Organocatalytic Synthesis of Drugs and Bioactive Natural Products

1-{(1S,2S,4R)-7,7-Dimethyl-1-[(pyrrolidin-1-yl)methyl]bicyclo [2.2.1]heptan-2-yl}-1H-benzo[d]imidazole

A three-step synthesis of 1-{(1S,2S,4R)-7,7-dimethyl-1-[(pyrrolidin-1-yl)methyl]bicyclo[2.2.1]heptan-2-yl}-1H-benzo[d]imidazole, prepared from camphor derived diamine, is disclosed. The absolute configuration at the chiral center bearing benzo[d]imidazole moiety was confirmed by NOESY. The structure of a newly synthesized compound was confirmed by 1H- and 13C-NMR, 2D NMR, IR spectroscopy, and high resolution mass-spectrometry.

New boro amino amide organocatalysts for asymmetric cross aldol reaction of ketones with carbonyl compounds

Distinct types of new boron fused primary amino amide organocatalysts were designed and synthesized from commercially available amino acids. Their catalytic activities were investigated in asymmetric crossed aldol reaction of ketones with aromatic aldehydes to afford the corresponding chiral anti-aldol adducts with good chemical yields, moderate diastereoselectivity and good to excellent enantioselectivities (up to 94% yields, up to 90 : 10 dr, up to 94% ee).

Efficient methods for the synthesis of chiral 2-oxazolidinones as pharmaceutical building blocks

Although the wide variety of heterocyclic compounds is common knowledge, chiral 2-oxazolidinones are recognized as some of the most important heterocycles in medicinal chemistry. Many important pharmaceutical molecules have been constructed based on the chiral 2-oxazolidinone backbone. Therefore, the development of even more efficient catalytic methods for the synthesis of chiral 2-oxazolidinones remains a very important pursuit in the field of synthetic organic chemistry. This review summarizes the coupling reactions of epoxides and isocyanates for the preparation of 2-oxazolidinones. Both metal catalysts and organocatalysts promote these reactions. Optically pure 2-oxazolidinones are prepared from optically pure epoxide substrates via these catalytic methods. A synthetic example of a commercially available pharmaceutical compound utilizing this method is also introduced.

Synthetic drives for useful drug molecules through organocatalytic methods

The treatment of various pathological conditions in human beings involves the use of safe and efficacious drug substances. But there are different complications associated with the treatment of various disease states including drug resistance, adverse drug reactions, toxicity, etc. To minimize these problems, there is an urgent need to develop new therapeutics with suitable pharmacokinetic and pharmacodynamic properties. So, the organocatalytic methods are emerged as a potential synthetic tool to accelerate the design of new drug candidates with improved physicochemical and pharmacological properties, selectivity, and efficiency for the treatment of life-threatening diseases. Organocatalytic reactions refer to the chemical reaction that is accelerated by organic catalysts instead of using organometallic catalysts. Organocatalysts are more advantageous in comparison to metallic catalysts because organocatalysts are cost-effective, stable, efficient, non-toxic, readily available, and easy to handle. In addition to this, the organocatalysis method involves an eco-friendly reaction by minimizing the formation of by-products and reducing the chemical hazards. Organocatalysts are categorized into four classes such as Lewis acids, Lewis bases, Bronsted acids, and Bronsted bases. These catalysts are generally involved in various reactions mechanisms such as Aldol reaction, Diels–Alder reactions, Michael Addition and Knoevenagal reactions, etc. The utility of organocatalyst in synthetic chemistry results in the development of medicinally active compounds with diverse structural features.

Horizons in Asymmetric Organocatalysis: En Route to the Sustainability and New Applications

Nowadays, the development of new enantioselective processes is highly relevant in chemistry due to the relevance of chiral compounds in biomedicine (mainly drugs) and in other fields, such as agrochemistry, animal feed, and flavorings. Among them, organocatalytic methods have become an efficient and sustainable alternative since List and MacMillan pioneering contributions were published in 2000. These works established the term asymmetric organocatalysis to label this area of research, which has grown exponentially over the last two decades. Since then, the scientific community has attended to the discovery of a plethora of organic reactions and transformations carried out with excellent results in terms of both reactivity and enantioselectivity. Looking back to earlier times, we can find in the literature a few examples where small organic molecules and some natural products could act as effective catalysts. However, with the birth of this type of catalysis, new chemical architectures based on amines, thioureas, squaramides, cinchona alkaloids, quaternary ammonium salts, carbenes, guanidines and phosphoric acids, among many others, have been developed. These organocatalysts have provided a broad range of activation modes that allow privileged interactions between catalysts and substrates for the preparation of compounds with high added value in an enantioselective way. Here, we briefly cover the history of this chemistry, from our point of view, including our beginnings, how the field has evolved during these years of research, and the road ahead.

Bifunctional amino sulfonamide-catalyzed asymmetric conjugate addition to alkenyl alkynyl ketimines as enone surrogates

A bifunctional amino sulfonamide-catalyzed asymmetric conjugate addition of aldehydes to alkenyl alkynyl ketimines as reactive surrogates for enones has been developed. Use of a phenylcyclopropane-based amino sulfonamide catalyst, which can activate and orient the ketimines through hydrogen bonding, affords the desired conjugate adducts with high chemo-, diastereo- and enantioselectivity.

