Catalyst-Free sp3 C-H Acyloxylation: Regioselective Synthesis of 1-Acyloxy Derivatives of the Natural Product Tanshinone IIA

Cascade synthesis of miltirone derivatives via arylation, decarboxylation, and aromatization for their potential as antitumor agents

Miltirone is a valuable bioactive natural product isolated from the well-known Chinese herb Danshen. In this study, palladium-catalyzed C(sp3) - H arylation, decarboxylation and aromatization cascade approach are reported that allows the direct introduction of various aryl groups at the A-ring benzylic methylene of various miltirone substrates (CA2 - CA31). The evaluation of the cytotoxic activity was performed against three human cancer cell lines. Among the synthesized compounds, the derivative CA7 (IC50 = 0.45 μM) exhibited excellent MDA-MB-231 cells inhibition activity. Derivative CA7 inhibited MDA-MB-231 cells migration, significantly suppressed the colony formation downregulated mitochondrial membrane potential and induced reactive oxygen species accumulation leads to apoptosis of MDA-MB-231 cells. CA7 with potential anticancer properties warranting further development.

Electrochemical oxidative site-selective direct C-H activation of tanshinone IIA

Natural products play a pivotal role in the advancement of state-of-the-art pharmaceuticals. To augment their therapeutic efficacy, structural modifications of these compounds are routinely performed. In this study, we introduce an efficient and environmentally benign electrochemical oxidative method for site-selective direct C-H activation of tanshinone IIA under metal-free, oxidant-free, and base-free conditions. Moderate to excellent yields up to 92% of the desired tanshinone IIA derivatives were obtained with a broad substrate scope. Biological activity assays demonstrate that compounds 2k, 2q and 2w possess superior antitumor efficacy compared to tanshinone IIA.

Unveiling Na2-Eosin Y-Catalyzed and Water-Assisted Visible-Light Activation of Oxygen Molecules for the Dicarbonylation of Pyrazole Amines

A novel approach employing visible light-mediated activation of triplet oxygen molecules has been established. The reaction occurs at room temperature between pyrazole amine and phenylglyoxal monohydrate in the presence of Na2-eosin Y. Water played the dual role of solvent and reagent/additive. Photoactivation of triplet oxygen species was used to demonstrate the initiation of the hydrogen atom transfer (HAT) process. The conversion of the reaction mixture was found to be dependent on the amount of water present. Control experiments confirmed the importance of light, the photocatalyst, oxygen, the base, and water. The process tolerated various substitutions in both pyrazole amine and phenylglyoxal derivatives, enabling the synthesis of various dicarbonylpyrazole amines 15 and pyrazolooxazine derivatives 16 in moderate to good yields. 2 equiv of phenylglyoxal 10 gave a different reaction pathway, yielding highly diastereoselective pyrazolooxazine derivatives, confirmed by X-ray diffraction analysis. Collectively, this sustainable and environmentally friendly synthetic technique offers a promising method for the efficient preparation of pyrazole-based heterocyclic compounds. The high regioselectivity observed during the formation of trans-tetrahydropyrazolo[3,4-d][1,3]oxazine has been clarified through computational methods. These investigations emphasize the underlying factors and mechanisms that encourage the formation of this specific product, providing valuable insights into the reaction's selectivity and efficiency.

Design, synthesis and biological evaluation of tanshinone IIA derivatives as NLRP3 inflammasome inhibitors

Natural product structures have long provided valuable pharmacophores and even candidates for drug discovery. Tanshinone scaffold showed moderately inhibitory activity in NLRP3 inflammasome/IL-1β pathway. Herein, we designed a series of derivatives on different regions of Tanshinone IIA (TNA) scaffold. The biological evaluation identified compound T10, a scaffold hybrid of TNA and salicylic acid, as a potent NLRP3 inflammasome inhibitor. Mechanistically, T10 inhibits the production of ROS and prevents NLRP3 inflammasome-dependent IL-1β production. In addition, treatment with T10 significantly attenuated inflammatory response in DSS-induced peritonitis. Our work describes a potential tanshinone-based derivative, which needs to be further structurally optimized as NLRP3 inflammasome inhibitors for treating inflammatory disorders.

