Wittig Reactions in Water Media Employing Stabilized Ylides with Aldehydes. Synthesis of α,β-Unsaturated Esters from Mixing Aldehydes, α-Bromoesters, and Ph3P in Aqueous NaHCO3

Wittig Reaction in Deep Eutectic Solvents: Expanding the DES Toolbox in Synthesis

Wittig reaction between substituted phosphonium salts and (hetero)aromatic and alkyl carbonyl compounds in Deep Eutectic Solvents has been developed under a scalable and friendly protocol. Highly efficient reactions were successfully run with a wide range of bases including organic (DBU, LiTMP, t-BuOK) and inorganic (NaOH, K2CO3) ones in ChCl/Gly 1 : 2 (mol/mol) as solvent under mild conditions, at room temperature and under air. The proposed protocol was applied to a wide range of substrates, including (hetero)aromatic aldehydes with substituents as halogens (I, Br, Cl), EDG (alkoxy, methyl), EWG (NO2, CF3) or reactive groups as CN, esters, and ketones. Vinylic, alkynyl and cycloalkyl, alicyclic and α,β-unsaturated aldehydes can also be used. Highly electrophilic ketones gave good yields. The diastereoselectivity of the reaction is in complete agreement with the E/Z ratio predictable under traditional conditions. We demonstrated that the protocol is scalable to 2 g (5 mmol) of phosphonium salt, furthermore the proposed workup protocol allows to remove TPPO without need of additional chromatographic purification.

Synthesis of N2-trans-isosafrole-dG-adduct Bearing DNAs and the Bypass Studies with Human TLS Polymerases κ and η

Safrole is a natural product present in many plants and plant products, including spices and essential oils. During cellular metabolism, it converts to a highly reactive trans-isosafrole (SF) intermediate that reacts with genomic DNA and forms N2-SF-dG and N6-SF-dA DNA adducts, which are detected in the oral tissue of cancer patients with betel quid chewing history. To study the SF-induced carcinogenesis and to probe the role of low fidelity translesion synthesis (TLS) polymerases in bypassing SF adducts, herein, we report the synthesis of N2-SF-dG modified DNAs using phosphoramidite chemistry. The N2-SF-dG modification in the duplex DNA does not affect the thermal stability and retains the B-form of helical conformation, indicating that this adduct may escape the radar of common DNA repair mechanisms. Primer extension studies showed that the N2-SF-dG adduct is bypassed by human TLS polymerases hpolκ and hpolη, which perform error-free replication across this adduct. Furthermore, molecular modeling and dynamics studies revealed that the adduct reorients to pair with the incoming nucleotide, thus allowing the effective bypass. Overall, the results indicate that hpolκ and hpolη do not distinguish the N2-SF-dG adduct, suggesting that they may not be involved in the safrole-induced carcinogenicity.

Novel 3-hydroxypyridin-4(1H)-One derivatives as ferroptosis inhibitors with iron-chelating and reactive oxygen species scavenging activities and therapeutic effect in cisplatin-induced cytotoxicity

Recent advances in understanding the role of iron and ROS in cell death suggest new therapeutic avenues to treat organ damage including acute kidney injury (AKI). Inhibiting ferroptosis was expected to have great potential for the treatment of this disease. Ferroptosis is characterized by iron-dependent lipid peroxidation and currently, a majority of reported ferroptosis inhibitors belong to either radical-trapping antioxidants or iron chelators. However, clinically used iron chelators such as deferoxamine and deferiprone have limited efficacy against ferroptosis (generally with EC50 > 100 μM), despite their proven safety. Herein, we present the rational design of novel ferroptosis inhibitors by incorporating the naturally occurring cinnamic acid scaffold and the 3-hydroxypyridin-4(1H)-one iron-chelating pharmacophore. Through ABTS˙+ radical-scavenging assay, oxygen radical absorbance capacity (ORAC) measurement, Fe3+ affinity evaluation, and anti-erastin-induced HT22 cell ferroptosis assays, we identified compound 9c as the most prospective ferroptosis inhibitor (ABTS˙+, IC50 = 4.35 ± 0.05 μM; ORCA = 23.79 ± 0.56 TE; pFe3+ = 18.59; EC50 = 14.89 ± 0.08 μM, respectively). Notably, 9c dose-dependently alleviated cell death in cisplatin-induced AKI model. Our results provide insight into the development of new ferroptosis inhibitors through rational incorporation of pharmacophores from existing ferroptosis inhibitors, and compound 9c could be a promising lead compound worth further investigation.

