Chemistry and biology of the tetrahydroisoquinoline antitumor antibiotics

eFluorination for the Rapid Synthesis of Carbamoyl Fluorides from Oxamic Acids

In this letter, we disclose the anodic oxidation of oxamic acids in the presence of Et3N·3HF as a practical, scalable, and robust method to rapidly access carbamoyl fluorides from readily available and stable precursors. The simplicity of this method also led us to develop the first flow electrochemical preparation of carbamoyl fluorides, demonstrating scale-up feasibility as a proof of concept.

Chemo-enzymatic total synthesis: current approaches toward the integration of chemical and enzymatic transformations

A steadily increasing number of reports have been published on chemo-enzymatic synthesis methods that integrate biosynthetic enzymatic transformations with chemical conversions. This review focuses on the total synthesis of natural products and classifies the enzymatic reactions into three categories. The total synthesis of five natural products: cotylenol, trichodimerol, chalcomoracin, tylactone, and saframycin A, as well as their analogs, is outlined with an emphasis on comparing these chemo-enzymatic syntheses with the corresponding natural biosynthetic pathways.

Efficient Enzymatic Synthesis of Carbamates in Water Using Promiscuous Esterases/Acyltransferases

Biocatalysis provides an attractive approach to facilitate synthetic reactions in aqueous media. Motivated by the discovery of promiscuous aminolysis activity of esterases, we exploited the esterase from Pyrobaculum calidifontis VA1 (PestE) for the synthesis of carbamates from different aliphatic, aromatic, and arylaliphatic amines and a set of carbonates such as dimethyl-, dibenzyl-, or diallyl carbonate. Thus, aniline and benzylamine derivatives, aliphatic and even secondary amines could be efficiently converted into the corresponding benzyloxycarbonyl (Cbz)- or allyloxycarbonyl (Alloc)-protected products in bulk water, with (isolated) yields of up to 99 %.

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.

Synthetic Methods for Azaheterocyclic Phosphonates and Their Biological Activity: An Update 2004-2024

The increasing importance of azaheterocyclic phosphonates in the agrochemical, synthetic, and medicinal field has provoked an intense search in the development of synthetic routes for obtaining novel members of this family of compounds. This updated review covers methodologies established since 2004, focusing on the synthesis of azaheterocyclic phosphonates, of which the phosphonate moiety is directly substituted onto to the azaheterocyclic structure. Emphasizing recent advances, this review classifies newly developed synthetic approaches according to the ring size and providing information on biological activities whenever available. Furthermore, this review summarizes information on various methods for the formation of C-P bonds, examining sustainable approaches such as the Michaelis-Arbuzov reaction, the Michaelis-Becker reaction, the Pudovik reaction, the Hirao coupling, and the Kabachnik-Fields reaction. After analyzing the biological activities and applications of azaheterocyclic phosphonates investigated in recent years, a predominant focus on the evaluation of these compounds as anticancer agents is evident. Furthermore, emerging applications underline the versatility and potential of these compounds, highlighting the need for continued research on synthetic methods to expand this interesting family.

One-pot C(sp3)-H difluoroalkylation of tetrahydroisoquinolines and isochromans via electrochemical oxidation and organozinc alkylation

The C(sp3)-H difluoroalkylation for the introduction of carbonylated CF2 groups into tetrahydroisoquinolines (THIQs) and isochromans has been achieved by using electrochemical oxidation and organozinc alkylation. This one-pot process proceeded smoothly under transition-metal catalyst- and chemical oxidant-free conditions, and the desired products were obtained in good to high yields with a broad scope, except for N-Boc-THIQ. In addition, the gram-scale experiment successfully demonstrated the promising scalability. This is the first example of an electrochemical method for C(sp3)-H difluoroalkylation of amines and ethers.

Selective Ring-Opening Amination of Isochromans and Tetrahydroisoquinolines

The molecular structure-editing through selective C-C bond cleavage allows for the precise modification of molecular structures and opens up new possibilities in chemical synthesis. By strategically cleaving C-C bonds and editing the molecular structure, more efficient and versatile pathways for the synthesis of complex compounds could be designed, which brings significant implications for drug development and materials science. o-Aminophenethyl alcohols and amines are the essential key motifs in bioactive and functional material molecules. The traditional synthesis of these compounds usually requires multiple steps which could generate inseparable isomers and induce low efficiencies. By leveraging a molecular editing strategy, we herein reported a selective ring-opening amination of isochromans and tetrahydroisoquinolines for the efficient synthesis of o-aminophenethyl alcohols and amines. This innovative chemistry allows for the precise cleavage of C-C bonds under mild transition metal-free conditions. Notably, further synthetic application demonstrated that our method could provide an efficient approach to essential components of diverse bioactive molecules.

Rhodium(II)-Catalyzed Denitrogenative Annulation for the Synthesis of Substituted Tetrahydroisoquinolines

Tetrahydroisoquinoline (THIQ) derivatives stand out as a promising class of compounds due to their diverse range of biological activities, making them particularly valuable in drug discovery. To enhance their structural diversity, an Rh-catalyzed denitrogenative annulation method has been introduced for synthesizing these derivatives. An intriguing aspect of this method is the ability of the Brønsted acid to prevent further annulation while facilitating the production of the desired THIQ derivatives, achieving impressive yields of up to 86%. This synthetic approach was subsequently leveraged to create an analogue of cyclocelabenzine, a compound showing potential as an anti-inflammatory agent.

