We report the first total synthesis of the complex cyclobutane-containing Lycopodium alkaloid annotinolide B. Our approach leverages a sequential quinoline dearomatization strategy that enables the transformation of this readily accessible heteroaromatic precursor to a tricyclic N-acyl dihydropyridone intermediate. Extensive studies aimed at forging the signature cyclobutane revealed a β-silyl acrylate to be essential for the success of a key [2 + 2] photocycloaddition reaction. Further functional group transformations and a final one-pot methylation/lactonization sequence furnish annotinolide B in 20 steps.

The psammaplysins are a unique group of bromotyrosine-derived natural products isolated from the Psammaplysilla genus of marine sponges. Aside from the various biological activities they possess, synthetic chemists have been drawn to the family for decades due to the intriguing 5/7-spiroisoxazoline-oxepine core common to all members. Herein, we describe our synthetic approach towards the psammaplysin family in the context of this broader work. Our route centers upon the use of a carefully choreographed alkoxymethylenation/1,3-dipolar cycloaddition to construct the key spiroisoxazoline-oxepine ring system, followed by its functionalization and divergent coupling to access various family members. We also detail the development of the first asymmetric approach to this class of marine natural products.

We describe the development of a unified synthetic strategy for the preparation of all known 5/5-spirocyclic spiroindimicin (SPM) alkaloids, namely spiroindimicins B-G. The present synthetic route relies on four fundamental transformations: Grignard-based fragment coupling between halogenated pyrrolemetal and isatin partners, Suzuki coupling to generate a triaryl scaffold encompassing all requisite skeletal atoms of the natural products, Lewis acid-mediated spirocyclization to construct the 5/5-spirocyclic core, and chemoselective lactam reduction. The developed syntheses are step-economic (6-7 steps from commercial materials), scalable, and amenable to analogue synthesis. Preliminary investigations into a catalytic asymmetric spirocyclization towards an enantioselective SPM synthesis are also described. Further studies of the antiparasitic properties of this class have revealed promising activity against T. brucei for certain congeners. Together with our prior approach to the 6/5-family members, our work constitutes a synthetic solution to all known spiroindimicin natural products.

The psammaplysins are a unique class of brominated marine alkaloids bearing a signature 5/7-spiroisoxazoline-oxepine core linked to a variable tyramine-derived unit. Here, we report the total synthesis of several members of this family via a dipolar cycloaddition between an in situ generated nitrile oxide and an unusual 7-membered enediol diether dipolarophile. Carefully orchestrated oxidative transformation towards the fully functionalized spirocycle and direct coupling with tyramine-derived amines provides access to five representative family members, psammaplysins A, M, O, and Q, and ceratinamide A, the latter four for the first time.

We describe the first total synthesis of the unusual cyclopropane-containing indole alkaloid (–)-rauvomine B via a strategy centered upon intramolecular cyclopropanation of a tetracyclic N-sulfonyl triazole. Preparation of this precursor evolved through two generations of synthesis, with the ultimately successful route involving a palladium-catalyzed stereospecific allylic amination, a cis-selective Pictet–Spengler reaction, and ring-closing metathesis as important bond-forming reactions. The key cyclopropanation step was found to be highly dependent on the structure and conformational strain of the indoloquinolizidine N-sulfonyl triazole precursor, the origins of which are explored computationally through DFT studies. Overall, our synthesis proceeds in 11 total steps and 2.4% yield from commercial materials.

Total syntheses of the 5/5-spirocyclic indoline alkaloids (±)-spiroindimicins B, C, D, E, F, and G have been achieved via a modular approach. Our route features direct coupling of halogenated pyrrolemetal and isatin partners, Suzuki coupling to append the indole unit, Lewis acid-mediated spirocyclization, and divergent functionalization to give various family members. These syntheses are concise (six or seven steps from commercial materials) and highly amenable to analogue synthesis.

