Asymmetric total syntheses of (-)-renieramycin M and G and (-)-jorumycin using aziridine as a lynchpin

A New Renieramycin T Right-Half Analog as a Small Molecule Degrader of STAT3

Constitutive activation of STAT3 contributes to tumor development and metastasis, making it a promising target for cancer therapy. (1R,4R,5S)-10-hydroxy-9-methoxy-8,11-dimethyl-3-(naphthalen-2-ylmethyl)-1,2,3,4,5,6-hexahydro-1,5-epiminobenzo[d]azocine-4-carbonitrile, DH_31, a new derivative of the marine natural product Renieramycin T, showed potent activity against H292 and H460 cells, with IC50 values of 5.54 ± 1.04 µM and 2.9 ± 0.58 µM, respectively. Structure-activity relationship (SAR) analysis suggests that adding a naphthalene ring with methyl linkers to ring C and a hydroxyl group to ring E enhances the cytotoxic effect of DH_31. At 1-2.5 µM, DH_31 significantly inhibited EMT phenotypes such as migration, and sensitized cells to anoikis. Consistent with the upregulation of ZO1 and the downregulation of Snail, Slug, N-cadherin, and Vimentin at both mRNA and protein levels, in silico prediction identified STAT3 as a target, validated by protein analysis showing that DH_31 significantly decreases STAT3 levels through ubiquitin-proteasomal degradation. Immunofluorescence and Western blot analysis confirmed that DH_31 significantly decreased STAT3 and EMT markers. Additionally, molecular docking suggests a covalent interaction between the cyano group of DH_31 and Cys-468 in the DNA-binding domain of STAT3 (binding affinity = -7.630 kcal/mol), leading to destabilization thereafter. In conclusion, DH_31, a novel RT derivative, demonstrates potential as a STAT3-targeting drug that significantly contribute to understanding of the development of new targeted therapy.

Evolution of a Synthetic Strategy toward the Syntheses of Bis-tetrahydroisoquinoline Alkaloids

ConspectusThe bis-tetrahydroisoquinoline (bis-THIQ) natural products represent a medicinally important class of isoquinoline alkaloids that exhibit broad biological activities with particularly potent antitumor properties, as exemplified by the two U.S. FDA approved molecules trabectidin and lurbinectedin. Accordingly, other members within the bis-THIQ family have emerged as prime targets for synthetic chemists, aiming to innovate an orthogonal chemical production of these compounds. With the ability of these complementary strategies to reliably and predictably manipulate molecular structures with atomic precision, this should allow the preparation of synthetic derivatives not existing in nature as new drug leads in the development of novel medicines with desired biological functions.Beyond the biological perspective, bis-THIQ natural products also possess intricate and unique structures, serving as a source of intellectual stimulation for synthetic organic chemists. Within our laboratory, we have developed an integrated program that combines reaction development and target-directed synthesis, leveraging the architecturally complex molecular framework of bis-THIQ natural products as a driving force for the advancement of novel reaction methodologies. In this Account, we unveil our synthetic efforts in a comprehensive story, describing how our synthetic strategy toward bis-THIQ natural products, specifically jorunnamycin A and jorumycin, has evolved over the course of our studies through our key transformations comprising (a) the direct functionalization of isoquinoline N-oxide to prepare the bis-isoquinoline (bis-IQ) intermediate, (b) the diastereoselective and enantioselective isoquinoline hydrogenation to forge the pentacyclic skeleton of the natural product, and (c) the late-stage oxygenation chemistry to adjust the oxidation states of the A- and E-rings. First, we detail our plan in utilizing the aryne annulation strategy to prepare isoquinoline fragments for the bis-THIQ molecules. Faced with unpromising results in the direct C-H functionalization of isoquinoline N-oxide, we lay out in this Account our rationale behind the design of each isoquinoline coupling partner to overcome these challenges. Additionally, we reveal the inspiration for our hydrogenation system, the setup of our pseudo-high-throughput screening, and the extension of the developed hydrogenation protocols to other simplified isoquinolines.In the context of non-natural bis-THIQ molecules, we have successfully adapted this tandem coupling/hydrogenation approach in the preparation of perfluorinated bis-THIQs, representing the first set of electron-deficient non-natural analogues. Finally, we include our unsuccessful late-stage oxygenation attempts prior to the discovery of the Pd-catalyzed C-O cross-coupling reaction. With this full disclosure of the chemistry developed for the syntheses of bis-THIQs, we hope our orthogonal synthetic tactics will provide useful information and serve as an inspiration for the future development of bis-THIQ pharmaceuticals.