Genetic toolbox for Photorhabdus and Xenorhabdus: pSEVA based heterologous expression systems and CRISPR/Cpf1 based genome editing for rapid natural product profiling

BACKGROUND

Bacteria of the genus Photorhabdus and Xenorhabdus are motile, Gram-negative bacteria that live in symbiosis with entomopathogenic nematodes. Due to their complex life cycle, they produce a large number of specialized metabolites (natural products) encoded in biosynthetic gene clusters (BGC). Genetic tools for Photorhabdus and Xenorhabdus have been rare and applicable to only a few strains. In the past, several tools have been developed for the activation of BGCs and the deletion of individual genes. However, these often have limited efficiency or are time consuming. Among the limitations, it is essential to have versatile expression systems and genome editing tools that could facilitate the practical work.

RESULTS

In the present study, we developed several expression vectors and a CRISPR-Cpf1 genome editing vector for genetic manipulations in Photorhabdus and Xenorhabdus using SEVA plasmids. The SEVA collection is based on modular vectors that allow exchangeability of different elements (e.g. origin of replication and antibiotic selection markers with the ability to insert desired sequences for different end applications). Initially, we tested different SEVA vectors containing the broad host range origins and three different resistance genes for kanamycin, gentamycin and chloramphenicol, respectively. We demonstrated that these vectors are replicative not only in well-known representatives, e.g. Photorhabdus laumondii TTO1, but also in other rarely described strains like Xenorhabdus sp. TS4. For our CRISPR/Cpf1-based system, we used the pSEVA231 backbone to delete not only small genes but also large parts of BGCs. Furthermore, we were able to activate and refactor BGCs to obtain high production titers of high value compounds such as safracin B, a semisynthetic precursor for the anti-cancer drug ET-743.

CONCLUSIONS

The results of this study provide new inducible expression vectors and a CRISPR/CPf1 encoding vector all based on the SEVA (Standard European Vector Architecture) collection, which can improve genetic manipulation and genome editing processes in Photorhabdus and Xenorhabdus.

Development of Cyclic N,O-Aminal-Embedded Bis-tetrahydroisoquinoline Analogues as Potential DNA Alkylation Agents

This work described a novel "functional hybrid" design for bis-tetrahydroisoquinoline (bis-THIQ) analogues as potential DNA alkylation agents by replacing the labile C21-carbinolamine on the bis-THIQ skeleton of ET-743 with a chemically stable cyclic N,O-aminal functionality. In vitro anti-proliferation evaluation has proven that it is a successful approach to deliver new bis-THIQ analogues with common cytotoxicities, among which several exhibited sub-micromolar-range IC50 against the proliferation of human cancer cell lines A549, HepG2, and MDA-MB-231, respectively.

Chiral phosphoric acid-catalyzed enantioselective [5+1] cycloaddition reaction of C,N-cyclic azomethine imines with isocyanides

The first catalytic enantioselective [5+1] cycloaddition reactions of C,N-cyclic azomethine imines with isocyanides are reported herein. The method displays a broad substrate scope and atom-economy. A series of chiral tetrahydroisoquinoline containing indole skeletons were obtained in up to 90% yield with 95% ee under mild reaction conditions. A possible catalytic model was also proposed.

Catalytic divergencies in the mechanism of L-arginine hydroxylating nonheme iron enzymes

Many enzymes in nature utilize a free arginine (L-Arg) amino acid to initiate the biosynthesis of natural products. Examples include nitric oxide synthases, which generate NO from L-Arg for blood pressure control, and various arginine hydroxylases involved in antibiotic biosynthesis. Among the groups of arginine hydroxylases, several enzymes utilize a nonheme iron(II) active site and let L-Arg react with dioxygen and α-ketoglutarate to perform either C3-hydroxylation, C4-hydroxylation, C5-hydroxylation, or C4-C5-desaturation. How these seemingly similar enzymes can react with high specificity and selectivity to form different products remains unknown. Over the past few years, our groups have investigated the mechanisms of L-Arg-activating nonheme iron dioxygenases, including the viomycin biosynthesis enzyme VioC, the naphthyridinomycin biosynthesis enzyme NapI, and the streptothricin biosynthesis enzyme OrfP, using computational approaches and applied molecular dynamics, quantum mechanics on cluster models, and quantum mechanics/molecular mechanics (QM/MM) approaches. These studies not only highlight the differences in substrate and oxidant binding and positioning but also emphasize on electronic and electrostatic differences in the substrate-binding pockets of the enzymes. In particular, due to charge differences in the active site structures, there are changes in the local electric field and electric dipole moment orientations that either strengthen or weaken specific substrate C-H bonds. The local field effects, therefore, influence and guide reaction selectivity and specificity and give the enzymes their unique reactivity patterns. Computational work using either QM/MM or density functional theory (DFT) on cluster models can provide valuable insights into catalytic reaction mechanisms and produce accurate and reliable data that can be used to engineer proteins and synthetic catalysts to perform novel reaction pathways.

Naturally Occurring and Widespread Resistance to Bioactive Natural Products

Naturally occurring resistances diminish the effectiveness of antibiotics, and present significant challenges to human health. Human activities are usually considered as the main drivers of the dissemination of antibiotic resistance, however, the origin of the clinical antibiotic resistance can be traced to the environmental microbes, and the clinically relevant resistance determinants have already pre-existed in nature before the antibiotics come into clinic. In this concept, we present the naturally occurring and widespread resistance determinants recently discovered during the biosynthesis study of bioactive compounds. These widely prevalent resistances in environmental microbes, including antibiotic producers and non-producers, advance the understanding of the origin of resistance, and provide prediction for the clinically relevant resistance to aid in the rational design of more effective drug analogues to combat resistance.

