Synthesis of palmyrolide A and its cis-isomer and mechanistic insight into trans-cis isomerisation of the enamide macrocycle

Total Synthesis and Structural Reassignment of Laingolide A

The asymmetric total synthesis of four diastereomers of laingolide A was achieved, which led to the unambiguous assignment of the stereochemistry of the natural product. The salient features of the convergent, fully stereocontrolled approach were a copper-catalysed stereospecific Kumada-type coupling, a Julia-Kocienski olefination and an RCM/alkene migration sequence to access the desired macrocyclic enamide.

Tertiary Enamides: Versatile and Available Substrates in Synthetic Chemistry

BACKGROUND

Enamines and their variant enamides as powerful and versatile synthons have attracted great attention in synthetic chemistry. Enamides display unique stability and reduce enaminic reactivity in view of the electron-withdrawing effect of N-acyl group. A great deal of satisfactory achievements in the synthesis and application of enamides has been made in recent years. Especially, tertiary enamides without N-H bond regarded as low reactivity of compounds in the past can act as excellent nucleophiles to react with electrophiles for the construction of various nitrous molecules.

OBJECTIVE

This review focuses on recent advances on tertiary enamides in the synthetic strategies and applications including addition, coupling reaction, functionalization and electro- or photo-chemical reaction.

CONCLUSION

Tertiary enamides as electron-deficient nucleophiles display a satisfactory balance between stability and reactivity to offer multiple opportunities for the construction of various functionalized nitrogencontaining compounds. Further exploration of the reactive mechanisms involved tertiary enamides and the development of novel and efficient transformations to generate ever more complex building blocks starting from tertiary enamides are particularly worth pursuing.

Total Synthesis of Laingolide B Stereoisomers and Assignment of Absolute Configuration

Total synthesis of (-)-(2 R,9 S)- and (+)-(2 S,9 S)-stereoisomers of laingolide B has been accomplished by using sequential ring-closing metathesis (RCM) and alkene isomerization to construct the macrocyclic trans- N-methyl enamide moiety. The Myers alkylation was used to secure the C2 stereochemistry of the two RCM precursors from a common (9 S)-C3-C9 alkyl iodide. The absolute configuration of laingolide B has been assigned as (2 S,9 R) by comparison of the optical rotation data.

To each his own: isonitriles for all flavors. Functionalized isocyanides as valuable tools in organic synthesis

The term functionalized isocyanides refers to all those isocyanides in which a neighbouring functional group can finely tune the reactivity of the isocyano group or can be exploited in post-functionalization processes. In this manuscript, we have reviewed all the isocyanides in which the pendant functional group causes either deviation from or reinforces the normal reactivity of the isocyano group and categorized them to highlight their common features and differences. An analysis of their synthetic potential and the possible unexplored directions for future research studies is also addressed.

Efforts To Access the Potent Antitrypanosomal Marine Natural Product Janadolide: Synthesis of Des-tert-butyl Janadolide and Its Biological Evaluation

To identify novel antitrypanosomal agents based on Janadolide, a potent macrocyclic polyketide-peptide hybrid, a macrolactonization strategy was explored. We prepared des-tert-butyl Janadolide and evaluated its antitrypanosomal activity. Our findings suggest that the tert-butyl group is necessary for the desired bioactivity.

Total Synthesis of Kanamienamide and Clarification of Biological Activity

The total synthesis of kanamienamide, an enamide with an enol ether and an 11-membered macrolactone of marine origin, was achieved. The synthesis features the construction of an enamide adjacent to an enol ether by Buchwald amidation and an 11-membered ring by Mitsunobu lactonization. In addition, on the basis of the biological assay of synthetic 1, we clarified that kanamienamide (1) was not an apoptosis-like cell death inducer, as reported in the isolation paper, and revealed its real biological activity as a necrosis-like cell death inducer.

