Heterocycles as Key Substrates in Multicomponent Reactions: The Fast Lane towards Molecular Complexity

First-row transition metal for isocyanide-involving multicomponent reactions (IMCR)

First-row transition metal catalyzed transformations that are able to construct complex molecules from simple, readily obtainable feedstocks have become a keystone of modern synthetic organic chemistry. Particularly, the multicomponent reaction (MCR) involving carbon-carbon (C-C) as well as carbon-heteroatom (C-X) bond formation plays an essential role in many chemical conversions, and insurgencies in these reactions powerfully improve the overall synthetic efficiency. Recently, MCRs emerges rapidly because of its greener sides like eco-friendly nature, swift and straightforward execution, high atom/step economy, and construction of aimed product with lowest or no by-product, usually in quantitative yield. Curiously, the exceptional divalent carbon atoms of isocyanides make them predominantly useful components in multicomponent reactions. As a result of widespread research over the past few decades, numerous well-designed and effective procedures for the first-row TM-catalyzed MCR to afford the various entities have been reported. These aspects are summarized in this review article. A particular focus on comparative discussion of various first-row transition-metal catalyzed isocyanide-based multicomponent reactions through mechanistic details included in the review article.

Heterocycle-Based Multicomponent Reactions in Drug Discovery: From Hit Finding to Rational Design

In the context of the structural complexity necessary for a molecule to selectively display a therapeutical action and the requirements for suitable pharmacokinetics, a robust synthetic approach is essential. Typically, thousands of relatively similar compounds should be prepared along the drug discovery process. In this respect, heterocycle-based multicomponent reactions offer advantages over traditional stepwise sequences in terms of synthetic economy, as well as the fast access to chemsets to study the structure activity relationships, the fine tuning of properties, and the preparation of larger amounts for preclinical phases. In this account, we briefly summarize the scientific methodology backing the research line followed by the group. We comment on the main results, clustered according to the targets and, finally, in the conclusion section, we offer a general appraisal of the situation and some perspectives regarding future directions in academic and private research.

Palladium-Catalyzed Cascade 5-endo-dig Cyclization of Ynamides to Form 4-Alkynyloxazolones

The selective synthesis of 4-alkynyloxazolones and their further applications as substrates to electrophile-promoted nucleophilic cyclization have been developed. The reaction of ynamides with terminal alkynes proceeded smoothly to give 4-alkynyloxazolones in the presence of a catalytic amount of palladium(II) acetate. The products were obtained with the sequential formation of new C-C and C-O bonds via a cascade procedure. The first step involved a carbon-oxygen bond formation, via a 5-endo-dig closure, which was confirmed by X-ray analyses of the crystalline sample. Subsequently, the reaction of 4-alkynyloxazolones with an electrophilic selenium source gave 3-phenylselanyl benzofuran derivatives via an electrophile-promoted nucleophilic cyclization.

Two decades of recent advances of Passerini reactions: synthetic and potential pharmaceutical applications

This perspective describes the applications of Passerini reactions in the last two decades from 2000 to 2021 in pharmaceutical applications and synthesis of peptides, natural products, macrocycles, dendrimers, and versatile types of heterocycles.

High-component reactions (HCRs): An overview of MCRs containing seven or more components as versatile tools in organic synthesis

Recently, multi-component reactions (MCRs) have gained special attention due to their versatility for the synthesis of polycyclic heterocycles. Moreover, their applicability can become more widespread as they can be combined together as a union of MCRs. In this overview, the authors have tried to collect the MCRs containing more than seven components that can lead to effectual heterocycles in organic and/or pharmaceutical chemistry. The review contains papers published up to the end of 2020. The subject is classified based on the number of substrates, such as seven-, eight-, nine-, ten-, and more components. The authors expect their report to be helpful for researchers to clarify their route to significant MCRs.

