Heterocycle-functional gramine analogues: Solvent- and catalyst-free synthesis and their inhibition activities against cell proliferation

Metabolic Activation and Cytotoxicity of Gramine Mediated by CYP3A in Rats

Gramine (GRM), which occurs in Gramineae plants, has been developed to be a biological insecticide. Exposure to GRM was reported to induce elevations of serum ALT and AST in rats, but the mechanisms of the observed hepatotoxicity have not been elucidated. The present study aimed to identify reactive metabolites that potentially participate in the toxicity. In rat liver microsomal incubations fortified with glutathione or N-acetylcysteine, one oxidative metabolite (M1), one glutathione conjugate (M2), and one N-acetylcysteine conjugate (M3) were detected after exposure to GRM. The corresponding conjugates were detected in the bile and urine of rats after GRM administration. CYP3A was the main enzyme mediating the metabolic activation of GRM. The detected GSH and NAC conjugates suggest that GRM was metabolized to a quinone imine intermediate. Both GRM and M1 showed significant toxicity to rat primary hepatocytes.

Synthesis and Hemolytic Activity of Bile Acid-Indole Bioconjugates Linked by Triazole

New formyl and acetyl derivatives of bile acid propargyl esters and their bioconjugates with modified gramine molecules have been obtained using the click chemistry method to study their hemolytic potency. The structures of all compounds were confirmed by spectral (1H- and 13C NMR and FT-IR) analysis and mass spectrometry (ESI-MS) as well as PM5 semiempirical methods. According to the results, the structural modification of formyl and acetyl bile acid derivatives, leading to the formation of new propargyl esters and indole bioconjugates, reduces their hemolytic activity. According to molecular docking studies, the tested ligands are highly likely to exhibit a similar affinity, as native ligands, for the active sites of specific protein domains (PDB IDs: 2Q85 and 5V5Z). The obtained results may be helpful for the development of selective bile acid bioconjugates as effective antibacterial, antifungal, or antioxidant agents.

Recent Developments of Gramine: Chemistry and Biological Activity

The natural alkaloid gramine has attracted significant attention in both academic and industrial circles because of its potential and diverse biological activities, including antiviral, antibacterial, antifungal, anti-inflammatory and antitumor activities; application in therapy for Alzheimer's disease; serotonin-receptor-related activity; insecticidal activity; and application as an algicide. In this review, we focus on the research advances that have been made for gramine-based molecules since their discovery, providing key information on their extraction and separation, chemical synthesis and diverse biological activities. Data regarding their mechanisms of action are also presented. This comprehensive and critical review will serve as a guide for developing more drug candidates based on gramine skeletons.

Novel Steroidal[17,16-d]pyrimidines Derived from Epiandrosterone and Androsterone: Synthesis, Characterization and Configuration-Activity Relationships

Two series of novel steroidal[17,16-d]pyrimidines derived from natural epiandrosterone and androsterone were designed and synthesized, and these compounds were screened for their potential anticancer activities. The preliminary bioassay indicated that some of these prepared compounds exhibited significantly good cytotoxic activities against human gastric cancer (SGC-7901), lung cancer (A549), and hepatocellular liver carcinoma (HepG2) cell lines compared with 5-fluorouracil (5-FU), epiandrosterone, and androsterone. Especially the respective pairs from epiandrosterone and androsterone showed significantly different inhibitory activities, and the possible configuration-activity relationships have also been summarized and discussed based on kinase assay and molecular docking, which indicated that the inhibition activities of these steroidal[17,16-d]pyrimidines might obviously be affected by the configuration of the hydroxyl group in the part of the steroidal scaffold.