Epiphytic and endophytic microbiome of the seagrass Zostera marina: Do they contribute to pathogen reduction in seawater?

Seagrass meadows provide crucial ecosystem services for coastal environments and were shown to reduce the abundance of waterborne pathogens linked to infections in humans and marine organisms in their vicinity. Among potential drivers, seagrass phenolics released into seawater have been linked to pathogen suppression, but the potential involvement of the seagrass microbiome has not been investigated. We hypothesized that the microbiome of the eelgrass Zostera marina, especially the leaf epiphytes that are at direct interface between the seagrass host and the surrounding seawater, inhibit waterborne pathogens thereby contributing to their removal. Using a culture-dependent approach, we isolated 88 bacteria and fungi associated with the surfaces and inner tissues of the eelgrass leaves (healthy and decaying) and the roots. We assessed the antibiotic activity of microbial extracts against a large panel of common aquatic, human (fecal) and plant pathogens, and mined the metabolome of the most active extracts. The healthy leaf epibiotic bacteria, particularly Streptomyces sp. strain 131, displayed broad-spectrum antibiotic activity superior to some control drugs. Gram-negative bacteria abundant on healthy leaf surfaces, and few endosphere-associated bacteria and fungi also displayed remarkable activities. UPLC-MS/MS-based untargeted metabolomics analyses showed rich specialized metabolite repertoires with low annotation rates, indicating the presence of many undescribed antimicrobials in the extracts. This study contributes to our understanding on microbial and chemical ecology of seagrasses, implying potential involvement of the seagrass microbiome in suppression of pathogens in seawater. Such effect is beneficial for the health of ocean and human, especially in the context of climate change that is expected to exacerbate all infectious diseases. It may also assist future seagrass conservation and management strategies.

Targeting Alzheimer's Disease: Evaluating the Efficacy of C-1 Functionalized N-Aryl-Tetrahydroisoquinolines as Cholinergic Enzyme Inhibitors and Promising Therapeutic Candidates

We have synthesized 22 C-1 functionalized-N-aryl-1,2,3,4-tetrahydroisoquinoline derivatives showing biological activities towards cholinergic enzymes. Synthesis was performed using visible-light-promoted photo-redox chemistry, starting from a common intermediate, and the application of this synthetic methodology drastically simplified synthetic routes and purification of desired compounds. All synthesized derivates were divided into four groups based on the substituents in the C-1 position, and their inhibition potencies towards two cholinergic enzymes, acetyl- and butyrylcholinesterase were evaluated. Most potent derivatives were selected, and kinetic analysis was further carried out to obtain insights into the mechanisms of inhibition of these two enzymes. Further validation of the mode of inhibition of cholinergic enzymes by the two most potent THIQ compounds, 3c and 3i, was performed using fluorescence-quenching titration studies. Molecular docking studies further confirmed the proposed mechanism of enzymes' inhibition. In silico predictions of physicochemical properties, pharmacokinetics, drug-likeness, and medicinal chemistry friendliness of the selected most potent derivatives were performed using Swiss ADME tool. This was followed by UPLC-assisted log P determination and in vitro BBB permeability studies performed in order to assess the potential of the synthesized compounds to pass the BBB.

Isocyanide-based Multicomponent Reactions (IMCRs) in Water or Aqueous Biphasic Systems

BACKGROUND

Isocyanide is an intriguing one-carbon synthon that is frequently employed in a variety of carbon-carbon and carbon-heteroatom bond-forming reactions. Isocyanide-based multicomponent reactions (IMCRs) are effective synthetic tools in organic synthesis for the preparation of complex heterocyclic molecules. The IMCRs in water have become an attractive research direction, enabling simultaneous growth of both IMCRs and green solvents towards ideal organic synthesis.

OBJECTIVE

The goal of this review is to provide a general overview of IMCRs in water or biphasic aqueous systems for accessing various organic molecules, as well as an examination of their benefits and mechanistic insights.

CONCLUSION

High atom economies, mild reaction conditions, high yields, and catalyst-free processes are crucial features of these IMCRs in water or biphasic aqueous systems.

Two-Dimensional Porphyrinic Metal-Organic Framework Composites as a Photocatalytic Platform for Chemoselective Hydrogenation

Chemoselective hydrogenation with high efficiency under ambient conditions remains a great challenge. Herein, an efficient photocatalyst, the 2D porphyrin metal-organic framework composite AmPy/Pd-PPF-1(Cu), featuring AmPy (1-aminopyrene) sitting axially on a paddle-wheel unit, has been rationally fabricated. The 2D AmPy/Pd-PPF-1(Cu) composite acts as a photocatalytic platform, promoting the selective hydrogenation of quinolines to tetrahydroquinolines with a yield up to 99%, in which ammonia borane serves as the hydrogen donor. The AmPy molecules coordinated on a 2D MOF not only enhance the light absorption capacity but also adjust the layer spacing without affecting the network structure of 2D Pd-PPF-1(Cu) nanosheets. Through deuterium-labeling experiments, in situ X-ray photoelectron spectroscopy, electron paramagnetic resonance studies, and density functional theory calculations, it is disclosed that Cu paddle-wheel units in 2D AmPy/Pd-PPF-1(Cu) nanosheets behave as the active site for transfer hydrogenation, and metalloporphyrin ligand and axial aminopyrene molecules can enhance the light absorption capacity and excite photogenerated electrons to Cu paddle-wheel units, assisting in photocatalysis.