Nitrile biosynthesis in nature: how and why?

Covering: up to the end of 2023Natural nitriles comprise a small set of secondary metabolites which however show intriguing chemical and functional diversity. Various patterns of nitrile biosynthesis can be seen in animals, plants, and microorganisms with the characteristics of both evolutionary divergence and convergence. These specialized compounds play important roles in nitrogen metabolism, chemical defense against herbivores, predators and pathogens, and inter- and/or intraspecies communications. Here we review the naturally occurring nitrile-forming pathways from a biochemical perspective and discuss the biological and ecological functions conferred by diversified nitrile biosyntheses in different organisms. Elucidation of the mechanisms and evolutionary trajectories of nitrile biosynthesis underpins better understandings of nitrile-related biology, chemistry, and ecology and will ultimately benefit the development of desirable nitrile-forming biocatalysts for practical applications.

Recent advances in the synthesis and activity of analogues of bistetrahydroisoquinoline alkaloids as antitumor agents

Ecteinascidin 743 (Et-743), also known by the trade name Yondelis®, is the pioneering marine natural product to be successfully developed as an antitumor drug. Moreover, it is the first tetrahydroisoquinoline natural product used clinically for antitumor therapy since Kluepfel, a Canadian scientist, discovered the tetrahydroisoquinoline alkaloid (THIQ) naphthyridinomycin in 1974. Currently, almost a hundred natural products of bistetrahydroisoquinoline type have been reported. Majority of these bistetrahydroisoquinoline alkaloids exhibit diverse pharmacological activities, with some family members portraying potent antitumor activities such as Ecteinascidins, Renieramycins, Saframycins, Jorumycins, among others. Due to the unique chemical structure and exceptional biological activity of these natural alkaloids, coupled with their scarcity in nature, research seeking to provide material basis for further bioactivity research through total synthesis and obtaining compound leads with medicinal value through structural modification, remains a hot topic in the field of antitumor drug R&D. Despite the numerous reviews on the total synthesis of bistetrahydroisoquinoline natural products, comprehensive reviews on their structural modification are apparently scarce. Moreover, structural modification of bioactive natural products to acquire lead compounds with improved pharmaceutical characteristics, is a crucial approach for innovative drug discovery. This paper presents an up-to-date review of both structural modification and activity of bistetrahydroisoquinoline natural products. It highlights how such alkaloids can be used as antitumor lead compounds through careful chemical modifications. This review offers valuable scientific references for pharmaceutical chemists engaged in developing novel antitumor agents based on such alkaloid modifications, as well as those with such a goal in future.

Recent Advances in the Total Synthesis of the Tetrahydroisoquinoline Alkaloids (2002-2020)

The tetrahydroisoquinoline (THIQ) natural products constitute one of the largest families of alkaloids and exhibit a wide range of structural diversity and biological activity. Ranging from simple THIQ natural products to complex trisTHIQ alkaloids such as the ecteinascidins, the chemical syntheses of these alkaloids and their analogs have been thoroughly investigated due to their intricate structural features and functionalities, as well as their high therapeutic potential. This review describes the general structure and biosynthesis of each family of THIQ alkaloids as well as recent advancements of the total synthesis of these natural products from 2002 to 2020. Recent chemical syntheses that have emerged harnessing novel, creative synthetic design, and modern chemical methodology will be highlighted. This review will hopefully serve as a guide for the unique strategies and tools used in the total synthesis of THIQ alkaloids, as well as address the longstanding challenges in their chemical and biosynthesis.