Efficient One-Pot Synthesis of Novel Caffeic Acid Derivatives as Potential Antimalarials

New protocol for the preparation of the novel caffeic acid derivatives using the Wittig reaction has been applied to follow the principles of green chemistry. The compounds have been evaluated against chloroquine-sensitive and chloroquine-resistant P. falciparum strains. Their cytotoxicity to normal human dermal fibroblasts and their propensity to induce hemolysis have been also determined. Ethyl (2E)-3-(2,3,4-trihydroxyphenyl)-2-methylpropenoate has exhibited the highest antiplasmodial activity against P. falciparum strains without the cytotoxic and hemolytic effects. This derivative is significantly more potent than caffeic acid parent structure. The application of our one-step procedure has been shown to be rapid and efficient. It allows for an easy increase of input data to refine the structure-activity relationship model of caffeates as the antimalarials. The one-step approach meets the conditions of "atom economy" and eliminates hazardous materials. Water has been used as the effective medium for the Wittig reaction to avoid toxic organic solvents.

Human Translesion Synthesis Polymerases polκ and polη Perform Error-Free Replication across N2-dG Methyleugenol and Estragole DNA Adducts

The secondary metabolites of polypropanoids, methyleugenol (MEG), and estragole (EG), found in many herbs and spices, are commonly used as food flavoring agents and as ingredients in cosmetics. MEG and EG have been reported to cause hepatocarcinogenicity in rodents, human livers, and lung cells. The formation of N2-dG and N6-dA DNA adducts is primarily attributed to the carcinogenicity of these compounds. Therefore, these compounds have been classified as "possible human carcinogens" by the International Agency for Research on Cancer and "reasonably anticipated to be a human carcinogen" by the National Toxicology Program. Herein, we report the synthesis of the N2-MEG-dG and N2-EG-dG modified oligonucleotides to study the mutagenicity of these DNA adducts. Our studies show that N2-MEG-dG and N2-EG-dG could be bypassed by human translesion synthesis (TLS) polymerases hpolκ and hpolη in an error-free manner. The steady-state kinetics of dCTP incorporation by hpolκ across N2-MEG-dG and N2-EG-dG adducts show that the catalytic efficiencies (kcat/Km) were ∼2.5- and ∼4.4-fold higher, respectively, compared to the unmodified dG template. A full-length primer extension assay demonstrates that hpolκ exhibits better catalytic efficiency than hpolη. Molecular modeling and dynamics studies capturing pre-insertion, insertion, and post-insertion steps reveal the structural features associated with the efficient bypass of the N2-MEG-dG adduct by hpolκ and indicate the reorientation of the adduct in the active site allowing the successful insertion of the incoming nucleotide. Together, these results suggest that though hpolκ and hpolη perform error-free TLS across MEG and EG during DNA replication, the observed carcinogenicity of these adducts could be attributed to the involvement of other low fidelity polymerases.

Methoxylated Cinnamic Esters with Antiproliferative and Antimetastatic Effects on Human Lung Adenocarcinoma Cells

Lung cancer is the leading cause of cancer mortality worldwide, and malignant melanomas are highly lethal owing to their elevated metastatic potential. Despite improvements in therapeutic approaches, cancer treatments are not completely effective. Thus, new drug candidates are continuously sought. We synthesized mono- and di-methoxylated cinnamic acid esters and investigated their antitumor potential. A cell viability assay was performed to identify promising substances against A549 (non-small-cell lung cancer) and SK-MEL-147 (melanoma) cells. (E)-2,5-dimethoxybenzyl 3-(4-methoxyphenyl)acrylate (4m), a monomethoxylated cinnamic acid derivative, was identified as the lead antitumor compound, and its antitumor potential was deeply investigated. Various approaches were employed to investigate the antiproliferative (clonogenic assay and cell cycle analysis), proapoptotic (annexin V assay), and antimigratory (wound-healing and adhesion assays) activities of 4m on A549 cells. In addition, western blotting was performed to explore its mechanism of action. We demonstrated that 4m inhibits the proliferation of A549 by promoting cyclin B downregulation and cell cycle arrest at G2/M. Antimigratory and proapoptotic activities of 4m on A549 were also observed. The antitumor potential of 4m involved its ability to modulate the mitogen-activated protein kinases/extracellular signal-regulated kinase (MAPK/ERK) signaling pathway once phosphorylated-ERK expression was considerably reduced in response to treatment. Our findings demonstrate that 4m is a promising anticancer drug candidate.

