Template Catalysis Research Articles

Manganese-catalyzed base-free addition of saturated nitriles to unsaturated nitriles by template catalysis.

The coupling of mononitriles into dinitriles is a desirable strategy, given the prevalence of nitrile compounds and the synthetic and industrial utility of dinitriles. Herein, we present an atom-economical approach for the heteroaddition of saturated nitriles to α,β- and β,γ-unsaturated mononitriles to generate glutaronitrile derivatives using a catalyst based on earth-abundant manganese. A broad range of such saturated and unsaturated nitriles were found to undergo facile heteroaddition with excellent functional group tolerance, in a reaction that proceeds under mild and base-free conditions using low catalyst loading. Mechanistic studies showed that this unique transformation takes place through a template-type pathway involving an enamido complex intermediate, which is generated by addition of a saturated nitrile to the catalyst, and acts as a nucleophile for Michael addition to unsaturated nitriles. This work represents a new application of template catalysis for C-C bond formation.

Template catalysis by manganese pincer complexes: oxa- and aza-Michael additions to unsaturated nitriles.

Activation of C[triple bond, length as m-dash]N bonds by metal-ligand cooperation provides a new route for the functionalization of nitriles. Herein, we report the electrophilic activation of unsaturated nitriles by dearomatized manganese pincer complexes for the oxa- and aza-Michael addition reactions under very mild and neutral conditions. Derivatives of acrylonitrile and allyl cyanide furnished the corresponding β-addition products by reacting with alcohols and amines. Mechanistically, the catalysis is mostly ligand based. Reaction of the dearomatized PNN-Mn complex with 2-pentenenitrile or 3-pentenenitrile furnished an enamido-Mn complex. The equilibrium between an enamido complex and a ketimido complex, and reversible C-C bond formation with the ligand are proposed to play central roles in the catalysis.

Exploring supramolecular aggregation behaviour of bioactive thiazolidine-4-carboxylic acid derivatives

A target synthesis of selected biocompatible chiral Thiazolidine-4-carboxylic acid derivatives was attempted to investigate the influence of number, type and position of hydrogen bonding functionalities and solvent molecules in the crystal lattice on the supramolecular aggregation behaviour leading to formation of molecular assemblies. The single crystal X-ray diffraction studies of (R)-thiazolidine-4-carboxylic acid (T4CA, zwitter ion form), 2-propionyl T4CA and (2S,4R)-3-(tert-butoxycarbonyl)-2-(4-methoxyphenyl)T4CA and other reported thiozolidine 4-carboxylic acid derivatives were used to establish the solid state aggregation behaviour. The 1D, 2D and 3D agregrational behaviour of synthesized thiozolidine-4-carboxylic acid derivatives was explored from their crystal packing diagrams and was further extended in light of some appropriate literature reported thiozolidine-4-carboxylic acid derivatives. The explored 1D, 2D and 3D supramolecular aggregrational behaviour in case of the thiazolidine-4-carboxylic acid derivatives can be explored for their further applications as biocompatible supramolecular assemblies towards gas storage, biosensing and template catalysis.

Open flow non-enzymatic template catalysis and replication.

Template induced replication is the basis of multiplication and reproduction in nature and underlies the importance of gaining a detailed understanding of its mechanisms in terms of chemical reaction networks. We analyze numerically the stationary state solutions for a class of autocatalytic reactions based on reversible template assisted ligation with first and second order catalysis and governed by mass-action kinetics. Chemical thermodynamics leads to constraints on the reaction rate constants which result in very low template yield in systems subject to fixed external concentrations. When however the network is driven out of equilibrium via open flow in a well-mixed reactor, the template yield can be increased significantly for very small fluid flow rates. This can be understood in terms of driven unidirectional pathways, as determined by stoichiometric network analysis.

