Impact of whey protein hydrolysates on the formation of 2,5-dimethylpyrazine in baked food products.

Peptides have been reported to serve as precursors in the generation of alkylpyrazines, key aroma compounds in heated foods. Most previous studies, concerned with the generation of pyrazines via the Maillard reaction, were conducted using model systems of varying complexities. However, the formation of pyrazines in real food systems has received less attention. The aim of this study was to investigate the impact of adding protein hydrolysates as precursors for the generation of alkylpyrazines in baked food products such as bread and cookies. Two whey protein hydrolysates, obtained using either trypsin or proteinase from Aspergillus melleus, were used in the presented study. 2,5-Dimethylpyrazine was produced in both food systems. Therefore, its formation was quantitatively monitored using a stable isotope dilution assay. Additionally, sensory evaluation was performed. Results demonstrated that the addition of the protein hydrolysates were effective in promoting the generation of 2,5-dimethylpyrazine and other aroma compounds in two well-known food products.

The synthesis and in vitro biological evaluation of novel fluorinated tetrahydrobenzo[j]phenanthridine-7,12-diones against Mycobacterium tuberculosis.

Tuberculosis (TB) still has a major impact on public health. In order to efficiently eradicate this life-threatening disease, the exploration of novel anti-TB drugs is of paramount importance. As part of our program to design new 2-azaanthraquinones with anti-mycobacterial activity, various "out-of-plane" tetrahydro- and octahydrobenzo[j]phenanthridinediones were synthesized. In this study, the scaffold of the most promising hits was further optimized in an attempt to improve the bioactivity and to decrease enzymatic degradation. The rudiment bio-evaluation of a small library of fluorinated tetrahydrobenzo[j]phenanthridine-7,12-dione derivatives indicated no significant improvement of the bio-activity against intracellular and extracellular Mycobacterium tuberculosis (Mtb). Though, the derivatives showed an acceptable toxicity against J774A.1 macrophages and early signs of genotoxicity were absent. All derivatives showed to be metabolic stabile in the presence of both phase I and phase II murine or human microsomes. Finally, the onset of reactive oxygen species within Mtb after exposure to the derivatives was measured by electron paramagnetic resonance (EPR). Results showed that the most promising fluorinated derivative is still a possible candidate for the subversive inhibition of mycothione reductase.

Cocoa-specific flavor components and their peptide precursors.

Essential precursors of the cocoa-specific roasting-flavor notes were formed during proteolysis of the cocoa vicilin-class(7S) globulin by a mixture of cocoa aspartic protease and carboxypeptidase. These could be partially purified by ligand-exchange chromatography. Many constituents of this peptide fraction were destroyed by post-treatment with pepsin, but the cocoa-specific flavor-precursor peptides were largely resistant against pepsin treatment. However, these peptides were not generated when the cocoa vicilin-class(7S) globulin was digested with a mixture of pepsin and carboxypeptidase. By nano-liquid chromatography mass spectrometry, the peptide composition of these peptide fractions were compared in order to identify the putative precursors of the cocoa-specific flavor components. These peptides were assigned to five regions of the cocoa vicilin-class(7S) globulin. Analyzing the roasting products of the different protein fractions by headspace solid-phase microextraction, followed by gas chromatography mass spectrometry, eight volatile compounds were detected, whose occurrence correlated with the sensory detection of cocoa-specific flavor notes.

N-Acyl Homoserine Lactone Derived Tetramic Acids Impair Photosynthesis in Phaeodactylum tricornutum.

Marine bacteria contribute substantially to nutrient cycling in the oceans and can engage in close interactions with microalgae. Many microalgae harbor characteristic satellite bacteria, many of which participate in N-acyl homoserine lactone (AHL) mediated quorum sensing. In the diffusion-controlled phycosphere, AHLs can reach high local concentrations, with some of them transforming into tetramic acids, compounds with a broad bioactivity. We tested a representative AHL, N-(3-oxododecanoyl) homoserine lactone, and its tetramic acid rearrangement product on the diatom Phaeodactylum tricornutum. While cell growth and photosynthetic efficiency of photosystem II were barely affected by the AHL, exposure to its tetramic acid rearrangement product had a negative effect on photosynthetic efficiency and led to growth inhibition and cell death in the long term, with a minimum inhibitory concentration between 20 and 50 µΜ. These results strengthen the view that AHLs may play an important role in shaping the outcome of microalgae-bacteria interactions.