Naturally derived indole alkaloids targeting regulated cell death (RCD) for cancer therapy: from molecular mechanisms to potential therapeutic targets

Regulated cell death (RCD) is a critical and active process that is controlled by specific signal transduction pathways and can be regulated by genetic signals or drug interventions. Meanwhile, RCD is closely related to the occurrence and therapy of multiple human cancers. Generally, RCD subroutines are the key signals of tumorigenesis, which are contributed to our better understanding of cancer pathogenesis and therapeutics. Indole alkaloids derived from natural sources are well defined for their outstanding biological and pharmacological properties, like vincristine, vinblastine, staurosporine, indirubin, and 3,3′-diindolylmethane, which are currently used in the clinic or under clinical assessment. Moreover, such compounds play a significant role in discovering novel anticancer agents. Thus, here we systemically summarized recent advances in indole alkaloids as anticancer agents by targeting different RCD subroutines, including the classical apoptosis and autophagic cell death signaling pathways as well as the crucial signaling pathways of other RCD subroutines, such as ferroptosis, mitotic catastrophe, necroptosis, and anoikis, in cancer. Moreover, we further discussed the cross talk between different RCD subroutines mediated by indole alkaloids and the combined strategies of multiple agents (e.g., 3,10-dibromofascaplysin combined with olaparib) to exhibit therapeutic potential against various cancers by regulating RCD subroutines. In short, the information provided in this review on the regulation of cell death by indole alkaloids against different targets is expected to be beneficial for the design of novel molecules with greater targeting and biological properties, thereby facilitating the development of new strategies for cancer therapy.

Diarylamine-Guided Carboxamide Derivatives: Synthesis, Biological Evaluation, and Potential Mechanism of Action

Diarylamines are a class of important skeleton widely existing in drugs or natural products. To discover novel diarylamine analogues as potential drugs, two series of diamide and carboxamide derivatives containing diarylamine scaffold were designed, synthesized and evaluated for their potential cytotoxic activities. The bioassay results indicated that some of the obtained compounds (C5, C6, C7, C11) exhibited good cytotoxic effect on cancer cell lines (SGC-7901, A875, HepG2), especially, compound C11 present significantly selective proliferation inhibition activity on cancer and normal cell lines (MARC145). In addition, the possible apoptosis induction for highly potential molecules was investigated, which present compound C11 could be used as novel lead compound for discovery of promising anticancer agents.

Design, Synthesis, and Cytotoxic Activity of Novel Natural Arylsulfonamide-Inspired Molecules

Primary arylsulfonamide functional groups feature prominently in diverse pharmaceuticals. However, natural arylsulfonamides are relatively infrequent. In this work, two novel arylsulfonamide natural products were first synthesized, and then a series of novel molecules derived from natural arylsulfonamides were designed and synthesized, and their in vitro cytotoxic activities against A875, HepG2, and MARC145 cell lines were systematically evaluated. The results indicate that some of these arylsulfonamide derivatives exhibit significantly good cytotoxic activity against the tested cell lines compared with the control 5-fluorouracil (5-FU), such as compounds 10l, 10p, 10q, and 10r. In particular, the potential molecule 10q, containing a carbazole moiety, exhibited the highest inhibitory activity against all tested cell lines, with IC50 values of 4.19 ± 0.78, 3.55 ± 0.63, and 2.95 ± 0.78 μg/mL, respectively. This will offer the potential to discover novel drug-like compounds from the sparsely populated area of natural products that can lead to effective anticancer agents.

Synthesis of indole derivatives as diabetics II inhibitors and enzymatic kinetics study of α-glucosidase and α-amylase along with their in-silico study

In this study, we have investigated a series of indole-based compounds for their inhibitory study against pancreatic α-amylase and intestinal α-glucosidase activity. Inhibitors of carbohydrate degrading enzymes appear to have an essential role as antidiabetic drugs. All analogous exhibited good to moderate α-amylase (IC₅₀ = 3.80 to 47.50 μM), and α-glucosidase inhibitory interactions (IC₅₀ = 3.10-52.20 μM) in comparison with standard acarbose (IC₅₀ = 12.28 μM and 11.29 μM). The analogues 4, 11, 12, 15, 14 and 17 had good activity potential both for enzymes inhibitory interactions. Structure activity relationships were deliberated to propose the influence of substituents on the inhibitory potential of analogues. Docking studies revealed the interaction of more potential analogues and enzyme active site. Further, we studied their kinetic study of most active compounds showed that compounds 15, 14, 12, 17 and 11 are competitive for α-amylase and non- competitive for α-glucosidase.

