Recent advances in total synthesis of protoberberine and chiral tetrahydroberberine alkaloids

Covering: Up to 2024Due to the widespread distribution of protoberberine alkaloids (PBs) and tetrahydroberberine alkaloids (THPBs) in nature, coupled with their myriad unique physiological activities, they have garnered considerable attention from medical practitioners. Over the past few decades, synthetic chemists have devised various total synthesis methods to attain these structures, continually expanding reaction pathways to achieve more efficient synthetic strategies. Simultaneously, the chiral construction of THPBs has become a focal point. In this comprehensive review, we categorically summarized the developmental trajectory of the total synthesis of these alkaloids based on the core closure strategies of protoberberine and tetrahydroberberine.

Recent Applications of Protoberberines as Privileged Starting Materials for the Development of Novel Broad-Spectrum Antiviral Agents: A Concise Review (2017-2023)

Berberine is a well-known phytochemical with significant antiviral activity against a wide range of viruses. Due to having a unique backbone consisting of four interconnected rings, it can be used as a platform for the design and development of novel semisynthetic antiviral agents. The question here is whether novel broad-spectrum antiviral drugs with enhanced activity and toxicity potential can be obtained by attempting to modify the structure of this privileged lead compound. The present study aims to review the results of recent studies in which berberine and its close analogues (protoberberine alkaloids) have been used as starting materials for the production of new semisynthetic antiviral structures. For this purpose, relevant studies published in high-quality journals indexed in databases such as Scopus, Web of Science, PubMed, etc. in the time frame of 2017 to 2023 were collected. Our selection criterion in the current review focuses on the studies in which protoberberines were used as starting materials for the production of semisynthetic agents with antiviral activity during the indicated time period. Correspondingly, studies were identified in which semisynthetic derivatives with significant inhibitory activity against a wide range of viruses including human immunodeficiency virus (HIV), enterovirus 71 (EV71), zika virus (ZIKV), influenza A/B, cytomegalovirus (CMV), respiratory syncytial virus (RSV), and coxsackieviruses were designed and synthesized. Our conclusion is that, despite the introduction of diverse semisynthetic derivatives of berberine with improved activity profiles compared to the parent natural leads, sufficient derivatization has not been done yet and more studies are needed.

Environmentally friendly Nafion-catalyzed synthesis of 3-substituted isoquinoline by using hexamethyldisilazane as a nitrogen source under microwave irradiation

This study developed an eco-friendly method to synthesize 3-arylisoquinoline from 2-alkynylbenzaldehydes using Nafion® NR50 as an acidic catalyst and hexamethyldisilazane (HMDS) as a nitrogen source. The reaction proceeded via a 6-exo-dig cyclization under microwave irradiation, giving the corresponding isoquinolines in excellent yields. The advantages of this protocol include: (1) the use of recyclable acid catalysts, (2) transition-metal-free catalysis, and (3) the effective formation of the target product. These features make this methodology a promising approach for the sustainable and efficient synthesis of 3-arylisoquinoline. Some structures were also confirmed by single-crystal X-ray diffraction analysis.

Diverse saturated heterocycles from a hydroacylation/conjugate addition cascade

Rhodium-catalyzed hydroacylation using alkynes substituted with pendant nucleophiles, delivers linear α,β-unsaturated enone intermediates with excellent regioselectivity. These adducts are used to construct a broad range of diversely substituted, saturated O-, N- and S-heterocycles in a one-pot process. Judicious choice of cyclisation conditions enabled isolation of O-heterocycles with high levels of diastereoselectivity. A variety of derivatisation reactions are also performed, generating functionalised hydroacylation products. This sequence serves as a general approach for the synthesis of fully saturated heterocycles.