Impact of different enzymatic hydrolysates of whey protein on the formation of pyrazines in Maillard model systems.

The generation of pyrazines in model systems containing enzymatically hydrolyzed whey protein under dry heating conditions was studied. Pyrazines are important Maillard flavor compounds. Hydrolysates, obtained with different peptidases (pepsine, chymosine, thermolysin and a non-specific peptidase from Aspergillus melleus), contained a varying peptide profile and free amino acid content. The impact of each hydrolysate on the generation of flavor volatiles was measured by HS-SPME-GC/MS. The presence of oligopeptides had an enhancing role on the generation of pyrazines while, in contrast, free amino acids contributed to a lesser extent in pyrazine formation, except in the hydrolysate using the non-specific peptidase because of its high free amino acid content. Typically, 2,5(6)-dimethylpyrazine was the most abundant pyrazine found, although in the chymotripsine hydrolysate also other pyrazines were dominant. The hydrolysate obtained from the non-specific peptidase contained a larger variety of pyrazines, including the typical Strecker aldehydes originating from specific amino acids. This study demonstrates that oligopeptides are important Maillard flavor precursors.

Synthesis of 1,4-Oxazepane-2,5-diones via Cyclization of Rotationally Restricted Amino Acid Precursors and Structural Reassignment of Serratin.

Several natural products containing a 1,4-oxazepane-2,5-dione-core are known. One example is serratin, isolated from Serratia marcescens. Because of the presence of a carboxylic amide, which has a preference for a trans-conformation, and the presence of a labile lactone in this core, many synthetic methodologies commonly used for the cyclization toward medium-sized heterocycles cannot be applied. As N-acyl amino acids lacking a third substituent at nitrogen failed to undergo ring-closure, several N-protecting groups were evaluated. With the use of the removable PMB-group, an N-unsubstituted 1,4-oxazepane-2,5-dione was synthesized. Via the application of pseudoprolines (i.e. serine-derived oxazolidines as another type of protecting group), a compound with the presumed structure of the natural product serratin was obtained. As a result of the differences in spectral data, the incorrect structural assignment of the natural product serratin was identified. Instead of the predicted seven-membered heterocycle, a symmetrical serratamolide analogue is proposed to be the correct structure of serratin.

Detection and Toxicity Evaluation of Pyrrolizidine Alkaloids in Medicinal Plants Gynura bicolor and Gynura divaricata Collected from Different Chinese Locations.

Two edible plants in Southeast Asia, Gynura bicolor and G. divaricata, are not only known to be nutritive but also useful as medicinal herbs. Previous phytochemical investigation of Gynura species showed the presence of hepatotoxic pyrrolizidine alkaloids (PAs), indicating the toxic risk of using these two plants. The present study was designed to analyze the distribution of PA components and tried to evaluate the preliminary toxicity of these two Gynura species. Eight samples of G. bicolor and G. divaricata from five different Chinese locations were collected and their specific PAs were qualitatively characterized by applying an UPLC/MS/MS spectrometry method. Using a pre-column derivatization HPLC method, the total retronecine ester-type PAs in their alkaloids extracts were quantitatively estimated as well. Finally, their genotoxicity was investigated with an effective high-throughput screening method referred to as Vitotox™ test and their potential cytotoxicity was tested on HepG2 cells. It was found that different types of PAs were widely present in Gynura species collected from south of China. Among them, no significant genotoxic effects were detected with serial concentrations through the present in vitro assay. However, the cytotoxicity assay of Gynura plants collected from Jiangsu displayed weak activity at the concentration of 100 mg/ml. It is important to note that this research validates in part the indication that the use of Gynura species requires caution.

The Chemical Route to a Carbon Dioxide Neutral World.