Selective and effective anticancer agents: Synthesis, biological evaluation and structure-activity relationships of novel carbazole derivatives

Carbazole alkaloids is an important class of natural products with diverse biological functions. So, the aim of this article is to explore new chemical entities containing carbazole scaffold as potential novel cytotoxic agents based on our developed three-component indole-to-carbazole reaction. Two series of carbazole derivatives were designed and synthesized, and their in vitro cytotoxic activities against three cell lines (A875, HepG2, and MARC145) were evaluated. The results indicated that some of these carbazole derivatives exhibited significantly good cytotoxic activities against tested cell lines compared with the control 5-fluorouracil (5-FU). Especially, carbazole acylhydrazone compounds 7g and 7p displayed high inhibitory activity on cancer cells, but almost no activity on normal cells. Further analysis of induced apoptosis for potential compounds indicated that the potential antitumor agents induced cell death in A875 cells at least partly (initially) by apoptosis, which might be used as promising lead scaffold for discovery of novel carbazole-type cytotoxic agents.

α-Aminoazoles/azines: key reaction partners for multicomponent reactions

Aromatic α-aminoazaheterocycles are the focus of significant investigations and exploration by researchers owing to their key role in diverse biological and physiological processes. The existence of their derivatives in numerous drugs and alkaloids is due to their heterocyclic nitrogenous nature. Therefore, the synthesis of a structurally diverse range of their derivatives through simple and convenient methods represents a vital field of synthetic organic chemistry. Multicomponent reactions (MCRs) provide a platform to introduce desirable structure diversity and complexity into a molecule in a single operation with a significant reduction in the use of harmful organic waste, and hence have attracted particular attention as an excellent tool to access these derivatives. This review covers the advances made from 2010 to the beginning of 2020 in terms of the utilization of α-aminoazaheterocycles as synthetic precursors in MCRs.

Gramine-based structure optimization to enhance anti-gastric cancer activity

Gramine is a natural indole alkaloid with a wide range of biological activities, but its anti-gastric cancer activity is poor. Herein, a pharmacophore fusion strategy was adopted to design and synthesize a new series of indole-azole hybrids on the structural basis of gramine. Based on our previous studies, different nitrogen-containing five-membered heterocyclic rings and terminal alkyne group were introduced into the indole-based scaffold to investigate their effect on improving the anti-gastric cancer activity of gramine derivatives. Structure-activity relationship (SAR) studies highlighted the role played by terminal alkyne in enhancing the inhibitory effect, and compound 16h displayed the best antiproliferative activity against gastric cancer MGC803 cells with IC₅₀ value of 3.74 μM. Further investigations displayed compound 16h could induce mitochondria-mediated apoptosis, and caused cell cycle arrest at G2/M phase. Besides, compound 16h could inhibit the metastasis ability of MGC803 cells. Our studies may provide a new strategy for structural optimization of gramine to enhance anti-gastric cancer activity, and provide a potential candidate for the treatment of gastric cancer.

The importance of indole and azaindole scaffold in the development of antitumor agents

With some indoles and azaindoles being successfully developed as anticancer drugs, the design and synthesis of indole and azaindole derivatives with remarkable antitumor activity has received increasing attention and significant progress has been made. This paper reviews the recent progress in the study of tumorigenesis, mechanism of actions and structure activity relationships about anticancer indole and azindole derivatives. Combining structure activity relationships and molecular targets-related knowledge, this review will help researchers design more effective, safe and cost-effective anticancer indoles and azindoles agents.

Discovery of novel indole derivatives containing dithioacetal as potential antiviral agents for plants

Thirty unreported indole derivatives containing dithioacetal moiety were synthesized and evaluated for anti-plant viral activity. Bioassay results displayed that some of the target compounds showed better activities against tobacco mosaic virus (TMV) than the commercial Ribavirin in vivo. In particular, anti-TMV curative, protective and inactivating activity of 4p were 55.1, 57.2, and 80.3%, respectively, and EC₅₀ value for inactivating activity was 88.5 μg/mL. The observation of transmission electron microscope showed that 4p may have a certain destructive effect on TMV particles. To further study, microscale thermophoresis analysis result also demonstrated that 4p powerfully interacted with TMV coat protein in vitro. Hence, this study provides a strong evidence suporting that indole derivatives might be applied as new antiviral agents.

