Decarboxylation Product Research Articles

Pore fluid evolution, distribution and water-rock interactions of carbonate cements in red-bed sandstone reservoirs in the Dongying Depression, China

The compositions, distribution and its interaction with rocks of the evolving pore fluids controls the distribution of carbonate cements and reservoir storage spaces. The reservoir quality of the red-bed sandstone reservoirs in the Dongying Depression was investigated by an integrated and systematic analysis including carbonate cement petrology, mineralogy, carbon and oxygen isotope ratios and fluid inclusions. The investigation was also facilitated by probing the mineral origins, precipitation mechanisms, pore fluid evolution and distribution, and water-rock interaction of carbonate cements and their influences on reservoir quality. Diagenetic-evolving fluids in the interbedded mudstones are the main source for the precipitation of calcite cements that completely fill the intergranular volume (CFIV calcite) with heavier oxygen and carbon isotopes. The ferro-carbonate cements in the reservoir sandstone are enriched in lighter carbon and oxygen isotopes. In addition to the cations released by the conversion of clay minerals in reservoirs, products of organic acid decarboxylation and the associated feldspar dissolution process provide important sources for such carbonate cementation. The carbon isotopes of CO2 and the oxygen isotopic composition of fluids equilibrated with the CFIV calcite, ferro-calcite, dolomite and ankerite cements indicate that the pore in the red-bed reservoirs experienced high salinity fluids, which evolved from the early-formed interbedded mudstones, through organic acid input and to organic acid decarboxylation. Pore fluids from nearby mudstones migrated from the edge to the centre of sandbodies, causing strong calcite cementation along the sandbody boundaries and forming tight cementation zones. Pore fluids associated with organic CO2 and acids and organic acid decarboxylation are mainly distributed in the internal portion of sandbodies, causing feldspar dissolution and precipitation of ferro-carbonate cements. The distribution of pore fluids caused the zonal distribution of carbonate cements in sandbodies during different periods. This may be advantageous to preserve the porosity of reservoirs as exemplified by the distribution of high-quality reservoirs in the red-bed sandbodies.

Canolol, tocopherols, plastochromanol‐8, and phytosterols content in residual oil extracted from rapeseed expeller cake obtained from roasted seed

Due to the high canolol content rapeseed oil is increasingly often pressed from seeds subjected to the roasting process. However, there is a lack of data on the contents of canolol in residual oil produced from cake, a by‐product of cold pressing. The aim of this study was to investigate the contents of bioactive substances contained in expeller cake generated in cold pressing of rapeseed oil from seeds roasted at a temperature of 140, 160, and 180°C for 5, 10, and 15 min. Contents of tocopherols, plastochromanol‐8, and canolol were analyzed using the NP‐HPLC‐FL method, while contents of phytosterols – by GC‐FID. Based on the recorded data it may be concluded that 180°C is the best temperature for seed roasting, since at that temperature the greatest amount of canolol is formed and most of it passes to oil in the course of cold pressing. Contents of tocopherols in the tested oils ranged from 88.48 to 90.51 mg/100 g. A lower tocopherol content was recorded in residual oil of the press cakes in comparison to cold‐pressed oil, particularly in the case of samples roasted at a temperature of 160 and 180°C. Content of PC‐8 was higher in residual oil by over 4 mg/100 g in comparison to cold‐pressed oil. Also the total content of phytosterols in oils produced by solvent extraction from cake was higher than in cold‐pressed oil. Contents of phytosterols ranged from 4141.9 to 4826.1 μg/g oil.Practical application: Rapeseeds increasingly often are subjected to roasting prior to the cold pressing process. During roasting canolol is formed, which as a product of decarboxylation of sinapic acid, more efficiently penetrates to oil in comparison to sinapic acid. However, there is no data concerning the amounts of canolol remained in press cake. This study investigated the effect of temperature of rapeseed roasting on the content of bioactive compounds (tocopherols, PC‐8, phytosterols, and canolol) in residual oil from press cake. Results recorded in this study facilitate selection of roasting parameters so that the lowest possible amounts of bioactive compounds are retained in cake and they rather pass to cold‐pressed oil, enriching it and indirectly contributing to an enhancement of its oxidative stability. On the other hand, these results show that the expeller cake (from roasted seeds) as a by‐product can be further treated as a good source of bioactive compounds including canolol. They can also be used as a practical supplement to animal feed.This study investigates the effect of rapeseed roasting at a temperature of 140, 160, and 180°C for 5, 10, and 15 min on the content of residual oil and its composition in terms of such bioactive substances as tocopherols, PC‐8, phytosterols, and canolol. It is seen that residual oil extracted from rapeseed cake subjected to roasting has lower contents of tocopherols (particularly in the case of samples roasted at 160 and 180°C). PC‐8 is more effectively extracted with an organic solvent, since its content in residual oil was by 4 mg/100 g higher than in cold‐pressed oil. Also the content of phytosterols is higher in residual oil than in cold‐pressed oil. Contents of phytosterols ranges from 4141.9 to 4826.1 mg/g oil. Based on the recorded data it may be concluded that 180°C is the best temperature for seed roasting, since at that temperature the greatest amount of canolol is formed and most of it passes to oil in the course of cold pressing.

