Single-Crystal Cobalt Phosphide Nanorods as a High-Performance Catalyst for Reductive Amination of Carbonyl Compounds

The development of metal phosphide catalysts for organic synthesis is still in its early stages. Herein, we report the successful synthesis of single-crystal cobalt phosphide nanorods (Co₂P NRs) containing coordinatively unsaturated Co-Co active sites, which serve as a new class of air-stable, highly active, and reusable heterogeneous catalysts for the reductive amination of carbonyl compounds. The Co₂P NR catalyst showed high activity for the transformation of a broad range of carbonyl compounds to their corresponding primary amines using an aqueous ammonia solution or ammonium acetate as a green amination reagent at 1 bar of H₂ pressure; these conditions are far milder than previously reported. The air stability and high activity of the Co₂P NRs is noteworthy, as conventional Co catalysts are air-sensitive (pyrophorous) and show no activity for this transformation under mild conditions. P-alloying is therefore of considerable importance for nanoengineering air-stable and highly active non-noble-metal catalysts for organic synthesis.

Coexposure to Inhaled Aldehydes or Carbon Dioxide Enhances the Carcinogenic Properties of the Tobacco-Specific Nitrosamine 4-Methylnitrosamino-1-(3-pyridyl)-1-butanone in the A/J Mouse Lung

Tobacco smoke is a complex mixture of chemicals, many of which are toxic and carcinogenic. Hazard assessments of tobacco smoke exposure have predominantly focused on either single chemical exposures or the more complex mixtures of tobacco smoke or its fractions. There are fewer studies exploring interactions between specific tobacco smoke chemicals. Aldehydes such as formaldehyde and acetaldehyde were hypothesized to enhance the carcinogenic properties of the human carcinogen, 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) through a variety of mechanisms. This hypothesis was tested in the established NNK-induced A/J mouse lung tumor model. A/J mice were exposed to NNK (intraperitoneal injection, 0, 2.5, or 7.5 μmol in saline) in the presence or absence of acetaldehyde (0 or 360 ppmv) or formaldehyde (0 or 17 ppmv) for 3 h in a nose-only inhalation chamber, and lung tumors were counted 16 weeks later. Neither aldehyde by itself induced lung tumors. However, mice receiving both NNK and acetaldehyde or formaldehyde had more adenomas with dysplasia or progression than those receiving only NNK, suggesting that aldehydes may increase the severity of NNK-induced lung adenomas. The aldehyde coexposure did not affect the levels of NNK-derived DNA adduct levels. Similar studies tested the ability of a 3 h nose-only carbon dioxide (0, 5, 10, or 15%) coexposure to influence lung adenoma formation by NNK. While carbon dioxide alone was not carcinogenic, it significantly increased the number of NNK-derived lung adenomas without affecting NNK-derived DNA damage. These studies indicate that the chemicals in tobacco smoke work together to form a potent lung carcinogenic mixture.

Phytol derived from chlorophyll hydrolysis in plants is metabolized via phytenal

Phytol is the isoprenoid alcohol bound in ester linkage to chlorophyll, the most abundant photosynthetic pigment in plants. During leaf senescence, large amounts of phytol are released by chlorophyll degradation. However, the pathway of phytol catabolism in plants is unknown. We hypothesized that phytol degradation in plants might involve its oxidation into the long-chain aldehyde phytenal. Using GC-MS for aldehyde quantification after derivatization with methylhydroxylamine, phytenal was identified in leaves, whereas other long-chain aldehydes (phytanal and pristanal) were barely detectable. We found that phytenal accumulates during chlorotic stresses, for example, salt stress, dark-induced senescence, and nitrogen deprivation. The increase in the phytenal content is mediated at least in part independently of enzyme activities, and it is independent of light. Characterization of phytenal accumulation in the pao1 mutant affected in chlorophyll degradation revealed that phytenal is an authentic phytol metabolite derived from chlorophyll breakdown. The increase in phytenal was even stronger in mutants affected in the production of other phytol metabolites including vte5-2 (tocopherol deficient) and pes1 pes2 (fatty acid phytyl ester deficient). Therefore, phytenal accumulation is controlled by competing, alternative pathways of phosphorylation (leading to tocopherol production) or esterification (fatty acid phytyl ester production). As a consequence, the content of phytenal is maintained at low levels, presumably to minimize its toxic effects caused by its highly reactive aldehyde group that can form covalent bonds with and inactivate the amino groups of proteins.