Simple primary β-amino alcohols as organocatalysts for the asymmetric Michael addition of β-keto esters to nitroalkenes

Simple primary β-amino alcohols act as an efficient organocatalysts in the asymmetric Michael addition of β-keto esters with nitroalkenes affording highly pure chiral Michael adducts. Also, both enantiomers of the adducts were obtained, depending on the specific catalyst used and reaction temperature.

Proton-deuterium exchange of acetone catalyzed in imidazolium-based ionic liquid-D2O mixtures

The reaction of the proton–deuterium exchange of acetone in imidazolium-based ionic liquid (IL)–deuterium oxide mixtures was studied in detail via NMR spectroscopy. Certain ILs exhibit considerable catalytic properties and contribute to the course of reaction up to the complete deuteration. The efficiency of deuterium exchange crucially depends on the features of ILs; the type of anion and chain length of cation. The linear secondary isotope effects on the NMR chemical shifts of the ¹³C atoms in acetone were observed depending on the deuteration level of the molecule.

The reaction of the proton–deuterium exchange of acetone in imidazolium-based ionic liquid (IL)–deuterium oxide mixtures was studied in detail via NMR spectroscopy.

Ambident Reactivity of Imidazolium Cations as Evidence of the Dynamic Nature of N-Heterocyclic Carbene-Mediated Organocatalysis

This work reveals ambident nucleophilic reactivity of imidazolium cations towards carbonyl compounds at the C2 or C4 carbene centers depending on the steric properties of the substrates and reaction conditions. Such an adaptive behavior indicates the dynamic nature of organocatalysis proceeding via a covalent interaction of imidazolium carbenes with carbonyl substrates and can be explained by generation of the H-bonded ditopic carbanionic carbenes.

Organocatalysis: Trends of Drug Synthesis in Medicinal Chemistry

Background:

The continuous increase in challenges associated with the effective treatment of life threatening diseases influences the development of drug therapies with suitable physicochemical properties, efficiency and selectivity. So, organocatalysis is a potential synthetic tool which is accelerating the development of new drug molecules.

Methods:

Organocatalysis reactions can be carried out at lower temperatures and in milder pH conditions as compared to metal based catalysed reactions. Due to ready availability of catalysts, stability, purity, low toxicity and easy in handling of the chemical reactions, it has become an attractive technique to synthesise complex molecules with diverse structures. Here, the impact of various catalysts in organic synthesis with methods is discussed.

Results:

Organic catalysts are used widely in various chemical reactions such as Michael Addition, aldol reaction, Diels-Alder reactions and Knoevenagal reactions. It was observed that the use of organocatalyst results in the formation of stereo active molecules with diverse biological activities.

Conclusion:

This review also focuses on the various scopes and limitations of organocatalytic reactions in the production of medicinally useful drug molecules. Organocatalysts possess several advantages over traditional metal catalysts because they are non-toxic, readily available, stable, efficient, and easy to handle which involves environmentally friendly reaction.

Brønsted Acid-Catalyzed, Diastereo- and Enantioselective, Intramolecular Oxa-Diels-Alder Reaction of ortho-Quinone Methides and Unactivated Dienophiles

A stereoselective, phosphoric acid-catalyzed synthesis of dihydrochromenochromenes has been developed using transient ortho-quinone methides ( o-QMs). Three contiguous stereogenic centers were formed with excellent yields, partially as single diastereomers and with moderate to excellent enantioselectivity. This intramolecular hetero-Diels-Alder reaction features unactivated dienophiles and o-QM precursors tethered by a simple phenoxy linker and furnishes cycloadducts with a prominent structural motif found in many natural products. Through an appropriate choice of dienophile configuration and backbone substitution either exo- or endo-stereoisomers were formed selectively with up to a 96:04 enantiomeric ratio.

F10BINOL-derived chiral phosphoric acid-catalyzed enantioselective carbonyl-ene reaction: theoretical elucidation of stereochemical outcomes

An enantioselective carbonyl-ene reaction of 1,1-disubstituted olefins with ethyl glyoxylate was accomplished using an F₁₀BINOL-derived chiral phosphoric acid of which the perfluoro-binaphthyl skeleton is beneficial not only for adopting high catalytic activity but also for creating an effective chiral environment.

An F₁₀BINOL-derived chiral phosphoric acid was shown to be an effective catalyst for an enantioselective carbonyl-ene reaction of 1,1-disubstituted olefins with ethyl glyoxylate as the common enophile. The perfluoro-binaphthyl skeleton is beneficial not only for adopting high catalytic activity but also for creating an effective chiral environment for enantioselective transformations. Indeed, the reaction afforded enantio-enriched homoallylic alcohols in high yields with high enantioselectivities. Theoretical studies identified that the multi-point C–H···O hydrogen bonds and the π interactions between the substrates and the 6-methoxy-2-naphthyl substituents at the 3,3′-positions of the F₁₀BINOL skeleton play a crucial role in determining the stereochemical outcomes. The significance of the perfluoro-binaphthyl skeleton in achieving the high enantioselectivity was also evaluated through a structural analysis of the catalysts.

