Passerini reaction-amine deprotection-acyl migration peptide assembly: efficient formal synthesis of cyclotheonamide C

Total Synthesis of 4-epi-Bengamide E

Bengamide E is a bioactive natural product that was isolated from Jaspidae sponges by Crews and co-workers in 1989. It displays a wide range of biological activities, including antitumor, antibiotic, and anthelmintic properties. With the aim of investigating the structural feature essential for their activity, several total syntheses of Bengamide E and its analogues have been reported in the literature. Nevertheless, no synthesis of the stereoisomer with modification of its configuration at C-4 carbon has been reported so far. Here, we report the first total synthesis of the 4-epi-Bengamide E. Key reactions in the synthesis include a chemoenzimatic desymmetrization of biobased starting materials and a diastereoselective Passerini reaction using a chiral, enantiomerically pure aldehyde, and a lysine-derived novel isocyanide.

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.

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.

Tubulysin Synthesis Featuring Stereoselective Catalysis and Highly Convergent Multicomponent Assembly

A concise and modular total synthesis of the highly potent N14-desacetoxytubulysin H (1) has been accomplished in 18 steps in an overall yield of up to 30%. Our work highlights the complexity-augmenting and route-shortening power of diastereoselective multicomponent reaction (MCR) as well as the role of bulky ligands to perfectly control both the regioselective and diastereoselective synthesis of tubuphenylalanine in just two steps. The total synthesis not only provides an operationally simple and step economy but will also stimulate major advances in the development of new tubulysin analogues.

Diversity oriented synthesis of β-carbolinone and indolo-pyrazinone analogues based on an Ugi four component reaction and subsequent cyclisation of the resulting indole intermediate

One pot two step synthesis of β-carbolinone and indolo-pyrazinone analogues via acid mediated cyclisation of Ugi intermediate has been developed with a wide substrate scope.

Multicomponent synthesis of hydrazino depsipeptides

Hydrazino depsipeptides, a new class of backbone extended peptidomimetics were prepared by the Passerini reaction of α-hydrazino acids, carbonyl compounds and isocyanides.

Efficient isocyanide-less isocyanide-based multicomponent reactions

Isocyanides are the "Jekyll and Hyde" of organic chemistry allowing for extremely interesting transformations that are not only extremely odorous but also noxious. Therefore, an isocyanide-less isocyanide-based multicomponent reaction (IMCR) has been developed, and this protocol is expected to replace many of the old procedures in the future not only in IMCR but in other areas of organic chemistry as well.

Passerini/Tsuji-Trost strategies towards achieving lactams and cyclopentane derivatives

The Passerini reaction of α,β-unsaturated aldehydes affords suitable substrates for the Tsuji-Trost reaction with various carbon based-nucleophiles. The resulting α,β-unsaturated amides may be cyclized to lactams or converted into cyclopentane derivatives if bis-nucleophiles are used in the Tsuji-Trost step.

A sequential Ugi multicomponent/Cu-catalyzed azide-alkyne cycloaddition approach for the continuous flow generation of cyclic peptoids

The development of a continuous flow multistep strategy for the synthesis of linear peptoids and their subsequent macrocyclization via Click chemistry is described. The central transformation of this process is an Ugi four-component reaction generating the peptidomimetic core structure. In order to avoid exposure to the often toxic and malodorous isocyanide building blocks, the continuous approach was telescoped by the dehydration of the corresponding formamide. In a concurrent operation, the highly energetic azide moiety required for the subsequent intramolecular copper-catalyzed azide-alkyne cycloaddition (Click reaction) was installed by nucleophilic substitution from a bromide precursor. All steps yielding to the linear core structures can be conveniently coupled without the need for purification steps resulting in a single process generating the desired peptidomimetics in good to excellent yields within a 25 min reaction time. The following macrocyclization was realized in a coil reactor made of copper without any additional additive. A careful process intensification study demonstrated that this transformation occurs quantitatively within 25 min at 140 °C. Depending on the resulting ring strain, either a dimeric or a monomeric form of the cyclic product was obtained.