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.

Semisynthesis of 5-O-ester derivatives of renieramycin T and their cytotoxicity against non-small-cell lung cancer cell lines

The semisynthesis of 5-O-ester derivatives of renieramycin T was accomplished through the photoredox reaction of renieramycin M (1), a bistetrahydroisoquinolinequinone alkaloid isolated from the Thai blue sponge Xestospongia sp. This process led to the conversion of compound 1 to renieramycin T (2), which was subsequently subjected to Steglich esterification with appropriate acylating agents containing linear alkyl, N-tert-butoxycarbonyl-L-amino, and heterocyclic aromatic substituent. Notably, the one-pot transformation, combining the photoredox reaction and esterification led to the formation of 7-O-ester derivatives of renieramycin S due to hydrolysis. Subsequently, the in vitro cytotoxicity of the 17 semisynthesized derivatives against human non-small-cell lung cancer (NSCLC) cells in parallel with normal cell lines was evaluated. Among the tested compounds, 5-O-(3-propanoyl) ester of renieramycin T (3b) exhibited potent cytotoxic activity with half-maximal inhibitory concentration (IC50) values at 33.44 and 33.88 nM against H292 and H460 cell lines, respectively. These values were within the same range as compound 1 (IC50 = 34.43 and 35.63 nM) and displayed twofold higher cytotoxicity compared to compound 2 (IC50 = 72.85 and 83.95 nM). The steric characteristics and aromatic orientation of the 5-O-ester substituents played significant roles in their cytotoxicity. Notably, derivative 3b induced apoptosis with minimal necrosis, in contrast to the parental compound 1. Hence, the relationship between the structure and cytotoxicity of renieramycin-ecteinascidin hybrid alkaloids was investigated. This study emphasizes the potential of the series of 5-O-ester derivatives of renieramycin T as promising leads for the further development of potential anti-NSCLC agents.

Isochromenylium/Isoquinolinium-Mediated One-Pot Annulation to Hexahydropyrazinoisoquinolines. Synthesis of Quinocarcinol

A novel annulation protocol has been successfully developed in this work for the quick generation of 1,3,4,6,11,11a-hexahydro-2H-pyrazino[1,2-b]isoquinolines from easily accessible o-alkynylbenzaldehydes. Various hexahydropyrazinoisoquinolines, including those previously unavailable with electron-deficient substituents, have been achieved via the newly developed continuously operational isochromenylium/isoquinolinium-mediated procedure. It also perfectly served as a key step to generate the basic skeleton in the new total synthesis of quinocarcinol, accompanied by the development and application of a direct late-stage stereoselective sp3 C-H hydroxymethylation.

Design, synthesis, and biological evaluation of simplified tetrahydroisoquinoline analogs

A series of tetrahydroisoquinoline derivatives were prepared and their antitumor activity was studied against several human carcinoma cell lines, including Ketr3, BEL-7402, BGC-823, KB, HCT-8, MCF-7, HeLa, A2780, A549, and HT-1080. Compound 20, an analog of phthalascidin 650, exhibited good broad-spectrum antitumor activity in vitro. However, compounds 19 and 21, in which the side chains at C-22 are simplified, showed no obvious antitumor activity, indicating that the C-22 side chain of this type of compound has a greater impact on its activity. The difference in the in vivo activity between compound 20 and phthalascidin 650 also shows a significant effect of the substituents on the skeleton structure on the in vivo activity.

Synthesis of biologically important tetrahydroisoquinoline (THIQ) motifs using quantum dot photocatalyst and evaluation of their anti-bacterial activity

Our study introduces an efficient photocatalytic approach for synthesizing biologically significant C1-substituted tetrahydroisoquinoline (THIQ) motifs, employing WS2 quantum dots (QDs) as catalysts. This method enables the formation of C-C and C-P bonds at the C1 position of the THIQ motif. The resulting compounds exhibit substantial antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) bacteria, with low minimum inhibitory concentration (MIC) values. Notably, the WS2 QD catalyst demonstrates recyclability and suitability for gram-scale reactions, underscoring the sustainability and scalability of our approach. Overall, our research presents a versatile and cost-effective strategy for synthesizing C1-substituted THIQ derivatives, highlighting their potential as novel therapeutic agents in biology and medicinal chemistry.

Cobalt-Catalyzed Enantioselective C-H Annulation of Benzylamines with Alkynes: Application to the Modular and Asymmetric Syntheses of Bioactive Molecules

The transition metal-catalyzed enantioselective C-H functionalization strategy has revolutionized the logic of natural product synthesis. However, previous applications have heavily relied on the use of noble metal catalysts such as rhodium and palladium. Herein, we report the efficient synthesis of C1-chiral 1,2-dihydroisoquinolines (DHIQs) via enantioselective C-H/N-H annulation of picolinamides with alkynes catalyzed by a more sustainable and cheaper 3d metal catalyst, cobalt(II) acetate tetrahydrate. A wide range of enantiomerically enriched DHIQs were obtained in good yields with excellent enantioselectivities (up to 98% yield and >99% ee). The robustness and synthetic potential of this method were demonstrated by the modular and asymmetric syntheses of several tetrahydroisoquinoline alkaloids, including (S)-norlaudanosine, (S)-laudanosine, (S)-xylopinine, (S)-sebiferine, and (S)-cryptostyline II, and the asymmetric syntheses of key intermediates of (+)-solifenacin, FR115427, and (+)-NPS R-568.

