Synthesis of seven-membered nitrogen heterocycles through the Ugi multicomponent reaction

Diastereoselective Synthesis of Highly Functionalized γ-Lactams via Ugi Reaction/Michael Addition

The γ-lactam ring is a prominent feature in medicinal chemistry, and its synthesis has garnered significant interest due to its valuable properties. Among the γ-lactams, 2-oxopyrrolidine-3-carbonitrile derivatives stand out as versatile synthons that can be readily transformed into a variety of other functional groups. In this work, we successfully synthesized highly functionalized 3-cyano-2-pyrrolidinones with moderate to good overall yields using the Ugi reaction followed by intramolecular Michael addition. The process demonstrated excellent diastereoselectivity and showed good tolerance to a range of isonitriles and carbonyl compounds.

Multicomponent reactions driving the discovery and optimization of agents targeting central nervous system pathologies

The ongoing quest to discover effective treatments for diseases remains a significant challenge for the scientific community. Multicomponent reactions (MCRs) have emerged as powerful tools in accelerating drug discovery, enabling the rapid generation of chemical libraries with high diversity in a time-efficient and environmentally sustainable manner. In this review, we focus on central nervous system (CNS) disorders, particularly Alzheimer's disease, Parkinson's disease, schizophrenia, depression, and epilepsy, where MCRs have contributed to the development of promising ligands in recent years. Rather than providing an exhaustive overview, this review aims to highlight key studies that address major CNS pathologies, relevant drug targets, and various MCR approaches. We have carefully selected representative articles and apologize to the authors whose important contributions may not be included. By concentrating on these pivotal studies, we strive to offer a clear and concise perspective on current research trends and breakthroughs in this field.

Stefano Marcaccini: a pioneer in isocyanide chemistry

Stefano Marcaccini was one of the pioneers in the use of isocyanide-based multicomponent reactions in organic synthesis. Throughout his career at the University of Florence he explored many different faces of isocyanide chemistry, especially those geared towards the synthesis of biologically relevant heterocycles. His work inspired many researchers who contributed to other important developments in the field of multicomponent reactions and created a school of synthetic chemists that continues today. In this manuscript we intend to review the articles on isocyanide multicomponent reactions published by Dr. Marcaccini and analyse their influence on the following works by other researchers. With this, we hope to highlight the immense contribution of Stefano Marcaccini to the development of isocyanide chemistry and modern organic synthesis as well as the influence of his research on future generations. We believe that this review will not only be a well-deserved tribute to the figure of Stefano Marcaccini, but will also serve as a useful inspiration for chemists working in this field.

New oxacycles on the block: benzodioxepinones via a Passerini reaction

Oxacycles and benzoxepanes are privileged motifs present in a variety of natural products and functional molecules. However, their synthetic access is limited. Here, we demonstrate a rapid synthesis of unprecedented benzoxepanes from readily available starting materials in one step via a Passerini multicomponent reaction. The reaction proceeds smoothly under mild reaction conditions. We have obtained a single-crystal X-ray structure, revealing a butterfly conformation, combined with useful structural features. In addition, we have performed both a full interaction map on the X-ray structure and a profile analysis of a virtual library based on the proposed scaffold with a special focus on certain physicochemical parameters to demonstrate their potential usage in drug discovery.

Reinvestigation of Passerini and Ugi scaffolds as multistep apoptotic inducers via dual modulation of caspase 3/7 and P53-MDM2 signaling for halting breast cancer

