Enantioselective synthesis and anti-parasitic properties of aporphine natural products

Isolation, biological activity, and synthesis of isoquinoline alkaloids

Covering: 2019 to 2023Isoquinoline alkaloids, an important class of N-based heterocyclic compounds, have attracted considerable attention from researchers worldwide. To follow up on our prior review (covering 2014-2018) and present the progress of this class of compounds, this review summarizes and provides updated literature on novel isoquinoline alkaloids isolated during the period of 2019-2023, together with their biological activity and underlying mechanisms of action. Moreover, with the rapid development of synthetic modification strategies, the synthesis strategies of isoquinoline alkaloids have been continuously optimized, and the total synthesis of these classes of natural products is reviewed critically herein. Over 250 molecules with a broad range of bioactivities, including antitumor, antibacterial, cardioprotective, anti-inflammatory, neuroprotective and other activities, are isolated and discussed. The total synthesis of more than nine classes of isoquinoline alkaloids is presented, and thirteen compounds constitute the first total synthesis. This survey provides new indications or possibilities for the discovery of new drugs from the original naturally occurring isoquinoline alkaloids.

Selective Activity Against Amastigote Forms of Trypanosoma cruzi and Leishmania infantum of Diastereomeric Dicentrine N-oxides

As part of our continuous research for the discovery of bioactive compounds against Trypanosoma cruzi and Leishmania infantum, the alkaloid (6aS)-dicentrine (1) was oxidized to afford (6aS,6S)- (2) and (6aS,6R)- (3) dicentrine-N-oxides. Evaluation of the cytotoxicity against NCTC cells indicated that 2 and 3 are non-toxic (CC50>200 μM) whereas 1 demonstrated CC50 of 52.0 μM. Concerning T. cruzi activity against amastigotes, derivatives 2 and 3 exhibited EC50 values of 9.9 μM (SI>20.2) and 27.5 μM (SI>7.3), respectively, but 1 is inactive (EC50>100 μM). Otherwise, when tested against L. infantum amastigotes, 1 and 3 exhibited EC50 values of 10.3 μM (SI=5.0) and 12.7 μM (SI>15.7), respectively, being 2 inactive (EC50>100 μM). Comparing the effects of positive controls benznidazol (EC50=6.5 μM and SI>30.7) and miltefosine (EC50=10.2 μM and SI=15.2), it was observed a selective antiparasitic activity to diastereomers 2 and 3 against T. cruzi and L. infantum. Considering stereochemical aspects, it was suggested that the configuration of the new stereocenter formed after oxidation of 1 played an important role in the bioactivity against amastigotes of both tested parasites.

Synthesis and Evaluation of (Bis)benzyltetrahydroisoquinoline Alkaloids as Antiparasitic Agents

Visceral leishmaniasis and Chagas disease are neglected tropical diseases (NTDs) that severely impact the developing world. With current therapies suffering from poor efficacy and safety profiles as well as emerging resistance, new drug leads are direly needed. In this work, 26 alkaloids (9 natural and 17 synthetic) belonging to the benzyltetrahydroisoquinoline (BI) family were evaluated against both the pro/trypomastigote and amastigote forms of the parasites Leishmania infantum and Trypanosoma cruzi, the causative agents of these diseases. These alkaloids were synthesized via an efficient and modular enantioselective approach based on Bischler-Napieralski cyclization/Noyori asymmetric transfer hydrogenation to build the tetrahydroisoquinoline core. The bis-benzyltetrahydroisoquinoline (BBI) alkaloids were prepared using an Ullmann coupling of two BI units to form the biaryl ether linkage, which enabled a comprehensive survey of the influence of BI stereochemistry on bioactivity. Preliminary studies into the mechanism of action against Leishmania mexicana demonstrate that these compounds interfere with the cell cycle, potentially through inhibition of kinetoplast division, which may offer opportunities to identify a new target/mechanism of action. Three of the synthesized alkaloids showed promising druglike potential, meeting the Drugs for Neglected Disease initiative (DNDi) criteria for a hit against Chagas disease.