Synthesis and cytotoxic activity of some (+)-salsolidine derivatives

On the basis of typical for secondary amino group reactions a number of derivatives of alkaloid (+)-salsolidine was synthesised. Cytotoxic properties of obtained compounds towards the HEK293, A549, MCF-7 and SH-SY5Y cell lines have been evaluated. As a result of the screening, the hit compound - 2-(chloroacetyl)-6,7-dimethoxy-1-methyl-1,2,3,4-tetrahydroisoquinoline (11) was identified, that inhibited the metabolic activity of A-549, MCF-7 and SH-SY5Y tumour cell lines with the IC50 values of 3.83 ± 0.78 µM, 5.84 ± 1.62 µM and 2.89 ± 0,92 µM correspondingly. Based on the effect of 11 on the cell cycle progression and the molecular docking data, it was preliminary assumed that the cytotoxic activity of the 11 can be realised through its interaction with the active site of the cyclin-dependent kinase CDK9 (PDB code 3BLR).

Divergent transformation of C,N-cyclic-N'-acyl azomethine imines by reaction with diazo compounds

C,N-cyclic-N'-acyl azomethine imines with isoquinoline skeletons were investigated for their reactivity with diazo compounds via two different pathways. During the reaction with ethyl diazoacetate, an α-diazoacetate moiety was introduced at the C1-position of the resulting tetrahydroisoquinolines. Alternatively, diazomethane or trimethylsilyldiazomethane was used to synthesize 3-benzazepine derivatives via ring expansion.

Visible-light promoted photoredox catalysis in flow: addition of biologically important α‑amino radicals to michael acceptors

Visible light promoted photoredox catalyzed formation of α-amino radicals from cyclic tertiary amine compounds and their subsequent addition to Michael acceptors performed in flow conditions allowed access to a wide range of functionalized N-aryl-substituted tetrahydroisoquinolines (THIQs) and N-aryl-substituted tetrahydro-β-carbolines (THBCs). Visible light in conjunction with Ru(bpy)3Cl2 photocatalyst allowed the formation and high reactivities of α-amino radicals in flow conditions at room temperature. These reactions gave valuable products with high efficiencies; some previously unavailable reaction pathways photo or thermal reaction conditions; i.e. direct synthesis of 1-substituted (THBCs) via α-amino radical path were successfully realized in flow. The use of custom-made FEP tube microreactor proved to be the key to succesfull α-amino-radical formation and overall reaction performance in flow. Three types of light transparent custom-made microfluidic devices were tested, among them glass/silicon and FEP type reactor showed very good results in the conversion of tested compounds. Plausible reaction mechanism is proposed in accordance with known principles of photo activation of tertiary amines. Visible light promoted C(sp3)-H functionalization of N-aryl-protected tetrahydroisoquinolines and N-aryl-protected tetrahydro-β-carbolines in microflow conditions via a-amino radical pathway with various coupling partners in excellent yields and efficiencies.

Charting the Evolution of Chemoenzymatic Strategies in the Syntheses of Complex Natural Products

Bolstered by recent advances in bioinformatics, genetics, and enzyme engineering, the field of chemoenzymatic synthesis has enjoyed a rapid increase in popularity and utility. This Perspective explores the integration of enzymes into multistep chemical syntheses, highlighting the unique potential of biocatalytic transformations to streamline the synthesis of complex natural products. In particular, we identify four primary conceptual approaches to chemoenzymatic synthesis and illustrate each with a number of landmark case studies. Future opportunities and challenges are also discussed.

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.

Synthesis and characterization of novel acyl hydrazones derived from vanillin as potential aldose reductase inhibitors

In the polyol pathway, aldose reductase (AR) catalyzes the formation of sorbitol from glucose. In order to detoxify some dangerous aldehydes, AR is essential. However, due to the effects of the active polyol pathway, AR overexpression in the hyperglycemic state leads to microvascular and macrovascular diabetic problems. As a result, AR inhibition has been recognized as a potential treatment for issues linked to diabetes and has been studied by numerous researchers worldwide. In the present study, a series of acyl hydrazones were obtained from the reaction of vanillin derivatized with acyl groups and phenolic Mannich bases with hydrazides containing pharmacological groups such as morpholine, piperazine, and tetrahydroisoquinoline. The resulting 21 novel acyl hydrazone compounds were investigated as an inhibitor of the AR enzyme. All the novel acyl hydrazones derived from vanillin demonstrated activity in nanomolar levels as AR inhibitors with IC50 and KI values in the range of 94.21 ± 2.33 to 430.00 ± 2.33 nM and 49.22 ± 3.64 to 897.20 ± 43.63 nM, respectively. Compounds 11c and 10b against AR enzyme activity were identified as highly potent inhibitors and showed 17.38 and 10.78-fold more effectiveness than standard drug epalrestat. The synthesized molecules' absorption, distribution, metabolism, and excretion (ADME) effects were also assessed. The probable-binding mechanisms of these inhibitors against AR were investigated using molecular-docking simulations.

Formal Synthesis of Ecteinascidin 743 from N-Cbz-l-tyrosine

A formal total synthesis of ecteinascidin 743 and lurbinectedin is achieved. Key features involve a Pictet-Spengler cyclization coupling of the tetrahydroisoquinoline and phenylalaninol moieties prepared by a common route with high yield and selectivity, a Parikh-Doering oxidation with good chemoselectivity and functionality tolerance, and a light-mediated A-ring elaboration of pentacyclic methoxyquinone substrates. By the approach, the known advanced intermediate (4-step conversion to Et-743) can be obtained conveniently in 21 total steps from N-Cbz-l-tyrosine.

