines were prepared and characterized using the Suzuki–Miyaura coupling reaction with accordingly selected bromo-derivatives and arylboronic acids. The reaction conditions were carefully optimized allowing high yield of isolated products and also the construction of unsymmetrically substituted diarylpyridines, difficult to access by other methods.

The gut microbiota-derived metabolites of ellagitannins and green tea catechins, urolithin A (uroA) and 5-(3′,4′,5′-trihydroxyphenyl)-γ-valerolactone (M4), respectively, are among the main compounds absorbed into human system after ingestion of these polyphenols. The aim of this study was to establish the effects of M4, uroA, and their combinations on LNCaP cells, an androgen dependent prostate cancer in vitro model.. The LNCaP cells were incubated with increasing concentrations of tested metabolites. The cell proliferation was determined by measurement of DNA-bisbenzimide H 33 258 complexes fluorescence. The isobolographic analysis was used to establish the type of interaction between metabolites. The apoptosis, androgen receptor (AR) localization, and phosphorylation of Akt kinase were measured by flow cytometry. Prostate-specific antigen (PSA) secretion was determined by ELISA. M4 showed modest antiproliferative activity in LNCaP cells (IC50 = 117 µM; CI: 81 – 154). UroA decreased proliferation (IC50 = 32.7 µM; CI: 24.3 – 41.1) and induced apoptosis of LNCaP cells. The mixture of M4 with uroA had synergistic antiproliferative effect. Moreover, M4 potentiated inhibition of PSA secretion and enhanced retention of AR in cytoplasm caused by uroA. Interestingly, uroA increased levels of pSer473 Akt in LNCaP cells. These results show that colonic metabolites may contribute to chemoprevention of prostate cancer by varied polyphenol-rich diet or composite polyphenol preparations.

This study is a continuation of a research program aimed at identifying potent drugs against bacterial infections, in which a series of organic compounds: dicarboxylic acid imides and thioimides, isoquinoline derivatives and open chain compounds, were examined for antimicrobial properties against Staphylococcus auneus and Escheiichia coli. In effect of this investigation, the most active compounds (35-40, 47) were selected for in vitiv tests against fourteen clinically important pathogenic isolates, the methicillin resistant Staphylococcus aueus (MRSA) and several reference Gram-negative bacteria: Prteus vulgaris, Pseudomonas aeruginosa, Klebsiella pneumonia, Stenonophoinonas inaltophilia, and Acinetobacter baumannii. The obtained data revealed that seven compounds (three dithioimides, 35, 39, 47, and four thioimides, 36-38, 40) exhibit effective antibacterial activity against the tested Staphylococcus auirus MSSA and MRSA strains. Among them, dicarboxylic acid thioimides 37 and 38 were proven to be the most active.

We have developed a strategy for the stereoselective synthesis of cyclolignans related to podophyllotoxin and its derivatives. The crucial step of the synthesis is the photocyclization of a chiral atropoisomeric 1,2-bisbenzylidenesuccinate amide ester, which can be prepared from suitable aromatic aldehydes, diethyl succinate and l-prolinol. The photocyclization was found to be more efficient when irradiation was performed in a home-built continuous flow photochemical reactor. The in-flow irradiation also allowed us to perform the reaction on a multigram scale. The chiral auxiliary was removed by reductive cleavage with the Schwartz's reagent to give the cytotoxic 1R,2R-cis-podophyllic aldehyde, which in turn could be easily reduced to the corresponding alcohol, completing the formal synthesis of (-)-podophyllotoxin.