AlCl3-catalyzed O-alkylative Passerini reaction of isocyanides, cinnamaldehydes and various aliphatic alcohols for accessing α-alkoxy-β,γ-enamides

The inexpensive Lewis acid AlCl₃ was found to be an efficient catalyst for the O-alkylative Passerini reaction of isocyanides, cinnamaldehydes and alcohols.

Combinatorial multicomponent access to natural-products-inspired peptidomimetics: discovery of selective inhibitors of microbial metallo-aminopeptidases

The development of selective inhibitors of microbial metallo-aminopeptidases is an important goal in the pursuit of antimicrobials for therapeutic applications. Herein, we disclose a combinatorial approach relying on two Ugi reactions for the generation of peptidomimetics inspired by natural metallo-aminopeptidase inhibitors. The library was screened for inhibitory activity against the neutral metallo-aminopeptidase of Escherichia coli (ePepN) and the porcine kidney cortex metallo-aminopeptidase (pAPN), which was used as a model of the M1-aminopeptidases of mammals. Six compounds showed typical dose-response inhibition profiles toward recombinant ePepN, with two of them being very potent and highly selective for ePepN over pAPN. Another compound showed moderate ePepN inhibition but total selectivity for this bacterial enzyme over its mammalian orthologue at concentrations of physiological relevance. This strategy proved to be useful for the identification of lead compounds for further optimization and development.

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

In the recent past, the design and synthesis of peptide mimics (peptidomimetics) has received much attention. This because they have shown in many cases enhanced pharmacological properties over their natural peptide analogues. In particular, the incorporation of cyclic constructs into peptides is of high interest as they reduce the flexibility of the peptide enhancing often affinity for a certain receptor. Moreover, these cyclic mimics force the molecule into a well-defined secondary structure. Constraint structural and conformational features are often found in biological active peptides. For the synthesis of cyclic constrained peptidomimetics usually a sequence of multiple reactions has been applied, which makes it difficult to easily introduce structural diversity necessary for fine tuning the biological activity. A promising approach to tackle this problem is the use of multicomponent reactions (MCRs), because they can introduce both structural diversity and molecular complexity in only one step. Among the MCRs, the isocyanide-based multicomponent reactions (IMCRs) are most relevant for the synthesis of peptidomimetics because they provide peptide-like products. However, these IMCRs usually give linear products and in order to obtain cyclic constrained peptidomimetics, the acyclic products have to be cyclized via additional cyclization strategies. This is possible via incorporation of bifunctional substrates into the initial IMCR. Examples of such bifunctional groups are N-protected amino acids, convertible isocyanides or MCR-components that bear an additional alkene, alkyne or azide moiety and can be cyclized via either a deprotection-cyclization strategy, a ring-closing metathesis, a 1,3-dipolar cycloaddition or even via a sequence of multiple multicomponent reactions. The sequential IMCR-cyclization reactions can afford small cyclic peptide mimics (ranging from four- to seven-membered rings), medium-sized cyclic constructs or peptidic macrocycles (>12 membered rings). This review describes the developments since 2002 of IMCRs-cyclization strategies towards a wide variety of small cyclic mimics, medium sized cyclic constructs and macrocyclic peptidomimetics.

Facile and rapid route for the synthesis of novel conformationally constrained norstatine analogs via PADAM-cyclization methodology

The following report describes novel methodology for the rapid synthesis of unique conformationally constrained norstatine analogs of potential biological relevance. A PADAM (Passerini reaction - Amine Deprotection - Acyl Migration reaction) sequence is followed by a TFA-mediated microwave-assisted cyclization to generate the final benzimidazole isostere of the norstatine scaffold in moderate to good yields. The applicability of this solution phase methodology to the preparation of a small collection of compounds is discussed.

Novel application of α-azido aldehydes in multicomponent reactions: synthesis of triazolo-fused dihydrooxazinones via a Passerini reaction-dipolar cycloaddition strategy

α-Azido aldehydes can be employed in Passerini reactions with isocyanides and various propiolic acids to afford the three-component adducts in moderate to good yields. These compounds undergo a straightforward azide-alkyne dipolar cycloaddition to furnish triazolo-fused dihydrooxazinones.