Biosynthesis, total synthesis, and biological profiles of Ergot alkaloids

A gene regulating ergot alkaloid biosynthesis in Metarhizium brunneum

Ergot alkaloid synthesis (eas) gene clusters found in several fungi encode biosynthesis of agriculturally and pharmaceutically important ergot alkaloids. Although the biosynthetic genes of the ergot alkaloid pathway have been well characterized, regulation of those genes is unknown. We characterized a gene with sequence similarity to a putative transcription factor and that was found adjacent to the eas cluster of Metarhizium brunneum, a plant symbiont and insect pathogen. Function of the novel gene, easR, was explored by CRISPR-Cas9-derived gene knockouts. To maximize potential for ergot alkaloid accumulation, strains of M. brunneum were injected into larvae of the insect Galleria mellonella. Larvae infected with the wild type contained abundant ergot alkaloids, but those infected with easR knockouts lacked detectable ergot alkaloids. The easR knockout strains had significantly reduced or no detectable mRNA from eas cluster genes in RNAseq and qualitative RT-PCR analyses, whereas the wild-type strain contained abundant mRNA from all eas genes. These data demonstrate that the product of easR is required for ergot alkaloid accumulation and provide evidence that it has a role in the expression of ergot alkaloid biosynthesis genes. Larvae infected with an easR knockout survived significantly longer than those infected with the wild type (P < 0.0001), indicating a role for EasR, and indirectly confirming a role for ergot alkaloids, in the virulence of M. brunneum to insects. Homologs of easR were found associated with eas clusters of at least 15 other ergot alkaloid-producing fungi, indicating that EasR homologs may contribute to regulation of ergot alkaloid synthesis in additional fungi.

IMPORTANCE

Ergot alkaloids produced by several species of fungi are important as contaminants of food and feed in agriculture and also as the foundation of numerous pharmaceuticals prescribed for dementia, migraines, hyperprolactinemia, and several other disorders. Information on control of the ergot alkaloid pathway may contribute to strategies to limit their production in agricultural settings or increase their yield for pharmaceutical production. Our results demonstrate that a previously uncharacterized gene clustered with the ergot alkaloid synthesis genes is required for the sufficient transcription of the ergot alkaloid biosynthesis genes. This observation suggests the gene encodes a factor regulating transcription of those biosynthetic genes.

Serotonin 2A Receptor (5-HT2AR) Agonists: Psychedelics and Non-Hallucinogenic Analogues as Emerging Antidepressants

Psychedelics make up a group of psychoactive compounds that induce hallucinogenic effects by activating the serotonin 2A receptor (5-HT2AR). Clinical trials have demonstrated the traditional psychedelic substances like psilocybin as a class of rapid-acting and long-lasting antidepressants. However, there is a pressing need for rationally designed 5-HT2AR agonists that possess optimal pharmacological profiles in order to fully reveal the therapeutic potential of these agonists and identify safer drug candidates devoid of hallucinogenic effects. This Perspective provides an overview of the structure-activity relationships of existing 5-HT2AR agonists based on their chemical classifications and discusses recent advancements in understanding their molecular pharmacology at a structural level. The encouraging clinical outcomes of psychedelics in depression treatment have sparked drug discovery endeavors aimed at developing novel 5-HT2AR agonists with improved subtype selectivity and signaling bias properties, which could serve as safer and potentially nonhallucinogenic antidepressants. These efforts can be significantly expedited through the utilization of structure-based methods and functional selectivity-directed screening.

Synthetic Strategies toward Lysergic Acid Diethylamide: Ergoline Synthesis via α-Arylation, Borrowing Hydrogen Alkylation, and C-H Insertion

Lysergic acid diethylamide (LSD), a semisynthetic ergoline alkaloid analogue and hallucinogen, is a potent psychoplastogen with promising therapeutic potential. While a variety of synthetic strategies for accessing ergoline alkaloids have emerged, the complexity of the tetracyclic ring system results in distinct challenges in preparing analogues with novel substitution patterns. Methods of modulating the hallucinogenic activity of LSD by functionalization at previously inaccessible positions are of continued interest, and efficient syntheses of the ergoline scaffold are integral toward this purpose. Here, we report novel C-C bond forming strategies for preparing the ergoline tetracyclic core, focusing on the relatively unexplored strategy of bridging the B- and D-ring systems last. Following cross-coupling to first join the A- and D-rings, we explored a variety of methods for establishing the C-ring, including intramolecular α-arylation, borrowing hydrogen alkylation, and rhodium-catalyzed C-H insertion. Our results led to a seven-step formal synthesis of LSD and the first methods for readily introducing substitution on the C-ring. These strategies are efficient for forming ergoline-like tetracyclic compounds and analogues, though they each face unique challenges associated with elaboration to ergoline natural products. Taken together, these studies provide important insights that will guide future synthetic strategies toward ergolines.

Photoredox catalysis enabling decarboxylative radical cyclization of γ,γ-dimethylallyltryptophan (DMAT) derivatives: formal synthesis of 6,7-secoagroclavine

An unusual photoredox-catalyzed radical decarboxylative cyclization cascade reaction of γ,γ-dimethylallyltryptophan (DMAT) derivatives containing unactivated alkene moieties has been developed, providing green and efficient access to various six-, seven-, and eight-membered ring 3,4-fused tricyclic indoles. This type of cyclization, which was hitherto very difficult to comprehend in ergot biosynthesis and to accomplish by more conventional procedures, enables the synthesis of ergot alkaloid precursors. In addition, this work describes a mild, environmentally friendly method to activate, reductively and oxidatively, natural carboxylic acids for decarboxylative C-C bond formation by exploiting the same photocatalyst.

