Synthesis of new ent-labdane diterpene derivatives from andrographolide and evaluation of their anti-inflammatory activities

Advances in the Structures, Pharmacological Activities, and Biosynthesis of Plant Diterpenoids

More and more diterpenoids have attracted extensive attention due to the diverse chemical structures and excellent biological activities, and have been developed into clinical drugs or consumer products. The vast majority of diterpenoids are derived from plants. With the long-term development of plant medicinal materials, the natural resources of many plant diterpenoids are decreasing, and the biosynthetic mechanism of key active components has increasingly become a research hotspot. Using synthetic biology to engineer microorganisms into "cell factories" to produce the desired compounds is an essential means to solve these problems. In this review, we depict the plant-derived diterpenoids from chemical structure, biological activities, and biosynthetic pathways. We use representative plant diterpenes as examples to expound the research progress on their biosynthesis, and summarize the heterologous production of plant diterpenoids in microorganisms in recent years, hoping to lay the foundation for the development and application of plant diterpenoids in the future.

Discovery of Pesticide Candidates from Natural Plant Products: Semisynthesis and Characterization of Andrographolide-Based Esters and Study of Their Pesticidal Properties and Toxicology

To explore the use of nonfood plant-derived secondary metabolites for plant protection, a series of ester derivatives for controlling the major migratory agricultural pests were obtained by structural modification of andrographolide, a labdane diterpenoid isolated from Andrographis paniculata. Compound Id showed good insecticidal activity against the fall armyworm Spodoptera frugiperda Smith. Compounds IIa (LC50: 0.382 mg/mL) and IIIc (LC50: 0.563 mg/mL), the acaricidal activities of which were, respectively, 13.1 and 8.9 times that of andrographolide (LC50: 4.996 mg/mL), exhibited strong acaricidal and control effects against Tetranychus cinnabarinus Boisduval. Against Aphis citricola Van der Goot, compounds IIIc and IVb displayed 3.9- and 3.7-fold pronounced aphicidal activity of andrographolide. Effects of compound Id on three protective enzymes (superoxide dismutase, peroxidase, and catalase) of S. frugiperda were also observed. The obvious differences of epidermal cuticle structures of mites treated with compound IIa were determined by scanning electron microscopy. Structure-activity relationships indicated that 14-ester derivatives of andrographolide showed potential insecticidal/acaricidal activities and can be further utilized as lead compounds.

Cytotoxic and Anti-Inflammatory Activity of 3,19-Isopropylidene-/Arylidene-Andrographolide Analogs

A series of 3,19-isopropylidene-/or arylidene-andrographolide analogs were synthesized and their structures were confirmed by NMR spectroscopic methodology. Twenty-five analogs were evaluated for their in vitro cytotoxic activity against HT-29, HepG2 and LNCaP cancer cell lines based on the sulforhodamine B (SRB) assay. Analog 2 f exhibited the most potent cytotoxic activity, with IC50 values of 11.14 and 9.25 μM on HepG2 and LNCaP cancer cell lines, respectively. Esterification of hydroxy functional group at position C-14 in andrographolide analogs, 2 a and 2 b, showed somewhat higher cytotoxicity than the precursor. In addition, andrographolide analogs (2 a-2 d, 2 f, 3 a, 4 a and 4 h) were evaluated for the NO inhibitory activity in the LPS stimulated RAW264.7 macrophages. The most active analog 2 a significantly reduced nitric oxide (NO) production from LPS stimulated RAW264.7 cells, with IC50 values of 0.34±0.02 μM providing encouraging results for anti-inflammatory compound development.

