One-Pot AgOAc-Mediated Synthesis of Polysubstituted Pyrroles from Primary Amines and Aldehydes: Application to the Total Synthesis of Purpurone

Synthesis and applications of symmetric amino acid derivatives

Symmetric α-amino acid derivatives can be used for the synthesis of intermolecularly linked peptides such as dimer-type peptides, and modified peptides in which two amino acids are intramolecularly linked. They are also synthetic intermediates for the total synthesis of natural products and functional molecules. These symmetric amino acid derivatives must be prepared based on organic synthesis. It is necessary to develop an optimal synthetic strategy for constructing the target symmetric amino acid derivative. In this review, we will introduce strategies for synthesizing symmetric amino acid derivatives. Additionally, selected applications of these amino acids in the life sciences will be described.

Design, synthesis, in silico and biological evaluations of novel polysubstituted pyrroles as selective acetylcholinesterase inhibitors against Alzheimer's disease

The objective of this study was to design new polysubstituted pyrrole derivatives as selective acetylcholinesterase (AChE) inhibitors to target Alzheimer's disease. In this context, a highly efficient, one-pot, sequential, multi-component synthesis of a diverse range of polysubstituted pyrroles was developed through a sequential domino strategy by the condensation of amines with 1,1-bis(methylthio)-2-nitroethene (BMTNE), Knovenagle reaction of arylglyoxals with malono derivatives and subsequent Michael addition and intramolecular cyclization reaction in EtOH at reflux. Thirty-nine synthesized compounds were evaluated as AChE and butyrylcholinesterase (BChE) inhibitors. Among the synthesized compounds, compound 4ad (IC₅₀ = 2.95 ± 1.31 µM) was the most potent and selective AChE inhibitor with no significant inhibition against butyrylcholinesterase BChE. A kinetic study of 4ad revealed that this compound inhibited AChE in an uncompetitive mode. Based on a molecular modeling study, compound 4ad due to its small size properly fitted into the active site of AChE compared to BChE and stabilized by H-bond and hydrophobic interactions with the critical residues of the AChE binding pocket. Consequently, it was proposed that the 4ad derivative can be an ideal lead candidate against AD with a simple and practical operation of synthetic procedures.

Catalytic redox-neutral C-H functionalisation with TEMPO in water to access aminomethyl-substituted pyrroles

A redox-neutral C-H functionalisation in water employing catalytic TEMPO to synthesize aminomethyl-substituted pyrroles is reported. Starting from cheap and commercial chemical feedstocks (ketoesters and anilines), our approach delivered targeted products in good yields and represents an endeavour to address redox economy in radical transformations.

Anti-HIV Effects of Baculiferins Are Regulated by the Potential Target Protein DARS

Baculiferins are a group of marine sponge-derived polycyclic alkaloids with anti-HIV (human immunodeficiency virus) activities. To identify additional baculiferin-based congeners for SAR analysis and to investigate the mode of action, a total of 18 new baculiferin-type derivatives were synthesized. The inhibitory activities of the congeners against the HIV-1 virus were evaluated in vitro, and the relevant SAR was discussed. Compound 18 exerted the most potent activity toward VSV-G-pseudotyped HIV-1 (IC₅₀ of 3.44 μM) and HIV-1 strain SF33 (IC₅₀ of 2.80 μM) in vitro. To identify the cellular targets, three photoaffinity baculiferin probes were simultaneously synthesized. Photoaffinity labeling experiments together with LC-MS/MS data identified aspartate-tRNA ligase (DARS) as a putative target protein of 18. The overexpression and knockdown of DARS in HEK293T cells provided additional data to demonstrate that DARS is a potential target protein in the regulation of HIV virus infection. The modes of antiviral baculiferins 13 and 18 binding to DARS were determined by a molecular docking simulation. Thus, baculiferin 18 is considered a promising lead as a new molecular target for the development of anti-HIV agents.

Direct synthesis of pentasubstituted pyrroles and hexasubstituted pyrrolines from propargyl sulfonylamides and allenamides

Multisubstituted pyrroles are important fragments that appear in many bioactive small molecule scaffolds. Efficient synthesis of multisubstituted pyrroles with different substituents from easily accessible starting materials is challenging. Herein, we describe a metal-free method for the preparation of pentasubstituted pyrroles and hexasubstituted pyrrolines with different substituents and a free amino group by a base-promoted cascade addition-cyclization of propargylamides or allenamides with trimethylsilyl cyanide. This method would complement previous methods and support expansion of the toolbox for the synthesis of valuable, but previously inaccessible, highly substituted pyrroles and pyrrolines. Mechanistic studies to elucidate the reaction pathway have been conducted.