ADVERTISEMENT RETURN TO ARTICLES ASAPPREVFirst ReactionsNEXTSalvaging Salvinorin: From Hallucinogen to Potential Therapeutic through Chemical SynthesisA modular synthesis design enables exploration of bioactive salvinorin chemical space.Bhawyanth DuvvuruBhawyanth DuvvuruUT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, Texas 75390, United StatesMore by Bhawyanth Duvvuru and Myles W. Smith*Myles W. SmithUT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, Texas 75390, United States*Email: [email protected]More by Myles W. Smithhttps://orcid.org/0000-0002-0231-0059Cite this: ACS Cent. Sci. 2023, XXXX, XXX, XXX-XXXPublication Date (Web):August 10, 2023Publication History Published online10 August 2023https://doi.org/10.1021/acscentsci.3c00955Published 2023 by American Chemical SocietyRIGHTS & PERMISSIONSACS AuthorChoiceCC: Creative CommonsBY: Credit must be given to the creatorArticle Views-Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (831 KB) Get e-AlertscloseSUBJECTS:Chemical structure,Chemical synthesis,Ketones,Pharmaceuticals,Receptors Get e-Alerts

The Myrioneuron alkaloids are a relatively small family of plant-derived alkaloids that present an intriguing array of structural intricacy and biological properties. As such, these natural products have drawn interest from the synthetic community, resulting in creative total syntheses of several family members. This review showcases recent synthetic efforts towards these polycyclic alkaloids. 1 Introduction 1.1 Biological Activity 1.2 Proposed Biosynthesis 2 Synthetic Studies toward the Myrioneuron Alkaloids 2.1 Total Synthesis of Myrioxazines A and B 2.2 Total Synthesis of Myrionine, Myrionidine, and Schoberine 2.3 Total Synthesis of Myrifabrals A and B 2.4 Total Synthesis of Myrioneurinol 3 Conclusions and Outlook

2,2-Disubstituted indoxyls are commonly found within natural products and bioactive molecules. Among the numerous methods to access such motifs, the dearomative transformation of indoles represents an attractive approach. Despite much development, a potential gap exists in the oxidative union of readily accessible 2-substituted indoles with nucleophilic partners, where a general transformation accommodating 2-alkyl substitution and a broad range of nucleophiles is lacking. Herein, we describe the development of a user-friendly solution to this challenge and highlight its utility in the synthesis of complex alkaloids.

We report a total synthesis of the Myrioneuron alkaloid myrioneurinol enabled by the recognition of hidden symmetry within its polycyclic structure. Our approach traces myrioneurinol's complex framework back to a symmetrical diketone precursor, a double reductive amination of which forges its central piperidine unit. By employing an inexpensive chiral amine in this key desymmetrizing event, four stereocenters of the natural product including the core quaternary stereocenter are set in an absolute sense, providing the first asymmetric entry to this target. Other noteworthy strategic maneuvers include utilizing a bicyclic alkene as a latent cis-1,3-bis(hydroxymethyl) synthon and a topologically controlled alkene hydrogenation. Overall, our synthesis proceeds in 18 steps and ∼1% yield from commercial materials.

Direct dimerization simplifies the synthesis of himastatin and elucidates its mode of action.

Direct dimerization simplifies the synthesis of himastatin and elucidates its mode of action

The spiroindimicins are a unique class of chlorinated indole alkaloids characterized by three heteroaromatic rings structured around a congested spirocyclic stereocenter. Here, we report the first total synthesis of (+)-spiroindimicin A, which bears a challenging C-3’/C-5’’-linked spiroindolenine. We detail our initial efforts to effect a biomimetic oxidative spirocyclization from its proposed natural precursor, lynamicin D, and describe how these studies shaped our final abiotic 9-step solution to this complex alkaloid built around a key asymmetric Pd-catalyzed spirocyclization. Scalable access to spiroindimicins A, H, and their congeners has enabled discovery of their activity against several parasites relevant to human health, providing potential starting points for new therapeutics for the neglected tropical diseases leishmaniasis and African sleeping sickness.

Cyclobutenes are highly useful synthetic intermediates as well as important motifs in bioactive small molecules. Herein, we report a regio-, chemo-, and enantioselective synthesis of cyclobutenes from olefins using N-sulfonyl-1,2,3-triazoles as vicinal dicarbene equivalents or alkyne [2 + 2] cycloaddition surrogates. Terminal and cis-olefins can be transformed into enantioenriched cyclopropanes via rhodium catalysis. Then, in one pot, treatment of these intermediates with tosyl hydrazide and base effects diazo formation followed by rhodium-catalyzed ring expansion to yield enantioenriched cyclobutenes. These cyclobutenes can be transformed into highly substituted, enantioenriched cyclobutanes, including structures relevant to natural product scaffolds.

