Novel applications of resin bound α-amino acids for the synthesis of benzodiazepines (via Wang resin) and ketopiperazines (via hydroxymethyl resin)

Ugi 5-center-4-component reaction of α-amino aldehydes and its application in synthesis of 2-oxopiperazines

A synthetic route leading to densely functionalized 2-oxopiperazines is presented. The strategy employs a 5-center-4-component variant of Ugi multicomponent reaction followed by a deprotection/cyclization sequence. N-Boc-α-amino aldehydes were used for the first time as carbonyl components in a key Ugi 5-center-4-component reaction (U-5C-4CR). It is shown that the presented synthetic route can lead to rigid, heterocyclic scaffolds, as demonstrated by the synthesis of tetrahydro-2H-pyrazino[1,2-a]pyrazine-3,6,9(4H)-trione β-turn mimetic and derivatives of 1,6-dioxooctahydropyrrolo[1,2-a]pyrazine and 3,8-dioxohexahydro-3H-oxazolo[3,4-a]pyrazine.

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.

Isocyanide Multicomponent Reactions on Solid Phase: State of the Art and Future Application

Drug discovery efforts largely depend on access to structural diversity. Multicomponent reactions allow for time-efficient chemical transformations and provide advanced intermediates with three or four points of diversification for further expansion to a structural variety of organic molecules. This review is aimed at solid-phase syntheses of small molecules involving isocyanide-based multicomponent reactions. The majority of all reported syntheses employ the Ugi four-component reaction. The review also covers the Passerini and Groebke-Blackburn-Bienaymé reactions. To date, the main advantages of the solid-phase approach are the ability to prepare chemical libraries intended for biological screening and elimination of the isocyanide odor. However, the potential of multicomponent reactions has not been fully exploited. The unexplored avenues of these reactions, including chiral frameworks, DNA-encoded libraries, eco-friendly synthesis, and chiral auxiliary reactions, are briefly outlined.

Two decades of recent advances of Ugi reactions: synthetic and pharmaceutical applications

Multicomponent reactions (MCRs) are powerful synthetic tools in which more than two starting materials couple with each other to form multi-functionalized compounds in a one-pot process, the so-called "tandem", "domino" or "cascade" reaction, or utilizing an additional step without changing the solvent, the so-called a sequential-addition procedure, to limit the number of synthetic steps, while increasing the complexity and the molecular diversity, which are highly step-economical reactions. The Ugi reaction, one of the most common multicomponent reactions, has recently fascinated chemists with the high diversity brought by its four- or three-component-based isonitrile. The Ugi reaction has been introduced in organic synthesis as a novel, efficient and useful tool for the preparation of libraries of multifunctional peptides, natural products, and heterocyclic compounds with stereochemistry control. In this review, we highlight the recent advances of the Ugi reaction in the last two decades from 2000-2019, mainly in the synthesis of linear or cyclic peptides, heterocyclic compounds with versatile ring sizes, and natural products, as well as the enantioselective Ugi reactions. Meanwhile, the applications of these compounds in pharmaceutical trials are also discussed.

Stereoselective Synthesis of Benzo[e][1,4]oxazino[4,3-a][1,4]diazepine-6,12-diones with Two Diversity Positions

Herein, we report a stereoselective formation of tetrahydro-6H-benzo[e][1,4]oxazino[4,3-a][1,4]diazepine-6,12(11H)-diones. Their preparation consisted in solid-phase synthesis of linear intermediates starting from polymer-supported Ser(tBu)-OH. Using various 2-nitrobenzoic acids and bromoketones, the key intermediates were obtained in five steps and subjected to trifluoroacetic acid-mediated cleavage from the resin, followed by stereoselective reduction with triethylsilane. Subsequent catalytic hydrogenation of the nitro group and cyclization yielded the target compounds with full retention of the C^12a stereocenter configuration.

Synthesis of Tetrazolo-Fused Benzodiazepines and Benzodiazepinones by a Two-Step Protocol Using an Ugi-Azide Reaction for Initial Diversity Generation

A two-step strategy for the synthesis of arrays of tricyclic tetrazolo-fused benzodiazepines and benzodiazepinones has been investigated. The protocol uses ortho-N-Boc phenylisocyanides and phenylglyoxaldehydes or ethyl glyoxylate in the 4-component Ugi-Azide reaction to afford MCR (Multi Component Reactions) derived adducts equipped with the desired diversity inputs. A subsequent acidic treatment (TFA/DCE) allows a simultaneous deprotection-cyclization leading to the final products.