Discovery of andrographolide hit analog as a potent cyclooxygenase-2 inhibitor through consensus MD-simulation, electrostatic potential energy simulation and ligand efficiency metrics

Cyclooxygenase-2 (COX-2) is the key enzyme responsible for the conversion of arachidonic acid to prostaglandins that display pro-inflammatory properties and thus, it is a potential target protein to develop anti-inflammatory drugs. In this study, chemical and bio-informatics approaches have been employed to find a novel potent andrographolide (AGP) analog as a COX-2 inhibitor having better pharmacological properties than aspirin and rofecoxib (controls). The full amino acid sequenced human Alpha fold (AF) COX-2 protein (604AA) was selected and validated for its accuracy against the reported COX-2 protein structures (PDB ID: 5F19, 5KIR, 5F1A, 5IKQ and 1V0X) followed by multiple sequence alignment analysis to establish the sequence conservation. The systematic virtual screening of 237 AGP analogs against AF-COX-2 protein yielded 22 lead compounds based on the binding energy score (< - 8.0 kcal/mol). These were further screened out to 7 analogs by molecular docking analysis and investigated further for ADMET prediction, ligand efficiency metrics calculations, quantum mechanical analysis, MD simulation, electrostatic potential energy (EPE) docking simulation, and MM/GBSA. In-depth analysis revealed that AGP analog A3 (3-[2-[(1R,4aR,5R,6R,8aR)-6-hydroxy-5,6,8a-trimethyl-2-methylidene-3,4,4a,5,7,8-hexahydro-1H-naphthalen-1-yl]ethylidene]-4-hydroxyoxolan-2-one) forms the most stable complex with the AF-COX-2 showing the least RMSD value (0.37 ± 0.03 nm), a good number of hydrogen bonds (protein-ligand H-bond = 11, and protein H-bond = 525), minimum EPE score (- 53.81 kcal/mol), and lowest MM-GBSA before and after simulation (- 55.37 and - 56.25 kcal/mol, respectively) value compared to other analogs and controls. Thus, we suggest that the identified A3 AGP analog could be developed as a promising plant-based anti-inflammatory drug by inhibiting COX-2.

Anti-Cancer Agent: The Labdane Diterpenoid-Andrographolide

In spite of the progress in treatment strategies, cancer remains a major cause of death worldwide. Therefore, the main challenge should be the early diagnosis of cancer and the design of an optimal therapeutic strategy to increase the patient's life expectancy as well as the continuation of the search for increasingly active and selective molecules for the treatment of different forms of cancer. In the recent decades, research in the field of natural compounds has increasingly shifted towards advanced and molecular level understandings, thus leading to the development of potent anti-cancer agents. Among them is the diterpene lactone andrographolide, isolated from Andrographis paniculata (Burm.f.) Wall. ex Nees that showed shows a plethora of biological activities, including not only anti-cancer activity, but also anti-inflammatory, anti-viral, anti-bacterial, neuroprotective, hepatoprotective, hypoglycemic, and immunomodulatory properties. Andrographolide has been shown to act as an anti-tumor drug by affecting specific molecular targets that play a part in the development and progression of several cancer types including breast, lung, colon, renal, and cervical cancer, as well as leukemia and hepatocarcinoma. This review comprehensively and systematically summarized the current research on the potential anti-cancer properties of andrographolide highlighting its mechanisms of action, pharmacokinetics, and potential side effects and discussing the future perspectives, challenges, and limitations of use.

Pd-Catalyzed Ring-Opening/Arylation/Cyclization of 2-Aminothiazole Derivatives Provides Modular Access to Isocytosine Analogues

We report a Pd-catalyzed ring-opening/arylation/cyclization reaction sequence between 2-aminothiazoles and aryl (pseudo)halides that provides modular access to isocytosine analogues. The scope of the reaction is broad with respect to both coupling partners and a robustness test demonstrated the functional group tolerance of the methodology. Visual kinetic analysis revealed that the product may inhibit catalyst turnover for some substrates.