Synthesis and bioevaluation of novel steroidal isatin conjugates derived from epiandrosterone/androsterone

Steroids are classes of natural products widely distributed in nature, which have been demonstrated to exhibit broad biological functions, and have also attracted increasing interest from bioorganic and pharmaceutical researches. In order to develop novel chemical entities as potential cytotoxic agents, a series of steroidal isatin conjugations derived from epiandrosterone and androsterone were efficiently prepared and characterized, and all these obtained compounds were screened for their potential cytotoxic activities. The preliminary bioassay indicated that most of the newly synthesized compounds exhibited good cytotoxic activities against human gastric cancer (SGC-7901), melanoma (A875), and hepatocellular liver carcinoma (HepG2) cell lines compared with 5-fluorouracil (5-FU), which might be considered as promising scaffold for further development of potential anticancer agents.

Synthesis, Antiviral Activity, and Induction of Plant Resistance of Indole Analogues Bearing Dithioacetal Moiety

A series of compounds with potential activity to induce plant resistance was synthesized from indole and thiol compounds and methodically evaluated for antiviral activity. The results indicated that some of the synthesized compounds had high antipotato virus Y (PVY), anticucumber mosaic virus, and antitobacco mosaic virus activities. Notably, compound D21 exhibited the best activity against PVY among these compounds in vivo, and the 50% effective concentrations (EC50) of protection activity is 122 μg/mL, which was distinctively better than the corresponding values for ribavirin (653 μg/mL), Ningnanmycin (464 μg/mL), and Xiangcaoliusuobingmi (279 μg/mL). Interestingly, we found that the protection activity of D21 was associated with improvement of chlorophyll content and defense-related enzyme activities. Moreover, D21 could trigger the malate dehydrogenase (MDH) signaling pathway, as further confirmed by the MDH activity evaluation. Hence, D21 can protect plants against viral activity and has potential as a novel activator for plant resistance induction.

Natural Products for Drug Discovery: Discovery of Gramines as Novel Agents against a Plant Virus

Plant viral diseases seriously affect crop yield and quality. The natural product gramine (1) and its simple structural analogues 2-35 were synthesized from indoles, amines, and aldehydes in one step. The antiviral effects of these alkaloids were evaluated systematically. Most of these compounds were found to have higher antiviral effects than commercial ribavirin for the first time. Especially compounds 22, 30, and 31 exhibited significantly higher effects than ningnanmycin, thereby emerging as novel antiviral leads for further optimization. The preliminary implementation indicated that these compounds likely inhibit the assembly of tobacco mosaic virus (TMV) by cross-linking TMV capsid protein. Gramine analogues were also found to have broad-spectrum fungicidal effects. Although gramine has been reported to have influence on germination and development of Erysiphe graminis, these compounds displayed no fungicidal effects against Blumeria graminis f. sp. tritici on wheat in our test. Some of these compounds also exhibited certain insecticidal activities.

Bioactive heterocycles containing a 3,4,5-trimethoxyphenyl fragment exerting potent antiproliferative activity through microtubule destabilization

Novel bioactive heterocycles containing a 3,4,5-trimethoxyphenyl fragment as antiproliferative agents by targeting tubulin were synthesized and their preliminary structure activity relationships (SARs) were explored. Among all these chemical agents, 2-(Benzo[d]oxazol-2-ylthio)-N-(4-methoxybenzyl)-N-(3,4,5-trimethoxyphenyl)acetamide (4d) exhibited the potent antiproliferative activity against MGC-803 cells with an IC₅₀ value of 0.45 μM by induction of G2/M pahse arrest and cell apoptosis. In addition, 4d could change the membrane potential (ΔΨ) of the mitochondria against MGC-803 cells. Importantly, 4d acted as a novel tubulin polymerization inhibitor binding to colchicine site with an IC₅₀ value of 3.35 μM.

Nicotinamide-based diamides derivatives as potential cytotoxic agents: synthesis and biological evaluation

A series of diamides derivatives containing nicotinamide unit were designed, synthesized and evaluated for their potential cytotoxic activities against human cancer cell lines. All the synthesized compounds were characterized using spectroscopic methods mainly including ¹H NMR, ¹³C NMR and MS. The bio-evaluation results indicated that some of the obtained compounds (such as 4d, 4h, 4i) exhibited good to moderate cytotoxic effects on lung cancer cell lines (NCI-H460, A549, and NCI-H1975), especially, compound 4d exhibited the highly potential inhibitory activities against NCI-H460 cell line with the IC₅₀ values of 4.07 ± 1.30 μg/mL, which might be developed as novel lead compounds for potential cytotoxic agents.