Synthesis of 7,12-bis(4-(di(1H-pyrrol-2-yl)methyl)phenyl)benzo[k]fluoranthene from a new dialdehyde as a novel fluorometric bis-Dipyrromethane derivative

Dipyrromethanes are useful mediator structures which can be used as a part of other molecules such as bis-porphyrins and their derivations. Various methods have been developed for their synthesis. This study presents the synthesis of a new bis-dipyrromethane, 7,12-bis(4-(di(1H-pyrrol-2-yl)methyl)phenyl)benzo[k]fluoranthene, using the Lewis acid catalyzed reaction between a new dialdehyde and pyrrole at room temperature. The UV spectroscopic and fluorometric properties of the final product and precursors were determined. The newly synthesized product with desirable UV spectroscopic and fluorometric properties has the potential to be applied as a part of bis-porphyrins or it can be used for other purposes in future studies.

Patients Stratification Strategies to Optimize the Effectiveness of Scavenging Biogenic Aldehydes: Towards a Neuroprotective Approach for Parkinson's Disease

Parkinson’s disease (PD) is a clinically heterogeneous disorder with a multi-factorial pathology. Various molecular mechanisms are involved in the pathogenesis of PD, converging to oxidative stress and proteinopathy. The accumulation of reactive aldehydes (i.e., the dopamine metabolite DOPAL, lipid-peroxidation products, and advanced glycation end-products) has been reported in PD patients’ brains. Aldehydes easily react with primary amines such as lysine residues, which are involved in several regulatory processes in cells. Therefore, aldehyde adducts lead to severe consequences, including neuronal proteostasis, mitochondrial dysfunction, and cell death. In this review, we analyzed the scavenging role of amines toward toxic aldehydes in the brain. Interestingly, small molecules like metformin, rasagiline, hydralazine are already clinically available and used in the therapy for PD and other diseases. Hence, we propose to reevaluate this class of drugs as a disease-modifiers for PD, and we suggest that improved analysis of their pharmacology and bioavailability in the brain, together with a more precise patients stratification, should be considered before planning future clinical trials.

Cell-free in vitro reduction of carboxylates to aldehydes: With crude enzyme preparations to a key pharmaceutical building block

The scarcity of practical methods for aldehyde synthesis in chemistry necessitates the development of mild, selective procedures. Carboxylic acid reductases catalyze aldehyde formation from stable carboxylic acid precursors in an aqueous solution. Carboxylic acid reductases were employed to catalyze aldehyde formation in a cell-free system with activation energy and reducing equivalents provided through auxiliary proteins for ATP and NADPH recycling. In situ product removal was used to suppress over-reduction due to background enzyme activities, and an N-protected 4-formyl-piperidine pharma synthon was prepared in 61% isolated yield. This is the first report of preparative aldehyde synthesis with carboxylic acid reductases employing crude, commercially available enzyme preparations.

Ontogenesis of Aldehyde Pheromones in Two Synanthropic Bed Bug Species (Heteroptera: Cimicidae)

Bed bugs produce volatile aldehydes that have alarm and aggregation functions. Using two synanthropic bed bug species, Cimex lectularius L. and C. hemipterus (Fabricius), developmental changes were examined for (E)-2-hexenal, 4-oxo-(E)-2-hexenal, (E)-2-octenal, and 4-oxo-(E)-2-octenal, the four most abundant aldehydes shared between the two species. Quantitative analyses of the aldehydes in the nymphal exuviae indicated that the aldehydes' ratio remained similar throughout nymphal development. In general, (E)-2-octenal was most abundant, and (E)-2-hexenal and 4-oxo-(E)-2-octenal were least abundant. The fourth aldehyde, 4-oxo-(E)-2-hexenal, was present in intermediate quantities. The quantities and percent abundances of the aldehydes in nymphal exuviae and the adults were significantly different between C. lectularius and C. hemipterus. The ratio between (E)-2-hexenal and (E)-2-octenal was determined in adult male and female bed bugs of each species. Adult C. hemipterus had a higher proportion of (E)-2-hexenal than C. lectularius, while no sex differences were found. This work provides the first systematic quantification of four aldehydes [(E)-2-hexenal, 4-oxo-(E)-2-hexenal, (E)-2-octenal and 4-oxo-(E)-2-octenal] for all five of the nymphal stages for both C. lectularius and C. hemipterus.