Novel Derivatives of Nicotinic Acid as Promising Anticancer Agents

BACKGROUND

Cancer has become the second leading cause of death worldwide. Despite of the availability of significant number of anticancer agents, cancer is still incurable especially at the last stages. Remarkable targets for anticancer research and drug discovery are heterocyclic compounds, and among them, superior effect has been shown by the nitrogen containing compounds than non-nitrogen containing compounds. Nicotinic acid, a nitrogen containing moiety and its derivatives have gained an immense importance in the development of anticancer drugs owing to the wide variety of biological properties displayed by them.

OBJECTIVE

The objective of this review is to provide researchers the information about various synthetic approaches used for the synthesis of anticancer drugs of nicotinic acid from 2001 onwards and to reveal their application and importance in the treatment of this dreadful disease.

CONCLUSION

As indicated by this review, considerable work has been done in terms of synthesis and investigation of anticancer potential of nicotinamide derivatives. The information provided in this article may be of great value for the researchers seeking to develop efficient anticancer drugs.

Novel Pyran-Linked Phthalazinone-Pyrazole Hybrids: Synthesis, Cytotoxicity Evaluation, Molecular Modeling, and Descriptor Studies

A series of novel pyran-linked phthalazinone-pyrazole hybrids were designed and synthesized by a facile one-pot three-component reaction employing substituted phthalazinone, 1H-pyrazole-5-carbaldehyde, and active methylene compounds. Optimization studies led to the identification of L-proline and ethanol as efficient catalyst and solvent, respectively. This was followed by evaluation of anticancer activity against solid tumor cell lines of lung and cervical carcinoma that displayed IC₅₀ values in the range of 9.8–41.6 µM. Molecular modeling studies were performed, and crucial interactions with the target protein were identified. The drug likeliness nature of the compounds and molecular descriptors such as molecular flexibility, complexity, and shape index were also calculated to understand the potential of the synthesized molecules to act as lead-like molecule upon further detailed biological investigations as well as 3D-QSAR studies.

The Ugi three-component reaction and its variants

A broad variety of α-aminoamide-based compounds have been synthesized via the three-component version of the Ugi reaction (U-3CR) or by any of its variants (Ugi-Zhu-3CR, Orru-3CR, Ugi-4C-3CR, Ugi-Joullié-3CR, GBB-3CR, Ugi-Reissert-3CR, and so on).

Construction of hybrid polycyclic quinolinobenzo[a]phenazinone architectures using solid-state melt reaction (SSMR)

An efficient and versatile protocol for the synthesis of hybrid polycyclic quinolinobenzo[a]phenazinones has been developed under SSMR condition via intramolecular domino Knoevenagel-hetero-Diels-Alder reaction involving the generation of two new six membered fused rings and three contiguous stereogenic centers.

Recent Synthetic Approaches and Biological Evaluations of Amino Hexahydroquinolines and Their Spirocyclic Structures

In this review, the recent synthetic approaches of amino hexahydroquinolines and their spirocyclic structures were highlighted. The synthetic routes include, two-components, three-components or fourcomponents reactions. The two-component [3+3] atom combination reaction represents the simplest method. It involves Michael addition of the electron rich β-carbon of β-enaminones to the activated double bond of cinnamonitriles followed by cyclization to yield hexahydroquinoline compounds. The bioactivity profiles and SAR studies of these compounds were also reviewed with emphasis to the utility of these substances as antimicrobial, anticancer and antitubercular agents, as well as calcium channel modulators.

Green synthesis of spiro[indoline-3,4'-pyrano[2,3-c]pyrazoles] using Fe3O4@l-arginine as a robust and reusable catalyst

The synthesized Fe3O4@l-arginine showed strong catalytic performance in the one-pot synthesis of spiropyranopyrazoles via the reactions of hydrazines, β-keto esters, isatins, and malononitrile or ethyl cyanoacetate under solvent-free conditions. The biologically active heterocyclic compounds including spiropyranopyrazole derivatives were efficiently synthesized in short reaction times and excellent yields in the presence of Fe3O4/l-arginine at room temperature. The highlighted features of the Fe3O4@l-arginine nanocomposite are highly stable, easy to separate, low loading, cost-effective with easy preparation and reusability of the catalyst. The heterogeneous nanocomposite was fully characterized by SEM, EDX, FT-IR, XRD and TEM analysis.