Asymmetric Total Synthesis of Chaetoglobin A

An asymmetric total synthesis of chaetoglobin A was achieved. Atroposelective oxidative coupling of a phenol incorporating all but one carbon of the final product was used as a key step to generate axial chirality. The stereochemical outcome of the catalytic oxidative phenolic with the highly substituted phenol used herein was found to be opposite that of the simpler congeners reported previously, providing a cautionary tale about extrapolating asymmetric processes from simple to more complex substrates. Optimization of the postphenolic coupling steps including formylation, oxidative dearomatization, and selective deprotection steps are outlined. The tertiary acetates of chaetoglobin A were exceptionally labile due to activation by the adjacent keto groups, which complicated each of these steps. In contrast, the final oxygen to nitrogen exchange proceeded readily and the spectroscopic data from the synthetic material matches that of the isolated natural product in all respects.

Dearomative logic in natural product total synthesis

Covering: 2011 to 2022The natural world is a prolific source of some of the most interesting, rare, and complex molecules known, harnessing sophisticated biosynthetic machinery evolved over billions of years for their production. Many of these natural products represent high-value targets of total synthesis, either for their desirable biological activities or for their beautiful structures outright; yet, the high sp3-character often present in nature's molecules imparts significant topological complexity that pushes the limits of contemporary synthetic technology. Dearomatization is a foundational strategy for generating such intricacy from simple materials that has undergone considerable maturation in recent years. This review highlights the recent achievements in the field of dearomative methodology, with a focus on natural product total synthesis and retrosynthetic analysis. Disconnection guidelines and a three-phase dearomative logic are described, and a spotlight is given to nature's use of dearomatization in the biosynthesis of various classes of natural products. Synthetic studies from 2011 to 2021 are reviewed, and 425 references are cited.

Late-Stage Diversification: A Motivating Force in Organic Synthesis

Interest in therapeutic discovery typically drives the preparation of natural product analogs, but these undertakings contribute significant advances for synthetic chemistry as well. The need for a highly efficient and scalable synthetic route to a complex molecular scaffold for diversification frequently inspires new methodological development or unique application of existing methods on structurally intricate systems. Additionally, synthetic planning with an aim toward late-stage diversification can provide access to otherwise unavailable compounds or facilitate preparation of complex molecules with diverse patterns of substitution around a shared carbon framework. For these reasons among others, programs dedicated to the diversification of natural product frameworks and other complex molecular scaffolds have been increasing in popularity, a trend likely to continue given their fruitfulness and breadth of impact. In this Perspective, we discuss our experience using late-stage diversification as a guiding principle for the synthesis of natural product analogs and reflect on the impact such efforts have on the future of complex molecule synthesis.

Stereoselective Synthesis of 1-Aminocyclopropanecarboxylic Acid Carnosadines via Inter-intramolecular Double Alkylation with Optically Active 2-Methylaziridine Derivatives

The stereoselective and short-step synthesis of N-protected allo-carnosadine, ent-carnosadine, and carnosadine lactam was accomplished from a common cyclopropane intermediate. The inter-intramolecular double alkylation of diethyl malonate with an optically active 2-methylaziridine derivative gave the key cyclopropane in excellent yield and optical purity. The following monohydrolysis of the diester moiety using different reaction conditions provided both diastereomers of monoacids, which were converted to three carnosadine derivatives in 5-6 steps from the common diester.

Chemical Research on Antitumor Isoquinoline Marine Natural Products and Related Compounds

The biologically active, naturally occurring 1,2,3,4-tetrahydroisoquinoline-quinone (THIQ) family members isolated from Actinomycetes and marine organisms have been studied thoroughly over the past five decades. Among them, marine natural products along with their reduced compounds, such as renieramycins and ecteinascidins, have attracted interest due to their fantastic structures and meager availability in nature as well as their potent antitumor profiles. As part of our search for new anticancer metabolites through the isolation and characterization of anticancer THIQ compounds from Thai marine animals, we have developed a fascinating THIQ natural product chemistry and medicinal chemistry based on knowledge of the chemistry of saframycin antibiotics as well as their isolation, characterization, transformation, partial synthesis, and total synthesis. This review mainly presents our contributions during 1999-2019 to the field of research on biologically active renieramycin along with ecteinascidin marine natural products.