Steroidal[17,16-d]pyrimidines derived from dehydroepiandrosterone: A convenient synthesis, antiproliferation activity, structure-activity relationships, and role of heterocyclic moiety

A series of steroidal[17,16-d]pyrimidines derived from dehydroepiandrosterone were designed and prepared by a convenient heterocyclization reaction. The in vitro anticancer activities for these obtained compounds were evaluated against human cancer cell lines (HepG2, Huh-7, and SGC-7901), which demonstrated that some of these heterocyclic pyrimidine derivatives exhibited significantly good cytotoxic activities against all tested cell lines compared with 5-fluorouracil (5-FU), especially, compound 3b exhibited high potential growth inhibitory activities against all tested cell lines with the IC₅₀ values of 5.41 ± 1.34, 5.65 ± 1.02 and 10.64 ± 1.49 μM, respectively, which might be used as promising lead scaffold for discovery of novel anticancer agents.

Structure-activity relationship (SAR) study and design strategies of nitrogen-containing heterocyclic moieties for their anticancer activities

The present review article offers a detailed account of the design strategies employed for the synthesis of nitrogen-containing anticancer agents. The results of different studies describe the N-heterocyclic ring system is a core structure in many synthetic compounds exhibiting a broad range of biological activities. Benzimidazole, benzothiazole, indole, acridine, oxadiazole, imidazole, isoxazole, pyrazole, triazoles, quinolines and quinazolines including others drugs containing pyridazine, pyridine and pyrimidines are covered. The following studies of these compounds suggested that these compounds showed their antitumor activities through multiple mechanisms including inhibiting protein kinase (CDK, MK-2, PLK1, kinesin-like protein Eg5 and IKK), topoisomerase I and II, microtubule inhibition, and many others. Our concise representation exploits the design and anticancer potency of these compounds. The direct comparison of anticancer activities with the standard enables a systematic analysis of the structure-activity relationship among the series.

Acylhydrazone derivatives as potential anticancer agents: Synthesis, bio-evaluation and mechanism of action

A series of novel acylhydrazone derivatives were designed, synthesized and evaluated for their potential cytotoxic effects against human cancer cell lines. The preliminary results indicated that some of the obtained compounds (such as 8b, 13c) exhibited good to moderate cytotoxic activities against human HepG2, Huh-7, and BCG-823 cell lines. Especially, compounds 8c and 8e presented obviously selective cytotoxic activities against Huh-7 in vitro (8c, IC50=7.74±2.18μg/mL; 8e, IC50=4.46±1.05μg/mL) compared to 5-FU (IC50=10.41±3.41μg/mL). The highly potential compounds to induce apoptosis in HepG2 cells were analyzed by flow cytometry, and the apoptotic effects of compounds 8b and 13c were further evaluated using Annexin V-FITC/propidium iodide dual staining assay.

Discovery of novel isatin-dehydroepiandrosterone conjugates as potential anticancer agents

A series of isatin-dehydroepiandrosterone hybrids were synthesised via a convenient condensation procedure, and which were evaluated for their potential anticancer activities. The preliminary assays indicated that some of the newly obtained compounds exhibited good antitumor activities against human hepatocellular liver carcinoma (HepG2), heptoma (Huh-7), melanoma (A875) and 5-fluorouracil-resistant human hepatocellular carcinoma (BEL-7402/5-FU) cell lines compared with 5-fluorouracil (5-FU), which might be considered as promising lead scaffold for further design and synthesis of highly potential anticancer agents.