Total Synthesis of (+)-Isolysergol

The enantioselective synthesis of (+)-isolysergol was completed in 18 steps, and an overall yield of 11% was obtained from (2R)-(+)-phenyloxirane as a chiral pool. Key features of the synthesis include a stereoselective intramolecular 1,3-dipolar addition of nitrone with terminal olefin and a Cope elimination to furnish the D ring. A rhodium-catalyzed intramolecular [3 + 2] annulation of a benzene ring with α-imino carbenoid was designed to afford the 3,4-fused indole scaffold at the late stage of the synthesis.

The Bright Side of Psychedelics: Latest Advances and Challenges in Neuropharmacology

The need to identify effective therapies for the treatment of psychiatric disorders is a particularly important issue in modern societies. In addition, difficulties in finding new drugs have led pharmacologists to review and re-evaluate some past molecules, including psychedelics. For several years there has been growing interest among psychotherapists in psilocybin or lysergic acid diethylamide for the treatment of obsessive-compulsive disorder, of depression, or of post-traumatic stress disorder, although results are not always clear and definitive. In fact, the mechanisms of action of psychedelics are not yet fully understood and some molecular aspects have yet to be well defined. Thus, this review aims to summarize the ethnobotanical uses of the best-known psychedelic plants and the pharmacological mechanisms of the main active ingredients they contain. Furthermore, an up-to-date overview of structural and computational studies performed to evaluate the affinity and binding modes to biologically relevant receptors of ibogaine, mescaline, N,N-dimethyltryptamine, psilocin, and lysergic acid diethylamide is presented. Finally, the most recent clinical studies evaluating the efficacy of psychedelic molecules in some psychiatric disorders are discussed and compared with drugs already used in therapy.

Synthesis of indole derivatives as prevalent moieties present in selected alkaloids

Indoles are a significant heterocyclic system in natural products and drugs. They are important types of molecules and natural products and play a main role in cell biology. The application of indole derivatives as biologically active compounds for the treatment of cancer cells, microbes, and different types of disorders in the human body has attracted increasing attention in recent years. Indoles, both natural and synthetic, show various biologically vital properties. Owing to the importance of this significant ring system, the investigation of novel methods of synthesis have attracted the attention of the chemical community. In this review, we aim to highlight the construction of indoles as a moiety in selected alkaloids.

Synthesis and Reactivity of Uhle’s Ketone and Its Derivatives

Uhle’s ketone and its derivatives are highly versatile intermediates for the synthesis of a variety of 3,4-fused tricyclic indole frameworks, i.e. indole alkaloids of the ergot family, that are found in various bioactive natural products and pharmaceuticals. Therefore, the development of a convenient preparative method for this structural motif as well as its opportune/useful derivatization have been the subject of longstanding interest in the fields of synthetic organic chemistry and medicinal chemistry. Herein, we summarize recent and less recent methods for the preparation of Uhle’s ketone and its derivatives as well as its main reactivity towards the synthesis of bioactive substances. Regarding the preparation, it can be roughly classified into two categories: (a) using 4-unfunctionalized and 4-functionalized indole derivatives as starting materials to construct a fused six-member ring, and (b) constructing the indole ring through intramolecular cycloaddition. Principally, the reactivity of the cyclic Uhle’s ketone shown here is derived from the classical electrophilicity of the carbonyl carbon or the acidity of the α-hydrogen and, though less intensively investigated, chemical reactions that induce ring expansion to form novel ring skeletons.

1 Introduction

2 Synthesis

2.1 Disconnection A: Cyclization Reaction of the Opportune 3,4-Disubstituted Indole

2.2 Disconnection B: Intramolecular Friedel–Crafts Cyclization

2.3 Disconnection B: Intramolecular Cyclization via Metal–Halogen Exchange

2.4 Disconnection C: Intramolecular Diels–Alder Furan Cycloaddition

2.5 Disconnection D: Intramolecular Dearomatizing [3 + 2] Annulation

3 Reactivity

3.1 Use of Uhle’s Ketone for Lysergic Acid

3.2 Use of Uhle’s Ketone for Rearranged Clavines

3.3 Use of Uhle’s Ketone for Medicinal Chemistry

4 Conclusion and Outlook

Concise catalytic asymmetric synthesis of (R)-4-amino Uhle's ketone

A practical and asymmetric synthesis of (R)-4-amino-5-oxo-1,3,4,5-tetrahydrobenz[cd]indole, an enantiopure framework shared by most ergot alkaloids, was accomplished. Our method involves a Rh(i)-catalyzed 6-exo-trig intramolecular cyclization of an appropriate 4-pinacolboronic ester d-tryptophan aldehyde followed by the oxidation of the resulting secondary benzylic alcohol with a Cu(i)-ABNO catalyst and final deprotection under acidic conditions. This new procedure offers significant advantages over previous synthetic approaches, including brevity, mild reaction conditions, preservation of chiral integrity, and high overall yield and avoids the use of stoichiometric amounts of strongly basic and pyrophoric organometallic reagents.

Biomimetic Total Syntheses of Ergot Alkaloids via Decarboxylative Giese Coupling

Biomimetic total syntheses of Festuclavine and Pyroclavine were achieved by a sequential radical coupling. The key steps include intramolecular decarboxylative Giese reaction to form the central C ring and 4-nitrobenzenesulfonyl (Ns)-directed indole C4-H olefination to introduce the indole C4 component. In addition, D-ring formation was completed by decarboxylative alkenylation and intramolecular S_N2 reaction.