NiFe2O4@SiO2 nPr@glucose catalyzed synthesis of novel 5-pyrazolin-1,2,4- triazazolidine-3-ones (thiones)

INTRODUCTION

NiFe2O4@SiO2nPr@glucose catalyzed synthesis of novel 5-pyrazolin-1,2,4-triazazolidine-3- ones (thiones).

MATERIALS AND METHODS

Amino glucose- functionalized silica- coated NiFe2O4 nanoparticles (NiFe2O4@SiO2 nPr@glucose amine or NiFe2O4@SiP@GA) were synthesized and characterized by X-ray powder diffraction (XRD), X-ray spectroscopy (EDX), transmission electron microscope (TEM), field emission scanning electron microscope (FE-SEM), vibrating sample magnetometry (VSM) and fourier transform infrared spectroscopy (FT-IR).

RESULTS AND DISCUSSION

NiFe2O4@SiP@GA supply an eco-friendly procedure for the synthesis of some novel 5- pyrazolin-1,2,4-triazazolidine-3-ones or thiones through one-pot reaction of thiosemicarbazide (hydrazinecarbothioamide) and synthetized pyrazole carbaldehydes. These compounds were obtained in high yields in short reaction times. The catalyst could be easily recovered and reused for six cycles with almost consistent activity. The structures of the synthesized 5-pyrazolin-1,2,4-triazazolidine-3-ones or thiones were confirmed by 1H NMR, 13C NMR and FTIR spectral data and elemental analyses.

CONCLUSION

In conclusion, we have investigated NiFe2O4@SiO2nPr@amino glucose as a new, eco-friendly, inexpensive, mild and reusable catalyst for the synthesis of 5-pyrazolin-1,2,4-triazazolidine-3-ones or thiones. High yield, a simple work- up procedure, adherence to the basics of green chemistry, environmental friendly and based on natural ingredients, ease of separation and recyclability of the magnetic catalyst and waste reduction are some advantages of this method.

α-Amidoaldehydes as Substrates in Rhodium-Catalyzed Intermolecular Alkyne Hydroacylation: The Synthesis of α-Amidoketones

We show that readily available α‐amidoaldehydes are effective substrates for intermolecular Rh‐catalyzed alkyne hydroacylation reactions. The catalyst [Rh(dppe)(C₆H₅F)][BAr^F₄] provides good reactivity, and allows a broad range of aldehydes and alkynes to be used as substrates, delivering α‐amidoketone products. High yields and high levels of regioselectivity are achieved. The use of α‐amidoaldehydes as substrates establishes that 1,4‐dicarbonyl motifs can be used as controlling groups in Rh‐catalyzed hydroacylation reactions.

Aldehyde Production in Crude Lysate- and Whole Cell-Based Biotransformation Using a Noncanonical Redox Cofactor System

It is challenging to biosynthesize industrially important aldehydes, which are readily consumed by the numerous alcohol dehydrogenases (ADHs) in cells. In this work, we demonstrate that a nicotinamide mononucleotide (NMN⁺)-dependent redox cofactor cycling system enables aldehyde accumulation in Escherichia coli crude lysates and whole cells. By specifically delivering reducing power to a recombinant enoate reductase, but not to endogenous ADHs, we convert citral to citronellal with minimal byproduct formation (97-100% and 83% product purity in crude lysate- and whole cell-based biotransformation, respectively). We envision the system's universal application to lowering the noise in biomanufacturing by silencing the host's metabolic background.