Wittig and Wittig-Horner Reactions under Sonication Conditions

Carbonyl olefinations are among the most important organic syntheses that form C=C bonds, as they usually have high yields and in addition offer excellent stereoselectivity. Due to these advantages, carbonyl olefinations have important pharmaceutical and industrial applications. These reactions contain an additional step of an α-functionalized carbanion to an aldehyde or ketone to produce alkenes, but syntheses performed using metal carbene complexes are also known. The Wittig reaction is an example of carbonyl olefination, one of the best ways to synthesize alkenes. This involves the chemical reaction between an aldehyde or ketone with a so-called Wittig reagent, for instance phosphonium ylide. Triphenylphosphine-derived ylides and trialkylphosphine-derived ylides are the most common phosphorous compounds used as Wittig reagents. The Wittig reaction is commonly involved in the synthesis of novel anti-cancer and anti-viral compounds. In recent decades, the use of ultrasound on the Wittig reaction (and on different modified Wittig syntheses, such as the Wittig-Horner reaction or the aza-Wittig method) has been studied as a green synthesis. In addition to the advantage of green synthesis, the use of ultrasounds in general also improved the yield and reduced the reaction time. All of these chemical syntheses conducted under ultrasound will be described further in the present review.

Rhodium(III)-catalyzed oxidative cross-coupling of benzoxazinones with styrenes via C-H activation

Vinylarenes represent an important class of core skeleton embedded in natural products, organic materials, and pharmaceutical molecules. Therefore, numerous efforts have been devoted to developing efficient methods for their preparation. Among them, transition-metal-catalyzed oxidative coupling of arenes and alkenes has proved to be a powerful method due to its high atom and step economy. Although a wide range of oxidative alkenylations of arenes have been developed, the alkenes employed in most cases are still limited to electron-deficient alkenes. Reported herein is a Rh(III)-catalyzed C-H cross-coupling of benzoxazinones and simple unactivated styrenes to furnish a variety of vinylarene scaffolds. This established protocol is characterized by wide functional group compatibility, high yields, and excellent regio- and chemo-selectivity. Mechanistic studies and gram-scale experiments on this high-value conversion are disclosed. Moreover, the potential utility of this method was highlighted by a series of further transformations.

Total synthesis of thioamycolamide A using diastereoselective sulfa-Michael addition as the key step

The total synthesis of the antitumor natural product thioamycolamide A has been accomplished in 19.1% overall yield featuring a diastereoselective sulfa-Michael reaction.

Wittig reagents for chemoselective sulfenic acid ligation enables global site stoichiometry analysis and redox-controlled mitochondrial targeting

Triphenylphosphonium ylides, known as Wittig reagents, are one of the most commonly used tools in synthetic chemistry. Despite their considerable versatility, Wittig reagents have not yet been explored for their utility in biological applications. Here we introduce a chemoselective ligation reaction that harnesses the reactivity of Wittig reagents and the unique chemical properties of sulfenic acid, a pivotal post-translational cysteine modification in redox biology. The reaction, which generates a covalent bond between the ylide nucleophilic α-carbon and electrophilic γ-sulfur, is highly selective, rapid and affords robust labelling under a range of biocompatible reaction conditions, which includes in living cells. We highlight the broad utility of this conjugation method to enable site-specific proteome-wide stoichiometry analysis of S-sulfenylation and to visualize redox-dependent changes in mitochondrial cysteine oxidation and redox-triggered triphenylphosphonium generation for the controlled delivery of small molecules to mitochondria.