Selective induction of breast cancer apoptosis is viewed as the mainstay of various ongoing oncology drug discovery programs. Passerini scaffolds have been recently exploited as selective apoptosis inducers via a caspase 3/7 dependent pathway. Herein, the optimized Passerini caspase activators were manipulated to synergistically induce P53-dependent apoptosis via modulating the closely related P53-MDM2 signaling axis. The adopted design rationale and synthetic routes relied on mimicking the general thematic features of lead MDM2 inhibitors incorporating multiple aromatic rings. Accordingly, the cyclization of representative Passerini derivatives and related Ugi compounds into the corresponding diphenylimidazolidine and spiro derivative was performed, resembling the nutlin-based and spiro MDM-2 inhibitors, respectively. The study was also extended to explore the apoptotic induction capacity of the scaffold after simplification and modifications. MTT assay on MCF-7 and MDA-MB231 breast cancer cells compared to normal fibroblasts (WI-38) revealed their promising cytotoxic activities. The flexible Ugi derivatives 3 and 4, cyclic analog 8, Passerini adduct 12, and the thiosemicarbazide derivative 17 were identified as the study hits regarding cytotoxic potency and selectivity, being over 10-folds more potent (IC50 = 0.065-0.096 μM) and safer (SI = 4.4-18.7) than doxorubicin (IC50 = 0.478 μM, SI = 0.569) on MCF-7 cells. They promoted apoptosis induction via caspase 3/7 activation (3.1-4.1 folds) and P53 induction (up to 4 folds). Further apoptosis studies revealed that these compounds enhanced gene expression of BAX by 2 folds and suppressed Bcl-2 expression by 4.29-7.75 folds in the treated MCF-7 cells. Docking simulations displayed their plausible binding modes with the molecular targets and highlighted their structural determinants of activities for further optimization studies. Finally, in silico prediction of the entire library was computationally performed, showing that most of them could be envisioned as drug-like candidates.

Isocyanide-Based Multicomponent Reactions in Water: Advanced Green Tools for the Synthesis of Heterocyclic Compounds

Reaction rate acceleration using green methods is an intriguing area of research for chemists. In this regard, water as a "green solvent" plays a crucial role in the acceleration of some organic transformations and reveals exclusive selectivity and reactivity in comparison with conventional organic solvents. In particular, multicomponent reactions (MCRs) as sustainable tools lead to the rapid generation of small-molecule libraries in water and aqueous media due to the prominent role of the hydrophobic effect. MCRs, as diversity-oriented synthesis (DOS) methods, have great efficiency with simple operations, atom, pot, and step economy synthesis, and mechanistic beauty. Among diverse classes of MCRs, isocyanide-based multicomponent reactions (I-MCRs), as sustainable and versatile reactions, have gained considerable attention in the synthesis of diverse heterocycle rings, especially in drug design because of the peculiar nature of isocyanide as a particular active reactant. I-MCRs that are performed in water are mild, environmentally friendly, and easily controlled, and have a reduced number of workup, purification, and extraction steps, which fit well with the advantages of "green" chemistry. Performing these powerful organic transformations in water and aqueous media is accompanied by acceleration owing to negative activation volumes, which originate from connecting several reactants together to generate a single product. It should be noted that the combination of MCR strategy and aqueous phase reaction is of growing interest for the development of sustainable synthetic techniques in organic conversions. However, an exclusive account focusing on the recent progress in eco-friendly I-MCRs for the construction of heterocycles in water and aqueous media is particularly lacking. This review highlights the progress of various kinds of I-MCRs in water and aqueous media as benign methods for the efficient construction of vital heterocyclic scaffolds, with a critical discussion of the subject in the period 2000-2021. We hope that this themed collection will be of interest and beneficial for organic and pharmaceutical chemists and will inspire more reaction development in this fascinating field.

The synthesis of seven- and eight-membered rings by radical strategies

Radical strategies for preparation of seven- or eight-membered rings.

The 100 facets of the Passerini reaction

This perspective aims at celebrating the 100th anniversary of the discovery of the Passerini three component reaction. After being nearly neglected for many years, now this reaction has become quite popular, thanks to the achievements of the last 30 years, which have revealed several chances of exploitation in organic synthesis. Though not being comprehensive, this review means to show the various ways that have been used in order to expand the utility of the Passerini reaction. Post-MCR transformations to give heterocycles or peptidomimetics, variants through single component replacement, stereochemical issues, and applications in total syntheses will be especially covered.