Green Synthesis of Thiazole Derivatives using Multi-component Reaction of Aldehydes, Isothiocyanate and Alkyl Bromides: Investigation of Antioxidant and Antimicrobial Activity

Aims & Objective: In this work, the multicomponent reaction of aldehydes, benzoylisothiocyanate and alkyl bromides in the presence of ammonium acetate, sodium cyanide and a catalytic amount of KF/Clinoptilolite nanoparticles (KF/CP NPs) in the water at 100oC was investigated.

MATERIALS AND METHODS

In these reactions, thiazole derivatives were produced in good to excellent yields and short time. Also, the antioxidant activity was studied for some newly synthesized compounds using the DPPH radical trapping and reducing of ferric ion experiments and comparing results with the synthetic antioxidants (TBHQ and BHT).

RESULTS

As a result, the compounds 4b showed excellent DPPH radical trapping and reducing the strength of ferric ion. These compounds have biological potential because of the thiazole core. For this reason, the antimicrobial activity of some synthesized compounds was studied by employing the disk diffusion test on Gram-positive bacteria and Gram-negative bacteria.

CONCLUSION

The results of the disk diffusion test showed that these compounds prevented bacterial growth.

Volatile Profile in Yogurt Obtained from Saanen Goats Fed with Olive Leaves

The aim of this study was to evaluate the development of volatile compounds in yogurt samples obtained from goats fed a dietary supplementation with olive leaves (OL). For this purpose, thirty Saanen goats were divided into two homogeneous groups of 15 goats each: a control group that received a standard diet (CG) and an experimental group whose diet was supplemented with olive leaves (OLG). The trial lasted 28 days, at the end of which the milk of each group was collected and used for yogurt production. Immediately after production, and after 7 days of storage at 4 °C in the absence of light, the yogurt samples were characterized in terms of fatty acid profile, oxidative stability and volatile compounds by the solid-phase microextraction (SPME)-GC/MS technique. Dietary OL supplementation positively affected the fatty acid composition, inducing a significant increase in the relative proportion of unsaturated fatty acids, mainly oleic acid (C18:1 cis9) and linolenic acid (C18:3). With regard to the volatile profile, both in fresh and yogurt samples stored for 7 days, the OL supplementation induced an increase in free fatty acids, probably due to an increase in lipolysis carried out by microbial and endogenous milk enzymes. Specifically, the largest variations were found for C6, C7, C8 and C10 free fatty acids. In the same samples, a significant decrease in aldehydes, mainly heptanal and nonanal, was also detected, supporting-at least in part-an improvement in the oxidative stability. Moreover, alcohols, esters and ketones appeared lower in OLG samples, while no significant variations were observed for lactones. These findings suggest the positive role of dietary OL supplementation in the production of goats' milk yogurt, with characteristics potentially indicative of an improvement in nutritional properties and flavor.

One-Step Dynamic Imine Chemistry for Preparation of Chitosan-Stabilized Emulsions Using a Natural Aldehyde: Acid Trigger Mechanism and Regulation and Gastric Delivery

Chitosan is a polysaccharide widely used as a structuring agent in foods and other materials because of its positive charge (amino groups). At present, however, it is difficult to form and stabilize emulsions using chitosan due to its high hydrophilicity. In this study, oil-in-water emulsions were prepared using a one-pot green-chemistry method. The chitosan and aldehyde molecules were in situ interfacially conjugated during homogenization, which promoted the adsorption of chitosan onto the oil droplet surfaces where they created a protective coating. The universality of this method was verified by using chitosan with different molecular weights and four kinds of natural aldehydes [cinnamaldehyde (CA), citral (CT), citronella (CN), and vanillin (VL)]. Chitosan with higher molecular weight facilitated the formation of emulsions. By harnessing the dynamic covalent nature of imine bonds, chitosan emulsions with an imine link display dynamic behavior with acid-catalyzed hydrolysis. The aldehyde structure could control the pH point of trigger for breakdown of emulsions, which was 1.0, 3.0, 4.0, and 4.0 for CA emulsion, CT emulsion, CN emulsion, and VL emulsion, respectively. At pH 6.5, aldehyde helped to decrease the interfacial tension of chitosan to about 10 mN/m, while this value would increase if the pH decreased by adding acid during the measurement. Chemical kinetics studies indicated that the hydrophobicity and conjugation effect of the aldehyde together determined the trigger points and properties of the emulsion. Finally, we used the optimized emulsions to encapsulate and control the release of curcumin. The gastric release behavior of the curcumin depended on aldehyde structure: VL > CN > CT ≈ CA. Hence, a tailor-made trigger release emulsion system can be achieved by rational selection and design of aldehyde structure to control hydrophobicity and conjugation effect of aldehydes.