Self-sufficient redox biotransformation of lignin-related benzoic acids with Aspergillus flavus.

Aromatic carboxylic acids are readily obtained from lignin in biomass processing facilities. However, efficient technologies for lignin valorization are missing. In this work, a microbial screening was conducted to find versatile biocatalysts capable of transforming several benzoic acids structurally related to lignin, employing vanillic acid as model substrate. The wild-type Aspergillus flavus growing cells exhibited exquisite selectivity towards the oxidative decarboxylation product, 2-methoxybenzene-1,4-diol. Interestingly, when assaying a set of structurally related substrates, the biocatalyst displayed the oxidative removal of the carboxyl moiety or its reduction to the primary alcohol whether electron withdrawing or donating groups were present in the aromatic ring, respectively. Additionally, A. flavus proved to be highly tolerant to vanillic acid increasing concentrations (up to 8 g/L), demonstrating its potential application in chemical synthesis. A. flavus growing cells were found to be efficient biotechnological tools to perform self-sufficient, structure-dependent redox reactions. To the best of our knowledge, this is the first report of a biocatalyst exhibiting opposite redox transformations of the carboxylic acid moiety in benzoic acid derivatives, namely oxidative decarboxylation and carboxyl reduction, in a structure-dependent fashion.

Reaction of 4-hydroxy-6H-1,3-oxazin-6-ones with guanidine. Synthesis of new 1,3,5-triazine derivatives

2-(2-Furyl)- and 2-(2-thienyl)-5-alkyl-4-hydroxy-6H-1,3-oxazin-6-ones react with guanidine in methanol in the presence of an equimolar amount of sodium methoxide to give previously unknown sodium 4-amino-6-hetaryl-1,3,5-triazin-2-ylacetates. The reactions of 2-(2-furyl)- and 2-(2-thienyl)-5-phenyl-4-hydroxy-6H-1,3-oxazin-6-ones with guanidine under analogous conditions are accompanied by decarboxylation, yielding 4-benzyl-6-hetaryl-1,3,5-triazin-2-amines. The corresponding decarboxylation products are also obtained by treatment of sodium 2-(4-amino-6-hetaryl-1,3,5-triazin-2-yl)propionates with aqueous HCl.

Reactions of Cg10062, a cis-3-Chloroacrylic Acid Dehalogenase Homologue, with Acetylene and Allene Substrates: Evidence for a Hydration-Dependent Decarboxylation.

