A class of oral N-[(1S,3S)-1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carbonyl]- N′-(amino-acid-acyl)hydrazine: Discovery, synthesis, in vitro anti-platelet aggregation/in vivo anti-thrombotic evaluation and 3D QSAR analysis

Novel derivatives of thiohydantoin-containing tetrahydro-β-carboline possess activity against influenza virus at late stages of viral cycle without affecting viral neuraminidase

Influenza infection represents a serious challenge for virological surveillance and healthcare systems in all countries globally. Despite obvious success in control of influenza through vaccination and antiviral drug development, this infection remains poorly controlled due to antigenic drift and fast selection of drug-resistant viral variants. The design of novel drugs with alternative targets and mechanisms of action is, therefore, an important goal for medical science worldwide. In the current study, we describe the chemical synthesis of novel tetrahydro-β-carboline derivatives containing a thiohydantoin fragment, as well as their antiviral activity against influenza virus A/Puerto Rico/8/34 (H1N1). In general, the library of compounds was of low toxicity. Of the 23 compounds under investigation, 10 (43.5%) displayed a selectivity index (SI) of 10 or higher, their activity strongly exceeding that of the reference compound rimantadine. The most active compounds have also demonstrated suppressing activity against the phylogenetically distinct influenza virus of type B. These compounds, similar to the reference compound zanamivir, were active at very late stages of the viral cycle (4-6 h postinfection), suggesting interference with processes of virion assembly and budding. However, no direct inhibiting activity against viral neuraminidase has been demonstrated. The results obtained can be considered as a rationale for further structural optimization and study of this group as potential broad-range antivirals effective against influenza viruses.

Design, Synthesis and Biological Activity Evaluation of β-Carboline Derivatives Containing Nitrogen Heterocycles

A series of β-carboline derivatives containing nitrogen heterocycles were designed and synthesized. All compounds were screened for their antitumor activity against four human tumor cell lines (A549, K562, PC-3, T47D). Notably, compound N-(4-(morpholinomethyl)phenyl)-2-((5-(1-(3,4,5-trimethoxyphenyl)-9H-pyrido[3,4-b]indol-3-yl)-1,3,4-oxadiazol-2-yl)thio)acetamide (8q) exhibited significant inhibitory activity against PC-3 cells with an IC50 value of 9.86 µM. Importantly, compound 8q effectively suppressed both the proliferation and migration of PC-3 cells. Mechanistic studies revealed that compound 8q induced cell apoptosis and caused the accumulation of reactive oxygen species (ROS), leading to cell cycle arrest in the G0/G1 phase in PC-3 cells.

Synthesis, structure-activity relationship, and biological evaluation of quinolines for development of anticancer agents

Tetrahydro-β-carbolines (THβCs) are a kind of natural alkaloids with multiple pharmaceutical activities. Herein, a focused compound library derived from THβCs was synthesized and their anticancer activities were studied in several cancer cell lines. Among them, three compounds showed considerable anticancer activities with low micromolar to submicromolar IC₅₀ values. The abilities to induce apoptosis and alter mitochondrial membrane potential levels, which are comparable to those of the commercial anticancer drug adriamycin, were confirmed by one representative compound (21) on the B16/F10 cell line. Our preliminary structure-activity relationship studies indicated that alkylamines with suitable lengths are very important for potency improvement.

(1R,3S)-THCCA-Asn: To show the discovery of selective inhibitor of thrombin by successfully combining virtual screening and biological assay