Tanshinone IIA: Pharmacology, total synthesis, and progress in structure-modifications

Tanshinone IIA, a major bioactive constituent of Danshen, a Chinese herbal medicine, has gained extensive exploration owing to its unique structural features and multiple promising biological activities. This review focuses on the pharmacology, total synthesis, and structural modifications of tanshinone IIA. We hope this review will contribute to a better understanding of the progress in the field and provide constructive suggestions for further study of tanshinone IIA.

Advances in plant-derived natural products for antitumor immunotherapy

In recent years, immunotherapy has emerged as a novel antitumor strategy in addition to traditional surgery, radiotherapy and chemotherapy. It uniquely focuses on immune cells and immunomodulators in the tumor microenvironment and helps eliminate tumors at the root by rebuilding the immune system. Despite remarkable breakthroughs, cancer immunotherapy still faces many challenges: lack of predictable and prognostic biomarkers, adverse side effects, acquired treatment resistance, high costs, etc. Therefore, more efficacious and efficient, safer and cheaper antitumor immunomodulatory drugs have become an urgent requirement. For decades, plant-derived natural products obtained from land and sea have provided the most important source for the development of antitumor drugs. Currently, more attention is being paid to the discovery of potential cancer immunotherapy modulators from plant-derived natural products, such as polysaccharides, phenols, terpenoids, quinones and alkaloids. Some of these agents have outstanding advantages of multitargeting and low side effects and low cost compared to conventional immunotherapeutic agents. We intend to summarize the progress of comprehensive research on these plant-derived natural products and their derivatives and discuss their possible mechanisms in regulating the immune system and their efficacy as monotherapies or in combination with regular chemotherapeutic agents.

Design, synthesis and biological evaluation of tanshinone IIA-based analogues: Potent inhibitors of microtubule formation and angiogenesis

We report the structural optimization of tanshinone IIA, a natural product which possesses anti-tumor properties but low water-solubility, weak antiproliferative activity and poor PK properties. A new series of ring A/C/D modified tanshinone analogues were synthesized and studied for their antiproliferative capacities against six human cancer cell lines. SAR study revealed that ring A cleavage of tanshinone IIA led to improved anti-cancer activity. Introduction of a methoxy group to the phenyl ring could enhance the anti-cancer activity even further. Compound 2f with methoxy group at C-8 position was selected as an early lead with IC₅₀ values of 0.28-3.16 μM against six tested cell lines. 2f could bind to tubulin colchicine site, inhibit tubulin assembly and disrupt the normal formation of microtubule networks. Cellular mechanistic studies revealed that 2f induced apoptotic cell death of A549 cells in a dose-dependent manner. In vitro investigations showed that 2f impeded the tubule-formation of HUVECs and potently inhibited the proliferation, migration and invasion of A549 cells as well as HUVECs. Furthermore, the in vivo anti-angiogenic effect of 2f was confirmed via a zebrafish model test. The satisfactory physicochemical property and metabolic stability of 2f, as well as improved water-solubility, further suggested that 2f could serve as a promising tubulin inhibitor and anti-angiogenic agent.

Tanshinones and their Derivatives: Heterocyclic Ring-Fused Diterpenes of Biological Interest

The available scientific literature regarding tanshinones is very abundant, and after its review, it is noticeable that most of the articles focus on the properties of tanshinone I, cryptotanshinone, tanshinone IIA, sodium tanshinone IIA sulfonate and the dried root extract of Salvia miltiorrhiza (Tan- Shen). However, although these products have demonstrated important biological properties in both in vitro and in vivo models, their poor solubility and bioavailability have limited their clinical applications. For these reasons, many studies have focused on the search for new pharmaceutical formulations for tanshinones, as well as the synthesis of new derivatives that improve their biological properties. To provide new insights into the critical path ahead, we systemically reviewed the most recent advances (reported since 2015) on tanshinones in scientific databases (PubMed, Web of Science, Medline, Scopus, and Clinical Trials). With a broader perspective, we offer an update on the last five years of new research on these quinones, focusing on their synthesis, biological activity on noncommunicable diseases and drug delivery systems, to support future research on its clinical applications.