Cg10062 is a cis-3-chloroacrylic acid dehalogenase (cis-CaaD) homologue from Corynebacterium glutamicum with an unknown function and an uninformative genomic context. It shares 53% pairwise sequence similarity with cis-CaaD including the six active site amino acids (Pro-1, His-28, Arg-70, Arg-73, Tyr-103, and Glu-114) that are critical for cis-CaaD activity. However, Cg10062 is a poor cis-CaaD: it lacks catalytic efficiency and isomer specificity. Two acetylene compounds (propiolate and 2-butynoate) and an allene compound, 2,3-butadienoate, were investigated as potential substrates. Cg10062 functions as a hydratase/decarboxylase using propiolate as well as the cis-3-chloro- and 3-bromoacrylates, generating mixtures of malonate semialdehyde and acetaldehyde. The two activities occur sequentially at the active site using the initial substrate. With 2,3-butadienoate and 2-butynoate, Cg10062 functions as a hydratase and converts both to acetoacetate. Mutations of the proposed water-activating residues (E114Q, E114D, and Y103F) have a range of consequences from a reduction in wild type activity to a switch of activities (i.e., hydratase into a hydratase/decarboxylase or vice versa). The intermediates for the hydration and decarboxylation products can be trapped as covalent adducts to Pro-1 when NaCNBH3 is incubated with the E114D mutant and 2,3-butadienoate or 2-butynoate, and the Y103F mutant and 2-butynoate. Three mechanisms are presented to explain these findings. One mechanism involves the direct attack of water on the substrate, whereas the other two mechanisms use covalent catalysis in which a covalent bond forms between Pro-1 and the hydration product or the substrate. The strengths and weaknesses of the mechanisms and the implications for Cg10062 function are discussed.

Hydrothermal decarboxylation of unsaturated fatty acids over PtSnx/C catalysts

Abstract Decarboxylation of fatty acids is a path to fuel-range hydrocarbons from renewable plant and seed oils. Pt/C is an effective hydrothermal catalyst for decarboxylating saturated fatty acids without added hydrogen, but it has shown low selectivity and activity for decarboxylating unsaturated fatty acids, which are prevalent in plant oils from soy and algae. To develop better decarboxylation catalysts, we compared three different Sn containing alloys, Pt3Sn/C, PtSn/C, and PtSn3/C, to Pt/C by performing batch reactions in liquid water at 350 °C for two hours with stearic (C18:0), oleic (C18:1), and linoleic (C18:2) acids. Pt/C gave yields of 0.70 ± 0.05, 0.16 ± 0.03, and 0.083 ± 0.009 for the C17 alkane, but none of the direct decarboxylation products (i.e., C17 alkenes), for the oleic and linoleic acid feeds. Stearic acid was the major byproduct from the unsaturated fatty acids. In contrast, the PtSnx/C catalysts provided two to three times higher C17 alkane yields at identical conditions. Experiments in D2O showed that water molecules were a source of hydrogen for saturation of the fatty acids. These results show that PtSnx alloys give better performance than Pt alone for the hydrothermal conversion of renewable fatty acids to fuel range hydrocarbons.

Biofuels production from hydrothermal decarboxylation of oleic acid and soybean oil over Ni-based transition metal carbides supported on Al-SBA-15

Several Ni-based transition metal carbide catalysts supported on Al-SBA-15 were studied for the hydrothermal decarboxylation of oleic acid and soybean oil to produce diesel range hydrocarbons with no added H2. The effect of pre-reduction, sub-critical, and super-critical water conditions on the catalyst activity and selectivity was investigated. Both the conversion of oleic acid and selectivity of decarboxylation products under super-critical conditions for each catalyst were about two times greater than at sub-critical conditions. In addition, the potential of these catalysts for utilizing aqueous phase reforming (APR) of glycerol for in situ H2 production to meet process demands was demonstrated. The performance of the catalysts increases with the addition of glycerol, especially for the NiWC/Al-SBA-15 catalyst. With the addition of glycerol, the NiWC/Al-SBA-15 catalyst showed greater conversion of oleic acid and selectivity to heptadecane; however, most of the oleic acid was hydrogenated to produce stearic acid. The highest conversion of oleic acid and selectivity for heptadecane was 97.3% and 5.2%, respectively. Furthermore, the NiWC/Al-SBA-15 catalyst exhibited good potential for hydrolyzing triglycerides (soybean oil) to produce fatty acids and glycerol, and then generating H2in situ from the APR of the glycerol produced. A complete conversion of soybean oil and hydrogenation of produced oleic acid were obtained over the NiWC/Al-SBA-15 at super-critical conditions.