Design, synthesis and anti-hepatocellular carcinoma activity of 3-arylisoquinoline alkaloids

This article describes the syntheses and biological activity of five 3-arylisoquinoline natural products corydamine (1), N-formyl Corydamine (2), hypecumine (3), Decumbenine B (XW) and 2-(1,3-dioxolo [4,5-h]isoquinolin-7-yl)-4,5-dimethoxy-N-methyl-Benzeneethanamine (A), and twelve analogues. Among them, 1, 2, and A were synthesized for the first time. In vitro screening for anti-proliferative activity showed that derivative 1a could significantly inhibit the proliferation of HCC cells (IC₅₀ = 9.82 μM on Huh7 cells and 6.83 μM on LM9 cells), and arrest cell cycle at G₂/M phase. The mechanistic studies further suggested compound 1a was a dual inhibitor of Topo I and Topo II, and Topo II inhibitory activity was superior to etoposide. In addition, 1a could significantly inhibit the invasion and migration of cancer cells by inhibiting the expression of MMP-9, and induce apoptosis through inhibiting the activation of the PI3K/Akt/mTOR signaling pathway. Moreover, in vivo studies demonstrated 1a could obviously reduce the growth of xenograft tumor and possessed good pharmacokinetic parameters, which indicated the potential value of 1a in treating liver cancer.

Two-pot synthesis and photophysical studies of 1,6-disubstituted 5-aza-indoles from succinaldehyde and N-aryl propargylic-imines

A two-pot synthesis of 5-aza-indoles has been developed from aqueous succinaldehyde and N-aryl propargylic-imines. This overall protocol involves: (i) the metal-free [3 + 2] annulation of aqueous succinaldehyde and N-aryl propargylic-imines to access 2-alkynyl-pyrrole-3-aldehydes and (ii) Ag-catalyzed 6-endo-dig-cyclization to obtain substituted 5-aza-indoles in the second pot. The 5-aza-indoles showed engaging photophysical activities, and the practicality of this pot-economic gram-scale synthesis has been demonstrated.

Natural STAT3 inhibitors: A mini perspective

Signal transducer and activator of transcription 3 (STAT3) plays pivotal role in several cellular processes such as cell proliferation and survival and has been found to be aberrantly activated in many cancers. STAT3 is largely believed to be one of the key oncogenes and crucial therapeutic targets. Much research has suggested the leading mechanisms for regulating the STAT3 pathway and its role in promoting tumorigenesis. Therefore, intensive efforts have been devoted to develop potent STAT3 inhibitors and several of them are currently undergoing clinical trials. Nevertheless, many natural products were identified as STAT3 inhibitors but attract less attention compared to the small molecule counterpart. In this review, the development of natural STAT3 inhibitors with an emphasis on their biological profile and chemical synthesis are detailed. The current state of STAT3 inhibitors and the future directions and opportunities for STAT3 inhibitor are discussed.

Novel Inhibitors of an Insect Pest Chitinase: Design and Optimization of 9-O-Aromatic and Heterocyclic Esters of Berberine

OfChi-h, a lepidopteran-exclusive glycoside hydrolase family 18 (GH18) chitinase from the agricultural insect pest Ostrinia furnacalis, is a promising molecular target candidate for pest control and management. Berberine (BER), a traditional Chinese medicine, binds to a wide variety of glycosyl hydrolases via an identical mechanism, showing potential as a pesticide lead compound. In this work, we found that BER was a moderate inhibitor of OfChi-h with a Ki of 16.1 μM. To improve its efficacy, a series of BER derivatives featuring an ester bond linked to an aromatic or heterocyclic aromatic ring at the 9-position were designed and evaluated as effective OfChi-h inhibitors. The most potent compound, compound 19e with a nicotinate group, exhibited a Ki of 0.093 μM. Molecular docking analysis suggested that the common binding mode of BER derivatives featured a network of π-π stacking and electrostatic interactions and that the group at the 9-position enhanced the van der Waals and hydrogen bonding interactions. Administration of the BER derivative 19c to 4th-instar O. furnacalis larvae in an artificial diet led to their impaired growth and metamorphosis. This work provides a new starting point for the modification of BER for use in pest control.