Excessive CO2 emissions in the atmosphere from anthropogenic activity can be divided into point sources and diffuse sources. The capture of CO2 from flue gases of large industrial installations and its conversion into fuels and chemicals with fast catalytic processes seems technically possible. Some emerging technologies are already being demonstrated on an industrial scale. Others are still being tested on a laboratory or pilot scale. These emerging chemical technologies can be implemented in a time window ranging from 5 to 20 years. The massive amounts of energy needed for capturing processes and the conversion of CO2 should come from low-carbon energy sources, such as tidal, geothermal, and nuclear energy, but also, mainly, from the sun. Synthetic methane gas that can be formed from CO2 and hydrogen gas is an attractive renewable energy carrier with an existing distribution system. Methanol offers advantages as a liquid fuel and is also a building block for the chemical industry. CO2 emissions from diffuse sources is a difficult problem to solve, particularly for CO2 emissions from road, water, and air transport, but steady progress in the development of technology for capturing CO2 from air is being made. It is impossible to ban carbon from the entire energy supply of mankind with the current technological knowledge, but a transition to a mixed carbon-hydrogen economy can reduce net CO2 emissions and ultimately lead to a CO2 -neutral world.

Lithium Halomethylcarbenoids: Preparation and Use in the Homologation of Carbon Electrophiles.

α-Halomethyllithium carbenoids are useful homologating reagents which - reacting under proper reaction conditions as carbanions - enable the installation via nucleophilic addition of a reactive halomethyl fragment onto a preformed carbon-heteroatom bond. The pronounced thermolability represented - since seminal studies by Köbrich - the Achilles' heel of these reagents: the use of Barbier-type methodologies (i.e., the electrophile should be present in the reaction mixture prior to the formation of the carbenoid) was pivotal in order to suppress decomposition through α-elimination processes. Nowadays, the use of low temperatures (-78 °C) guarantees reliable procedures and, significantly, the employment of microreactor technologies allows external trapping to be performed even at higher temperatures as reported by Luisi. We will discuss the α-halomethyllithium-mediated homologations of a series of carbon electrophiles such as carbonyl compounds, imines, esters, Weinreb amides, and isocyanates.

The use of gas chromatography-mass spectrometry/combustion/isotope ratio mass spectrometry to demonstrate progesterone treatment in bovines.

Currently, no analytical method is available to demonstrate progesterone administration in biological samples collected in rearing animals, and therefore, tracking the abuse of this popular growth promoter is arduous. In this study, a method is presented to reveal progesterone (PG) treatment on the basis of carbon isotope measurement of 5ß-pregnane-3α, 20α-diol (BAA-PD), a major PG metabolite excreted in bovine urine, by gas chromatography-mass spectrometry/combustion/isotope ratio mass spectrometry (GC-MS/C/IRMS). 5-Androstene-3ß,17α-diol (AEdiol) is used as endogenous reference compound. Intermediate precisions (n=11) of 0.56‰ and 0.68‰ have been determined for AEdiol and BAA-PD, respectively. The analytical method was used for the very first time to successfully differentiate urine samples collected in treated and untreated animals.

LiAlH4 -Induced Selective Ring Rearrangement of 2-(2-Cyanoethyl)aziridines toward 2-(Aminomethyl)pyrrolidines and 3-Aminopiperidines as Eligible Heterocyclic Building Blocks.

2-(2-Cyanoethyl)aziridines and 2-aryl-3-(2-cyanoethyl)aziridines were deployed as substrates for an In(OTf)3 -mediated regio- and stereoselective ring rearrangement upon treatment with LiAlH4, affording a variety of novel 2-(aminomethyl)pyrrolidines and 3-aminopiperidines, respectively. Further synthetic elaboration of the obtained 3-aminopiperidines resulted in the formation of a peculiar and unexplored conformationally constrained imidazolidinone and diketopiperazine scaffold.

Simultaneous Detection of Androgen and Estrogen Abuse in Breeding Animals by Gas Chromatography-Mass Spectrometry/Combustion/Isotope Ratio Mass Spectrometry (GC-MS/C/IRMS) Evaluated against Alternative Methods.

