Catalytic Protonation Research Articles

Dual-State Fluorescent Probe for Ultrafast and Sensitive Detection of Nerve Agent Simulants in Solution and Vapor.

The development of fluorescent probes for detecting nerve agents has been the main concern focus of research because of their lethal toxicity for humans. Herein, a probe (PQSP) based on the quinoxalinone unit and the styrene pyridine group was synthesized and could visually detect a sarin simulant diethyl chlorophosphate (DCP) with excellent sensing properties in solution and solid states. Interestingly, PQSP showed an apparent intramolecular charge-transfer process by catalytic protonation after reacting with DCP in methanol, accompanied with the aggregation recombination effect. The sensing process was also verified by nuclear magnetic resonance spectra, scanning electron microscopy, and theoretical calculations. In addition, the papered test strips of loading probe PQSP exhibited an ultrafast response time within 3 s and high sensitivity with a limit of detection of 3 ppb for the detection of DCP vapor. Therefore, this research provides a designed strategy for developing the probes with dual-state emission fluorescence in solution and solid states for detecting DCP sensitively and rapidly, which can be fabricated as chemosensors to visually detect nerve agents in practice.

Lipid Membrane State Change by Catalytic Protonation and the Implications for Synaptic Transmission.

In cholinergic synapses, the neurotransmitter acetylcholine (ACh) is rapidly hydrolyzed by esterases to choline and acetic acid (AH). It is believed that this reaction serves the purpose of deactivating ACh once it has exerted its effect on a receptor protein (AChR). The protons liberated in this reaction, however, may by themselves excite the postsynaptic membrane. Herein, we investigated the response of cell membrane models made from phosphatidylcholine (PC), phosphatidylserine (PS) and phosphatidic acid (PA) to ACh in the presence and absence of acetylcholinesterase (AChE). Without a catalyst, there were no significant effects of ACh on the membrane state (lateral pressure change mN/m). In contrast, strong responses were observed in membranes made from PS and PA when ACh was applied in presence of AChE (>5 mN/m). Control experiments demonstrated that this effect was due to the protonation of lipid headgroups, which is maximal at the pK (for PS: ; for PA: ). These findings are physiologically relevant, because both of these lipids are present in postsynaptic membranes. Furthermore, we discussed evidence which suggests that AChR assembles a lipid-protein interface that is proton-sensitive in the vicinity of pH . Such a membrane could be excited by hydrolysis of micromolar amounts of ACh. Based on these results, we proposed that cholinergic transmission is due to postsynaptic membrane protonation. Our model will be falsified if cholinergic membranes do not respond to acidification.

Catalytic Friedel–Crafts Alkylation of Electron Rich Aromatic Derivatives with α-Aryl Diazoacetates Mediated by Brønsted Acids

The catalytic protonation of aryl diazoacetates by strong Brønsted acids, followed by a Friedel-Crafts alkylation reaction with electron rich aromatic compounds, is reported. The reaction provided in a direct fashion 24 geminal diarylacetates in yields of ≤92%.

Mechanistic role of protonated polar additives in ethanol for selective transformation of biomass-related compounds

We report on a combined experimental, spectroscopic and theoretical study of acid catalysed dehydration-etherification of fructose in ethanol for understanding the mechanistic role of polar solvent additives and product selectivity. Herein, we show that polar solvent additives (e.g. tetrahydrofuran, acetone, acetonitrile, gamma-valerolactone, dimethyl sulfoxide) protonated with a common solid acid catalyst in ethanol allow transformation of biomass-related compounds into desired dehydration or etherification products. Fructose in ethanol with DMSO additive is selectively transformed into 5-hydroxymethylfurfural with negligible formation of 5-ethoxymethylfurfural due to preferential DMSO protonation according to its polarity. Spectroscopic methods and density functional theory show that additives having higher polarity than ethanol are readily protonated and act as the key catalytic protonation species and as the key stabilization species for reaction intermediates. Understanding the mechanism of protonated polar additives in reaction systems allows one to tailor selectivity in acid-catalyzed dehydration-etherification schemes and to develop sustainable chemistry for biomass resources.

Deracemizing α-Branched Carboxylic Acids by Catalytic Asymmetric Protonation of Bis-Silyl Ketene Acetals with Water or Methanol.

We report a highly enantioselective catalytic protonation of bis-silyl ketene acetals. Our method delivers α-branched carboxylic acids, including nonsteroidal anti-inflammatory arylpropionic acids such as Ibuprofen, in high enantiomeric purity and high yields. The process can be incorporated in an overall deracemization of α-branched carboxylic acids, involving a double deprotonation and silylation followed by the catalytic asymmetric protonation.

ChemInform Abstract: Novel Catalytic Enantioselective Protonation (Proton Transfer) in Michael Addition of Benzenethiol to α-Acrylacrylates: Synthesis of (S)-Naproxen and α-Arylpropionic Acids or Esters.

A novel synthesis of optically active 2-phenylpropionic acids or esters via catalytic enantioselective protonation in the Michael addition of benzenethiol to 2-phenylacrylates is described; the synthetic utility is further demonstrated by the asymmetric synthesis of (S)-Naproxen.

ChemInform Abstract: Catalytic Asymmetric Protonation of Achiral Lithium Enolates Mediated by a Chiral Tetraamine Ligand with Water as a Proton Source.