Combined spectroscopic and structural approaches to explore the mechanism of histidine-ligated heme-dependent aromatic oxygenases

The emergence of histidine-ligated heme-dependent aromatic oxygenases (HDAOs) has greatly enriched heme chemistry, and more studies are required to appreciate the diversity found in His-ligated heme proteins. This chapter describes recent methods in probing the HDAO mechanisms in detail, along with the discussion on how they can benefit structure-function studies of other heme systems. The experimental details are centered on studies of TyrHs, followed by explanation of how the results obtained would advance the understanding of the specific enzyme and also HDAOs. Spectroscopic methods, namely, electronic absorption and EPR spectroscopies, and X-ray crystallography are valuable techniques commonly used to characterize the properties of the heme center and the nature of heme-based intermediate. Herein, we show that the combination of these tools are extremely powerful, not only because one can acquire electronic, magnetic, and conformational information from different phases, but also because of the advantages brought by spectroscopic characterization on crystal samples.

Synthesis and biological evaluation of atropisomeric tetrahydroisoquinolines overcoming docetaxel resistance in triple-negative human breast cancer cells

Herein, atropisomeric 8-aryltetrahydroisoquinolines have been synthesized and biologically evaluated. Based on our structure-activity relationship study, a highly bioactive racemic compound has been produced, and it exhibited high antiproliferative activities against various cancer cell lines, including docetaxel-resistant breast cancer cell lines. Each enantiomer can be synthesized in an enantioselective manner by employing the chiral phosphoric acid-catalyzed atroposelective Pictet-Spengler cyclization. An axially (R)-configured enantiomer showed a higher biological activity compared with the axially (S)-configured enantiomer. Further biological studies suggested that the (R)-enantiomer overcomes docetaxel resistance via the downregulation of signal transducer and activator of transcription 3 activation and consequently induces cellular apoptosis in docetaxel-resistant triple-negative breast cancer cell lines.

Stereospecific [3+2] Cycloaddition of Chiral Arylallenes with C,N-Cyclic Azomethine Imines

A novel α,β-regioselective [3+2] cycloaddition reaction of arylallene with C,N-cyclic azomethine imine is reported. The axial-to-central chirality transfer phenomenon has been disclosed with chiral allenes in the reaction. The wide substrate scope, including different functional groups and natural products, reveals the generality of the methodology. Both experiments and density functional theory calculations have been used to elucidate a plausible mechanism.

C(sp3)-H Aerobic Alkenylation of Tetrahydroisoquinolines via Organic Electrosynthesis

A method for the C(sp³)-H alkenylation of N-aryl-tetrahydroisoquinoline (THIQ) has been developed by the combination of electrooxidation and a copper catalyst. The corresponding products were obtained with good to excellent yields under mild conditions. Besides, the addition of TEMPO as an electron mediator is crucial to this transformation, since the oxidative reaction could proceed under a low electrode potential. In addition, the catalytic asymmetric variant has also been demonstrated with good enantioselectivity.

Introduction of chirality at C1 position of 1-substituted-3,4-dihydroisoquinoline by its enantioselective reduction: synthesis of chiral 1-substituted-1,2,3,4-tetrahydroisoquinoline - a review

There is a wide range of biological activities associated with C1 chiral carbon containing 1-substituted-1,2,3,4-tetrahydroisoquinolines (1-substituted-THIQs) which constitute the isoquinoline alkaloids, a large group of natural products. This work summarizes several novel catalytic stereoselective approaches to enantioselectively reduce the 1-substituted-3,4-dihydroisoquinolines (1-substituted-DHIQs) to produce the desired 1-substituted-THIQs. The 1-substituted-DHIQs were prepared by using the Bischler-Napieralski reaction. The enantioselective reduction of 1-substituted-DHIQs was accomplished by using chiral hydride reducing agents, by hydrogenation with a chiral catalyst, by enantioselective reduction of DHIQs possessing a chiral auxiliary at the imine nitrogen by achiral metallic hydride reducing agents, or by enzymatic catalysis. Among these methods, much more work was carried out on the hydrogenation of 1-substituted-DHIQs in the presence of a chiral catalyst. This review summarizes articles and advancements on this topic from 1972 to 2023.

Organocatalytic asymmetric synthesis of oxazolidino spiropyrazolinones via N,O-acetalization/aza Michael addition domino reaction between N-Boc pyrazolinone ketimines and γ-hydroxyenones

A squaramide-catalyzed asymmetric N,O-acetalization/aza Michael addition domino reaction between N-Boc ketimines derived from pyrazolin-5-ones and γ-hydroxyenones has been developed for the construction of pyrazolinone embedded spirooxazolidines. A hydroquinine derived bifunctional squaramide catalyst was found to be the most effective for this cascade spiroannulation. This new protocol allows the generation of two stereocenters and the desired products are obtained in good yields with moderate to good diastereoselectivities (up to 3.3 : 1 dr) and high enantioselectivities (up to >99% ee) from a range of substituted N-Boc pyrazolinone ketimines and γ-hydroxyenones. The developed protocol is amenable for a scale-up reaction.