The administration of synthetic homologues of naturally occurring steroids can be demonstrated by measuring (13)C/(12)C isotopic ratios of their urinary metabolites. Gas chromatography-mass spectrometry/combustion/isotope ratio mass spectrometry (GC-MS/C/IRMS) was used in this study to appraise in a global approach isotopic deviations of two 17ß-testosterone metabolites (17α-testosterone and etiocholanolone) and one 17ß-estradiol metabolite (17α-estradiol) together with those of 5-androstene-3ß,17α-diol as endogenous reference compound (ERC). Intermediate precisions of 0.35‰, 1.05‰, 0.35‰, and 0.21‰, respectively, were observed (n = 8). To assess the performance of the analytical method, a bull and a heifer were treated with 17ß-testosterone propionate and 17ß-estradiol-3-benzoate. The sensitivity of the method permitted the demonstration of 17ß-estradiol treatment up to 24 days. For 17ß-testosterone treatment, the detection windows were 3 days and 24 days for the bull and the heifer, respectively. The capability of GC-MS/C/IRMS to demonstrate natural steroid abuse for urinary steroids was eventually compared to those of mass spectrometry (LC-MS/MS) when measuring intact steroid esters in blood and hair.

Influence of Free Amino Acids, Oligopeptides, and Polypeptides on the Formation of Pyrazines in Maillard Model Systems.

Pyrazines are specific Maillard reaction compounds known to contribute to the unique aroma of many products. Most studies concerning the generation of pyrazines in the Maillard reaction have focused on amino acids, while little information is available on the impact of peptides and proteins. The present study investigated the generation of pyrazines in model systems containing whey protein, hydrolyzed whey protein, amino acids, and glucose. The impact of thermal conditions, ratio of reagents, and water activity (a(w)) on pyrazine formation was measured by headspace solid-phase microextraction with gas chromatography/mass spectrometry (HS-SPME-GC/MS. The presence of oligopeptides from hydrolyzed whey protein contributed significantly to an increased amount of pyrazines, while in contrast free amino acids generated during protein hydrolysis contributed to a lesser extent. The generation of pyrazines was enhanced at low a(w) (0.33) and high temperatures (>120 °C). This study showed that the role of peptides in the generation of pyrazines in Maillard reaction systems has been dramatically underestimated.

Natural flavonoids as potential herbal medication for the treatment of diabetes mellitus and its complications.

Diabetes mellitus, together with its various complications, is becoming a serious threat to human health. Natural products are secondary metabolites widely distributed in plants, having a broad range of biological activities. The development of antidiabetic medication from natural products, especially those originating from plants with a traceable folk-usage history in treating diabetes, is receiving more attention. Many studies highlighted not only the benefits of natural flavonoids with hypoglycemic effects, but also their importance in the management of diabetic complications. This review describes selected natural flavonoids that have been validated for their hypoglycemic properties, together with their mechanisms of action. Also discussed are their activities in the treatment of diabetic complications demonstrated via laboratory diabetic animal models, in vitro and clinical trials using human subjects. Published papers from 2000 to date on flavonoids and diabetes were covered through accessing Web of Science and multiple databases for biomedical sciences. The major potential benefits of natural flavonoids discussed in this review clearly suggest that these substances are lead compounds with sufficient structural diversity of great importance in the antidiabetic drug developing process.

Synthesis of 2-Fluoro-1,4-benzoxazines and 2-Fluoro-1,4-benzoxazepin-5-ones by Exploring the Nucleophilic Vinylic Substitution (S(N)V) Reaction of gem-Difluoroenamides.

N-Benzoyl ß,ß-difluoroenamides and N-benzoyl fluoroynamides are novel structural units which have been explored as precursors in heterocyclic synthesis. The presence of two fluorine atoms at the ß-position of the enamide moiety endows unique electrophilic reactivity. Treatment of these enamides with oxygen nucleophiles gives rise to a nucleophilic vinylic substitution (S(N)V) reaction, which was directed toward 2-fluoro-1,4-benzoxazines and 2-fluoro-1,4-benzoxazepin-5-ones. Furthermore, fluorinated ynamides, a new type of building block, were prepared in excellent yields for the first time. In this case, ß-addition of nucleophiles across the triple bond is observed also.

cis-Cyclopropylamines as mechanism-based inhibitors of monoamine oxidases.