Biochemical and spectroscopic properties of Brucella microti glutamate decarboxylase, a key component of the glutamate-dependent acid resistance system

In orally acquired bacteria, the ability to counteract extreme acid stress (pH⩽2.5) ensures survival during transit through the animal host stomach. In several neutralophilic bacteria, the glutamate-dependent acid resistance system (GDAR) is the most efficient molecular system in conferring protection from acid stress. In Escherichia coli its structural components are either of the two glutamate decarboxylase isoforms (GadA, GadB) and the antiporter, GadC, which imports glutamate and exports γ-aminobutyrate, the decarboxylation product. The system works by consuming protons intracellularly, as part of the decarboxylation reaction, and exporting positive charges via the antiporter.Herein, biochemical and spectroscopic properties of GadB from Brucella microti (BmGadB), a Brucella species which possesses GDAR, are described. B. microti belongs to a group of lately described and atypical brucellae that possess functional gadB and gadC genes, unlike the most well-known “classical” Brucella species, which include important human pathogens. BmGadB is hexameric at acidic pH. The pH-dependent spectroscopic properties and activity profile, combined with in silico sequence comparison with E. coli GadB (EcGadB), suggest that BmGadB has the necessary structural requirements for the binding of activating chloride ions at acidic pH and for the closure of its active site at neutral pH. On the contrary, cellular localization analysis, corroborated by sequence inspection, suggests that BmGadB does not undergo membrane recruitment at acidic pH, which was observed in EcGadB. The comparison of GadB from evolutionary distant microorganisms suggests that for this enzyme to be functional in GDAR some structural features must be preserved.

Changes in the content of canolol and total phenolics, oxidative stability of rapeseed oil during accelerated storage

An oil sample was prepared by cold‐pressing from untreated (UTRO) and microwave‐treated (MWRO) rapeseed, and tertiary butyl‐hydroquinone (TBHQ) was added to another oil from untreated rapeseed. Microwave pretreatment significantly increased the total phenolics and canolol contents, as well as the initial acid value (AV), peroxide value (PV), and p‐anisidine value (pAV) of oil (p<0.001). However, there was found to be a difference in the rate of increase of AV, PV, and pAV of oil during the autoxidation with the following order of all these values observed: UTRO > UTRO + TBHQ > MWRO. During storage, significant linear correlations (p<0.001) were found between the PV, pAV, and canolol content (PV vs. Canolol = −0.960 to −0.890; pAV vs. Canolol = −0.889 to −0.968), and the DPPH activity was also linearly and significantly correlated with the content of total phenolics and canolol in oils. (DPPH vs. Tatal phenolics = 0.910–0.945; DPPH vs. Canolol = 0.941–0.962; p<0.001). When the autoxidation test was completed (on the 10th wk), it was found that the contents of canolol and total phenolics in MWRO were the highest, followed by UTRO + TBHQ, and UTRO. These results indicate that the MWRO exhibited superior oxidative stability.Practical application: Canolol, also known as vinylsyringol, is a phenolic compound that has been identified as a decarboxylation product of sinapic acid, and this type of compounds is known for scavenging free radicals. In this study, we evaluated the changes occurring during storage in the contents of canolol and the total phenolics, oxidative stability, and antioxidant capacity of rapeseed oil and found good correlation among the canolol content, oxidative stability, and antioxidant capacity. Therefore, we can use canolol as a native antioxidant for rapeseed oil production in the future.Canolol in rapeseed and rapeseed oil that is formed by thermal decarboxylation of sinapic acid under microwave irradiation. Canolol formation has been shown to improve the oxidative stability of oil from microtreated rapeseed. The results showed a very good correlation between the level of primary oxidative products (peroxide values), secondary oxidative products (p‐anisidine values) and the contents of canolol in the rapeseed oil during storage. So, canolol has potential applications in oil storage.

Identification and quantification of canolol and related sinapate precursors in Indian mustard oils and Canadian mustard products