Isoprenoids, as common constituents of all living cells, are exposed to oxidative agents—reactive oxygen species, for example, singlet oxygen or hydroxyl radicals. Despite this fact, products of oxidation of polyisoprenoids have never been characterized. In this study, chemical oxidation of isoprenoid alcohols (Prenol-2 and -10) was performed using singlet oxygen (generated in the presence of hydrogen peroxide/molybdate or upon photochemical reaction in the presence of porphyrin), oxygen (formed upon hydrogen peroxide dismutation) or hydroxyl radical (generated by the hydrogen peroxide/sonication, UV/titanium dioxide or UV/hydrogen peroxide) systems. The structure of the obtained products, hydroxy-, peroxy- and heterocyclic derivatives, was studied with the aid of mass spectrometry (MS) and nuclear magnetic resonance (NMR) methods. Furthermore, mass spectrometry with electrospray ionization appeared to be a useful analytical tool to detect the products of oxidation of isoprenoids (ESI–MS analysis), as well as to establish their structure on the basis of the fragmentation spectra of selected ions (ESI–MS/MS analysis). Taken together, susceptibility of polyisoprenoid alcohols to various oxidizing agents was shown for the first time. Electronic supplementary material The online version of this article (doi:10.1007/s11745-015-4104-y) contains supplementary material, which is available to authorized users.

A series of new N-aryl-substituted thiomorpholine-3,5-diones were synthesized. Crystal structures of seven compounds were established on the basis of X-ray crystallography. Stable at room temperature diastereomers were detected for (2-phenyl)-substituted derivatives using 1H NMR. The dynamic stereochemistry of compound 36 was studied with variable-temperature 1H NMR and the mechanism of diastereomers interconversion was proposed on the basis of quantum chemical calculations.

A simple synthetic procedure for the preparation of mono-N-tosylated-1,2-diamines derived from (+)-3-carene is described. (+)-3-Carene is transformed into the corresponding N -tosylaziridine derivative using chloramine-T trihydrate. Subsequent ring opening with sodium azide followed by reduction of the azide function gives the optically pure mono-N-tosylated-1,2-diamine. This ligand is effective in asymmetric transfer hydrogenations of aromatic ketones. It can also be transformed into other chiral ligands by alkylation of the amino group for application in the addition of diethylzinc to benzaldehydes.

Synthesis, structural studies and the use of the (−)-(S)- and (+)-(R) enantiomers of t-butylphenylphosphinothioic acid as a chiral solvating agent for the determination of enantiomeric purity is discussed. Systems that are the most extensively studied are emphasized.

Suzuki reaction of tribromo-2,6-lutidine with (2-methoxyphenyl)boronic acid gave 3,4,5-tris(2-methoxyphenyl)-2,6-lutidine in the form of a mixture of three atropisomers that were stable at room temperature. Each isomer was isolated and fully characterized, including by X-ray structure determination. One of the isomers, being a racemic mixture, was separated into individual enantiomers by using semipreparative chiral HPLC. Their absolute stereochemistry was initially assigned on the basis of computational calculation of the CD spectra and finally confirmed by X-ray analysis.

In this study, we synthesized several imperatorin analogs using imperatorin and xanthotoxin as substrates. The anti-cholinesterase activities of all compounds were evaluated in in vitro experiments according to the modified Ellman's method. For each synthesized compound, IC50 values for both enzymes were established. Galantamine hydrobromide was used as a positive control in the enzymatic experiments. All active compounds showed selectivity toward butyrylcholinesterase (BuChE) rather than acetylcholinesterase. The most active ones were 8-(3-methylbutoxy)-psoralen and 8-hexoxypsoralen with IC50 values for BuChE of around 16.5 and 16.4 µM, respectively. The results of our study may be considered as the beginning of a search for potential anti-Alzheimer's disease drugs based on the structure of natural furocoumarins.

The highly functionalized tetrahydropyridine 4 was obtained in an indium(III) chloride catalyzed multi-component reaction from benzaldehyde, 4-methoxyaniline, and ethyl acetoacetate (=ethyl 3-oxobutanoate) in the presence of [1,1′-binaphthalene]-2,2′-diol (binol). It was found that binol played a beneficial role in this reaction, allowing a substantial decrease of the amount of indium salt. Also, simple organic Bronsted acids may serve as effective organocatalysts in this process.