Berberine: A Promising Natural Isoquinoline Alkaloid for the Development of Hypolipidemic Drugs

Berberine, as a representative isoquinoline alkaloid, exhibits significant hypolipidemic activity in both animal models and clinical trials. Recently, a large number of studies on the lipid-lowering mechanism of berberine and studies for improving its hypolipidemic activity have been reported, but for the most part, they have been either incomplete or not comprehensive. In addition, there have been a few specific reviews on the lipid-reducing effect of berberine. In this paper, the physicochemical properties, the lipid-lowering mechanism, and studies of the modification of berberine all are discussed to promote the development of berberine as a lipid-lowering agent. Subsequently, this paper provides some insights into the deficiencies of berberine in the study of lipid-lowering drug, and based on the situation, some proposals are put forward.

Modular and Divergent Syntheses of Protoberberine and Protonitidine Alkaloids

A modularly convergent and divergent strategy was established for the family synthesis of both protoberberine and protonitidine alkaloids. The robust, scalable, and flexible synthetic route featured a collective preparation of protoberberine and protonitidine alkaloids from a common isoquinoline assembled from pyridyne as the key synthon, which was based on the selective N-C or C-C cyclization via distinct processes. Through the strategy, 20 protoberberine alkaloids, 5 protonitidine alkaloids, and 11 analogues with diverse substituents were comprehensively aquired.

Highly efficient synthesis and monoamine oxidase B inhibitory profile of demethyleneberberine, columbamine and palmatine

The biosynthesis of berberine alkaloids is thought to begin with the demethylation of berberine followed by methylation reactions to generate other type berberine alkaloids. This seemingly expeditious way to access berberine alkaloids has been stagnated for over half a century due to certain vexing synthetic problems, such as low isolated yield, complex operations and toxic reagents. We further investigated this bioinspired semi-synthesis strategy and significantly improved the synthetic efficacy, by providing a practical synthetic process for demethyleneberberine (DMB), columbamine and palmatine. Furthermore, we found that DMB (IC₅₀, 9.06 μM) inhibited the activity of monoamine oxidase B (MAO-B), an enzyme that deaminates dopamine and is particularly involved in the pathology of Parkinson's disease. Besides, columbamine was able to decrease MAO-B activity by approximately 40%. These findings provide perquisites for further in vivo investigation to confirm the therapeutic potentiality of berberine alkaloids, DMB in particular.

The Quest to Enhance the Efficacy of Berberine for Type-2 Diabetes and Associated Diseases: Physicochemical Modification Approaches

Berberine is a quaternary isoquinoline alkaloid that has been isolated from numerous plants which are still in use today as medicine and herbal supplements. The great deal of enthusiasm for intense research on berberine to date is based on its diverse pharmacological effects via action on multiple biological targets. Its poor bioavailability resulting from low intestinal absorption coupled with its efflux by the action of P-glycoprotein is, however, the major limitation. In this communication, the chemical approach of improving berberine's bioavailability and pharmacological efficacy is scrutinised with specific reference to type-2 diabetes and associated diseases such as hyperlipidaemia and obesity. The application of modern delivery systems, research from combination studies to preparation of berberine structural hybrids with known biologically active compounds (antidiabetic, antihyperlipidaemic and antioxidant), as well as synthesis approaches of berberine derivative are presented. Improvement of bioavailability and efficacy through in vitro and ex vivo transport studies, as well as animal models of bioavailability/efficacy in lipid metabolism and diabetes targets are discussed.

Recent Advances in Berberine Inspired Anticancer Approaches: From Drug Combination to Novel Formulation Technology and Derivatization

Berberine is multifunctional natural product with potential to treat diverse pathological conditions. Its broad-spectrum anticancer effect through direct effect on cancer cell growth and metastasis have been established both in vitro and in vivo. The cellular targets that account to the anticancer effect of berberine are incredibly large and range from kinases (protein kinase B (Akt), mitogen activated protein kinases (MAPKs), cell cycle checkpoint kinases, etc.) and transcription factors to genes and protein regulators of cell survival, motility and death. The direct effect of berberine in cancer cells is however relatively weak and occur at moderate concentration range (10–100 µM) in most cancer cells. The poor pharmacokinetics profile resulting from poor absorption, efflux by permeability-glycoprotein (P-gc) and extensive metabolism in intestinal and hepatic cells are other dimensions of berberine’s limitation as anticancer agent. This communication addresses the research efforts during the last two decades that were devoted to enhancing the anticancer potential of berberine. Strategies highlighted include using berberine in combination with other chemotherapeutic agents either to reduce toxic side effects or enhance their anticancer effects; the various novel formulation approaches which by order of magnitude improved the pharmacokinetics of berberine; and semisynthetic approaches that enhanced potency by up to 100-fold.