AbstractCanadian condiment yellow mustard seeds (also called white), oriental and brown mustard seeds and flour extracts and commercially produced Indian mustard oils were examined for bioactive phenolics primarily to identify the antioxidant properties. Phenolic compounds, namely sinapic acid, sinapoyl glucose and canolol, were quantified using high‐performance liquid chromatographic (HPLC) coupled with a diode array detector (DAD). Canolol was detected and confirmed in trace amounts for the first time in commercial oils that had not been preheated specific for canolol production, most likely due to heat applied during processing. Sinapic acid, sinapine and canolol derived from unheated/unroasted mustard seeds and canola extracts were confirmed utilizing HPLC‐DAD, ultra‐performance liquid chromatography‐tandem‐mass spectrometry (UPLC‐tandem‐MS) and nuclear magnetic resonance (NMR) spectroscopy.Practical applications: Oilseeds canola and mustard contain significant amounts of phenolic compounds, principally sinapic acid derivatives. The level and functionality of these phenolic is highly influenced by the processing conditions. In the current study, the phenolic composition of some commercial mustard seed, oil, meal and flour samples were profiled with special focus on the occurrence of canolol, the decarboxylation product of sinapic acid. This study suggests that optimizing the crushing, pressing, or extraction steps during processing is crucial to enrich mustard and canola products with benefits associated with these bioactives, especially canolol.The existence of sinapic acid derivatives was confirmed in the 70% aqueous methanolic extracts of commercial mustard products such as deheated mustard flour and oil. Extracts of mustard, in addition to canola, contain significant amounts of phenolics, mainly sinapine. Traditional ghani pressing, cold pressing and/or screw expeller pressing hold potential for enriching mustard and sinapate‐rich oil with benefits associated with canolol.

Amidoalkylation of Phosphorus Trichloride with Acetamide and Functionalized Cyclic Ketones-Evidence of Dominating Role of Side-Reactions

The course of the reaction between phosphorus trichloride, acetamide and ethyl oxoalkanecarboxylates was studied in terms of the production of side-products. When ethyl 2-oxocycloalkane- and 4-oxocyclohexanecarboxylates were used as substrates, not only mixtures of the expected products—aminophosphonocycloalkanecarboxylic acids and their ethyl esters but also the formation of three side-products, namely 1-aminocycloalkanephosphonic acids (products of decarboxylation of the latter ones) and 1-aminoethane-1,1-diphosphonic and 1-hydroxyethane-1,1diphosphonic acids (products of the reaction of substrate and solvent with phosphonylating agent) were observed. Ethyl 2-oxo-cyclooctanecarboxylate afforded the expected 2-amino-2-pohosphonocyclooctanecarboxylic acid in minute amounts. For comparison reactions of 1-butyloxocarbonyloxopiperidines afforded the desired aminopiperidinephosphonic acids in good yields and without formation of side-products.

Radiation effects on crystalline l-asparagine, revisited: Radical formation by EMR and periodic DFT after X-irradiation at 275 K

Radical formation by X-irradiation of single crystals of l-asparagine monohydrate at 275K has been investigated at 240K and 295K using Electron Paramagnetic Resonance (EPR), Electron Nuclear DOuble Resonance (ENDOR) and ENDOR-Induced EPR spectroscopic techniques. Free radical structures suggested by detailed analysis of the experimental data were assessed by Density Functional Theory calculations in a periodic approach. The combined experimental and computational evidence revealed three stable radical species at room temperature. Two of these could reliably be established as net H-abstracted species, one from the methylene group in the amino acid side chain and the second from the amino acid back-bone carbon atom. For the third room temperature radical species, a variety of deamination- and decarboxylation products were investigated and dismissed. Even if an unambiguous structure could not be established, this radical is tentatively suggested to descend from a side-chain O3-protonated amide anion by hydrogen atom transfer from the C3 to the C4 position.

ChemInform Abstract: Enantioselective Construction of Vicinal All‐Carbon Quaternary Centers via Catalytic Double Asymmetric Decarboxylative Allylation.

AbstractThe decarboxylation product (IIb) is a building block for the preparation of alkaloids like (‐)‐chimonanthine, (+)‐calycanthine, ent‐WIN 64821 and (‐)‐ditryptophenline.