Synthesis, Electrochemical and Spectroscopic Characterization of Selected Quinolinecarbaldehydes and Their Schiff Base Derivatives

A new approach to the synthesis of selected quinolinecarbaldehydes with carbonyl groups located at C5 and/or in C7 positions is presented in this paper in conjunction with spectroscopic characterization of the products. The classical Reimer-Tiemann, Vilsmeier-Haack and Duff aldehyde synthesis methods were compared due to their importance. Computational studies were carried out to explain the preferred selectivity of the presented formylation transformations. A carbene insertion reaction based on Reimer-Tiemann methodology is presented for making 7-bromo-8-hydroxyquinoline-5-carbaldehyde. Additionally, Duff and Vilsmeier-Haack reactions were used in the double formylation of quinoline derivatives and their analogues benzo[h]quinolin-10-ol, 8-hydroxy-2-methylquinoline-5,7-dicarbaldehyde, 8-(dimethylamino) quinoline-5,7-dicarbaldehyde and 10-hydroxybenzo[h]quinoline-7,9-dicarbaldehyde. Four Schiff base derivatives of 2,6-diisopropylbenzenamine were prepared from selected quinoline-5-carbaldehydes and quinoline-7-carbaldehyde by an efficient synthesis protocol. Their properties have been characterized by a combination of several techniques: MS, HRMS, GC-MS, FTIR, electronic absorption spectroscopy and multinuclear NMR. The electrochemical properties of 8-hydroxy-quinoline-5-carbaldehyde, 6-(dimethylamino)quinoline-5-carbaldehyde and its methylated derivative were investigated, and a strong correlation between the chemical structure and obtained reduction and oxidation potentials was found. The presence of a methyl group facilitates oxidation. In contrast, the reduction potential of methylated compounds was more negative comparing to non-methylated structure. Calculations of frontier molecular orbitals supported the finding. The structures of 8-hydroxy-2-methylquinoline-5,7-dicarbaldehyde and four Schiff bases were determined by single-crystal X-ray diffraction measurements.

Aldehydes as powerful initiators for photochemical transformations

Photochemistry, the use of light to promote organic transformations, has been known for more than a century but only recently has revolutionized the way modern chemists are thinking. Except from transition metal-based complexes, small organic molecules have been introduced as catalysts or initiators. In this review, we summarize the potential that (aromatic or aliphatic) aldehydes have as photoinitiators. The photophysical properties and photoreactivity of benzaldehyde are initially provided, followed by applications of aldehydes as initiators for polymerization reactions. Finally, the applications to date regarding aldehydes as photoinitiators in organic synthesis are presented.

Riley Oxidation of Heterocyclic Intermediates on Paths to Hydroporphyrins-A Review

Riley oxidation of advanced heterocyclic intermediates (dihydrodipyrrins and tetrahydrodipyrrins) is pivotal in routes to synthetic hydroporphyrins including chlorins, bacteriochlorins, and model (bacterio)chlorophylls. Such macrocycles find wide use in studies ranging from energy sciences to photomedicine. The key transformation (–CH₃ → –CHO) is often inefficient, however, thereby crimping the synthesis of hydroporphyrins. The first part of the review summarizes 12 representative conditions for Riley oxidation across diverse (non-hydrodipyrrin) substrates. An interlude summarizes the proposed mechanisms and provides context concerning the nature of various selenium species other than SeO₂. The second part of the review comprehensively reports the conditions and results upon Riley oxidation of 45 1-methyltetrahydrodipyrrins and 1-methyldihydrodipyrrins. A comparison of the results provides insights into the tolerable structural features for Riley oxidation of hydrodipyrrins. In general, Riley oxidation of dihydrodipyrrins has a broad scope toward substituents, but proceeds in only modest yield. Too few tetrahydrodipyrrins have been examined to draw conclusions concerning scope. New reaction conditions or approaches will be required to achieve high yields for this critical transformation in the synthesis of hydroporphyrins.