Synthesis and evaluation of ursolic acid-based 1,2,4-triazolo[1,5-a]pyrimidines derivatives as anti-inflammatory agents

Here, two series of novel ursolic acid-based 1,2,4-triazolo[1,5-a]pyrimidines derivatives were synthesized and screened for their anti-inflammatory activity by evaluating their inhibition effect of using LPS-induced inflammatory response in RAW 264.7 macrophages in vitro; the effects of different concentrations of the compounds on the secretion of nitric oxide (NO) and inflammatory cytokines including TNF-α and IL-6 were evaluated. Their toxicity was also assessed in vitro. Results showed that the most prominent compound 3 could significantly decrease production of the above inflammatory factors. Docking study was performed for the representative compounds 3, UA, and Celecoxib to explain their interaction with cyclooxygenase-2 (COX-2) receptor active site. In vitro enzyme study implied that compound 3 exerted its anti-inflammatory activity through COX-2 inhibition.

Andrographolide and its derivatives: Current achievements and future perspectives

Natural product andrographolide isolated from the plant Andrographis paniculata shows a plethora of biological activities, including anti-tumor, anti-bacterial, anti-inflammation, anti-virus, anti-fibrosis, anti-obesity, immunomodulatory and hypoglycemic activities. Based on extensive chemical structural modifications, a series of andrographolide derivatives with improved bioavailability and druggability has been developed. Moreover, greater understanding of their mechanisms of action at the molecular and cellular level has been thoroughly investigated. In this review, we give an outlook for the therapeutical potential of andrographolide and its derivatives in diverse diseases and highlighted the drug design, pharmacokinetic and mechanistic studies for the past ten years, together with a brief overview of the pharmacological effects. Notably, we focused to provide a critical enlightenment of the area of andrographolide and its derivatives with the intent of indicating the future perspectives, challenges and limitations. We believe that this review paper will benefit drug discovery where andrographolide was used as a template, shed light on the identification of drug targets for andrographolide and its analogs, as well as increase our knowledge for using them for therapeutic application, including the treatment for various forms of cancers.

Obeticholic Acid Derivative, T-2054 Suppresses Osteoarthritis via Inhibiting NF-κB-Signaling Pathway

Osteoarthritis (OA), a degenerative joint disorder, has been reported as the most common cause of disability worldwide. The production of inflammatory cytokines is the main factor in OA. Previous studies have been reported that obeticholic acid (OCA) and OCA derivatives inhibited the release of proinflammatory cytokines in acute liver failure, but they have not been studied in the progression of OA. In our study, we screened our small synthetic library of OCA derivatives and found T-2054 had anti-inflammatory properties. Meanwhile, the proliferation of RAW 264.7 cells and ATDC5 cells were not affected by T-2054. T-2054 treatment significantly relieved the release of NO, as well as mRNA and protein expression levels of inflammatory cytokines (IL-6, IL-8 and TNF-α) in LPS-induced RAW 264.7 cells. Moreover, T-2054 promoted extracellular matrix (ECM) synthesis in TNF-α-treated ATDC5 chondrocytes. Moreover, T-2054 could relieve the infiltration of inflammatory cells and degeneration of the cartilage matrix and decrease the levels of serum IL-6, IL-8 and TNF-α in DMM-induced C57BL/6 mice models. At the same time, T-2054 showed no obvious toxicity to mice. Mechanistically, T-2054 decreased the extent of p-p65 expression in LPS-induced RAW 264.7 cells and TNF-α-treated ATDC5 chondrocytes. In summary, we showed for the first time that T-2054 effectively reduced the release of inflammatory mediators, as well as promoted extracellular matrix (ECM) synthesis via the NF-κB-signaling pathway. Our findings support the potential use of T-2054 as an effective therapeutic agent for the treatment of OA.