Multicomponent Approach to Libraries of Substituted Dihydroorotic Acid Amides

A process featuring a sequential multicomponent reaction followed by a regioselective postcyclization strategy was implemented for the facile synthesis of N,N'-disubstituted dihydroorotic acid amides under mild conditions. We obtained, for the first time, a library of 29 derivatives, encompassing 19 N^α-substituted-N⁴-dihydroorotyl-4-aminophenylalanine derivatives, a key residue of gonadotropin-releasing hormone antagonist Degarelix. The corresponding products were prepared from easily accessible starting materials in good to excellent yields with broad substrate scope.

Two step, one-pot sequential synthesis of functionalized hybrid polyheterocyclic scaffolds via a solid state melt reaction (SSMR)

A new one pot assembly of highly functionalized benzo[a]phenazinone fused chromene/bicyclic scaffolds via a domino Knoevenagel intramolecular hetero-Diels-Alder (IMHDA) strategy using a solid state melt reaction (SSMR) of 2-hydroxynaphthalene 1,4-dione, o-phenylenediamine, O-allyl salicylaldehyde/O-vinyl salicylaldehyde derivatives is reported. The formation of five new bonds (two C-C bonds and three C-O bonds), three six-membered rings, and three stereogenic centers in a one-pot manner is very attractive. Ease of reaction with short time, good yields with water as the only byproduct and work up free procedure are some of the excellent features of the present protocol.

Progress in the Chemistry of Tetrahydroquinolines

Tetrahydroquinoline is one of the most important simple nitrogen heterocycles, being widespread in nature and present in a broad variety of pharmacologically active compounds. This Review summarizes the progress achieved in the chemistry of tetrahydroquinolines, with emphasis on their synthesis, during the period from mid-2010 to early 2018.

Synthesis of polyheterocycles via multicomponent reactions

Polyheterocycles are one of the most desired synthetic targets due to their numerous and valuable applications in various fields. Multicomponent reactions (MCRs) are highly convergent one-pot processes, in which three or more reagents are combined sequentially to construct complex products, with almost all the atoms coming from the starting reagents. In this context, the syntheses of 'heterocycles' via MCR-based processes have been reviewed a number of times. However, there is not a single review (recent or otherwise) covering the synthesis of 'polyheterocycles' via a direct MCR or via a one-pot process involving MCRs coupled to further cyclizations (via ionic, metal-catalyzed, pericyclic, or free-radical-mediated cyclizations). This issue is consequently the main topic of the present review, which considers work from the last decade. The work is categorized according to the key processes involved in the syntheses of polyheterocycles, aiming to give readers an easy understanding of this MCR-based chemistry and to provide insights for further investigations. The reaction mechanisms providing novel elements to these MCR-based methods for the synthesis of polyheterocycles are also discussed.

An efficient cascade synthesis of substituted 6,9-dihydro-1H-pyrazolo[3,4-f]quinoline- 8-carbonitriles

The synthesis of pyrazolo[3,4-f]quinoline-8-carbonitriles 4a–h and 6a–k involves the reaction of an aromatic aldehyde, 1H-indazol-6-amine and 3-(1H-indol-3-yl)-3-oxopropanenitrile or 3-oxo-3-arylpropanenitrile in ethanol under mild conditions.

Multiple Multicomponent Reactions: Unexplored Substrates, Selective Processes, and Versatile Chemotypes in Biomedicine

Multiple multicomponent reactions rapidly assemble complex structures. Despite being very productive, the lack of selectivity and the reduced number of viable transformations restrict their general application in synthesis. Hereby, we describe a rationale for a selective version of these processes based in the preferential generation of intermediates which are less reactive than the initial substrates. In this way, applying the Groebke-Blackburn-Bienaymé reaction on a range of α-polyamino-polyazines, we prepared a family compact heterocyclic scaffolds with relevant applications in medicinal and biological chemistry (live cell imaging probes, selective binders for DNA quadruplexes, and antiviral agents against human adenoviruses). The approach has general character and yields complex molecular targets in a selective, tunable and direct manner.