Key Male Glandular Odorants Attracting Female Ring-Tailed Lemurs

Among rodents, information about the external world is mainly acquired via the olfactory system, which is one of five sensory modalities. Several semiochemical signals are used for inter- and intraspecies communication [1]. In contrast, primates are generally regarded as vision-oriented mammals, and have been thought to trade their olfactory sensitivity for good sight. However, strepsirrhines have a well-developed olfactory system [2] and a larger repertoire of functional olfactory and vomeronasal receptor genes than haplorhines [3, 4]. Moreover, strepsirrhines are well known for their use of olfactory communication in social behavior. Ring-tailed lemurs are a species of Malagasy strepsirrhines, and use olfactory cues for conspecific communication. Male lemurs mark their scent by spreading volatiles from the antebrachial gland on their wrists. This study combined ethological and chemical approaches to identify a key odorant(s) in antebrachial secretions involved in the sexual communication of lemurs. The results of a behavioral assay indicated that females sniff the males' antebrachial secretions longer during the breeding season than during the nonbreeding season. By examining seasonal changes in volatiles using gas chromatography-mass spectrometry, we found that the secretion of three C12 and C14 aldehydes with a fruity and floral scent significantly increased during the breeding season in a testosterone-dependent manner. Females sniffed for longer at biologically relevant concentrations of two of the aldehydes (12-methyltridecanal and tetradecanal) and were attracted to a mixture of these plus the third aldehyde, dodecanal. Our results suggest that these aldehydes are putative lemur pheromones involved in the attractiveness of males to females during the breeding season.

Copper-catalyzed enantioselective conjugate addition of organometallic reagents to challenging Michael acceptors

The copper-catalyzed enantioselective conjugate addition (ECA) of organometallic nucleophiles to electron-deficient alkenes (Michael acceptors) represents an efficient and attractive methodology for providing a wide range of relevant chiral molecules. In order to increase the attractiveness of this useful catalytic transformation, some Michael acceptors bearing challenging electron-deficient functions (i.e., aldehydes, thioesters, acylimidazoles, N-acyloxazolidinones, N-acylpyrrolidinones, amides, N-acylpyrroles) were recently investigated. Remarkably, only a few chiral copper-based catalytic systems have successfully achieved the conjugate addition of different organometallic reagents to these challenging Michael acceptors, with excellent regio- and enantioselectivity. Furthermore, thanks to their easy derivatization, the resulting chiral conjugated products could be converted into various natural products. The aim of this tutorial review is to summarize recent advances accomplished in this stimulating field.

Allylic cross-coupling using aromatic aldehydes as α-alkoxyalkyl anions

The allylic cross-coupling using aromatic aldehydes as α-alkoxyalkyl anions is described. The synergistic palladium/copper-catalyzed reaction of aromatic aldehydes, allylic carbonates, and a silylboronate produces the corresponding homoallylic alcohol derivatives. This process involves the catalytic formation of a nucleophilic α-silyloxybenzylcopper(I) species and the subsequent palladium-catalyzed allylic substitution.

Deuteration of Formyl Groups via a Catalytic Radical H/D Exchange Approach

H/D exchange at formyl groups represents the straightforward approach to C-1 deuterated aldehydes. This transformation has been recently realized by transition metal and NHC carbene catalysis. Mechanistically, all these processes involve an ionic pathway. Herein we report a distinct photoredox catalytic, visible light mediated neutral radical approach. Selective control of highly reactive acyl radical in the energy barrier surmountable, reversible reaction enables driving the formation of deuterated products when an excess of D2O is employed. The power of the H/D exchange process has been demonstrated for not only aromatic aldehydes, but also aliphatic substrates, which have been difficult in transitional metal catalyzed H/D exchange reactions, and for selective late-stage deuterium incorporation into complex structures with uniformly high deuteration level (>90%).