The Molecular and Metabolic Influence of Long Term Agmatine Consumption

Agmatine (AGM), a product of arginine decarboxylation, influences multiple physiologic and metabolic functions. However, the mechanism(s) of action, the impact on whole body gene expression and metabolic pathways, and the potential benefits and risks of long term AGM consumption are still a mystery. Here, we scrutinized the impact of AGM on whole body metabolic profiling and gene expression and assessed a plausible mechanism(s) of AGM action. Studies were performed in rats fed a high fat diet or standard chow. AGM was added to drinking water for 4 or 8 weeks. We used (13)C or (15)N tracers to assess metabolic reactions and fluxes and real time quantitative PCR to determine gene expression. The results demonstrate that AGM elevated the synthesis and tissue level of cAMP. Subsequently, AGM had a widespread impact on gene expression and metabolic profiling including (a) activation of peroxisomal proliferator-activated receptor-α and its coactivator, PGC1α, and (b) increased expression of peroxisomal proliferator-activated receptor-γ and genes regulating thermogenesis, gluconeogenesis, and carnitine biosynthesis and transport. The changes in gene expression were coupled with improved tissue and systemic levels of carnitine and short chain acylcarnitine, increased β-oxidation but diminished incomplete fatty acid oxidation, decreased fat but increased protein mass, and increased hepatic ureagenesis and gluconeogenesis but decreased glycolysis. These metabolic changes were coupled with reduced weight gain and a curtailment of the hormonal and metabolic derangements associated with high fat diet-induced obesity. The findings suggest that AGM elevated the synthesis and levels of cAMP, thereby mimicking the effects of caloric restriction with respect to metabolic reprogramming.

Effect of metal ions on acetone dicarboxylic acid catalyzed peroxomonosulphate reactions

The oxidation of Fe(III), Ni(II) and Co(II) citrates by peroxomonosulphate (PMS) in the pH range 3.0–6.0 follows autocatalysis mechanism. The acetone dicarboxylic acid (ADC), the oxidative decarboxylation product from citrate, is found to catalyze the reaction. The added metal ions switch the reaction from the ADC catalyzed decomposition of PMS to the oxidation of citrates. Based on the results from alcohol quenching, a mechanism involving oxygen atom transfer is proposed.

Glycine Decarboxylase Is an Unusual Amino Acid Decarboxylase Involved in Tumorigenesis

Glycine decarboxylase (GLDC) is a metabolic oncogene that links glycine metabolism with tumorigenesis. In humans, GLDC is part of a multienzyme complex (which includes the lipoyl-containing H-protein) that couples the decarboxylation of glycine to the biosynthesis of serine. Details of the GLDC-catalyzed glycine decarboxylation reaction are critical to drug development but remain elusive. This is the first report on the mechanism of the GLDC-catalyzed reaction and shows that GLDC is an unusual PLP-containing α-amino acid decarboxylase that removes carbon dioxide from the glycine substrate without releasing the expected amine (methylamine, a metabolic precursor of toxic formaldehyde) as a product. In an unusual decarboxylation mechanism, the resulting aminomethyl moiety is instead transferred to an accessory H-protein. This study defines the role of H-protein in GLDC-catalyzed glycine decarboxylation. (1) H-Protein is not required for glycine decarboxylation but, instead, is required for the release of the aminomethyl moiety from the quinonoid adduct. (2) Glycine decarboxylation is reversible and presumably proceeds through a stable quinonoid intermediate. (3) The physiological product of glycine decarboxylation is H-protein-S-aminomethyl dihydrolipoyllysine and not methylamine (in the absence of H-protein, the aminomethyl moiety remains as a quinonoid adduct). Mechanistic insights obtained from this study will inform future efforts for targeted anticancer therapeutic development.

Identification of a proton-chloride antiporter (EriC) by Himar1 transposon mutagenesis in Lactobacillus reuteri and its role in histamine production

The gut microbiome may modulate intestinal immunity by luminal conversion of dietary amino acids to biologically active signals. The model probiotic organism Lactobacillus reuteri ATCC PTA 6475 is indigenous to the human microbiome, and converts the amino acid L-histidine to the biogenic amine, histamine. Histamine suppresses tumor necrosis factor (TNF) production by human myeloid cells and is a product of L-histidine decarboxylation, which is a proton-facilitated reaction. A transposon mutagenesis strategy was developed based on a single-plasmid nisin-inducible Himar1 transposase/transposon delivery system for L. reuteri. A highly conserved proton-chloride antiporter gene (eriC), a gene widely present in the gut microbiome was discovered by Himar1 transposon (Tn)-mutagenesis presented in this study. Genetic inactivation of eriC by transposon insertion and genetic recombineering resulted in reduced ability of L. reuteri to inhibit TNF production by activated human myeloid cells, diminished histamine production by the bacteria and downregulated expression of histidine decarboxylase cluster genes compared to those of WT 6475. EriC belongs to a large family of ion transporters that includes chloride channels and proton-chloride antiporters and may facilitate the availability of protons for the decarboxylation reaction, resulting in histamine production by L. reuteri. This report leverages the tools of bacterial genetics for probiotic gene discovery. The findings highlight the widely conserved nature of ion transporters in bacteria and how ion transporters are coupled with amino acid decarboxylation and contribute to microbiome-mediated immunomodulation.