Regioselective C-H Alkenylation and Unsymmetrical Bis-olefination of Heteroarene Carboxylic Acids with Ruthenium Catalysis in Water

An efficient weak carboxylate-assisted oxidative cross-dehydrogenative C-H/C-H coupling (CDC) of heteroarenes with readily available olefins has been devised employing water as green solvent under ruthenium(II) catalysis. The reaction is operationally simple, accommodates a large variety of heteroaromatic carboxylic acids as well as olefins, and facilitates a diverse array of high-value olefin-tethered heteroarenes in high yields (up to 87%). The potential of this ortho-C-H bond activation strategy has also been exploited toward tunable synthesis of densely functionalized heteroarenes through challenging unsymmetrical bis-olefination process in a one-pot sequential fashion. Mechanistic investigation demonstrates a reversible ruthenation process and C-H metalation step might not be involved in the rate-determining step.

Controlling Two-Photon Action Cross Section by Changing a Single Heteroatom Position in Fluorescent Dyes

The optimization of nonlinear optical properties for "real-life" applications remains a key challenge for both experimental and theoretical approaches. In particular, for two-photon processes, maximizing the two-photon action cross section (TPACS), the figure of merit for two-photon bioimaging spectroscopy, requires simultaneously controlling all its components. In the present Letter, a series of difluoroborates presenting various heterocyclic rings as an electron acceptor have been synthesized and their absorption, fluorescence, photoisomerization, and two-photon absorption features have been analyzed using both experimental and theoretical approaches. Our results demonstrate that the TPACS values can be fine-tuned by changing the position of a single heteroatom, which alters the fluorescence quantum yields without changing the intrinsic two-photon absorption cross section. This approach offers a new strategy for optimizing TPACS.

One-Pot, Tandem Wittig Hydrogenation: Formal C(sp3)-C(sp3) Bond Formation with Extensive Scope

A one-pot, tandem Wittig hydrogenation of aldehydes with stabilized ylides is reported, representing a formal C(sp³)-C(sp³) bond construction. The tandem reaction operates under mild conditions, is high yielding, and is broad in scope. Chemoselectivity for olefin reduction is observed, and the methodology is demonstrated in the synthesis of lapatinib analogues and a formal synthesis of (±)-cuspareine. Early insights suggest that the chemoselectivity observed in the reduction step is due to partial poisoning of the catalyst, after step one, thus adding to the power of the one-pot procedure.

Synthesis and Antioxidant Activity of Caffeic Acid Derivatives

A series of caffeic acid derivatives were synthesized via a modified Wittig reaction which is a very important tool in organic chemistry for the construction of unsaturated carbon⁻carbon bonds. All reactions were performed in water medium at 90 °C. The aqueous Wittig reaction worked best when one unprotected hydroxyl group was present in the phenyl ring. The olefinations in the aqueous conditions were also conducted with good yields in the presence of two unprotected hydroxyl groups. When the number of the hydroxyl groups was increased to three, the reaction yields were worse, and the derivatives 12, 13, and 18 were obtained with 74%, 37%, and 70% yields, respectively. Nevertheless, the Wittig reaction using water as the essential medium is an elegant one-pot synthesis and a greener method, which can be a safe alternative for implementation in organic chemistry. The obtained compounds were tested for their antioxidant activity, and 12, 13, and 18 showed the highest activities. Moreover, all synthesized compounds displayed no cytotoxicity, and can therefore be used in the pharmaceutical or cosmetic industry.

A macrocyclic silver polycarbene complex based on 1,2,4-triazole units: synthesis and postsynthetic modification

A method for the synthesis of a new rectangular 1,2,4-triazole-containing macrocycle via photochemical [2 + 2] cycloaddition with a metal–carbene template was developed.

Synthesis of phosphine oxide based amphiphilic molecules via ring-opening Wittig olefination of a macrocyclic phosphoranylidene and their property study as non-ionic surfactants

A novel ring-opening Wittig olefination approach was developed for the synthesis of amphiphilic phosphine oxides (PO) as non-ionic surfactants. The approach concurrently introduces the crucial functional groups (lipophilic chain and phosphine oxide moiety) present in the known PO surfactants and additional hydrophilic group (i.e., ethylene glycol units) in one step via Wittig olefination of a macrocyclic phosphoranylidene. A series of novel PO compounds were obtained from a variety of aldehydes and selected compounds were examined for their physiochemical properties (surface tension, critical micelle concentration and interfacial tension) and also for their abilities to form emulsions as non-ionic surfactants.