Application of Oxidative Ring Opening/Ring Closing by Reductive Amination Protocol for the Stereocontrolled Synthesis of Functionalized Azaheterocycles

The current Account gives an insight into the synthesis of some N-heterocyclic β-amino acid derivatives and various functionalized saturated azaheterocycles accessed from substituted cycloalkenes via ring C=C bond oxidative cleavage followed by ring closing across double reductive amination. The ring-cleavage protocol has been accomplished according to two common approaches: a) Os-catalyzed dihydroxylation/NaIO4 vicinal diol oxidation and b) ozonolysis. A comparative study on these methodologies has been investigated. Due to the everincreasing relevance of organofluorine chemistry in drug research as well as of the high biological potential of β-amino acid derivatives several illustrative examples to the access of various fluorine-containing piperidine or azepane β-amino acid derivatives are also presented in the current Account.

1 Introduction

2 Olefin-Bond Transformation by Oxidative Ring Cleavage

3 Synthesis of Saturated Azaheterocycles via Oxidative Ring-Opening/Ring-Closing Double Reductive Amination

3.1 Importance of Fluorine-Containing Azaheterocycles in Pharmaceutical Research

3.2 Synthesis of Azaheterocyclic Amino Acid Derivatives with a Piperidine or Azepane Framework through Oxidative Ring Opening/Reductive Amination

3.2.1 Synthesis of Piperidine β-Amino Esters

3.2.2 Synthesis of Azepane β-Amino Esters

3.2.3 Synthesis of Fluorine-Containing Piperidine γ-Amino Esters

3.3 Synthesis of Tetrahydroisoquinoline Derivatives through Oxidative Ring Opening/Reductive Amination Protocol

3.4 Synthesis of Functionalized Benzazepines through Reductive Amination

3.4.1 Synthesis of Benzo[c]azepines

3.4.2 Synthesis of Benzo[d]azepines

3.5 Synthesis of Various N-Heterocycles via Ozonolysis/Reductive Amination

3.5.1 Synthesis of Compounds with an Azepane Ring

3.5.2 Synthesis of Piperidine β-Amino Acids and Piperidine-Fused β-Lactams

3.5.3 Synthesis of γ-Lactams with a Piperidine Ring

3.5.4 Synthesis of other N-Heterocycles

4 Summary and Outlook

5 List of Abbreviations

Palladium-catalyzed Ugi-type reaction of 2-iodoanilines with isocyanides and carboxylic acids affording N-acyl anthranilamides

The first palladium-catalyzed Ugi-type multicomponent reaction for the synthesis of N-acyl anthranilamides from isocyanides, 2-iodoanilines and carboxylic acids has been developed. This method provides expeditious and highly efficient access to structurally diverse N-acyl anthranilamides from readily available starting materials with good functional group compatibility. The utility of this method has been demonstrated by the late stage functionalization of two commercial drugs: Flurbiprofen and Loxoprofen.

Multicomponent reactions as a potent tool for the synthesis of benzodiazepines

Benzodiazepines (BZDs), a diverse class of benzofused seven-membered N-heterocycles, display essential pharmacological properties and play vital roles in some biochemical processes. They have mainly been prescribed as potential therapeutic agents, which interestingly represent various biological activities such as anticancer, anxiolytic, antipsychotic, anticonvulsant, antituberculosis, muscle relaxant, and antimicrobial activities. The extensive biological activities of BZDs in various fields have encouraged medicinal chemists to discover and design novel BZD-based scaffolds as potential therapeutic candidates with the favorite biological activity through an efficient protocol. Although certainly valuable and important, conventional synthetic routes to these bicyclic benzene compounds contain methodologies often requiring multistep procedures, which suffer from waste materials generation and lack of sustainability. By contrast, multicomponent reactions (MCRs) have recently advanced as a green synthetic strategy for synthesizing BZDs with the desired scope. In this regard, MCRs, especially Ugi and Ugi-type reactions, efficiently and conveniently supply various complex synthons, which can easily be converted to the BZDs via suitable post-transformations. Also, MCRs, especially Mannich-type reactions, provide speedy and economic approaches for the one-pot and one-step synthesis of BZDs. As a result, various functionalized-BZDs have been achieved by developing mild, efficient, and high-yielding MCR protocols. This review covers all aspects of the synthesis of BZDs with a particular focus on the MCRs as well as the mechanism chemistry of synthetic protocols. The present manuscript opens a new avenue for organic, medicinal, and industrial chemists to design safe, environmentally benign, and economical methods for the synthesis of new and known BZDs.