Renieramycin-type alkaloids from marine-derived organisms: Synthetic chemistry, biological activity and structural modification

Marine natural products are known for their diverse chemical structures and extensive bioactivities. Renieramycins, the member of tetrahydroisoquinoline family of marine natural products, arouse interests because of their strong antitumor activities and similar structures to the first marine antitumor agent ecteinascidin-743, approved by the European Union. According to the literatures, researches on the pharmacological activities of renieramycins mainly focus on their antitumor activities. In addition, by structural modification, derivatives of renieramycins show stronger antiproliferative activity and less accidental necrosis activity on cells. Nevertheless, the difficulties in extraction and separation hinder their further development. Hence, the synthetic chemistry work of renieramycins plays a key role in their further development. In this review, currently reported researches on the synthetic chemistry, pharmacological activities and structural modification of renieramycins are summarized, which will benefit future drug development and innovation.

Synthetically important ring opening reactions by alkoxybenzenes and alkoxynaphthalenes

Alkoxybenzenes and alkoxynaphthalenes, as nucleophiles, have drawn great attention from organic chemists over the decades. Due to their high ring strain, those particular classes of molecules are often used in synthesis by utilizing their properties to undergo facile Friedel-Crafts alkylations. Different isomeric and low or densely substituted alkoxybenzenes are used for synthesis according to the structure of the target molecule. Isomeric methoxybenzenes, are the most commonly used molecule in this regard. This review aims to comprehensively cover the instances of different alkoxy-benzenes/naphthalenes used as nucleophiles for ring opening.

Preparation and Uses of Chlorinated Glycerol Derivatives

Crude glycerol (C3H8O3) is a major by-product of biodiesel production from vegetable oils and animal fats. The increased biodiesel production in the last two decades has forced glycerol production up and prices down. However, crude glycerol from biodiesel production is not of adequate purity for industrial uses, including food, cosmetics and pharmaceuticals. The purification process of crude glycerol to reach the quality standards required by industry is expensive and dificult. Novel uses for crude glycerol can reduce the price of biodiesel and make it an economical alternative to diesel. Moreover, novel uses may improve environmental impact, since crude glycerol disposal is expensive and dificult. Glycerol is a versatile molecule with many potential applications in fermentation processes and synthetic chemistry. It serves as a glucose substitute in microbial growth media and as a precursor in the synthesis of a number of commercial intermediates or fine chemicals. Chlorinated derivatives of glycerol are an important class of such chemicals. The main focus of this review is the conversion of glycerol to chlorinated derivatives, such as epichlorohydrin and chlorohydrins, and their further use in the synthesis of additional downstream products. Downstream products include non-cyclic compounds with allyl, nitrile, azide and other functional groups, as well as oxazolidinones and triazoles, which are cyclic compounds derived from ephichlorohydrin and chlorohydrins. The polymers and ionic liquids, which use glycerol as an initial building block, are highlighted, as well.

Concise total syntheses of (-)-jorunnamycin A and (-)-jorumycin enabled by asymmetric catalysis

The bis-tetrahydroisoquinoline (bis-THIQ) natural products have been studied intensively over the past four decades for their exceptionally potent anticancer activity, in addition to strong Gram-positive and Gram-negative antibiotic character. Synthetic strategies toward these complex polycyclic compounds have relied heavily on electrophilic aromatic chemistry, such as the Pictet-Spengler reaction, that mimics their biosynthetic pathways. Herein, we report an approach to two bis-THIQ natural products, jorunnamycin A and jorumycin, that instead harnesses the power of modern transition-metal catalysis for the three major bond-forming events and proceeds with high efficiency (15 and 16 steps, respectively). By breaking from biomimicry, this strategy allows for the preparation of a more diverse set of nonnatural analogs.