A novel ring-opening Wittig olefination approach was developed for the synthesis of amphiphilic phosphine oxides (PO) as non-ionic surfactants.

Bioactivity and structure-activity relationship of cinnamic acid esters and their derivatives as potential antifungal agents for plant protection

A series of cinnamic acid esters and their derivatives were synthesized and evaluated for antifungal activities in vitro against four plant pathogenic fungi by using the mycelium growth rate method. Structure−activity relationship was derived also. Almost all of the compounds showed some inhibition activity on each of the fungi at 0.5 mM. Eight compounds showed the higher average activity with average EC₅₀ values of 17.4–28.6 μg/mL for the fungi than kresoxim-methyl, a commercial fungicide standard, and ten compounds were much more active than commercial fungicide standards carbendazim against P. grisea or kresoxim-methyl against both P. grisea and Valsa mali. Compounds C1 and C2 showed the higher activity with average EC₅₀ values of 17.4 and 18.5 μg/mL and great potential for development of new plant antifungal agents. The structure−activity relationship analysis showed that both the substitution pattern of the phenyl ring and the alkyl group in the alcohol moiety significantly influences the activity. There exists complexly comprehensive effect between the substituents on the phenyl ring and the alkyl group in the alcohol moiety on the activity. Thus, cinnamic acid esters showed great potential the development of new antifungal agents for plant protection due to high activity, natural compounds or natural compound framework, simple structure, easy preparation, low-cost and environmentally friendly.

Recent advances in positional-selective alkenylations: removable guidance for twofold C–H activation

Recent advances in transition-metal catalyzed positional-selective alkenylations via twofold C–H activation directed by removable or traceless directing groups are reviewed.

Tandem Wittig/Diels–Alder diversification of genetically encoded peptide libraries

In this paper, we developed a tandem of two carbon–carbon bond-forming reactions to chemically diversify libraries of peptides displayed on a bacteriophage.

Phasic and Tonic mGlu7 Receptor Activity Modulates the Thalamocortical Network

Mutation of the metabotropic glutamate receptor type 7 (mGlu7) induces absence-like epileptic seizures, but its precise role in the somatosensory thalamocortical network remains unknown. By combining electrophysiological recordings, optogenetics, and pharmacology, we dissected the contribution of the mGlu7 receptor at mouse thalamic synapses. We found that mGlu7 is functionally expressed at both glutamatergic and GABAergic synapses, where it can inhibit neurotransmission and regulate short-term plasticity. These effects depend on the PDZ-ligand of the receptor, as they are lost in mutant mice. Interestingly, the very low affinity of mGlu7 receptors for glutamate raises the question of how it can be activated, namely at GABAergic synapses and in basal conditions. Inactivation of the receptor activity with the mGlu7 negative allosteric modulator (NAM), ADX71743, enhances thalamic synaptic transmission. In vivo administration of the NAM induces a lethargic state with spindle and/or spike-and-wave discharges accompanied by a behavioral arrest typical of absence epileptic seizures. This provides evidence for mGlu7 receptor-mediated tonic modulation of a physiological function in vivo preventing synchronous and potentially pathological oscillations.

Alstoscholarisines H-J, Indole Alkaloids from Alstonia scholaris: Structural Evaluation and Bioinspired Synthesis of Alstoscholarisine H

Alstoscholarisines H-J (1-3), new monoterpenoid indole alkaloids with an unprecedented skeleton created via the formation of a C-3/N-1 bond, were isolated from Alstonia scholaris. Their structures were established by extensive spectroscopic analyses and the assessment of single-crystal X-ray diffraction data. The total synthesis of alstoscholarisine H was achieved via the regioselective nucleophilic addition of pyridinium through a bioinspired iminium ion intermediate followed by Pictet-Spengler-like cyclization.

Gas hydrates model for the mechanistic investigation of the Wittig reaction “on water”

Water in action! A gas hydrate model consisting of 20 water molecules nicely illustrates acceleration of cis-Wittig reaction over trans-Wittig reaction "on water". "Bucky" water is a perfect model for describing chemical reactions "on water".