Total Synthesis of the Racemate of Laurolitsine

The total synthesis of laurolitsine was achieved for the first time. This reaction was accomplished in 14 steps with a 2.3% yield (this was calculated using 3-hydroxy-4-methoxybenzaldehyde as the starting material) starting from two simple materials, 3-hydroxy-4-methoxybenzaldehyde and 2-(3-hydroxy-4-methoxyphenyl)acetic acid, and the longest linear sequence consisted of 11 steps. The key steps included an electrophilic addition reaction in which a nitro group was reduced to an amino group using lithium tetrahydroaluminum and a Pd-catalyzed direct biaryl coupling reaction. In this paper, many of the experimental steps were optimized, and an innovative postprocessing method in which 2-(3-(benzyloxy)-4-methoxyphenyl)ethanamine is salted with oxalic acid was proposed.

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.

Therapeutic effectiveness of sinensetin against cancer and other human complications: A review of biological potential and pharmacological activities

BACKGROUND

Plant and their active phytoproducts have been used in modern medicine and playing an important role in the health sectors since a very early age. Human beings need a considerable amount of these plant-based phytochemicals for their health. The flavonoidal class phytochemical is an important class of natural products in modern healthcare because of their different pharmacological activities and health benefits. Flavonoidal class phytochemicals have been used to treat diabetes and related secondary complications in humans. Flavonoids have anti-apoptotic, anti-hyperlipidemic, anti-inflammatory, and anti-oxidant potential in the health sectors. Sinensetin, also called 3',4',5,6,7-pentametoksiflavon is a colorless compound with a molecular weight 372.37g/mol and is found to be present in the Orthosiphon stamineus.

METHODS

In the present investigation, we aim to collect scientific information on sinensetin and analyze it for its biological potential and therapeutic benefits against various types of disorders and complications. Medicinal importance and pharmacological activities data have been collected and analyzed in the present work for sinensetin through literature data analysis of different research works. Google Science Direct, PubMed, Scopus, and Google Scholar were mainly searched to collect the scientific information in the present work. The present work analyzed sinensetin's biological potential, pharmacological activities, and analytical aspects.

RESULTS

Literature data analysis of different scientific research works revealed the biological potential of phytochemicals in medicine, including flavonoids. Sinensetin has anti-tumor, anti-inflammatory, anti-oxidant, anti-diabetic, and antibacterial activities through their testing in different in vitro and in vivo models. Sinensetin has physiological functions, including anti-oxidant, anti-inflammation, and anti-cancer potential in medicine. Scientific data analysis signified the biological importance of sinensetin against tumors, gastric cancer, colorectal cancer, breast cancer, diabetes, influenza H1N1 infection, obesity, inflammation, colitis, brain disorders, and microbial infections. Further biological potential of sinensetin on enzymes and angiogenesis has been analyzed in the present work. Sinensetin was isolated through different analytical and extraction techniques, including chromatographic techniques.

CONCLUSION

Literature data analysis signified sinensetin's biological potential and pharmacological activities in medicine.

A Catalytic Asymmetric Pictet-Spengler Platform as a Biomimetic Diversification Strategy toward Naturally Occurring Alkaloids

Tetrahydroisoquinoline (THIQ) alkaloids constitute a large and diverse class of bioactive natural products, with the parent compounds and related downstream biosynthetic secondary metabolites spanning thousands of isolated structures. Chemoenzymatic synthetic approaches toward the relevant THIQs rely on Pictet–Spenglerases such as norcoclaurine synthase (NCS), the scope of which is strictly limited to dopamine-related phenolic substrates. To overcome these limitations in the context of chemical synthesis, we herein report asymmetric Pictet–Spengler reactions of N-carbamoyl-β-arylethylamines with diverse aldehydes toward enantioenriched THIQs. The obtained products proved to be competent intermediates in the synthesis of THIQ, aporphine, tetrahydroberberine, morphinan, and androcymbine natural products. Novel catalyst design with regard to the stabilization of cationic intermediates was crucial to accomplish high reactivity while simultaneously achieving unprecedented stereoselectivity for the reaction of biologically relevant substrates.