Enantio- and Regioselective Electrooxidative Cobalt-Catalyzed C-H/N-H Annulation with Alkenes

In recent years, the merging of electrosynthesis with 3d metal catalyzed C-H activation has emerged as a sustainable and powerful technique in organic synthesis. Despite the impressive advantages, the development of an enantioselective version remains elusive and poses a daunting challenge. Herein, we report the first electrooxidative cobalt-catalyzed enantio- and regioselective C-H/N-H annulation with olefins using an undivided cell at room temperature (up to 99 % ee). ^t Bu-Salox, a rationally designed Salox ligand bearing a bulky tert-butyl group at the ortho-position of phenol, was found to be crucial for this asymmetric annulation reaction. A strong cooperative effect between ^t Bu-Salox and 3,4,5-trichloropyridine enabled the highly enantio- and regioselective C-H annulation with the more challenging α-olefins without secondary bond interactions (up to 96 % ee and 97 : 3 rr). Cyclovoltametric studies, and the preparation, characterization, and transformation of cobaltacycle intermediates shed light on the mechanism of this reaction.

Diastereodivergent cis- and trans-fused [4 + 2] annulations of cyclic 1,3-dienes and 1-azadienes via ligand-controlled palladium catalysis

Despite the blossoming of reports of diastereodivergent synthesis over the past years, switchable control of the stereochemistry of the bridgehead atoms of the fused frameworks has been significantly underdeveloped. Here we disclose the ability of Pd⁰-π-Lewis base catalysis to finely reverse the concerted inverse-electron-demand aza-Diels-Alder cycloaddition reaction between cyclic 1,3-dienes and aurone-derived 1-azadienes. In contrast, the in situ-formed HOMO-energy-increased Pd⁰-η²-complexes of cyclic 1,3-dienes underwent a cascade vinylogous Michael addition/allylic amination process with 1-azadienes. Moreover, judicious selection of chiral ligands allowed for switchable diastereodivergent [4 + 2] annulations to be accomplished, resulting in the construction of both cis- and trans-fused tetrahydropyridine architectures in high yields with moderate to excellent stereoselectivity levels. A variety of acyclic 1,3-dienes and 1-heterodienes were also applied, and furnished a structural diversity of enantioenriched frameworks.

Synthesis of Novel 1-Oxo-2,3,4-trisubstituted Tetrahydroisoquinoline Derivatives, Bearing Other Heterocyclic Moieties and Comparative Preliminary Study of Anti-Coronavirus Activity of Selected Compounds

A series of novel 1-oxo-2,3,4-trisubstituted tetrahydroisoquinoline (THIQ) derivatives bearing other heterocyclic moieties in their structure were synthesized based on the reaction between homophthalic anhydride and imines. Initial studies were carried out to establish the anti-coronavirus activity of some of the newly obtained THIQ-derivatives against two strains of human coronavirus-229E and OC-43. Their antiviral activity was compared with that of their close analogues, piperidinones and thiomorpholinones, previously synthesized in our group, with aim to expand the range of the tested representative sample and to obtain valuable preliminary information about biological properties of a wider variety of compounds.

C(sp3)-H Alkenylation of Tetrahydroisoquinolines via Merging Electrochemistry and Organocatalysis

C(sp³)-H alkenylation of tetrahydroisoquinoline by merging Shono oxidation and the Morita-Baylis-Hillman reaction is developed, employing 4-dimethylaminopyridine as an organocatalyst and TEMPO/NaBr as an electrocatalyst. The reaction proceeds via the interception of an iminium cation intermediate, which is generated in situ from anodic oxidation, leading to aza-Morita-Baylis-Hillman reaction products. Additionally, the use of TEMPO and NaBr as mediators is crucial to avoid the decomposition of products by lowering the oxidation potential of the reaction.

Application of cinnamic acid in the structural modification of natural products: A review

Natural products can generally exhibit a variety of biological activities, but most show mediocre performance in preliminary activity evaluation. Natural products often require structural modification to obtain promising lead compounds. Cinnamic acid (CA) is readily available and has diverse biological activities and low cytotoxicity. Introducing CA into natural products may improve their performance, enhance biological activity, and reduce toxic side effect. Herein, we aimed to discuss related applications of CA in the structural modification of natural products and provide a theoretical basis for future derivatization and drug development of natural products. Published articles, web databases (PubMed, Science Direct, SCI Finder, and CNKI), and clinical trial websites (https://clinicaltrials.gov/) related to natural products and CA derivatives were included in the discussion. Based on the inclusion criteria, 128 studies were selected and discussed herein. Screening natural products of CA derivatives allowed for classification by their biological activities. The full text is organized according to the biological activities of the derivatives, with the following categories: anti-tumor, neuroprotective, anti-diabetic, anti-microbial, anti-parasitic, anti-oxidative, anti-inflammatory, and other activities. The biological activity of each CA derivative is discussed in detail. Notably, most derivatives exhibited enhanced biological activity and reduced cytotoxicity compared with the lead compound. CA has various advantages and can be widely used in the synthesis of natural product derivatives to enhance the properties of drug candidates or lead compounds.

Design, Synthesis, and Antimycobacterial Evaluation of Novel Tetrahydroisoquinoline Hydrazide Analogs

A series of novel 2-substituted-5,7-dichloro-1,2,3,4-tetrahydroisoquinoline-6-carbohydrazide were designed, synthesized and structures were confirmed by analytical methods, viz., ¹ H-NMR, ¹³ C-NMR and Mass spectrometry. Synthesized derivatives were evaluated for their anti-mycobacterial activity against Mycobacterium tuberculosis (Mtb) H37Ra. Among all the evaluated compounds, 10A25 containing biphenyl moiety exhibited significant inhibition with IC₅₀ 4.7 μM. 10A19, with an electron-withdrawing Iodo group in the ortho position of the phenyl exhibited significant anti-tubercular activity with IC₅₀ 8.8 μM. IC₅₀ values of the remaining compounds ranged from 9.2 to 73.6 μM. Molecular docking study of the significantly active compound 10A25 was performed to determine the putative binding position of the test ligand at the active site of the selected target proteins Mycobacterium tuberculosis enoyl reductase (InhA) PDB - 4TZK and peptide deformylase PDB - 3E3U. A suitable single crystal for one of the active compounds, 10A12, was generated and analysed to further confirm the structure of the compounds.