Thrombin is the most potent platelet aggregator. To discover the selective inhibitor of thrombin that is important to curing platelet aggregation-related diseases, docking experiments were performed to dock (1R,3S)-2,3,4,9-tetrahydro-β-carboline-3- carboxylic acid, [(1R,3S)-THCCA], and (1S,3S)-2,3,4,9-tetrahydro-β-carboline-3- carboxylic acid, [(1S,3S)-THCCA], into the p pocket of bovine thrombin. The ideal match supported that (1R,3S)-THCCA could be used as a potential lead compound. In this case 20 natural amino acids were theoretically introduced into the 3-carboxyl of (1R,3S)-THCCA and 20 derivatives, (1R,3S)-THCCA-amino acids, were docked into p pocket of bovine thrombin to perform virtual screening. The screening revealed that comparing to (1R,3S)-THCCA itself the DockScores of 16 derivatives were higher, and (1R,3S)-THCCA-Asn (4j) got the highest DockScore. Thus, 16 derivatives were synthesized for experimental study. The in vitro anti-platelet aggregation assay showed that at 100 μM of concentration the 16 derivatives failed to inhibit the platelet aggregation induced by both adenosine diphosphate and arachidonic acid. On the other hand, however, the IC₅₀ value of the 16 derivatives inhibiting the platelet aggregation induced by platelet activating factor and thrombin ranged from 9.44 μM to 194.64 μM and from 0.07 μM to 9.56 μM, respectively. The in vitro anti-platelet aggregation assay suggested that the 16 derivatives selectively inhibited the platelet aggregation induced by thrombin. In particular, the IC₅₀ of (1R,3S)-THCCA-Asn (4j) had the lowest value. On rat model at 1 nmol/kg of dosage the 16 derivatives effectively prevented thrombus formation. It is worth pointing out that even at 0.01 nmol/kg of dosage, 4j still effectively prevented thrombus formation. 4j hardly has effects on the proliferation of mammalian cells and rat tail bleeding time. In conclusion, the combination of virtual screening and biological assays successfully lead to the discovery of 4j as a promising candidate of selective inhibitor of thrombin.

Recent Update on the Anti-infective Potential of β-carboline Analogs

β-Carboline, a naturally occurring indole alkaloid, holds a momentous spot in the field of medicinal chemistry due to its myriad of pharmacological actions like anticancer, antiviral, antibacterial, antifungal, antileishmanial, antimalarial, neuropharmacological, anti-inflammatory and antithrombotic among others. β-Carbolines exhibit their pharmacological activity via diverse mechanisms. This review provides a recent update (2015-2020) on the anti-infective potential of natural and synthetic β-carboline analogs focusing on its antibacterial, antifungal, antiviral, antimalarial, antileishmanial and antitrypanosomal properties. In cases where enough details are available, a note on its mechanism of action is also added.

Discovery of β-Carboline Derivatives as a Highly Potent Cardioprotectant against Myocardial Ischemia-Reperfusion Injury

Timely myocardial reperfusion salvages ischemic myocardium from infarction, whereas reperfusion itself induces cardiomyocyte death, which is called myocardial ischemia/reperfusion (MI/R) injury. Herein, β-carboline derivative 17c was designed and synthesized with obvious myocardial protective activity for the first time. Pretreatment of 17c effectively protected the cardiomyocyte H9c2 cells from H₂O₂-induced lactate dehydrogenase leakage and restored the endogenous antioxidants, superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). Besides, 17c effectively protected the mitochondria through decreasing the reactive oxygen species overproduction and enhancing the mitochondrial membrane potential. As a result, 17c significantly reduced the necrosis of cardiomyocytes in H₂O₂-induced oxidative stress, which was more potent than polydatin. In MI/R injury rats, 17c pretreatment obviously increased the levels of SOD and GSH-Px and inhibited the apoptosis of cardiomyocytes. Through this way, the size of myocardial infarction was significantly reduced after MI/R injury in vivo, better than that of polydatin, suggesting that 17c is a promising cardioprotectant for the prevention of MI/R injury.

Recent evolution on synthesis strategies and anti-leishmanial activity of β-carboline derivatives - An update

Leishmaniasis is the most widespread pathogenic disease in several countries. Currently, no effective vaccines are available, and the control of Leishmaniasis primarily relies on decade-old chemotherapy. The treatment for the Leishmaniasis is not up to the mark. Current therapy for Leishmaniasis is ancient and requires hospitalization for the administration. These medications are also highly toxic and resistant. β-carboline, a natural indole containing alkaloid, holds a vital position in the field of medicinal chemistry with a diversified pharmacological action. The current review focuses mainly on the anti-leishmanial effects of β-carboline analogs and their synthetic strategies, structural activity relationship studies (SAR). The past ten years alterations unveiled by β-carboline analogs present in phytoconstituents and various derivatives of synthesized analogs with the mechanism of action were briefly shortlisted and illustrated.