Chemistry of Renieramycins. 17. A New Generation of Renieramycins: Hydroquinone 5-O-Monoester Analogues of Renieramycin M as Potential Cytotoxic Agents against Non-Small-Cell Lung Cancer Cells

A series of hydroquinone 5-O-monoester analogues of renieramycin M were semisynthesized via bishydroquinonerenieramycin M (5) prepared from renieramycin M (1), a major cytotoxic bistetrahydroisoquinolinequinone alkaloid isolated from the Thai blue sponge Xestospongia sp. All 20 hydroquinone 5-O-monoester analogues possessed cytotoxicity with IC₅₀ values in nanomolar concentrations against the H292 and H460 human non-small-cell lung cancer (NSCLC) cell lines. The improved cytotoxicity toward the NSCLC cell lines was observed from the 5-O-monoester analogues such as 5-O-acetyl ester 6a and 5-O-propanoyl ester 7e, which exhibited 8- and 10-fold increased cytotoxicity toward the H292 NSCLC cell line (IC₅₀ 3.0 and 2.3 nM, respectively), relative to 1 (IC₅₀ 24 nM). Thus, the hydroquinone 5-O-monoester analogues are a new generation of the renieramycins to be further developed as potential marine-derived drug candidates for lung cancer treatment.

Asymmetric Synthesis of Isoquinoline Alkaloids: 2004-2015

In the past decade, the asymmetric synthesis of chiral nonracemic isoquinoline alkaloids, a family of natural products showing a wide range of structural diversity and biological and pharmaceutical activity, has been based either on continuation or improvement of known traditional methods or on new, recently developed, strategies. Both diastereoselective and enantioselective catalytic methods have been applied. This review describes the stereochemically modified traditional syntheses (the Pictet-Spengler, the Bischler-Napieralski, and the Pomeranz-Fritsch-Bobbitt) along with strategies based on closing of the nitrogen-containing ring B of the isoquinoline core by the formation of bonds between C₁-N₂, N₂-C₃, C₁-N₂/N₂-C₃, and C₁-N₂/C₄-C_4a atoms. Methods involving introduction of substituents at the C1 carbon of isoquinoline core along with syntheses applying various biocatalytic techniques have also been reviewed.

Chemistry of Renieramycins. 15. Synthesis of 22-O-Ester Derivatives of Jorunnamycin A and Their Cytotoxicity against Non-Small-Cell Lung Cancer Cells

Eighteen 22-O-ester derivatives of jorunnamycin A (2) were prepared via 2, and their cytotoxicity against human non-small-cell lung cancer (NSCLC) cells was evaluated. Preliminary study of the structure-cytotoxicity relationship revealed that the ester part containing a nitrogen-heterocyclic ring elevated the cytotoxicity of the 22-O-ester derivatives. Among them, 22-O-(4-pyridinecarbonyl) ester 6a is the most potent compound (IC50 1.1 and 1.6 nM), exhibiting 21-fold and 5-fold increases in cytotoxicity against the H292 and H460 NSCLC cell lines, respectively, relative to renieramycin M (1), the major cytotoxic bistetrahydroisoquinolinequinone alkaloid of the Thai blue sponge Xestospongia sp.

Marine Invertebrate Metabolites with Anticancer Activities: Solutions to the "Supply Problem"

Marine invertebrates provide a rich source of metabolites with anticancer activities and several marine-derived agents have been approved for the treatment of cancer. However, the limited supply of promising anticancer metabolites from their natural sources is a major hurdle to their preclinical and clinical development. Thus, the lack of a sustainable large-scale supply has been an important challenge facing chemists and biologists involved in marine-based drug discovery. In the current review we describe the main strategies aimed to overcome the supply problem. These include: marine invertebrate aquaculture, invertebrate and symbiont cell culture, culture-independent strategies, total chemical synthesis, semi-synthesis, and a number of hybrid strategies. We provide examples illustrating the application of these strategies for the supply of marine invertebrate-derived anticancer agents. Finally, we encourage the scientific community to develop scalable methods to obtain selected metabolites, which in the authors' opinion should be pursued due to their most promising anticancer activities.