Multicomponent polysaccharide-protein bioconjugation in the development of antibacterial glycoconjugate vaccine candidates

A new synthetic strategy for the development of multivalent antibacterial glycoconjugate vaccines is described. The approach comprises the utilization of an isocyanide-based multicomponent process for the conjugation of functionalized capsular polysaccharides of S. pneumoniae and S. Typhi to carrier proteins such as diphtheria and tetanus toxoids. For the first time, oxo- and carboxylic acid-functionalized polysaccharides could be either independently or simultaneously conjugated to immunogenic proteins by means of the Ugi-multicomponent reaction, thus leading to mono- or multivalent unimolecular glycoconjugates as vaccine candidates. Despite the high molecular weight of the two or three reacting biomolecules, the multicomponent bioconjugation proved highly efficient and reproducible. The Ugi-derived glycoconjugates showed notable antigenicity and elicited good titers of functional specific antibodies. To our knowledge, this is the only bioconjugation method that enables the incorporation of two different polysaccharidic antigens to a carrier protein in a single step. Applications in the field of self-adjuvanting, eventually anticancer, multicomponent vaccines are foreseeable.

Green synthesis and antioxidant activity of novel series of benzofurans from euparin extracted of Petasites hybridus

A novel class of benzofuran derivatives is prepared from the isocyanide-based MCR, euparin and aldehydes in the presence of ZnO-nanorods as a catalyst in excellent yields at room temperature under solvent-free conditions as a green reaction medium. Also, the antioxidant activities of some synthesised compounds such as 4a, 4b, 10a and 10b were evaluated by DPPH radical scavenging and ferric reduction activity potential (FRAP) assays. Compound 10b, was shown moderate radical scavenging activity and very good reducing activity compared to standards (BHT and TBHQ).

Dihydroindeno[1,2-b]pyrroles: new Al3+selective off–on chemosensors for bio-imaging in living HepG2 cells

An approach for the expeditious synthesis of a new Al³⁺-selective turn-on dihydroindeno[1,2-b]pyrrole probe under environmentally benevolent conditions and its bio-imaging studies on HepG2 cell.

A facile atom economic one pot multicomponent synthesis of bioactive spiro-indenoquinoxaline pyrrolizines as potent antioxidants and anti-cancer agents

One pot method for the synthesis of biologically active novel spiro-indenoquinoxaline pyrrolizines by means of four-component reaction between ninhydrin, o-phenylenediamine, l-proline and quinolinyl chalcones in methanol via [3+2] cycloaddition.

One-pot syntheses of blue-luminescent 4-aryl-1H-benzo[f]isoindole-1,3(2H)-diones by T3P® activation of 3-arylpropiolic acids

In situ activation of 3-arylpropiolic acids with T3P^® (n-propylphosphonic acid anhydride) initiates a domino reaction furnishing 4-arylnaphtho[2,3-c]furan-1,3-diones in excellent yields. Upon employing these anhydrides as reactive intermediates blue-luminescent 4-aryl-1H-benzo[f]isoindole-1,3(2H)-diones are formed by consecutive pseudo three-component syntheses in a one-pot fashion. The Stokes shifts correlate excellently with the Hammett-Taft σ_R parameter indicating an extended degree of resonance stabilization in the vibrationally relaxed excited singlet state.

New tricks of well-known aminoazoles in isocyanide-based multicomponent reactions and antibacterial activity of the compounds synthesized

The well-known aminoazoles, 3-amino-5-methylisoxazole and 5-amino-N-aryl-1H-pyrazole-4-carboxamides, were studied as an amine component in Ugi and Groebke-Blackburn-Bienaymé multicomponent reactions. The first example of an application of aminoazoles in an Ugi four-component reaction was discovered and novel features of a Groebke-Blackburn-Bienaymé cyclocondensation are established and discussed. The heterocycles obtained were evaluated for their antibacterial activity and several of them demonstrated a weak antimicrobial effect, but for most of the compounds a 30-50% increase in biomass of Gram-positive strains (mainly B. subtilis) compared to control was observed.