Design and synthesis of 7-O-1,2,3-triazole hesperetin derivatives to relieve inflammation of acute liver injury in mice

Based on the previous research results of our research group, to further improve the anti-inflammatory activity of hesperetin, we substituted triazole at the 7-OH branch of hesperetin. We also evaluated the anti-inflammatory activity of 39 new hesperetin derivatives. All compounds showed inhibitory effects on nitric oxide (NO) and inflammatory factors in lipopolysaccharide-induced RAW264.7 cells. Compound d5 showed a strong inhibitory effect on NO (half maximal inhibitory concentration = 2.34 ± 0.7 μM) and tumor necrosis factor-α, interleukin (IL)-1β, and (IL-6). Structure-activity relationships indicate that 7-O-triazole is buried in a medium-sized hydrophobic cavity that binds to the receptor. Compound d5 can also reduce the reactive oxygen species production and significantly inhibit the expression of inducible NO synthase and cyclooxygenase-2 through the nuclear factor-κB signaling pathway. In vivo results indicate that d5 can reduce liver inflammation in mice with acute liver injury (ALI) induced by CCI₄. In conclusion, d5 may be a candidate drug for treating inflammation associated with ALI.

Synthesis and evaluation of andrographolide derivatives as potent anti-osteoporosis agents in vitro and in vivo

In this work, we found that 14-deoxy-11,12-didehydroandrographolide (2), a derivative of andrographolide (AP, 1), had greatly reduced cytotoxicity compared with AP and exhibited moderate anti-osteoclastogenesis activity. Thirty compounds were synthesized by introducing anti-osteoporosis chemotypes at C-19 of 2. Six of them exhibited stronger inhibition of osteoclastogenesis than AP. Of note, compound 12g displayed the most potent activity with IC₅₀ value of 0.35 μM. The expression levels of osteoclast-specific genes such as TRAcP, CTSK, NFATc1, and MMP-9 were also decreased by 12g treatment. Furthermore, Western blot and immunofluorescence analyses demonstrated that compound 12g inhibited osteoclast differentiation through downregulation of RANKL-induced NF-κB signaling pathway. In an ovariectomized (OVX) female mice model, compound 12g significantly ameliorated bone loss. Therefore, compound 12g exhibited promising in vivo efficacy and low toxicity, indicating its therapeutic potential for the treatment of osteoporosis.

Current Trends on Repurposing and Pharmacological Enhancement of Andrographolide

Andrographolide, the main bioactive component separated from Andrographis paniculata in 1951, has been scrutinized with a modern drug discovery approach for anti-inflammatory properties since 1984. Identification of new uses of existing drugs can be facilitated by searching for evidence linking them to known or yet undiscovered drug targets and human disease states to develop new therapeutic indications.Furthermore, a wide spectrum of biological properties of andrographolide such as anticancer, antibacterial, antiviral, hepatoprotective, antioxidant, anti-malarial, anti-atherosclerosis are also reported. However, poor water solubility and instability limit its clinical application. It becomes crucial to enhance its pharmacological function and find a new treatment option for more diseases. Therefore, this article reviews the major recent developments in andrographolide, including repurposing applications in different diseases and underlying mechanisms, particularly focusing on pharmacological enhancement of andrographolide such as derivatives, chemical modifications with potent biological activity and drug delivery. The repurposing and pharmacological enhancement of andrographolide would not only have exciting therapeutic potential to different diseases to facilitate drug marketing, but also decrease the economic burden on healthcare worldwide.

Synthesis, extracorporeal nephrotoxicity, and 3D-QSAR of andrographolide derivatives