Novel approach to 1,5-benzodiazepine-2-ones containing peptoid backbone via one-pot diketene-based Ugi-4CR

An efficient and simple route for preparation of substituted 1,5-benzodiazepine-2-one containing peptoid backbone is presented. The classical Ugi reaction is considerably extended by application of o-phenylenediamine and diketene as amine and oxo component. 1,3-Dihydro-1,5-benzodiazepine-2-one is generated in situ from these two building blocks combined with isocyanide and aromatic or aliphatic carboxylic acid to assemble the multifunctionalized titled scaffold in high yields. The reaction is performed in the mixture of toluene/CH(2)Cl(2) under reflux condition without catalyst. Conformational isomerism is seen in the solution phase because of restricted free rotation around amide and C-CO bands due to steric bulk of substitutions. In single crystal state, the product is found to possess dimeric structure arising from intermolecular hydrogen bonding.

Two step syntheses of fused quinoxaline-benzodiazepines and bis-benzodiazepines

A two-step solution phase synthesis employing a double UDC (Ugi/Deprotect/Cyclize) strategy has been utilized to obtain fused 6,7,6,6-quinoxalinone-benzodiazepines and 6,7,7,6-bis-benzodiazepines. Optimization of the methodology to produce these tetracyclic scaffolds was enabled by microwave irradiation, incorporation of trifluoroethanol as solvent, and the use of the convertible isocyanide, 4-tert-butyl cyclohexen-1-yl isocyanide.

1,4-Thienodiazepine-2,5-diones via MCR (II): scaffold hopping by Gewald and Ugi-deprotection-cyclization strategy

A second scaffold of 1,4-thienodiazepine-2,5-diones was discovered and is synthetically accessible from Gewald 2-aminothiophenes via Ugi-Deprotection-Cyclization (UDC) strategy. This approach yielded hybrid peptidomimetic diazepine structures with six points of diversity introduced from readily available starting materials. A virtual compound library (N = 50 000) was generated and evaluated for chemical space distribution and drug-like properties.

1,4-Thienodiazepine-2,5-diones via MCR (I): synthesis, virtual space and p53-Mdm2 activity

1,4-Thienodiazepine-2,5-diones have been synthesized via the Ugi-Deprotection-Cyclization (UDC) approach starting from Gewald 2-aminothiophenes in a convergent and versatile manner. The resulting scaffold is unprecedented, cyclic, and peptidomimetic with four points of diversity introduced from readily available starting materials. In addition to eighteen synthesized and characterized compounds, a virtual compound library was generated and evaluated for chemical space distribution and drug-like properties. A small focused compound library of 1,4-thienodiazepine-2,5-diones has been screened for the activity against p53-Mdm2 interaction. Biological evaluations demonstrated that some compounds exhibited promising antagonistic activity.

Use of cyclohexylisocyanide and methyl 2-isocyanoacetate as convertible isocyanides for microwave-assisted fluorous synthesis of 1,4-benzodiazepine-2,5-dione library

A new protocol in which cyclohexylisocyanide and methyl 2-isocyanoacetate are used as convertible isocyanides for Ugi/de-Boc/cyclization/Suzuki synthesis of biaryl-substituted 1,4-benzodiazepine-2,5-diones has been developed. Ugi reactions of Boc-protected anthranilic acids, fluorous benzaldehydes, amines, and cyclohexylisocyanide or methyl 2-isocyanoacetate were carried out at room temperature. Microwave-promoted de-Boc/cyclization reactions afforded 1,4-benzodiazepine-2,5-diones (BZDs). Suzuki coupling reactions further derivatized the BZD ring by removing the fluorous tag and introducing the biaryl group. A thirty three-member biaryl-substituted BZD library containing four points of diversity was prepared by microwave-assisted solution-phase fluorous parallel synthesis.

Emerging molecular diversity from the intra-molecular Ugi reaction: iterative efficiency in medicinal chemistry

This review details a now established area within the isonitrile multi-component reaction (IMCR) field of study, namely employing bi-functional reagents in the Ugi reaction for the construction of screening sets with the additional element or even possibly 'metric' of enhanced 'iterative efficiency potential'. The concept of 'iterative efficiency' will be briefly introduced, coupled with discussion on new synthetic routes to select bi-functional IMCR precursors and their use in the generation of pharmacologically relevant 'molecular diversity'.

Concise synthesis of isoquinoline via the Ugi and Heck reactions

[reaction: see text] Two types of isoquinoline scaffolds were successfully constructed in a combinatorial format via the Ugi four-component reaction and the Pd-catalyzed intramolecular Heck reaction, starting from readily available starting materials.