The spiroindimicins are a unique class of chlorinated indole alkaloids characterized by three heteroaromatic rings structured around a congested spirocyclic stereocenter. Here, we report the first total synthesis of (+)-spiroindimicin A, which bears a challenging C-3'/C-5''-linked spiroindolenine. We detail our initial efforts to effect a biomimetic oxidative spirocyclization from its proposed natural precursor, lynamicin D, and describe how these studies shaped our final abiotic 9-step solution to this complex alkaloid built around a key Pd-catalyzed asymmetric spirocyclization. Scalable access to spiroindimicins A, H, and their congeners has enabled discovery of their activity against several parasites relevant to human health, providing potential starting points for new therapeutics for the neglected tropical diseases leishmaniasis and African sleeping sickness.

The indoxyl unit is a common structural motif in alkaloid natural products and bioactive compounds. Here, we report a general method that transforms readily available 2-substituted indoles into 2,2-disubstituted indoxyls via nucleophile coupling with a 2-alkoxyindoxyl intermediate and showcase its utility in short total syntheses of the alkaloids brevianamide A (7 steps) and trigonoliimine C (6 steps). The developed method is operationally simple and demonstrates broad scope in terms of nucleophile identity and indole substitution, tolerating 2-alkyl substituents and free indole N–H groups, elements beyond the scope of most prior approaches. Spirocyclic indoxyl products are also accessible via intramolecular nucleophilic trapping.

A concise, asymmetric synthesis of the indole alkaloid (+)-tacamonine is reported involving a stereoselective radical cyclization of a 1-phenylsulfanyl tetrahydro-β-carboline bearing a pendant enoate ester side chain as a key step. In this process, a single stereocenter in the side chain allows for the formation of two stereocenters of the natural product in a highly diastereoselective fashion. Computational investigations of this key cyclization support the experimentally observed outcome and shed light on the factors impacting its stereoselectivity.

Pyrroloiminoquinone alkaloids represent a structurally intriguing class of natural products that display an array of useful biological properties. Here, we present a versatile and scalable platform for the synthesis of this diverse family - and in particular the antitumor discorhabdins - built upon sequential selective C-H functionalization of tryptamine. The utility of this strategy is showcased through short formal syntheses of damirones A-C, makaluvamines D and I, and discorhadbin E. Additionally, we describe efforts to develop the first catalytic asymmetric entry to the discorhabdin subclass.

This Article details the development of the iron-catalyzed conversion of olefins to radicals and their subsequent use in the construction of C-C bonds. Optimization of a reductive diene cyclization led to the development of an intermolecular cross-coupling of electronically-differentiated donor and acceptor olefins. Although the substitution on the donor olefins was initially limited to alkyl and aryl groups, additional efforts culminated in the expansion of the scope of the substitution to various heteroatom-based functionalities, providing a unified olefin reactivity. A vinyl sulfone acceptor olefin was developed, which allowed for the efficient synthesis of sulfone adducts that could be used as branch points for further diversification. Moreover, this reactivity was extended into an olefin-based Minisci reaction to functionalize heterocyclic scaffolds. Finally, mechanistic studies resulted in a more thorough understanding of the reaction, giving rise to the development of a more efficient second-generation set of olefin cross-coupling conditions.

Herein is shown how a novel catalytic asymmetric propargylation of 3,4-dihydro-β-carboline, followed by a designed Au(I)/Ag(I)-mediated 6-endo-dig cyclization, can directly deliver the indolenine-fused methanoquinolizidine core of the akuammiline alkaloid strictamine in its native oxidation state, ultimately achieving a 7-step formal asymmetric total synthesis. Also demonstrated are how the cyclization products can rearrange into vincorine-type skeletons and a further use for the developed propargylation with the first catalytic asymmetric total synthesis of decarbomethoxydihydrogambirtannine.