Synthesis and Antiviral/Fungicidal/Insecticidal Activities Study of Novel Chiral Indole Diketopiperazine Derivatives Containing Acylhydrazone Moiety

On the basis of the mechanism of acylhydrazone compounds inhibiting the assembly of TMV CP and the unique structural characteristics of diketopiperazine ring, a series of optically pure indole diketopiperazine acylhydrazone were designed and synthesized. In order to systematically study the effect of the spatial configuration of the compounds on the antiviral activity, four compounds with different spatial configurations at C6 and C12a were also prepared. The bioassay results indicated that most of these new compounds displayed moderate to good antiviral activity, among which compounds 23, 25, 27, 28, 31, and 5d showed a significantly higher activity than that of commercial ribavirin. An in-depth structure-activity relationship investigation showed that the spatial conformation was one of the most important factors in adjusting antiviral activity; the research results provided information about the possible optimum configuration for interaction of this molecular with its target protein. At the same time, these new compounds also exhibited broad-spectrum fungicidal activities against 14 kinds of phytopathogenic fungi. What's more, some of these compounds exhibited good insecticidal activity to Plutella xylostella and Culex pipiens pallens.

Design, synthesis, and biological evaluation of 2-substituted-2,3,4,9-tetrahydrospiro-β-carboline-3-carboxylic acid derivatives as first-in-class mast cell stabilizers

Mast cell degranulation plays a momentous role in myriad diseases like asthma, eczema, allergic rhinitis, and conjunctivitis as well as anaphylactic shock; hence, there is an unmet need for developing new mast cells stabilizers. The reported mast cell stabilizers have a heterocyclic moiety and an acidic group. Furthermore, the role of tryptophan in suppression of mast cell activation is established. Hence, we prepared constrained analogs of tryptophan, which are derivatives of 2,3,4,9-tetrahydrospiro-β-carboline-3-carboxylic acid, and evaluated them for ex vivo inhibition of compound 48/80-induced mast degranulation activity. By comparing IC₅₀ (μM) values with that of the standard drug sodium cromoglycate (IC₅₀  = 0.489 ± 0.003 μM), compounds with bulky groups like heptyl (compound 9; IC₅₀  = 0.389 ± 0.015 μM) and octyl (compound 10; IC₅₀  = 0.354 ± 0.023 μM) were found to be of similar potency as sodium cromoglycate. Furthermore, the polar group-containing compounds like the chloropropyl (compound 16; IC₅₀  = 0.382 ± 0.083 μM) and benzoyl derivative (compound 14; IC₅₀  = 00.469 ± 0.032 μM) were also found to be of similar potency as sodium cromoglycate. This is a seminal study of spiro-β-carboline mast cell stabilization having a wider scope in mast cell research; yet, the mechanism of action remains elusive.

Docking of THPDTPI: to explore P-selectin as a common target of anti-tumor, anti-thrombotic and anti-inflammatory agent

The impact of soluble P-selectin on tumor growth, thrombosis and inflammation has been individually documented. Whether the down-regulation of P-selectin expression can simultaneously slow the tumor growth, inhibit the thrombosis and attenuate the inflammatory response remains unknown. In this context, (2'S,5'S)- tetrahydropyrazino[1',2':1,6]-di{2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole}-1',4'-dione (THPDTPI) was designed as an inhibitor of P-selectin. The suitable docking of THPDTPI towards the active site of P-selectin, the significant down-regulation of THPDTPI to P-selectin expression, and the direct action of THPDTPI on P-selectin suggest that P-selectin could be a target of THPDTPI. In vivo THPDTPI possesses the anti-tumor activity, the anti-thrombotic activity and the anti-inflammatory activity. This implies that targeting P-selectin is of essential importance for this triple activity. The minimal effective doses of THPDTPI inhibiting the tumor growth, the rat arterial thrombosis and the mouse ear edema are 0.01 μmol/kg, 0.1 μmol/kg and 0.001 μmol/kg, respectively. Atomic force microscopy images and FT-MS spectra showed that the adhesion of THPDTPI onto the surfaces of the platelets may be the first step of P-selectin targeting. Besides, the dependence of the triple action of THPDTPI inhibiting the tumor growth, the thrombosis and the inflammation on the decrease of the soluble P-selectin led to the correlation of the soluble P-selectin with the serum TNF-α and serum IL-8.