Fe-catalyzed Decarbonylative Alkylative Spirocyclization of N-Arylcinnamamides: Access to Alkylated 1-Azaspirocyclohexadienones

For the convenient introduction of simple linear/branched alkyl groups into biologically important azaspirocyclohexadienones, a practical Fe-catalyzed decarbonylative cascade spiro-cyclization of N-aryl cinnamamides with aliphatic aldehydes to provide alkylated 1-azaspiro-cyclohexadienones was developed. Aliphatic aldehydes were oxidative decarbonylated into primary, secondary and tertiary alkyl radicals conveniently and allows for the subsequent cascade construction of dual C(sp³)-C(sp³) and C=O bonds via radical addition, spirocyclization and oxidation sequence.

Proteomic Profiling, Transcription Factor Modeling, and Genomics of Evolved Tolerant Strains Elucidate Mechanisms of Vanillin Toxicity in Escherichia coli

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is an economically important flavor compound that can be made in bacterial cell factories, but toxicity is a major problem for cells producing this aromatic aldehyde. Using (i) a global proteomic analysis supported by multiple physiological experiments, mutant analyses, and inferred transcription factor modeling and (ii) adaptive laboratory evolution (ALE) of vanillin tolerance combined with genome-wide analysis of the underlying mutations, mechanisms of vanillin toxicity in Escherichia coli have been elucidated. We identified 147 proteins that exhibited a significant change in abundance in response to vanillin, giving the first detailed insight into the cellular response to this aldehyde. Vanillin caused accumulation of reactive oxygen species invoking adaptations coordinated by a MarA, OxyR, and SoxS regulatory network and increased RpoS/DksA-dependent gene expression. Differential fumarase C upregulation was found to prevent oxidative damage to FumA and FumB during growth with vanillin. Surprisingly, vanillin-dependent reduction pf copper (II) to copper (I) led to upregulation of the copA gene and growth in the presence of vanillin was shown to be hypersensitive to inhibition by copper ions. AcrD and AaeAB were identified as potential vanillin efflux systems. Vanillin-tolerant strains isolated by ALE had distinct nonsynonymous single nucleotide polymorphisms (SNPs) in gltA that led to increased citrate synthase activity. Strain-specific mutations in cpdA, rob, and marC were also present. One strain had a large (∼10-kb) deletion that included the marRAB region. Our data provide new understanding of bacterial vanillin toxicity and identify novel gene targets for future engineering of vanillin-tolerant strains of E. coli IMPORTANCE A particular problem for the biotechnological production of many of the valuable chemicals that we are now able to manufacture in bacterial cells is that these products often poison the cells producing them. Solutions to improve product yields or alleviate such toxicity using the techniques of modern molecular biology first require a detailed understanding of the mechanisms of product toxicity. Here we have studied the economically important flavor compound vanillin, an aromatic aldehyde that exerts significant toxic effects on bacterial cells. We used high-resolution protein abundance analysis as a starting point to determine which proteins are upregulated and which are downregulated by growth with vanillin, followed by gene expression and mutant studies to understand the mechanism of the response. In a second approach, we evolved bacterial strains with higher vanillin tolerance. Their genome sequences have yielded novel insights into vanillin tolerance that are complementary to the proteomics data set.

Alcohol dehydrogenases from Proteus mirabilis contribute to alcoholic flavor

BACKGROUND

Cheese ripening involves a complex series of metabolic reactions and numerous concomitant secondary transformations. Alcohol dehydrogenase (ADH) converts aldehydes into their corresponding alcohols, which enrich cheese aroma.