Ketenimines from Isocyanides and Allyl Carbonates: Palladium-Catalyzed Synthesis of β,γ-Unsaturated Amides and Tetrazoles

The reaction of allyl ethyl carbonates with isocyanides in the presence of a catalytic amount of Pd(OAc)₂ provided ketenimines through β-hydride elimination of the allyl imidoylpalladium intermediates. The insertion of the isocyanide into the π-allyl Pd complex proceeded via an unusual η¹ -allyl Pd species. The resulting ketenimines were hydrolyzed to β,γ-unsaturated carboxamides during purification by flash column chromatography on silica gel or converted in situ into 1,5-disubstituted tetrazoles by [3+2] cycloaddition with hydrazoic acid or trimethylsilyl azide.

Synthesis and biological evaluation of palmyrolide A macrocycles as sodium channel blockers towards neuroprotection

Palmyrolide A is a neuroprotective macrolide isolated by Gerwick and coworkers in 2010. This natural product is known to suppress neuronal spontaneous calcium ion oscillations through its voltage-gated sodium channel blocking ability which is of significant interest in CNS drug discovery. Herein, we give a detailed account on total synthesis of (+)-palmyrolide A and synthesis of a focused library of macrocycles around the scaffold, followed by their biological evaluation. Use of the chiral pool approach, Zhu's oxidative homologation, access to unnatural cis-palmyrolide A, preparation of 18 new analogues and identification of macrolides with improved sodium channel blocking activity are the important features of the present paper. As a measure of potency as voltage-gated sodium channel blockers, all the synthesized analogues were profiled for their ability to inhibit the veratridine-stimulated Na(+) influx in murine primary neuronal cultures. Four macrocycles were found to be more potent or comparable to that of the natural product (-)-palmyrolide A. The most potent compound from this series 20 was structurally simplified and readily accessible in good quantities for further biological profiling.

Detailed analysis of (-)-palmyrolide a and some synthetic derivatives as voltage-gated sodium channel antagonists

A small library of synthetic (-)-palmyrolide A diastereomers, analogues, and acyclic precursors have been examined with respect to their interaction with voltage-gated sodium channels (VGSCs). Toward this goal, the ability of (-)-palmyrolide A and analogues to antagonize veratridine-stimulated Na(+) influx in primary cultures of mouse cerebrocortical neurons was assessed. We found that synthetic (-)-palmyrolide A and its enantiomer functioned as VGSC antagonists to block veratridine-induced sodium influx. A detailed NMR and computational analysis of four diastereomers revealed that none had the same combination of shape and electrostatic potential as exhibited by natural (-)-palmyrolide A. These data indicate that the relative configuration about the tert-butyl and methyl substituents appears to be a prerequisite for biological function. Additional testing revealed that the enamide double bond was not necessary for blocking veratridine-induced sodium influx, whereas the acyclic analogues and other macrolide diastereomers tested were inactive as inhibitors of VGSCs, suggesting that the intact macrolide was required.

Total synthesis of the macrocyclic N-Methyl enamides palmyrolide A and 2S-sanctolide A

Full details of the total syntheses of the initially reported and revised structures of the neuroprotective agent palmyrolide A are reported. The key macrocyclization step was achieved using a sequential ring-closing metathesis/olefin isomerization reaction. Furthermore, the total synthesis of the related macrolide (2S)-sanctolide A is reported. The synthesis used key elements from the synthesis of palmyrolide A, including the RCM/olefin isomerization sequence. The synthetic work described herein serves to facilitate the assignment of stereochemistry of the natural product sanctolide A and demonstrates the utility of this approach for the synthesis of macrocyclic tertiary enamide natural products.

Shellfish toxins targeting voltage-gated sodium channels

Voltage-gated sodium channels (VGSCs) play a central role in the generation and propagation of action potentials in excitable neurons and other cells and are targeted by commonly used local anesthetics, antiarrhythmics, and anticonvulsants. They are also common targets of neurotoxins including shellfish toxins. Shellfish toxins are a variety of toxic secondary metabolites produced by prokaryotic cyanobacteria and eukaryotic dinoflagellates in both marine and fresh water systems, which can accumulate in marine animals via the food chain. Consumption of shellfish toxin-contaminated seafood may result in potentially fatal human shellfish poisoning. This article provides an overview of the structure, bioactivity, and pharmacology of shellfish toxins that act on VGSCs, along with a brief discussion on their pharmaceutical potential for pain management.