Concise Syntheses of Hyrtioreticulins C and D via a C-4 Pictet-Spengler Reaction: Revised Signs of Specific Rotations

The first syntheses of hyrtioreticulins C and D via a Pictet-Spengler reaction at the C-4 position of the indole rings are described. The synthesis proceeds in only two steps from commercially available starting materials. In this Communication, the structures of the natural products were confirmed. Furthermore, we revise the signs of the specific rotations of hyrtioreticulins C and D.

IQCA-TASS: a nano-scaled P-selectin inhibitor capable of targeting thrombus and releasing IQCA/TARGD(S)S in vivo

Thrombosis is a serious threat to human health worldwide. Tetrahydroisoquinoline-3-carboxylic acid (IQCA) is an antithrombotic agent, while Thr-Ala-Arg-Gly-Asp(Ser)-Ser (TASS) can target thrombus.

Synthesis and in-vitro anti-leishmanial activity of (4-arylpiperazin-1-yl)(1-(thiophen-2-yl)-9H-pyrido[3,4-b]indol-3-yl)methanone derivatives

In the present study, we have reported synthesis and biological evaluation of a series of fifteen 1-(thiophen-2-yl)-9H-pyrido[3,4-b]indole derivatives against both promastigotes and amastigotes of Leishmania parasites responsible for visceral (L. donovani) and cutaneous (L. amazonensis) leishmaniasis. Among these reported analogues, compounds 7b, 7c, 7f, 7g, 7i, 7j, 7m, 7o displayed potent activity (15.55, 7.70, 7.00, 3.80, 14.10, 9.25, 3.10, 4.85μM, respectively) against L. donovani promastigotes than standard drugs miltefosine (15.70μM) and pentamidine (32.70μM) with good selectivity index. In further, in-vitro evaluation against amastigote forms, two compounds 7g (8.80μM) and 7i (7.50μM) showed significant inhibition of L. donovani amastigotes. Standard drug amphotericin B is also used as control to compare inhibition potency of compounds against both promastigote (0.24μM) and amastigote (0.05μM) forms.

Synthesis and evaluation of novel hybrids β-carboline-4-thiazolidinones as potential antitumor and antiviral agents

A series of novel hybrids β-carboline-4-thiazolidinones were synthesized and evaluated for their in vitro antitumor activity against human cancer cell lines and for antiviral activity towards Herpes simplex virus type-1 (HSV-1). From the N'-(2-ylidene-4-thiazolidinone)-β-carboline-3-carbohydrazide series (9-11), compounds 9c and 11d were the most active, showing growth inhibition 50% (GI₅₀) values less than 5 μM for all cell lines tested. Compound 9c, bearing the 4-dimethylaminophenyl group at C-1 of β-carboline was selected for further investigation concerning cell death and cell cycle profile, focusing on the human renal adenocarcinoma cell line 786-0. Treatments with 25 μM of compound 9c induced cell death after 15 h of treatment, characterized by phosphatidylserine exposure and loss of membrane integrity. Moreover, treatment with 12.5 μM promoted a sub-G1 arrest, which indicates cell death. Derivatives of the N-(2-substituted-aryl-4-thiazolidinone)-β-carboline-3-carboxamide series (18-23) showed a potent activity and high selectivity for glioma (U251) and ovarian (OVCAR-3) cancer cell lines. Also, some β-carboline-4-thiazolidinone hybrids showed potent antiviral activity against Herpes simplex virus type-1. The N-(2-substituted-aryl-4-thiazolidinone)-carboxamide moiety in 18, 19 and 22 confer a potent anti-HSV-1 activity for these derivatives, which presented EC₅₀ values of 0.80, 2.15 and 2.02 μM, respectively. The assay results showed that the nature of 4-thiazolidinone moiety and of the substituent attached at the 3- and 1- position of β-carboline nucleus influenced the antitumor and antiviral activities.