A recent update on new synthetic chiral compounds with antileishmanial activity

Parasitic diseases, including malaria, leishmaniasis, and trypanosomiasis, affect billions of people and are responsible for almost 500,000 deaths/year. In particular, leishmaniasis, a neglected tropical disease, is considered a global public health problem because current drugs have several drawbacks including to toxicity, high cost, and drug resistance, which result in a lack of effective and readily available therapies. Therefore, the synthesis of new, safe, and effective molecules still requires the attention of the scientific community. Moreover, it is well known that chirality plays a crucial role in the antiparasitic activity of molecules, driving the design of their synthesis. Therefore, in this review we report a recent update on new chiral compounds with promising antileishmanial activity, focusing on synthetic approaches. Where reported, in most cases the enantiopure compound has shown better potency against the protozoa than its enantiomer or corresponding racemic mixture.

A unified total synthesis of benzo[d][1,3]dioxole-type benzylisoquinoline alkaloids of aporphines, coptisines, and dibenzopyrrocolines

The first total synthesis of (S)-(+)-ovigerine, (S)-(+)-N-formylovigerine, and (6aS,6a'S)-(+)-ovigeridimerine of aporphine alkaloids with a benzo[d][1,3]dioxole structure feature was established. The strategy was based upon the well-known Pd-catalyzed arylation to set the aporphine framework, and Noyori asymmetric hydrogenation followed by diastereoselective resolution to achieve excellent enantioselectivity. By slightly modifying the total synthetic route and strategically combining it with a aza-Michael addition, Bischler-Napieralski reaction and N-arylation, this methodology was also applied to the total syntheses of benzo[d][1,3]dioxole-type benzylisoquinoline alkaloids of coptisines and dibenzopyrrocolines, including two impatiens, tetrahydrocoptisine, and quaternary coptisine bromide of coptisines and two dibenzopyrrocoline analogues, with the syntheses of all of these target compounds being efficient. Among the nine synthesized compounds, the total syntheses of the three aporphines and the two impatiens, all with ee values of greater than 99%, were reported for the first time. This work also represents the first unification of synthetic routes for the total synthesis of benzo[d][1,3]dioxole-type aporphines, coptisines, and dibenzopyrrocolines.

Advances Towards the Synthesis of Aporphine Alkaloids: C-Ring Formation via Approaches Based on One- and Two-Bond Disconnections

Aporphine compounds constitute a class of substances with important pharmacological properties, including anticancer, antiviral, anti-HIV, anti-inflammatory, and leishmanicidal activities. Consequently, several strategies to obtain the aporphine core have been reported. Herein this review, we provide an overview of two relevant approaches used to construct the C-ring in the synthetic routes developed. The first approach, which is based on a one-bond disconnection, allows C-ring formation using a 1-benzyl-1,2,3,4-tetrahydroisoquinoline intermediate (mainly) employing cyclization reactions catalyzed by metals or promoted by light. The second approach, which is derived from a two-bond disconnection, leads to C-ring formation via a sequence of reactions starting with [4+2] cycloadditions. Through these approaches, aporphinoids with a diverse range of substitution patterns and biological activities can be synthesized.

Synthesis of Aporphine Analogues via Palladium-Catalyzed Intramolecular Aryl-Aryl Dehydrogenative Coupling

Reported herein is an intramolecular dehydrogenative coupling of two inert aryl C-H bonds for the synthesis of aporphine analogues. The process represents a novel tool for the preparation of aporphines via palladiun-catalyzed C-H bond activation. The present reaction is compatible with various functional groups, and the coupling products have been further applied for the synthesis of natural products aporphine and zenkerine.

Tandem H/D Exchange-SET Reductive Deuteration Strategy for the Synthesis of α,β-Deuterated Amines Using D2O

α,β-Deuterated amines are crucial for the development of deuterated drugs. We intend to introduce the novel tandem H/D exchange-single electron transfer (SET) reductive deuteration strategy with high pot- and reagent-economy by the synthesis of α,β-deuterated amine using nitrile as the precursor. The H/D exchange of the -CH₂CN group was achieved by D₂O/Et₃N, which were also the required reagents in the tandem SmI₂-mediated SET reductive deuteration of the α-deuterated nitrile. The potential application of this method was further showcased by the synthesis of bevantolol-d₄.