Photodecarboxylation of N-Adamantyl- and N-Phenylphthalimide Dipeptide Derivatives

New dipeptide derivatives 1 and 3 were synthesized and their reactivity in the photochemical reaction of decarboxylation was investigated. The photodecarboxylation of N-adamantyl derivatives 1a and 1b and N-phenylphthalimide derivatives 3a and 3b probably takes place from the triplet excited state. The triplet excited state of 1a, 3a and 3b was characterized by laser flash photolysis. N-phenylphthalimides 3a and 3b undergo 2-5 times more efficient photodecarboxylation than N-adamantylphthalimides 1a and 1b. The aminoacid residue (Phe or Gly) at the C-terminus of the dipeptide does not influence the photodecarboxylation efficiency. Product selectivity in the photoreactions is determined by the conformation of the molecules. N-phenylphthalimides with the separated electron donor (carboxylate) and acceptor moiety (phthalimide) give only simple decarboxylation products, whereas N-adamantyl derivatives also give cyclization products.

Sinapic Acid and Its Derivatives: Natural Sources and Bioactivity

Sinapic acid is widespread in the plant kingdom (fruits, vegetables, cereal grains, oilseed crops, and some spices and medicinal plants) and as such is common in the human diet. Derivatives of sinapic acid are characteristic compounds in the Brassicaceae family. Sinapic acid shows antioxidant, antimicrobial, anti-inflammatory, anticancer, and anti-anxiety activity. 4-Vinylsyringol (a decarboxylation product of sinapic acid) is a potent antioxidative and antimutagenic agent which suppresses carcinogenesis and the induction of inflammatory cytokines. Sinapine (sinapoyl choline) is considered to be an acetylcholinesterase inhibitor which might have therapeutic applications in various disease treatments. Mainly due to their antioxidative activity, these compounds have been suggested for potential use in food processing, cosmetics, and the pharmaceutical industry, and this review aims to summarize current knowledge on the natural sources, chemistry, and biological activity of these substances.

GABAergic System in β-Cells: From Autoimmunity Target to Regeneration Tool

The γ-aminobutyric acid (GABA) is a product of decarboxylation of the amino acid glutamate mediated by the synthesizing enzyme glutamic acid decarboxylase (GAD) (1–3). Although GABA is a major inhibitory neurotransmitter of the brain, it is produced at high levels in pancreatic islets (4). β-Cells store GABA in synaptic-like microvesicles, and upon its secretion, GABA exerts many paracrine functions in pancreatic islets (4). While the total function of GABA in β-cells is incompletely understood (4), its synthesizing enzyme GAD is possibly one of the most significant pancreatic islet β-cell autoantigens (5). GAD is a primary target of autoantibodies, and anti-GAD antibodies are associated with the development of type 1 diabetes (T1D) (5). GABA activates three types of membrane receptors: GABAA and GABAC, which are ligand-gated Cl− channels, and GABAB, a ligand-gated Ca2+ or K+ channel (6). It has been demonstrated that β-cells mainly express the GABAB receptor (GABABR) and the GABAA receptor (GABAAR) and produce GABA through GAD (Fig. 1) (4); GABA colocalizes with insulin as shown by confocal microscopy (4,7). Activation of GABA receptors in islet β-cells increases insulin release (8), exerts protective and regenerative effects on islet β-cells (9), and reduces apoptosis in cultured islets (9). GABA has also been shown to increase DNA synthesis in the pancreatic cell line INS-1, and when injected in vivo it increased the number of Ki67+ islet β-cells (Fig. 1). Thus, GABA increases β-cell proliferation in vivo and in vitro, protects INS-1 cells from streptozotocin (STZ)-induced apoptosis, and prevents hyperglycemia in murine models of diabetes (9). FIG. 1. Regenerative and immunological abilities of the inhibitory neurotransmitter GABA. Extracellular glutamate, the precursor of …