Transformation of Renieramycin M into Renieramycins T and S by Intramolecular Photoredox Reaction of 7-Methoxy-6-methyl-1,2,3,4-tetrahydroisoquinoline-5,8-dione Derivatives

In connection with our studies of biologically active 1,2,3,4-tetrahydroisoquinoline marine natural products, we describe herein a useful intramolecular photoredox transformation of 7-methoxy-6-methyl-1,2,3,4-tetrahydroisoquinoline-5,8-dione tricyclic models into 5-hydroxy-tetrahydroisoquinol[1,3]dioxoles in excellent yields. We applied this methodology to the transformation of renieramycin M into renieramycins T and S and the transformation of saframycin A. The results of cytotoxicity studies are also presented.

Iron porphyrin-catalysed C(sp3)–H amination with alkyl azides for the synthesis of complex nitrogen-containing compounds

With the readily prepared iron porphyrin complex as a catalyst and starting with alkyl azides, a panel of nitrogen-containing skeletons representing the families of natural alkaloids and bioactive compounds could be prepared in good yields.

Multi-enzyme catalysed processes using purified and whole-cell biocatalysts towards a 1,3,4-substituted tetrahydroisoquinoline†‡

In this work, two multi-enzyme catalysed processes to access a 1,3,4-substituted tetrahydroisoquinoline (THIQ), using either purified enzymes or lyophilised whole-cell catalysts, are presented. A key focus was the first step in which the reduction of 3-hydroxybenzoic acid (3-OH-BZ) into 3-hydroxybenzaldehyde (3-OH-BA) was catalysed by a carboxylate reductase (CAR) enzyme. Incorporation of the CAR-catalysed step enables substituted benzoic acids as the aromatic components, which can potentially be obtained from renewable resources by microbial cell factories. In this reduction, the implementation of an efficient cofactor regeneration system of both ATP and NADPH was crucial. Two different recycling approaches, either using purified enzymes or lyophilised whole-cells, were established and compared. Both of them showed high conversions of the acid into 3-OH-BA (>80%). However, the whole-cell system showed superior performance because it allowed the combination of the first and second steps into a one-pot cascade with excellent HPLC yields (>99%, enantiomeric excess (ee) ≥ 95%) producing the intermediate 3-hydroxyphenylacetylcarbinol. Moreover, enhanced substrate loads could be achieved compared to the system employing only purified enzymes. The third and fourth steps were performed in a sequential mode to avoid cross-reactivities and the formation of several side products. Thus, (1R,2S)-metaraminol could be formed with high HPLC yields (>90%, isomeric content (ic) ≥ 95%) applying either purified or whole-cell transaminases from Bacillus megaterium (BmTA) or Chromobacterium violaceum (Cv2025). Finally, the cyclisation step was performed using either a purified or lyophilised whole-cell norcoclaurine synthase variant from Thalictrum flavum (ΔTfNCS-A79I), leading to the formation of the target THIQ product with high HPLC yields (>90%, ic > 90%). As many of the educts applied are from renewable resources and a complex product with three chiral centers can be gained by only four highly selective steps, a very step- and atom efficient approach to stereoisomerically pure THIQ is shown.

In this work, two multi-enzyme catalysed processes to access a 1,3,4-substituted tetrahydroisoquinoline (THIQ), using either purified enzymes or lyophilised whole-cell catalysts, are presented.

Newly Discovered Mechanisms of Antibiotic Self-Resistance with Multiple Enzymes Acting at Different Locations and Stages

Self-resistance determinants are essential for the biosynthesis of bioactive natural products and are closely related to drug resistance in clinical settings. The study of self-resistance mechanisms has long moved forward on the discovery of new resistance genes and the characterization of enzymatic reactions catalyzed by these proteins. However, as more examples of self-resistance have been reported, it has been revealed that the enzymatic reactions contribute to self-protection are not confined to the cellular location where the final toxic compounds are present. In this review, we summarize representative examples of self-resistance mechanisms for bioactive natural products functional at different cell locations to explore the models of resistance strategies involved. Moreover, we also highlight those resistance determinants that are widespread in nature and describe the applications of self-resistance genes in natural product mining to interrogate the landscape of self-resistance genes in drug resistance-related new drug discovery.

Recent advances in the dearomative functionalisation of heteroarenes

Dearomatisation reactions of (hetero)arenes have been widely employed as efficient methods to obtain highly substituted saturated cyclic compounds for over a century. In recent years, research in this area has shifted towards effecting additional C-C bond formation during the overall dearomative process. Moving away from classical hydrogenation-based strategies a wide range of reagents were found to be capable of initiating dearomatisation through nucleophilic addition (typically a reduction) or photochemically induced radical addition. The dearomatisation process gives rise to reactive intermediates which can be intercepted in an intra- or intermolecular fashion to deliver products with significantly increased molecular complexity when compared to simple dearomatisation. In this Perspective recent examples and strategies for the dearomative functionalisation of heteroaromatic systems will be discussed.

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.