Total Syntheses and Biological Evaluation of Both Enantiomers of Several Hydroxylated Dimeric Nuphar Alkaloids

Herein, we describe the first total syntheses of five members of the dimeric nuphar alkaloids: (+)-6,6'-dihydroxythiobinupharidine (+)-1 a, (+)-6-hydroxythiobinupharidine (+)-1 b, (-)-6,6'-dihydroxythionuphlutine (-)-2 a, (-)-6,6'-dihydroxyneothiobinupharidine (-)-3 a, and (+)-6,6'-dihydroxyneothionuphlutine (+)-4 a. The latter two have not been found in nature. We have also made each of their enantiomers (-)-1 a-b, (+)-2 a, (+)-3 a, and (-)-4 a. The key step in these syntheses was the dimerization of an α-aminonitrile (a hydrolytically stable surrogate for its corresponding hemiaminal) with chiral Lewis acid complexes. We have also reassigned the literature structures of (+)-1 a-1 b—for those instances in which the NMR spectra were obtained in CD3OD—to their corresponding CD3O-adducts. Our efforts provide for the first time apoptosis data for (-)-3 a, (+)-4 a, and all five non-natural enantiomers prepared. The data indicate high apoptotic activity regardless of the enantiomer or relative stereochemical configuration at C7 and C7'.

Regioselective electrophilic aromatic bromination: theoretical analysis and experimental verification

Electrophilic aromatic bromination is the most common synthetic method used to prepare aryl bromides, which are very useful intermediates in organic synthesis. To understand the experimental results in electrophilic aromatic brominations, ab initio calculations are used here for a tentative analysis of the positional selectivity. The calculated results agree well with the corresponding experimental data, and the reliability of the resulting positional selectivity was verified by the corresponding experimental data.

Selective Cleavage of Carbamate Protecting Groups from Aziridines with Otera's Catalyst

Otera’s distannoxane catalyst was found to promote the cleavage of carbamate groups from N-protected aziridines. This method enables the chemoselective cleavage of an aziridinyl N-carbobenzyloxy (Cbz) group in the presence of other N-Cbz groups. The selectivity is due to the longer, weaker N–C bond of aziridinyl carbamates, as inferred through IR and crystallographic analyses.

Asymmetric total synthesis of (-)-jorunnamycins A and C and (-)-jorumycin from L-tyrosine

Three renieramycin-type antitumor alkaloids, (-)-jorunnamycins A (1) and C (2) and (-)-jorumycin (3), have been synthesized by a new convergent approach, which features a highly regio- and stereoselective Pictet-Spengler cyclization to couple the isoquinoline and the trisubstituted phenylalaninol partners. This synthetic strategy opens an economical access to these important antitumor alkaloids with high yields: (-)-jorunnamycin A, as a common precursor to other renieramycin-type alkaloids and their analogues, is obtained with 18.1% overall yield from l-tyrosine.

Synthetic route to chiral indolines via ring-opening/C-N cyclization of activated 2-haloarylaziridines

A practical approach for the synthesis of 3-substituted indolines via regio- and stereoselective SN2-type ring-opening of 2-(2-halophenyl)-N-tosylaziridines with heteroatomic nucleophiles (O, N, and S) followed by palladium-catalyzed intramolecular C-N cyclization is reported in excellent yields (up to >99%) and enantiomeric excess (ee 99%).

Synthetic Studies on Potent Marine Drugs: Synthesis and the Crystal Structure of 6-tert-butyl-4-phenyl-4H-chromene-2-carboxylic Acid

4H-Chromene-2-carboxylic acid ester derivatives of renieramycin M might be of use for the structural-activity relationship studies of antitumor antibiotic tetrahydroisoquinoline natural products. Accordingly, 6-tert-butyl-4-phenyl-4H-chromene-2-carboxylic acid, one key intermediate, was synthesized via the condensation of (3E)-2-oxo-4-phenylbut-3-enoate methyl ester with 4-tert-butylphenol in the presence of AuCl3/3AgOTf (5 mol%), followed by cyclodehydration and aqueous hydrolysis. The product was unambiguously shown to the 4H-chromene-2-carboxylic acid by spectroscopy and X-ray crystallographic analysis. A packing diagram of the crystal structure shows that aromaticπ-stacking interactions and O–H⋯O hydrogen bond stabilize the structure in the solid.