Synthesis, spectroscopy, theoretical and biological studies of new gramine-steroids salts and conjugates

New gramine connections with bile acids (lithocholic, deoxycholic, cholic) and sterols (cholesterol, cholestanol) were synthesized. The structures of products were confirmed by spectral (NMR, FT-IR) analysis, mass spectrometry (ESI-MS) as well as PM5 semiempirical methods. Unexpectedly, the products of the reaction of gramine with cholesterol and cholestanol were symmetrical compounds consisting of two molecules of sterols connected by N(CH3)2 group. All new synthesized compounds interact in vitro with the human erythrocyte membrane and alter discoid erythrocyte shape inducing stomatocytosis or echinocytosis. Increase in the incorporation of the fluorescent dye merocyanine 540 (MC540) into the erythrocyte membrane indicates that new compounds at sublytic concentrations are capable of disturbing membrane phospholipids asymmetry and loosening the molecular packing of phospholipids in the bilayer. Gramine significantly decreases the membrane partitioning properties as well as haemolytic activity of lithocholic acid in its new salt. Moreover, both deoxycholic and cholic acids completely lost their membrane perturbing activities in the gramine salts. On the other hand, the capacity of new gramine-sterols connections to alter the erythrocyte membrane structure and its permeability is much higher in comparison with sterols alone. The dual effect of gramine on the bile acid and sterols cell membrane partitioning activity observed in our study should not be neglected in vivo.

Discovery of gramine derivatives that inhibit the early stage of EV71 replication in vitro

Enterovirus 71 (EV71) is a notable causative agent of hand, foot, and mouth disease in children, which is associated with an increased incidence of severe neurological disease and death, yet there is no specific treatment or vaccine for EV71 infections. In this study, the antiviral activity of gramine and 21 gramine derivatives against EV71 was investigated in cell-based assays. Eighteen derivatives displayed some degree of inhibitory effects against EV71, in that they could effectively inhibit virus-induced cytopathic effects (CPEs), but the anti-EV71 activity of the lead compound gramine was not observed. Studies on the preliminary modes of action showed that these compounds functioned by targeting the early stage of the EV71 lifecycle after viral entry, rather than inactivating the virus directly, inhibiting virus adsorption or affecting viral release from the cells. Among these derivatives, one (compound 4s) containing pyridine and benzothiazole units showed the most potency against EV71. Further studies demonstrated that derivative 4s could profoundly inhibit viral RNA replication, protein synthesis, and virus-induced apoptosis in RD cells. These results indicate that derivative 4s might be a feasible therapeutic agent against EV71 infection and that these gramine derivatives may provide promising lead scaffolds for the further design and synthesis of potential antiviral agents.

Discovery of highly potent and selective D4 ligands by interactive SAR study

A series of thienylmethylphenylpiperazins was synthesized and tested for affinity towards the five subtypes of dopaminergic receptors. Compound 5f showed more than 1000 folds selectivity to D4 receptors; analogue 5e showed the highest affinity to D4 receptors with Ki 3.9 nM. An interactive SAR approach was adopted and lead to compound 14a with Ki (D4) as low as 0.03 nM. Molecular docking studies showed a potential, first to report arene cation interaction between the D4 unique residue Arg-186 and the ligands' arene moiety, explaining the importance of having a strong negative electrostatic potential at this area of the compound structure.

Identification of adiponectin receptor agonist utilizing a fluorescence polarization based high throughput assay

Adiponectin, the adipose-derived hormone, plays an important role in the suppression of metabolic disorders that can result in type 2 diabetes, obesity, and atherosclerosis. It has been shown that up-regulation of adiponectin or adiponectin receptor has a number of therapeutic benefits. Given that it is hard to convert the full size adiponectin protein into a viable drug, adiponectin receptor agonists could be designed or identified using high-throughput screening. Here, we report on the development of a two-step screening process to identify adiponectin agonists. First step, we developed a high throughput screening assay based on fluorescence polarization to identify adiponectin ligands. The fluorescence polarization assay reported here could be adapted to screening against larger small molecular compound libraries. A natural product library containing 10,000 compounds was screened and 9 hits were selected for validation. These compounds have been taken for the second-step in vitro tests to confirm their agonistic activity. The most active adiponectin receptor 1 agonists are matairesinol, arctiin, (-)-arctigenin and gramine. The most active adiponectin receptor 2 agonists are parthenolide, taxifoliol, deoxyschizandrin, and syringin. These compounds may be useful drug candidates for hypoadiponectin related diseases.