First aromatic amine organocatalysed activation of α,β-unsaturated ketones

The first example of a chiral aromatic amine used to activate α,β-unsaturated ketones in aminocatalysis.

Fe3O4@l-Proline/Pd nanocomposite for one-pot tandem catalytic synthesis of (±)-warfarin from benzyl alcohol: synergistic action of organocatalyst and transition metal catalyst

One-pot synthesis of (±)-warfarin from scratch! The reported catalytic nanocomposite can carry out 3-way catalysis, namely, oxidation, aldol condensation and Michael addition, in a tandem fashion in PEG-400 and water as 'green' reaction media.

Urea Activation by an External Brønsted Acid: Breaking Self-Association and Tuning Catalytic Performance

In this work, we hypothesize that Brønsted acids can activate urea-based catalysts by diminishing its self-assembly tendency. As a proof of concept, we used the asymmetric Friedel–Crafts alkylation of indoles with nitroalkenes as a benchmark reaction. The resulting 3-substituted indole derivatives were obtained with better results due to cooperative effects of the chiral urea and a Brønsted acid additive. Such synergy has been rationalized in terms of disassembly of the supramolecular catalyst aggregates, affording a more acidic and rigid catalytic complex.

Organocatalytic Asymmetric Cascade Reactions Based on Gamma-Nitro Carbonyl Compound

The significant advancements in asymmetric organocascade reactions have been accomplished during the past decades, paving the way to the efficient and stereoselective construction of structurally complex scaffolds from simple and readily available starting materials. Nitro-containing cyclic compounds have become a privileged molecular library given their broad and promising activities in various therapeutic areas. In various approaches to build these valuable scaffolds, the utility of γ-nitrocarbonyl intermediates is one of the most efficient approaches due to its high efficiency, reliability and versatility. The strategies and catalyst systems described here highlight recent advances in the enantioselective synthesis of nitro-containing cyclic molecules via organocascade strategies based on γ-nitrocarbonyl intermediates. Various organocatalysts with distinct activation modes have found application in providing these sophisticated compounds. This review is organized according to the types of organocatalyst. These methods are of importance for the construction of complex chiral cyclic frameworks and the design of new pharmaceutical compounds. We believe that compounds based on nitro-containing cyclic skeletons have the potential to provide novel therapeutic agents and useful biological tools.

Application of the Asymmetric Pictet-Spengler Reaction in the Total Synthesis of Natural Products and Relevant Biologically Active Compounds

Tetrahydroisoquinolines are the framework of numerous natural products predominantly alkaloids, an important and one of the most wide spread families of naturally occurring compounds in the plant kingdom. Tetrahydroisoquinolines are commonly constructed through an old reaction, the so-called Pictet−Spengler Reaction (PSR). In this reaction, a β-aryl ethylamine undergoes an acid mediated condensation with a suitable aldehyde or ketone, followed by ring closure. In this review, we aim to highlight the applications of the asymmetric variant of this old name reaction in the total synthesis of natural products, chiefly, alkaloids, which exhibit significant biological properties.

Investigations towards the stereoselective organocatalyzed Michael addition of dimethyl malonate to a racemic nitroalkene: possible route to the 4-methylpregabalin core structure

Chiral derivatives of γ-aminobutyric acid are widely used as medicines and can be obtained by organocatalytic Michael additions. We show here the stereoselective synthesis of 4-methylpregabalin stereoisomers using a Michael addition of dimethyl malonate to a racemic nitroalkene. The key step of the synthesis operates as a kinetic resolution with a chiral squaramide catalyst. Furthermore, specific organocatalysts can provide respective stereoisomers of the key Michael adduct in up to 99:1 er.

Chiral amine-catalyzed asymmetric conjugate addition of aldehydes to α-phenylselenoenones as formal Z-allylating agents

α-Selenoenones could be employed as Z-allyl precursors in the chiral amine-catalyzed asymmetric conjugate addition of aldehydes.

Gold(I)-Mediated Thiourea Organocatalyst Activation: A Synergic Effect for Asymmetric Catalysis

Several group 11 metal complexes with chiral thiourea organocatalysts have been prepared and tested as organocatalysts. The promising results on the influence of metal-assisted thiourea organocatalysts in the asymmetric Friedel-Crafts alkylation of indole with nitrostyrene are described. Better results with the metal complexes have been achieved because of the cooperative effects between the chiral thiourea and the metal. The synergic effect between both species is higher than the effect promoted by each one separately, especially for gold(I). These outcomes are attributed to a pioneering gold(I) activation of the thiourea catalysts, affording a more acidic and rigid catalytic complex than that provided by the thiourea alone. Furthermore, the use of the gold-thiourea organocatalyst allows reducing the catalyst loading to 1-3 mol %. This contribution could become an important starting point for further investigations opening a new line of research overlooked so far in the literature.