Andrographolide is a traditional Chinese medicine monomer with many pharmacological activities, but has potential nephrotoxicity. Here, we aim to investigate the relationship between modification of andrographolide structure and its nephrotoxicity. Twenty-three andrographolide derivatives were synthesized, and their structures were confirmed by ¹ H-NMR and HRMS. Nephrotoxicity of these compounds against human renal tubular epithelial (HK-2) cells was evaluated using the MTT assay. The results indicated that most of them had significantly reduced nephrotoxicity, especially compounds III, V, and IX_c , with IC₅₀ values of 1,985, 1,300, and 806.9 μmol/L, respectively, which were obviously superior to andrographolide (IC₅₀ 30.60 μmol/L). However, compounds I_a -I_f (IC₅₀ values < 30 μmol/L), the 14-OH derivatives of andrographolide, showed higher nephrotoxicity than that of andrographolide. Three-dimensional quantitative structure-activity relationship (3D-QSAR) models of COMFA and COMSIA were established (COMFA: q²  = 0.639, r²  = 0.951; COMSIA: q²  = 0.569, r²  = 0.857). This model allowed proposing five new compounds with lower theoretical nephrotoxicity, which would be worthwhile to synthesize and evaluate. We believe that predicted models will help us to understand the structural modification requirements of andrographolide to reduce the nephrotoxicity, and further investigations will be needed to determine the mechanism involved in the effect of less nephrotoxic compounds.

Discovery and evaluation of novel synthetic 5-alkyl-4-oxo-4,5-dihydro-[1,2,4]triazolo[4,3-a]quinoxaline-1-carbox-amide derivatives as anti-inflammatory agents

To develop novel anti-inflammatory agents, a series of 5-alkyl-4-oxo-4,5-dihydro-[1, 2, 4]triazolo[4,3-a]quinoxaline-1-carboxamide derivatives were designed, synthesised, and evaluated for anti-inflammatory effects using RAW264.7 cells. Structures of the synthesised compounds were determined using ¹H NMR, ¹³C NMR, and HRMS. All the compounds were screened for anti-inflammatory activity based on their inhibitory effects against LPS-induced NO release. Among them, 5-(3,4,5-trimethoxybenzyl)-4-oxo-4,5-dihydro-[1, 2, 4]triazolo[4,3-a]quinoxaline-1-carboxamide (6p) showed the highest anti-inflammatory activity and inhibited NO release more potently than the lead compound D1. Further studies revealed that compound 6p reduced the levels of NO, TNF-α, and IL-6, and that its anti-inflammatory activity involves the inhibition of COX-2 and iNOS and downregulation of the mitogen-activated protein kinases (MAPK) signal pathway. Notably, compound 6p displayed more prominent anti-inflammatory activity than D1 and the positive control ibuprofen in the in vivo acute inflammatory model. Overall, these findings indicate that compound 6p is a therapeutic candidate for the treatment of inflammation.

Inducible nitric oxide synthase inhibitors: A comprehensive update

Inducible nitric oxide synthase (iNOS), which is expressed in response to bacterial/proinflammatory stimuli, generates nitric oxide (NO) that provides cytoprotection. Overexpression of iNOS increases the levels of NO, and this increased NO level is implicated in pathophysiology of complex multifactorial diseases like Parkinson's disease, Alzheimer's disease, multiple sclerosis, rheumatoid arthritis, and inflammatory bowel disease. Selective inhibition of iNOS is an effective approach in treatment of such complex diseases. l-Arginine, being a substrate for iNOS, is the natural lead to develop iNOS inhibitors. More than 200 research reports on development of nitric oxide synthase inhibitors by different research groups across the globe have appeared in literature so far. The first review on iNOS, in 2002, discussed the iNOS inhibitors under two classes that is, amino acid and non-amino acid derivatives. Other review articles discussing specific chemical classes of iNOS inhibitors also appeared during last decade. In the present review, all reports on both natural and synthetic iNOS inhibitors, published 2002 onwards, are studied, classified, and discussed to provide comprehensive information on iNOS inhibitors. The synthetic inhibitors are broadly classified into two categories that is, arginine and non-arginine analogs. The latter are further classified into amidines, five- or six-membered heterocyclics, fused cyclics, steroidal type, and chalcones analogs. Structures of the most/significantly potent compounds from each report are provided to know the functional groups important for incurring iNOS inhibitory activity and selectivity. This review is aimed to provide a comprehensive view to the medicinal chemists for rational designing of novel and potent iNOS inhibitors.