Cyclopropylamines, inhibitors of monoamine oxidases (MAO) and lysine-specific demethylase (LSD1), provide a useful structural scaffold for the design of mechanism-based inhibitors for treatment of depression and cancer. For new compounds with the less common cis relationship and with an alkoxy substituent at the 2-position of the cyclopropyl ring, the apparent affinity determined from docking experiments revealed little difference between the enantiomers. Using the racemate, kinetic parameters for the reversible and irreversible inhibition of MAO were determined. No inhibition of LSD1 was observed. For reversible inhibition, most compounds gave high IC50 values with MAO A, but sub-micromolar values with MAO B. After pre-incubation of the cyclopropylamine with the enzyme, the inhibition was irreversible for both MAO A and MAO B, and the activity was not restored by dilution. Spectral changes during inactivation of MAO A included bleaching at 456 nm and an increased absorbance at 400 nm, consistent with flavin modification. These derivatives are MAO B-selective irreversible inhibitors that do not show inhibition of LSD1. The best inhibitor was cis-N-benzyl-2-methoxycyclopropylamine, with an IC50 of 5 nm for MAO B and 170 nm for MAO A after 30 min pre-incubation. This cis-cyclopropylamine is over 20-fold more effective than tranylcypromine, so may be studied as a lead for selective inhibitors of MAO B that do not inhibit LSD1.

Profiling and elucidation of the phenolic compounds in the aerial parts of Gynura bicolor and G. divaricata collected from different Chinese origins.

Gynura bicolor and G. divaricata are not only known to be nutritive as cultured vegetables, but also beneficial as folk medicines in East Asia. As demonstrated by the current phytochemical knowledge, the genus Gynura is a promising source of phenolics with multiple medicinal activities. To expand this phytochemical knowledge, the phenolic secondary metabolites of G. bicolor and G. divaricata were studied. From the aerial parts of these two species, collected in five different Chinese locations, two fractions of phenolic compounds with different polarity were obtained by extraction and chromatographic separation. Using UPLC/MS/MS analysis, a total of 53 phenolics were either identified by comparison with respective reference compounds or tentatively characterized by their chromatographic behavior, UV-absorption patterns, and MS fragmentations. Some naturally existing positional isomers of O-caffeoylquinic acid, O-p-coumaroylquinic acid, O-feruloylquinic acid, and dicaffeoylquinic acid as well as their methyl esters were qualitatively characterized by their specific fragmentation patterns in targeted MS/MS. In addition, the aerial parts of the two Gynura species contained kaempferol, quercetin oligoglycosides, and a variety of derivatives of benzoic acid, hydroxycinnamic acid, and caffeic acid. Furthermore, the distribution of phenolic compounds in the two species from different Chinese origins was discussed. Finally, an investigation of the total phenolic content and in vitro antioxidant activity of the various phenolic fractions was completed, to evaluate the potential of the extracts of these species for medicinal development. The free-radical-scavenging activities of the extracts derived from plants originating from Nanjing were proven to be higher than those of the other extracts, which correlated well with their total phenolic content.

New short and general synthesis of three key Maillard flavour compounds: 2-Acetyl-1-pyrroline, 6-acetyl-1,2,3,4-tetrahydropyridine and 5-acetyl-2,3-dihydro-4H-1,4-thiazine.

A new general synthetic route towards three key Maillard flavour compounds, namely 2-acetyl-1-pyrroline, 6-acetyl-1,2,3,4-tetrahydropyridine and 5-acetyl-2,3-dihydro-4H-1,4-thiazine, was developed. The key step in the process is the methylenation reaction of azaheterocyclic carboxylic esters by means of dimethyltitanocene, giving rise to intermediate vinyl ethers which can be considered as excellent and stable precursors for the title compounds, as a simple acidic treatment of these precursors suffices to release the characteristic Maillard flavours.

Synthesis and biological evaluation of novel N-α-haloacylated homoserine lactones as quorum sensing modulators.

Novel N-α-haloacylated homoserine lactones, in which a halogen atom was introduced at the α-position of the carbonyl function of the N-acyl chain, have been studied as quorum sensing (QS) modulators and compared with a library of natural N-acylated homoserine lactones (AHLs). The series of novel analogues consists of α-chloro, α-bromo and α-iodo AHL analogues. Furthermore, the biological QS activity of the synthetic AHL analogues compared to the natural AHLs was evaluated. Halogenated analogues demonstrated a reduced activity in the Escherichia coli JB523 bioassay, with the α-iodo lactones being the less active ones and the α-chloro AHLs the most potent QS agonists. Most of the α-haloacylated analogues did not exhibit a significant reduction when tested in the QS inhibition test. Therefore, these novel analogues could be utilized as chemical probes for QS structure-activity studies.