Synthesis of Highly Functionalized 4-Amino-2-(trifluoromethyl)-1H-pyrroles

In this work, the reactivity of 5-bromo-1,1,1-trifluoro-4-methoxypent-3-en-2-one toward primary aliphatic amines was studied. The reaction was found to be extremely selective to synthesize a series of 1-alkyl-4-(aminoalkyl)-2-(trifluoromethyl)-1H-pyrroles (13 examples, up to 90% yield) and a series of highly functionalized β-enaminones (6 examples, up to 78% yield), with only the amount of amine and the reaction conditions needing to be controlled. The structure of the products was unambiguously determined by single crystal X-ray diffraction and 2D NMR experiments.

Lamellarin alkaloids: Isolation, synthesis, and biological activity

Lamellarins are marine alkaloids containing fused 14-phenyl-6H-[1]benzopyrano[4',3':4,5]pyrrolo[2,1-a]isoquinoline or non-fused 3,4-diarylpyrrole-2-carboxylate ring systems. To date, more than 50 lamellarins have been isolated from a variety of marine organisms, such as mollusks, tunicates, and sponges. Many of them, especially fused type I lamellarins, exhibit impressive biological activity, such as potent cytotoxicity, topoisomerase I inhibition, protein kinases inhibition, and anti-HIV-1 activity. Due to their useful biological activity and limited availability from natural sources, a number of synthetic methods have been developed. In this chapter, we present an updated and comprehensive review on lamellarin alkaloids summarizing their isolation, synthesis, and biological activity.

Sequential multicomponent catalytic synthesis of pyrrole-3-carboxaldehydes: evaluation of antibacterial and antifungal activities along with docking studies

A sequential multicomponent method is developed to access highly substituted N-arylpyrrole-3-carbaldehydes and tested for antibacterial and antifungal activities against bacterial strains.

Synthesis of 2,3-Ring Fused Pyrroles via Cu-Catalyzed 5-exo-dig Annulation of Alkyne-Tethered Enaminones

A copper-catalyzed annulation of alkyne-tethered enaminones for the synthesis of 2,3-ring fused pyrroles is reported. The 5-exo-dig cyclization/olefin migration reaction delivers the multisubstituted pyrroles in 59-99% yields with 16 examples. This strategy features easily available starting materials, mild reaction conditions, and a cheap ligand-free copper catalyst. The atom-economic transformation provides a simple access to a variety of synthetic useful pyrroles and their derivatives.

Design and synthesis of neolamellarin a derivatives targeting heat shock protein 90

In this study, we designed and synthesized a novel family of neolamellarin A derivatives that showed high inhibitory activity toward heat shock protein 90 (Hsp90), a kinase associated with cell proliferation. The 3,4-bis(catechol)pyrrole scaffold and the benzyl group with methoxy modification at N position of pyrrole are essential to the Hsp90 inhibitory activity and cytotoxicity of these compounds. Western blot analysis demonstrated that these compounds induced dramatic depletion of the examined client proteins of Hsp90, and accelerated cancer cell apoptosis. Docking simulations suggested that the binding mode of 9p was similar to that of the VER49009, a potent inhibitor of Hsp90. Further molecular dynamics simulation indicated that the hydrophobic interactions as well as the hydrogen bonds contributed to the high affinity of 9p to Hsp90.

Access to π-conjugated azaindole derivatives via rhodium(iii)-catalyzed cascade reaction of azaindoles and diazo compounds

Diazo compounds play an important role as a coupling partner to access unique π-conjugated 7-azaindole derivatives via rhodium(iii)-catalyzed double C–H activation/cyclization.

Chemodivergent, One-Pot, Multi-Component Synthesis of Pyrroles and Tetrahydropyridines under Solvent- and Catalyst-Free Conditions Using the Grinding Method

A highly efficient, chemoselective synthesis of a library of polysubstituted pyrroles and tetrahydropyridines has been achieved through the one-pot, multicomponent reactions of ethyl (E)-3-(aryl/alkyl amino) acrylates, 2,2-dihydroxy-1-arylethan-1-ones, and malononitrile under solvent- and catalyst-free grinding conditions. The selective formation of pyrrole or tetrahydropyridines relied on substitution of the N-aryl of ethyl (E)-3-(4-arylamino) acrylates. These reactions presumably occurred via a domino Knoevenagel condensation and Michael addition followed by an intramolecular cyclization sequence of reactions in a single transformation.