Efficient Heritable Gene Expression Readily Evolves in RNA Pools

Heritable gene expression arises readily in a simple non-genetic system employing known small-RNA biochemistry. Pooled cross-templating ribonucleotides show varied chemical competence on which selection acts, even calculating only minimal effects. Evolution can be quick—computed progress toward encoded gene expression can require only days or weeks for two millimolar, partly activated complementary 5′ ribonucleotides. After only one product selection cycle, early templating can become prevailing pool behavior. Subsequently, a selected templated product is efficiently amplified as a pool ages, frequently accumulated in the same order of concentration as incoming nucleotides. Pools spontaneously favor templating because sporadic nucleotide accumulations increase it—and selection increases templating in pools of all ages. Nonetheless, templated chemical competence appears most easily in young pools. Pool history is critical—pools can perish from periodic hazards (like tides), or alternatively, from hazards roughly constant in time (like rainfall). Selection is greatly enhanced in constant hazard pools—more effective if pools have varied ages. Stronger selection is disproportionately more effective. Selected evolutionary change has an uncomplicated molecular basis—progress from chemical product synthesis to templated, proto-genetic inheritance exploits identity between templating and entropic catalysis. Though discovered by computation, selection of an elevated product of template catalysis is plausible, independent of any chemical or mathematical assumption. Selected chemical variation before genetics (chance utility) therefore inaugurates inheritance, even when hindered by unstable, dilute nucleotides, erratically supplied in undependable quantities. Remarkably, such uncontrolled conditions are not necessarily hostile, but can instead accelerate appearance of primordial gene-like behavior.

ChemInform Abstract: Template Catalysis by Metal—Ligand Cooperation. C—C Bond Formation via Conjugate Addition of Non‐Activated Nitriles under Mild, Base‐Free Conditions Catalyzed by a Manganese Pincer Complex.

AbstractThe title transformation proves efficient for the Michael addition of non‐activated aliphatic nitriles onto α,β‐unsaturated carbonyl compounds, including ester and cyclic or acyclic keto derivatives.

Template Catalysis by Metal-Ligand Cooperation. C-C Bond Formation via Conjugate Addition of Non-activated Nitriles under Mild, Base-free Conditions Catalyzed by a Manganese Pincer Complex.

The first example of a catalytic Michael addition reaction of non-activated aliphatic nitriles to α,β-unsaturated carbonyl compounds under mild, neutral conditions is reported. A new de-aromatized pyridine-based PNP pincer complex of the Earth-abundant, first-row transition metal manganese serves as the catalyst. The reaction tolerates a variety of nitriles and Michael acceptors with different steric features and acceptor strengths. Mechanistic investigations including temperature-dependent NMR spectroscopy and DFT calculations reveal that the cooperative activation of alkyl nitriles, which leads to the generation of metalated nitrile nucleophile species (α-cyano carbanion analogues), is a key step of the mechanism. The metal center is not directly involved in the catalytic bond formation but rather serves, cooperatively with the ligand, as a template for the substrate activation. This approach of "template catalysis" expands the scope of potential donors for conjugate addition reactions.

Synthesis and characterization of mesoporous graphite carbon, and adsorption performance for benzene

In this paper, graphite carbon with a mesoporous structure was synthesized using the template–catalysis procedure with hydrated metal oxide nanoparticle as template and catalyst, phenol and formaldehyde as carbon source. XRD, Raman, BET and TEM analyses were performed to study the effluence of synthetic conditions on the structure of samples. The adsorption performances for benzene vapor were evaluated. The results show that CCo and CFe samples have mesoporous graphitized carbon structures. The molar amount of template to carbon source significantly affects the specific surface area, pore structure and adsorption–desorption performance. The specific surface area of CCo-1, with the best graphite structure, was 287.638 m2/g, the pore size was 19.075 nm, and the adsorption capacity for benzene vapor was 19.615 mmol/g. The synergistic effect between the cobalt element and graphite carbons affects the adsorption capacity of CCo-3, which was 34.643 mmol/g. However, the desorption efficiency was only 89 %, and the adsorption performance of CCo-3 material was degraded greatly after three times run.

New examples of template catalysis based processes: glycerol-like units as efficient promoters for dehydrative nucleophilic substitutions of ferrocenylmethanol

The direct high-yield synthesis without solvent and catalyst, under mild conditions, of eleven novel mono substituted ferrocenylmethyl ethers and amine derivatives from ferrocenemethanol and vicinal oxygenated alcohols and amines is here reported. The peculiar ability of these classes of non acidic compounds to favor the dehydrative nucleophilic substitution is attributed to the presence of vicinal oxygen atoms to the reactive group able to build a hydrogen bonding network with the reactant. The role of carbon dioxide and hexafluoroisopropanol was investigated to support the hypothesis that a template catalysis effect is occurring. The in vitro anti-fungal activity of some of these derivatives was tested on two plant fungi, Botrytis cinerea and Penicillium species, with moderate activity.