Histone acetyltransferase inhibitors: An overview in synthesis, structure-activity relationship and molecular mechanism

Acetylation, a key component in post-translational modification regulated by HATs and HDACs, is relevant to many crucial cellular contexts in organisms. Based on crucial pharmacophore patterns and the structure of targeted proteins, HAT inhibitors are designed and modified for higher affinity and better bioactivity. However, there are still some challenges, such as cell permeability, selectivity, toxicity and synthetic availability, which limit the improvement of HAT inhibitors. So far, only few HAT inhibitors have been approved for commercialization, indicating the urgent need for more successful and effective structure-based drug design and synthetic strategies. Here, we summarized three classes of HAT inhibitors based on their sources and structural scaffolds, emphasizing on their synthetic methods and structure-activity relationships and molecular mechanisms, hoping to facilitate the development and further application of HAT inhibitors.

A Unified Strategy for the Syntheses of the Isoquinolinium Alkaloids Berberine, Coptisine, and Jatrorrhizine

Total syntheses of the antibacterial alkaloids berberine, coptisine, and jatrorrhizine have been achieved in four steps through a unified route. The key step of this strategy is an efficient intramolecular Friedel-Crafts alkoxyalkylation which, following oxidation, establishes the isoquinolinium core of these natural products. Herein, the design and development of this synthetic strategy, which has enabled the shortest and most efficient syntheses of these alkaloids reported to date, is described.

Iron/zinc-catalyzed benzannulation reactions of 2-(2-oxo-alkyl)benzketones leading to naphthalene and isoquinoline derivatives

An efficient method for the synthesis of poly-substituted naphthalenes/isoquinolines via Fe(iii)/Zn(ii)-catalyzed [4 + 2] cycloaddition of 2-(2-oxo-alkyl)benzketones is described.

Selective construction of polycyclic spirooxindoles via a Cu(OTf)2/HOTf-catalyzed domino reaction of o-arylalkynylacetophenones and 3-phenacylideneoxindoles

Under the combined catalysis of Cu(OTf)₂/HOTf, the domino annulation reaction ofo-arylalkynyl acetophenones with 3-phenacylideneoxindoles in refluxing acetonitrile selectively afforded functionalized spiro[indoline-3,7′-tetrapheno[7,6-bc]furans].

Ag(i)-Catalyzed one-pot synthesis of 4-fluorobenzo[b][1,6] naphthyridines and 4-fluoroisoquinolines via iminofluorination of alkynes with Selectfluor

Ag(i)-Catalyzed one-pot synthesis of 4-fluorobenzo[b][1,6]naphthyridines is described from o-alkynylquinolinyl aldehydes through imines.

Ruthenium(0)-Catalyzed [4+2] Cycloaddition of Acetylenic Aldehydes with α-Ketols: Convergent Construction of Angucycline Ring Systems

Ruthenium(0) complexes modified by CyJohnPhos or RuPhos catalyze the successive C-C coupling of acetylenic aldehydes with α-ketols to form [4+2] cycloadducts as single diastereomers. This method enables convergent construction of type II polyketide ring systems of the angucycline class.

Selectfluor promoted NHC–oxazoline gold(i) complex catalyzed cycloaddition/oxidation reaction of enynones with alkenes

Two kinds of ortho- and meta-oxazoline substituted NHC–gold(i) complexes have been synthesized. These gold complexes could react with Selectfluor to give ionic chelated NHC–oxazoline gold(i) complexes which could smoothly catalyze the cycloaddition/oxidation reaction of enynones with alkene.

An efficient synthesis of isoquinolines via rhodium-catalyzed direct C–H functionalization of arylhydrazines

Rhodium-catalyzed C–H bond activation of arylhydrazines and coupling with internal alkynes has been realized.