Recent developments in the group-1B-metal-catalyzed synthesis of pyrroles

Pyrroles are important synthetic targets as a result of their occurrence in numerous biologically active molecules, their important roles in diverse living processes, and their utility as versatile intermediates.

Mild and ambient annulations for pyrrole synthesis from amines and arylacetaldehydes

A mild and ambient pyrrole synthesis via copper-catalyzed aerobic cyclization is described.

β-Cyclodextrin as a recyclable catalyst: aqueous phase one-pot four-component synthesis of polyfunctionalized pyrroles

An elegant, mild and straightforward methodology was explored for the first time towards the synthesis of polyfunctionalized pyrroles using β-cyclodextrin as a reusable supramolecular catalyst in aqueous medium.

Copper-catalyzed condensation of imines and α-diazo-β-dicarbonyl compounds: modular and regiocontrolled synthesis of multisubstituted pyrroles

The Cu-catalyzed condensation of ketimines and diazodicarbonyl compounds enables the rapid and regiocontrolled synthesis of pharmaceutically relevant multisubstituted pyrroles.

In the presence of a copper(ii) catalyst, enolizable imines bearing various N-substituents and α-diazo-β-ketoesters undergo denitrogenative and dehydrative condensation to afford highly substituted pyrroles in moderate to good yields with exclusive regioselectivity. The reaction likely involves nucleophilic addition of the imine nitrogen to a copper carbenoid, tautomerization of the resulting azomethine ylide to an α-enaminoketone, and a subsequent enamine–ketone cyclocondensation. With Yb(OTf)₃ as a unique cocatalyst, α-diazo-β-diketones also participate in the same condensation reaction. The present reaction is applicable to acyclic, exocyclic, and endocyclic imines with tolerance of a broad range of functional groups and heterocyclic moieties, thus opening a new convenient route for the synthesis of the lamellarin family of natural products.

Recent advances in the synthesis of pyrroles by multicomponent reactions

Pyrrole is one of the most important one-ring heterocycles. The ready availability of suitably substituted and functionalized pyrrole derivatives is essential for the progress of many branches of science, including biology and materials science. Access to this key heterocycle by multicomponent routes is particularly attractive in terms of synthetic efficiency, and also from the environmental point of view. We update here our previous review on this topic by describing the progress made in this area in the period between mid-2009 and the end of 2013.

An Au(i)-catalyzed rearrangement/cyclization cascade toward the synthesis of 2-substituted-1,4,5,6-tetrahydrocyclopenta[b]pyrrole

An Au(i)-catalyzed tandem reaction, involving a Meyer–Schuster rearrangement/1,2-migration/Paal–Knorr cyclization cascade has been successfully developed.

Synthesis of 1,4-enamino ketones by [3,3]-rearrangements of dialkenylhydroxylamines

The synthesis of 1,4-enamino ketones has been achieved through the [3,3]-rearrangement of dialkenylhydroxylamines generated from the addition of N-alkenylnitrones to electron-deficient allenes. The mild conditions required for this reaction, and the simultaneous installation of a fluorenyl imine N-protecting group as a consequence of the rearrangement, avoid spontaneous cyclization of the 1,4-enamino ketones to form the corresponding pyrroles and allow for the isolation and controlled divergent functionalization of these reactive intermediates. The optimization, scope, and tolerance of the new method are discussed with demonstrations of the utility of the products for the synthesis of pyrroles, 1,4-diones, and furans.

Reaction of α-amido sulfones with functionalized nitrocompounds: a new two-step synthesis of N-alkoxycarbonyl-2,5-disubstituted pyrroles

N-Alkoxycarbonyl-2,5-disubstituted pyrroles can be readily prepared by a new two-step procedure involving a preliminary addition of nitro ketals to α-amido sulfones followed by an acid promoted ring closure of the obtained intermediates through a cascade process.

A concise formation of N-substituted 3,4-diarylpyrroles – synthesis and cytotoxic activity

Sequential condensation of a phenacyl halide with a primary amine and a phenylacetaldehyde led to N-substituted 3,4-diarylpyrroles. Synthesis of analogs of the marine alkaloid halitulin and cytotoxic studies are reported.

Synthesis of multi-substituted pyrroles using enamides and alkynes catalyzed by Pd(OAc)2 with molecular oxygen as an oxidant

A cyclization reaction between enamides and alkynes catalyzed by palladium(ii) acetate is described. In this method, the molecular oxygen serves as an efficient oxidant for the Pd(ii)/Pd(0) catalytic cycle. The simple reaction conditions permit this methodology to be used as a general tool for the preparation of multi-substituted pyrroles.