Abstract Catalytic protonation of achiral lithium enolates (derived from 2-substituted-1-tetralones), mediated by a chiral tetraamine ligand [( R , R )- N , N ′-bis[1-phenyl-2-(1-piperidinyl)ethyl]-1,3-propanediamine (0.10 equiv.)], was achieved with high enantioselectivity (up to 93% ee) by using water (10% aqueous citric acid) as a proton source. A possible mechanism of highly efficient catalytic turnover of the chiral tetraamine ligand is discussed.

ChemInform Abstract: Catalytic Enantioselective Protonation of Lithium Enolates with Chiral Imides.

The catalytic enantioselective protonation of simple enolates was achieved using a catalytic amount of chiral imides and stoichiometric amount of achiral proton sources. Among the achiral proton so...

Catalytic mechanism and protonation state of pepsin-like aspartyl protease active site

Catalytic mechanism and protonation state of pepsin-like aspartyl protease active site

Enantioselective Reduction of Pyridines via Brønsted Acid Catalysis

An organocatalytic enantioselective reduction of 2-substituted simple and fused pyridines is reported. The reaction is designed to undergo catalytic protonation by Brønsted acid 1, followed by reduction by hydride transfer from the Hantzsch dihydropyridine 2. The hexahydroquinolinone and tetrahydropyridine products are formed in moderate to good yields with good enantioselectivities. The scope of the reaction was modestly investigated.

Highly Enantioselective Organocatalytic Transfer Hydrogenation of Quinolines

The highly enantioselective Brøn­sted acid catalyzed cascade transfer hydrogenation of 2-substituted quinoline derivatives 1 presented herein gives direct access to a variety of 2-aryl- and 2-alkyl-substituted tetrahydroquinolines 2 with good yields and excellent enantioselectivities. In this approach, sterically congested Brønsted acid 3 activates the quinoline 1 by catalytic protonation, which allows cascade hydrogenation in the presence of Hantzsch dihydropyridine 4 as cofactor. This first step is a 1,4-hydride addition, then an isomerization occurs, which is followed by a 1,2-hydride addition. Furthermore, this methodology (and subsequent N-methylation) was successfully applied to the synthesis of biologically active tetrahydroquinoline alkaloids: galipinine, cuspareine, and angustureine, which were obtained in good yields (79-89%) and excellent enantioselectivities (90-91%).

Nucleophilic addition to an achiral dehydroalanine Schiff base Ni(II) complex as a route to amino acids. A case of stereodetermining asymmetric protonation in the presence of TADDOL

We describe herein the elaboration of a new type of a substrate based on the Ni(II) complex of a Schiff base of dehydroalanine, 1, and Michael addition of nucleophiles to it, leading to the synthesis of racemic α-amino acids. We have also developed a catalytic method for the asymmetric 1,4 conjugate addition of achiral CH-acids to 1 promoted by TADDOLs with enantioselective catalytic protonation of the intermediate enolate in the stereodetermining stage of the reaction. A sizable 80% ee of the product was observed.

Catalytic enantioselective protonation of lithium enolates with chiral imides

The catalytic enantioselective protonation of simple enolates was achieved using a catalytic amount of chiral imides and stoichiometric amount of achiral proton sources. Among the achiral proton sources examined in the protonation of the lithium enolate of 2,2,6-trimethylcyclohexanone catalyzed by (S,S)-imide 1, 2, 6-di-tert-butyl-p-cresol (BHT) and its derivatives gave the highest enantiomeric excess. For example, 90% ee of (R)-enriched ketone was obtained when (S,S)-imide 1 (0.1 equiv) and BHT (1 equiv) were used. Use of 0.01 equiv of the chiral catalyst still caused a high level of asymmetric induction. For catalytic protonation of the lithium enolate of 2-methylcyclohexanone, chiral imide 6 possessing a chiral amide portion was superior to (S,S)-imide 1 as a chiral proton source and the enolate was effectively protonated with up to 82% ee.

Catalytic asymmetric protonation of achiral lithium enolates mediated by a chiral tetraamine ligand with water as a proton source

Catalytic protonation of achiral lithium enolates (derived from 2-substituted-1-tetralones), mediated by a chiral tetraamine ligand [( R, R)- N, N′-bis[1-phenyl-2-(1-piperidinyl)ethyl]-1,3-propanediamine (0.10 equiv.)], was achieved with high enantioselectivity (up to 93% ee) by using water (10% aqueous citric acid) as a proton source. A possible mechanism of highly efficient catalytic turnover of the chiral tetraamine ligand is discussed.

Asymmetric Catalytic Protonation of Silyl Enol Ethers with Chiral Palladium Complexes

Asymmetric Catalytic Protonation of Silyl Enol Ethers with Chiral Palladium Complexes

ChemInform Abstract: First Example of a Highly Enantioselective Catalytic Protonation of Silyl Enol Ethers Using a Novel Lewis Acid‐Assisted Broensted Acid System.

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Catalytic enantioselective protonation of samarium enolates by a C 2-symmetric chiral diol

Relatively high enantioselectivity (up to 93% ee) has been achieved in the catalytic protonation of samarium enolates by the use of a C 2-symmetric homochiral diol as the catalyst and trityl alcohol as an achiral proton source for regeneration of the catalyst.

First Example of a Highly Enantioselective Catalytic Protonation of Silyl Enol Ethers Using a Novel Lewis Acid-Assisted Brønsted Acid System

First Example of a Highly Enantioselective Catalytic Protonation of Silyl Enol Ethers Using a Novel Lewis Acid-Assisted Brønsted Acid System