4‐exo Cyclizations by Template Catalysis

4‐<i>exo</i> Cyclizations by Template Catalysis

Designed RNAs with Two Peptide-Binding Units as Artificial Templates for Native Chemical Ligation of RNA-Binding Peptides

The template effect plays important roles not only in modern synthetic and enzymatic catalysis but also in the ancient "RNA-polypeptide (RNP) world," which has been postulated to be a crucial stage in the origin of life. To mimic primitive template catalysis of peptide ligations by RNAs, we previously reported the design and synthesis of a ternary RNP complex in which the ligation of two peptides was significantly facilitated by a template RNA with two peptide-binding units. However, RNA molecules also promoted the ligation reaction in a nonspecific manner through electrostatic interactions between RNA and basic peptides. In this study, we suppressed this effect by reducing the length of the original template derived from the Tetrahymena intron RNA. This modification, however, decreased the template ability for the specific reaction. As an alternative RNA that was as effective as the original template, we found that a self-dimerizing RNA was a promising template for peptide ligation without a nonspecific effect.

Novel DNA Catalysts Based on G‐Quadruplex Recognition

An unlikely hero: Selective small-molecule recognition of a specific DNA secondary structure, instead of hybridization, can be exploited to template catalysis between two reactants. Here, we show that a proline-tethered quadruplex DNA, as shown in the figure, can serve as catalyst for the aldol reaction between a porphyrin-bearing aldehyde and a ketone.

Electrophilic aromatic chlorination and haloperoxidation of chloride catalyzed by polyfluorinated alcohols: a new manifestation of template catalysis.

We have demonstrated that a polyfluorinated alcohol, 2,2,2-trifluoroethanol, solvent enables haloperoxidase type activity and the oxychlorination of arenes (benzene and its alkylated derivatives) without a metal catalyst. The polyfluorinated alcohol has a dual function; it catalyzes electrophilic chlorination of less reactive arenes by several orders of magnitude and oxidation of chloride at lower H+ concentrations. DFT calculations show that a complementary charge template in the transition state explains the catalysis of the electrophilic chlorination.

Fluorinated alcohols enable olefin epoxidation by H2O2: template catalysis.

Experimental observations show that direct olefin epoxidation by H(2)O(2), which is extremely sluggish otherwise, occurs in fluorinated alcohol (R(f)OH) solutions under mild conditions requiring no additional catalysts. Theoretical calculations of ethene and propene epoxidation by H(2)O(2) in the gas phase and in the presence of methanol and of two fluorinated alcohols, presented in this paper, show that the fluoro alcohol itself acts as a catalyst for the reaction by providing a template that stabilizes specifically the transition state (TS) of the reaction. Thus, much like an enzyme, the fluoro alcohol provides a complementary charge template that leads to the reduction of the barrier by 5-8 kcal mol(-)(1). Additionally, the fluoro alcohol template keeps the departing OH and hydroxyalkenyl moieties in close proximity and, by polarizing them, facilitates the hydrogen migration from the latter to form water and the epoxide product. The reduced activation energy and structural confinement of the TS over the fluoro alcohol template render the epoxidation reaction observable under mild synthetic conditions.

Template Catalysis: Catalytic Metalation of Porphyrins by Apocytochrome b562

Template Catalysis: Catalytic Metalation of Porphyrins by Apocytochrome <i>b</i>₅₆₂

Template catalysis via non-transition metal complexes. New highly selective syntheses on phenol systems

Abstract

Template catalysis of acetyl transfer reactions

Acetyl adenylate, 2′(3′)-O- acetyl adenosine and 5′-O- acetyl adenosine, like adenosine itself, form ordered helices with polyuridylic acid in the presence of Na + and Mg 2+. The transfer of acetate from acetyl adenylate to [8- 14C]adenosine is facilitated in the presence of polyuridylic acid and occurs specifically to the 2′(3′)-position. Under the same condition, 2′(3′)-O- acetyl adenosine transfers acetate to the 5′-position of adenosine. However, 5′-O- acstyl adenosine transfers acetate to both the 2′(3′)- and 5′-positions of adenosine. These results establish that a polyuridylic acid template is capable of orienting adenosine derivatives in such a way as to bring about highly specific intramolecular acetyl transfer reactions.

Template catalysis: asymmetric polymerization of amino acids on clay minerals.

SURFACE catalysis and epitaxis are controlled by crystallographic factors. Molecules adsorbed on solid phase boundaries exhibit different physical chemical properties from the same molecules when present in a solution. In solid state conditions a lowering in activation energies is frequently observed and amino-acids may polymerize to peptides and proteins once they are attached on a solid surface. The mineral surface simply acts as a selective lattice.