Methyltriphenylphosphonium Methylcarbonate, an All-In-One Wittig Vinylation Reagent

The methyltriphenylphosphonium methylcarbonate salt [Ph3 PCH3 ][CH3 OCO2 ], obtained directly by quaternarization of triphenylphosphine with dimethylcarbonate, is a latent ylide that promotes Wittig vinylation of aldehydes and ketones. Alkenes are obtained simply by mixing [Ph3 PCH3 ][CH3 OCO2 ] and the carbonyl and heating in a solvent (no base, no halides, and no inorganic byproducts). Deuterium exchange experiments and the particularly short anion-cation distance measured by XRD in [Ph3 PCH3 ][CH3 OCO2 ] allowed to explain the nature and reactivity of this species. Green chemistry metrics (atom economy, mass index, environmental factor) indicate that this vinylation procedure is more efficient than comparable ones. Deuterated [Ph3 PCD3 ][CH3 OCO2 ] promoted the synthesis of deuterated olefins.

Synthesis of α,β-unsaturated esters via a chemo-enzymatic chain elongation approach by combining carboxylic acid reduction and Wittig reaction

α,β-Unsaturated esters are versatile building blocks for organic synthesis and of significant importance for industrial applications. A great variety of synthetic methods have been developed, and quite a number of them use aldehydes as precursors. Herein we report a chemo-enzymatic chain elongation approach to access α,β-unsaturated esters by combining an enzymatic carboxylic acid reduction and Wittig reaction. Recently, we have found that Mycobacterium sp. was able to reduce phenylacetic acid (1a) to 2-phenyl-1-ethanol (1c) and two sequences in the Mycobacterium sp. genome had high identity with the carboxylic acid reductase (CAR) gene from Nocardia iowensis. These two putative CAR genes were cloned, overexpressed in E. coli and one of two proteins could reduce 1a. The recombinant CAR was purified and characterized. The enzyme exhibited high activity toward a variety of aromatic and aliphatic carboxylic acids, including ibuprofen. The Mycobacterium CAR catalyzed carboxylic acid reduction to give aldehydes, followed by a Wittig reaction to afford the products α,β-unsaturated esters with extension of two carbon atoms, demonstrating a new chemo-enzymatic method for the synthesis of these important compounds.

Polyhydroxyalkanoate-based 3-hydroxyoctanoic acid and its derivatives as a platform of bioactive compounds

A library of 18 different compounds was synthesized starting from (R)-3-hydroxyoctanoic acid which is derived from the bacterial polymer polyhydroxyalkanoate (PHA). Ten derivatives, including halo and unsaturated methyl and benzyl esters, were synthesized and characterized for the first time. Given that (R)-3-hydroxyalkanoic acids are known to have biological activity, the new compounds were evaluated for antimicrobial activity and in vitro antiproliferative effect with mammalian cell lines. The presence of the carboxylic group was essential for the antimicrobial activity, with minimal inhibitory concentrations against a panel of bacteria (Gram-positive and Gram-negative) and fungi (Candida albicans and Microsporum gypseum) in the range 2.8-7.0 mM and 0.1-6.3 mM, respectively. 3-Halogenated octanoic acids exhibited the ability to inhibit C. albicans hyphae formation. In addition, (R)-3-hydroxyoctanoic and (E)-oct-2-enoic acids inhibited quorum sensing-regulated pyocyanin production in the opportunistic pathogen Pseudomonas aeruginosa PAO1. Generally, derivatives did not inhibit mammalian cell proliferation even at 3-mM concentrations, while only (E)-oct-2-enoic and 3-oxooctanoic acid had IC50 values of 1.7 and 1.6 mM with the human lung fibroblast cell line.

Plasmodium falciparum subtilisin-like protease 1: discovery of potent difluorostatone-based inhibitors

We here describe the development of potent inhibitors of the malaria parasite enzyme subtilisin-like protease 1 (PfSUB1).

The constituents of roots and stems of Illigera luzonensis and their anti-platelet aggregation effects

Phytochemical investigation of the roots and stems of Illigera luzonensis afforded two new aporphine alkaloids (1) and (2), one new bisdehydroaporphine alkaloid (3), and one new benzenoid (4), along with 28 known structures. The structures of new compounds were elucidated by spectral and MS analysis. Among the isolated compounds, (1) and (4–13) were subjected into the examination for their inhibitory effects on the aggregation of washed rabbit platelets.