RESULTS

In this study, we identified five ADH genes in Proteus mirabilis JN458, and these genes were overexpressed and characterized in Escherichia coli BL21 (DE3). The optimum pH was 7.0 for the purified recombinant ADH-1, ADH-2, and ADH-3 and 8.0 for ADH-4 and ADH-5. The optimum temperature was 40 °C for ADH-1, ADH-3, and ADH-5 and 45 °C for ADH-2 and ADH-4. The K_m value of ADH-1, ADH-2, and ADH-3 was 34.45, 16.90, and 10.01 µmol L^-1 for phenylacetaldehyde, respectively. The K_m value of ADH-4 and ADH-5 was 14.81 and 24.62 µmol L^-1 for 2-methylbutanal, respectively.

CONCLUSION

Proteus species play important roles during cheese ripening. The results of our study are important for further research on cheese flavor and for quality control during cheese production. © 2019 Society of Chemical Industry.

Enhancement in the Catalytic Activity of Human Salivary Aldehyde Dehydrogenase by Alliin from Garlic: Implications in Aldehyde Toxicity and Oral Health

BACKGROUND

Lower human salivary aldehyde dehydrogenase (hsALDH) activity increases the risk of aldehyde mediated pathogenesis including oral cancer. Alliin, the bioactive compound of garlic, exhibits many beneficial health effects.

OBJECTIVE

To study the effect of alliin on hsALDH activity.

METHODS

Enzyme kinetics was performed to study the effect of alliin on the activity of hsALDH. Different biophysical techniques were employed for structural and binding studies. Docking analysis was done to predict the binding region and the type of binding forces.

RESULTS

Alliin enhanced the dehydrogenase activity of the enzyme. It slightly reduced the Km and significantly enhanced the Vmax value. At 1 µM alliin concentration, the initial reaction rate increased by about two times. Further, it enhanced the hsALDH esterase activity. Biophysical studies indicated a strong complex formation between the enzyme and alliin (binding constant, Kb: 2.35 ± 0.14 x 103 M-1). It changes the secondary structure of hsALDH. Molecular docking study indicated that alliin interacts to the enzyme near the substrate binding region involving some active site residues that are evolutionary conserved. There was a slight increase in the nucleophilicity of active site cysteine in the presence of alliin. Ligand efficiency metrics values indicate that alliin is an efficient ligand for the enzyme.

CONCLUSION

Alliin activates the catalytic activity of the enzyme. Hence, consumption of alliincontaining garlic preparations or alliin supplements and use of alliin in pure form may lower aldehyde related pathogenesis including oral carcinogenesis.

Toxic trans-crotonaldehyde in mitochondria intercepted by oxyresveratrol contributing to anticancer

The aim of this study was to explore how the toxic trans-crotonaldehyde (TCA) in mitochondria or aldehyde dehydrogenase (ALDH) at different pHs was intercepted by oxyresveratrol (Oxy-Res) contributing to anticancer. Ultraviolet-visible (UV-vis) spectroscopy and Raman spectroscopy were employed. UV-vis spectra showed that the Oxy-Res red shifted the peak of the toxic TCA from 316 nm to 325 nm, while the peaks of the Oxy-Res shifted from 329 nm with 290 nm and 300 nm to 325 nm with 303 nm. In the mitochondria, the Oxy-Res blue shifted the peaks of the toxic TCA from 325 nm with 303 nm to 321 nm with 301 nm. Raman spectra revealed that the Oxy-Res caused shifting of the CHO of the toxic TCA from 1,689 cm^-1 to 1,671 cm^-1 with band decline. The CC of the toxic TCA at 1641 cm^-1 was split into 1,639 cm^-1 and 1,642 cm^-1 with band decline. The bands of the Oxy-Res at 1634 cm^-1 , 1,617 cm^-1 , and 1,595 cm^-1 disappeared. In the mitochondria, the CC of the toxic TCA at 1641 cm^-1 splitting disappeared. In ALDH, with the decrease of pH from 7.8 to 6.5, the CHO of the toxic TCA did not red shift from 1,689 cm^-1 to 1,674 cm^-1 up to pH 6.5. There was no change in the CC of the toxic TCA at 1640 cm^-1 in ALDH at different pHs. The conclusion of the study was that the CHO of the toxic TCA was intercepted by the Oxy-Res under the action of ALDH in the mitochondria, particularly at pH 7.8. © 2019 IUBMB Life, 2019.