Effective microwave-assisted approach to 1,2,3-triazolobenzodiazepinones via tandem Ugi reaction/catalyst-free intramolecular azide-alkyne cycloaddition

A novel catalyst-free synthetic approach to 1,2,3-triazolobenzodiazepinones has been developed and optimized. The Ugi reaction of 2-azidobenzaldehyde, various amines, isocyanides, and acids followed by microwave-assisted intramolecular azide-alkyne cycloaddition (IAAC) gave a series of target heterocyclic compounds in moderate to excellent yields. Surprisingly, the normally required ruthenium-based catalysts were found to not affect the IAAC, only making isolation of the target compounds harder while the microwave-assisted catalyst-free conditions were effective for both terminal and non-terminal alkynes.

Syntheses and medicinal chemistry of azepinoindolones: a look back to leap forward

Nitrogen-containing heterocyclic scaffolds constitute nearly 75% of small molecules which favorably act as drug candidates. For the past few decades, numerous natural and synthetic indole-based scaffolds have been reported for their diverse pharmacological profiles. In particular, indole-fused azepines, termed azepinoindolones, have come under the radar of medicinal chemists owing to their synthetic and pharmacological importance. A plethora of literature reports has been generated thereof, which calls for the need for the compilation of information to understand their current status in drug discovery. Accumulating reports of evidence suggest that compounds containing this privileged scaffold display their cytotoxic effects via inhibition of kinase, topoisomerase I, mitochondrial malate dehydrogenase (mMDH), and tubulin polymerization and as DNA minor groove binding agents. Herein, we endeavor to present a closer look at the advancements of various synthetic and derivatization methods of azepinoindolone-based compounds. We have further extended our efforts to discuss the pharmacological effects of azepinoindolones in the whole range of medicinal chemistry as anti-Alzheimer, anticancer, anti-inflammatory, antidiabetic, antileishmanial, and antipyranosomal agents and as drug delivery vectors. Our analysis of recent advances reveals that azepinoindolones will continue to serve as potential pharmaceutical modalities in the years to come and their substantial pool of synthetic methods will be ever expanding.

Controlling the stereochemistry in 2-oxo-aldehyde-derived Ugi adducts through the cinchona alkaloid-promoted electrophilic fluorination

In this report, we introduce a new strategy for controlling the stereochemistry in Ugi adducts. Instead of controlling stereochemistry directly during the Ugi reaction we have attempted to stereodefine the chiral center at the peptidyl position through the post-Ugi functionalization. In order to achieve this, we chose to study 2-oxo-aldehyde-derived Ugi adducts many of which partially or fully exist in the enol form that lacks the aforementioned chiral center. This in turn led to their increased nucleophilicity as compared to the standard Ugi adducts. As such, the stereocenter at the peptidyl position could be installed and stereodefined through the reaction with a suitable electrophile. Towards this end, we were able to deploy an asymmetric cinchona alkaloid-promoted electrophilic fluorination producing enantioenriched post-Ugi adducts fluorinated at the peptidyl position.

Stereodivergent access to all four stereoisomers of chiral tetrahydrobenzo[f][1,4]oxazepines, through highly diastereoselective multicomponent Ugi–Joullié reaction

Starting from easily accessible chiral enantiopure 1,2-amino alcohols and salicylaldehydes, a concise route to cyclic imines has been developed. These chiral cyclic imines undergo a highly diastereoselective Ugi–Joullié reaction to give trans tetrahydrobenzo[f][1,4]oxazepines with the introduction of up to 4 diversity inputs. The cis isomer may also be attained, thanks to a thermodynamically controlled base catalysed epimerization. Free secondary amines have been obtained using an unprecedented “removable” carboxylic acid.