A synthetic procedure leading to the preparation of a new family of enantiopure mono-N-tosylated-1,2-diamines derived from (R)-(+)-limonene is described. (+)-Limonene was transformed into the appropriate N-tosyl derivative using N-tosylaziridination based on chloramine-T trihydrate. Subsequent ring opening by sodium azide afforded the corresponding isomeric azides. Finally, reduction of the azide function gave enantiomerically pure mono-N-tosylated-1,2-diamines. The ligands obtained proved to be effective in the asymmetric transfer hydrogenation protocol on aromatic ketones and imines.

A series of differently substituted 3,5-diaryl-2,4,6-trimethylpyridines were prepared and characterized using the Suzuki–Miyaura coupling reaction with accordingly selected bromo-derivatives and arylboronic acids. The reaction conditions were carefully optimized allowing high yield of isolated products and also the construction of unsymmetrically substituted diarylpyridines, difficult to access by other methods.

Novel inhibitors of cholinesterases, especially butyrylcholinesterase (BuChE), were obtained by coupling melatonin-tacrine heterodimers via the carbamate bond. Compounds 14a-i possessed potent cholinesterase inhibitory activity (with IC50 values as low as 1.18 nM for acetylcholinesterase (AChE) and 0.24 nM for butyrylcholinesterase (BuChE)). These heterodimers exhibit selectivity toward BuChE, being from 4- to 256-fold more active toward BuChE than AChE, but still acting as better AChE inhibitors than tacrine 4.

( R )-(+)-Limonene was transformed into mono- N -tosylated-1,2-diamine derivatives using an N -tosylaziridination procedure followed by sodium azide treatment and reduction on Pd/C. The ligands obtained proved effective in the asymmetric transfer hydrogenation protocol on aromatic ketones.

A mild and efficient method for the synthesis of fulgimides is presented in which the peptide coupling reagent BOP is employed for dehydratation of fulgenic acid monoamides (succinamic acids). The disclosed method proved to be superior to those described in the literature.

Five perfluorocompounds [perfluoropentane, 4-(perfluoroethoxy)-perfluorobutane, 5-(perfluoroethyl)-perfluorotetrahydrofuran, 2-(trifluoromethyl)-perfluorotetrahydropyran, and 4-(trifluoromethyl)-perfluorotetrahydropyran] were analyzed by electron ionization (EI) and chemical ionization (CI), using methane and isobutane as reagent gases. Under CI conditions, isobutane does not lead to significative results whereas methane leads to high ionic yields [with respect to both CI (isobutane) and EI]. Under EI conditions, practically only fragment ions are observed, with the complete loss of molecular weight. In contrast under CI(CH4) conditions, [M–F]+ ions are produced. Under these conditions, the behavior of oxygen-containing molecules is strongly different from that of perfluoropentane. This is because oxygen can greatly stabilize the formation of the [M–F]+ carbocation by a π-electron donor effect, especially in the case of cyclic structures. Moreover, π-stabilization can be considered a useful tool to rationalize the position of tertiary carbon atom in trifluoromethyl-perfluoro-pyrane isomeric ions. The experimental data formed the starting point for the theoretical calculation, which allowed us to explore the mechanisms of the reactions of CH5+ ions with selected perfluorocompounds. The computational methods used show that a direct protonation of the perfluoroethers (PFEs) by CH5+ as well as iBu+ is very unlikely. In the theoretical calculations, the PFE molecule served rather as the F− donor, and the elimination of HF molecule occurred when the PFE molecule was placed close to H+ or CH5+ ions. The fact that the latter is very unstable and decomposes to a proton and methane molecule explains why the use of methane in CI is so successful in the generation of [M–F]+ ion. In contrast, the isobutonium cation rearranges to an isopropyl cation/methane complex rather than that it abstracts F− from the PFE molecule. Similar results can be expected for other PFEs and perfluoroalkanes (PFAs) because both CH5+ and H+ were able to abstract the HF molecule also by attacking along the perfluoroalkyl chain of the PFE. Copyright © 2011 John Wiley & Sons, Ltd.