Biomimetic synthesis of the natural product salviadione and its hybrids: discovery of tissue-specific anti-inflammatory agents for acute lung injury

Biomimetic synthesis of the natural product salviadione and its hybrids was achieved leading to tissue-specific anti-inflammatory agents for acute lung injury.

Acute lung injury (ALI) is an inflammatory disease with no effective pharmacological treatment. The therapeutic potential of the anti-inflammatory natural product tanshinone IIA (2) for ALI is seriously impaired by its poor pharmacokinetic (PK) properties. Inspired by the unique benzo[def]carbazole-3,5-dione (BCD) core of the natural product salviadione (5), a series of furan-fused BCD hybrids of 5 with 2 was rationally designed with the aim to improve both PK properties and the anti-inflammatory activity. A biomimetic synthetic approach featuring one-pot tandem N-heterocyclization was first developed for convenient assembly of salviadione (56% overall yield over 2 steps) and the designed hybrids (35–85% yields in one step). Compared to 2, most of the resulting compounds exhibited a markedly enhanced inhibitory effect against LPS-induced release of pro-inflammatory cytokines in macrophages. Particularly, compound 15a not only possessed the most potent activity in vitro, but also exhibited significantly improved metabolic stability (4- to 7-fold enhancement), pharmacokinetic properties (T_1/2 = 4.05 h; F = 30.2%), and preferable lung tissue distribution (11- to 300-fold selectivity). An in vivo study in mice showed that pretreatment with 15a at 5 mg kg^–1 distinctly attenuated LPS-induced ALI via lung tissue-specific anti-inflammatory actions, indicating that the furan-fused BCD core presents a unique chemotype with promising therapeutic potential for ALI.

Discovery of Indoleamine 2,3-Dioxygenase 1 (IDO-1) Inhibitors Based on Ortho-Naphthaquinone-Containing Natural Product

There is great interest in developing small molecules agents capable of reversing tumor immune escape to restore the body’s immune system. As an immunosuppressive enzyme, indoleamine 2,3-dioxygenase 1 (IDO-1) is considered a promising target for oncology immunotherapy. Currently, none of IDO-1 inhibitors have been launched for clinical practice yet. Thus, the discovery of new IDO-1 inhibitors is still in great demand. Herein, a series of diverse ortho-naphthaquinone containing natural product derivatives were synthesized as novel IDO-1 inhibitors. Among them, 1-ene-3-ketone-17-hydroxyl derivative 12 exhibited significantly improved enzymatic and cellular inhibitory activity against IDO-1 when compared to initial lead compounds. Besides, the molecular docking study disclosed that the two most potent compounds 11 and 12 have more interactions within the binding pocket of IDO-1 via hydrogen-bonding, which may account for their higher IDO-1 inhibitory activity.

Palladium-Catalyzed C-H Bond Acetoxylation via Electrochemical Oxidation

Here we describe the development of a method for the Pd-catalyzed electrochemical acetoxylation of C-H bonds. The oxidation step of the catalytic cycle is probed through cyclic voltammetry and bulk electrolysis studies of a preformed palladacycle of 8-methylquinoline. A catalytic system for C-H acetoxylation is then developed and optimized with respect to the cell configuration, rate of oxidation, and chemistry at the counter electrode. This transformation is then applied to substrates containing various directing groups and to the acetoxylation of both C(sp2)-H and C(sp3)-H bonds.

Total synthesis of (±)-tanshinol B, tanshinone I, and (±)-tanshindiol B and C

A concise and efficient approach was established for the divergent total synthesis of (±)-tanshinol B, (±)-tanshindiol B, (±)-tanshindiol C, and tanshinone I in 17–50% overall yield over 3–6 steps.

Diterpenoids of terrestrial origin

This review covers the isolation and chemistry of diterpenoids from terrestrial as opposed to marine sources and includes labdanes, clerodanes, abietanes, pimaranes, kauranes, cembranes and their cyclization products. The literature from January to December, 2016 is reviewed.