Starting from easily accessible enantiopure 1,2-aminoalcohols and salicylaldehydes, a concise and diastereodivergent route to tetrahydrobenzo[f][1,4]oxazepines has been developed.

Organophotoredox Catalysis: Visible-light-induced Multicomponent Synthesis of Chromeno[4, 3-b]chromene and Hexahydro-1H-xanthene Derivatives

Background:

In recent years, photoredox catalysis using eosin Y has gained considerable significance in organic chemistry. It is evolving as a powerful approach in modern organic synthesis for the activation of small molecules.

Objective:

The use of organic dyes to convert visible light into chemical energy by involving a single-electron transfer with organic substrates has innumerable applications.

Method and Results:

The present strategy is the first example of visible light promoted, aerobic, oxidative cyclization of chromeno[4,3-b]chromenes and hexahydro-1H-xanthenes via the formation of C–O and C–C bonds to afford excellent yield of the products in a simple one-pot operation under mild reaction conditions.

Conclusion:

The major advantages of the present methodology include short reaction time, cost effectiveness, easy work-up, broad substrate scope and high atom economy.

Multicomponent synthesis of α-acylamino and α-acyloxy amide derivatives of desmycosin and their activity against gram-negative bacteria

Bacterial resistance to the existing drugs requires constant development of new antibiotics. Developing compounds active against gram-negative bacteria thereby is one of the more challenging tasks. Among the many approaches to develop successful antibacterials, medicinal chemistry driven evolution of existing successful antibiotics is considered to be the most effective one. Towards this end, the C-20 aldehyde moiety of desmycosin was modified into α-acylamino and α-acyloxy amide functionalities using isonitrile-based Ugi and Passerini reactions, aiming for enhanced antibacterial and physicochemical properties. The desired compounds were obtained in 45-93% yield under mild conditions. The antibacterial activity of the resulting conjugates was tested against gram-negative Aliivibrio fischeri. The antibiotic strength is mostly governed by the amine component introduced. Thus, methylamine derived desmycosin bis-amide 4 displayed an enhanced inhibition rate vs. desmycosin (99% vs. 83% at 1 µM). Derivatives with long acyclic or bulky amine and isocyanide Ugi components reduced potency, whereas carboxylic acid reagents with longer chain length afforded increased bioactivity. In Passerini 3-component products, the butyric ester amide 22 displayed a higher activity (90% at 1 µM) than the parent compound desmycosin (2).

Multicomponent Synthesis of Polyphenols and their in vitro Evaluation as Potential β-Amyloid Aggregation Inhibitors

While plant polyphenols possess a variety of biological properties, exploration of chemical diversity around them is still problematic. Here, an example of application of the Ugi multicomponent reaction to the combinatorial assembly of artificial, yet "natural-like", polyphenols is presented. The synthesized compounds represent a second-generation library directed to the inhibition of β-amyloid protein aggregation. Chiral enantiopure compounds, and polyphenol-β-lactam hybrids have been prepared too. The biochemical assays have highlighted the importance of the key pharmacophores in these compounds. A lead for inhibition of aggregation of truncated protein AβpE3-42 was selected.

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.

Hexafluoroisopropanol as the Acid Component in the Passerini Reaction: One-Pot Access to β-Amino Alcohols

A new Passerini-type reaction in which hexafluoroisopropanol functions as the acid component is reported. The reaction tolerates a broad range of isocyanides and aldehydes, and the formed imidates can be reduced toward β-amino alcohols under mild and metal-free conditions. In addition, the imidate products were shown to undergo an unprecedented retro-Passerini-type reaction under microwave conditions, providing valuable mechanistic information about the Passerini reaction and its variations.

Copper-catalyzed radical Heck type cyclization: a three-component reaction of DABCO·(SO2)2, aryldiazonium tetrafluoroborates and dienes toward sulfonated benzo- seven-membered nitrogen heterocycles

A three-component reaction of the sulfur dioxide surrogate of DABCO·(SO₂)₂, aryldiazonium tetrafluoroborates and dienes has been developed, affording a series of sulfonated nitrogen heterocycles.