Medicinal chemistry perspectives of 1,2,3,4-tetrahydroisoquinoline analogs - biological activities and SAR studies

Isoquinoline alkaloids are a large group of natural products in which 1,2,3,4-tetrahydroisoquinolines (THIQ) form an important class. THIQ based natural and synthetic compounds exert diverse biological activities against various infective pathogens and neurodegenerative disorders. Due to these reasons, the THIQ heterocyclic scaffold has garnered a lot of attention in the scientific community which has resulted in the development of novel THIQ analogs with potent biological activity. The present review provides a much-needed update on the biological potential of THIQ analogs, their structural-activity relationship (SAR), and their mechanism of action. In addition, a note on commonly used synthetic strategies for constructing the core scaffold has also been discussed.

Aporphine Alkaloids from Ocotea puberula with Anti-Trypanosoma Cruzi Potential - Activity of Dicentrine-β-N-Oxide in the Plasma Membrane Electric Potentials

One new aporphine, dicentrine-β-N-oxide (1), together with five related known alkaloids dehydrodicentrine (2), predicentrine (3), N-methyllaurotetanine (4), cassythicine (5), and dicentrine (6) were isolated from the leaves of Ocotea puberula (Lauraceae). Antiprotozoal activity of the isolated compounds was evaluated in vitro against trypomastigote forms of Trypanosoma cruzi. Among the tested compounds, alkaloid 1 exhibited higher potential with EC₅₀ value of 18.2 μM and reduced toxicity against NCTC cells (CC₅₀ >200 μM - SI>11.0), similar to positive control benznidazole (EC₅₀ of 17.7 μM and SI=10.7). Considering the promising results of dicentrine-β-N-oxide (1) against trypomastigotes, the mechanism of parasite death caused by this alkaloid was investigated. As observed, this compound reached the plasma membrane electric potential directly after 2 h of incubation and triggered mitochondrial depolarization, which probably leads to trypomastigote death. Therefore, dicentrine-β-N-oxide (1), reported for the first time in this work, can contribute to future works for the development of new trypanocidal agents.

Amino acid-derived defense metabolites from plants: A potential source to facilitate novel antimicrobial development

For millennia, humanity has relied on plants for its medicines, and modern pharmacology continues to reexamine and mine plant metabolites for novel compounds and to guide improvements in biological activity, bioavailability, and chemical stability. The critical problem of antibiotic resistance and increasing exposure to viral and parasitic diseases has spurred renewed interest into drug treatments for infectious diseases. In this context, an urgent revival of natural product discovery is globally underway with special attention directed toward the numerous and chemically diverse plant defensive compounds such as phytoalexins and phytoanticipins that combat herbivores, microbial pathogens, or competing plants. Moreover, advancements in “omics,” chemistry, and heterologous expression systems have facilitated the purification and characterization of plant metabolites and the identification of possible therapeutic targets. In this review, we describe several important amino acid–derived classes of plant defensive compounds, including antimicrobial peptides (e.g., defensins, thionins, and knottins), alkaloids, nonproteogenic amino acids, and phenylpropanoids as potential drug leads, examining their mechanisms of action, therapeutic targets, and structure–function relationships. Given their potent antibacterial, antifungal, antiparasitic, and antiviral properties, which can be superior to existing drugs, phytoalexins and phytoanticipins are an excellent resource to facilitate the rational design and development of antimicrobial drugs.

Synthesis of 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline through nucleophilic addition of organozinc reagents to N,O-acetals

A new approach to access 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline has been developed through nucleophilic addition of organozinc reagents to N,O-acetals. A number of substituted organozinc reagents were amenable for this transformation, and the desired products were obtained with excellent yields. Moreover, Sc(OTf)3 proved to be an effective catalyst for the formation of 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline using such nucleophilic addition.