A novel lead of P-selectin inhibitor: Discovery, synthesis, bioassays and action mechanism

By docking 126 derivatives of β-carboline-3-carboxylic acid, tetrahydro-β-carboline-3-carboxylic acid and indoloquinolizine into the active pocket of P-selectin (2-(3-(hydroxymethyl)-9H-pyrido[3,4-b]indol-1-yl)ethyl)-l-phenylalanine (HMCEF) was assigned a novel inhibitor. ELISA and flow cytometry experiments showed that HMCEF effectively down-regulated P-selectin expression and supported the rationality of the computer assistant screening, while UV spectrum experiments demonstrated that HMCEF directly bound to P-selectin. In vivo HMCEF dose dependently inhibited the rats and mice to form thrombus and had a minimal effective dose of 20nmol/kg, dose dependently inhibited inflammatory response of mice and had a minimal effective dose of 20nmol/kg. The decrease of serum TNFα and IL-8 of the treated mice was proposed to be the action mechanism of HMCEF inhibiting thrombosis and inflammation. All data imply that HMCEF is a novel lead of P-selectin inhibitor.

Tetrahydro-β-carboline-3-carboxyl-thymopentin: a nano-conjugate for releasing pharmacophores to treat tumor and complications

To improve the therapeutic efficacy of cancer patients a novel conjugate of thymopentin (TP5) and (1S,3S)-1-methyl-tetrahydro-β-carboline-3-carboxylic acid (MTC) was presented. In water and mouse plasma MTCTP5 forms the nanoparticles of 14-139 nm in diameter, the suitable size for delivery in blood circulation. In mouse plasma MTCTP5 releases MTC, while in the presence of trypsin MTCTP5 releases MTC and TP5. On mouse and rat models the MTCTP5 dose dependently slows down the tumor growth, inhibits inflammatory response and blocks thrombosis. The anti-tumor activity as well as the anti-inflammation activity and anti-thrombotic activity of MTCTP5 are 100 fold and 10 fold higher than those of MTC, respectively, which are attributed to the fact that it down-regulates the plasma levels of TNF-α and IL-8 of the treated animals. The immunology enhancing activities in vitro and in vivo of MTCTP5 are similar to those of TP5, which is attributed to the fact that MTCTP5 up-regulates the plasma levels of IL-2 and CD4 as well as down-regulates the plasma level of CD8 of the treated animals. The plasma alanine transaminase, aspartate transaminase and creatinine assays indicate that MTCTP5 therapy does not injure the liver and the kidney of the animals. The survival time of MTCTP5 treated mice is significantly longer than that of TP5 treated mice.

Small molecule PZL318: forming fluorescent nanoparticles capable of tracing their interactions with cancer cells and activated platelets, slowing tumor growth and inhibiting thrombosis

Low selectivity of chemotherapy correlates with poor outcomes of cancer patients. To improve this issue, a novel agent, N-(1-[3-methoxycarbonyl-4-hydroxyphenyl]-β-carboline-3-carbonyl)-Trp-Lys-OBzl (PZL318), was reported here. The transmission electron microscopy, scanning electron microscopy, and atomic force microscopy images demonstrated that PZL318 can form nanoparticles. Fluorescent and confocal images visualized that PZL318 formed fluorescent nanoparticles capable of targeting cancer cells and tracing their interactions with cancer cells. In vitro, 40 μM of PZL318 inhibited the proliferation of tumorigenic cells, but not nontumorigenic cells. In vivo, 10 nmol/kg of PZL318 slowed the tumor growth of S180 mice and alleviated the thrombosis of ferric chloride-treated ICR mice, while 100 μmol/kg of PZL318 did not injure healthy mice and they exhibited no liver toxicity. By analyzing Fourier transform–mass spectrometry and rotating-frame Overhauser spectroscopy (ROESY) two-dimensional nuclear magnetic resonance spectra, the chemical mechanism of PZL318-forming trimers and nanoparticles was explored. By using mesoscale simulation, a nanoparticle of 3.01 nm in diameter was predicted containing 13 trimers. Scavenging free radicals, downregulating sP-selectin expression and intercalating toward DNA were correlated with the antitumor mechanism of PZL318.

Design, synthesis, and antiviral, fungicidal, and insecticidal activities of tetrahydro-β-carboline-3-carbohydrazide derivatives

According to our previous research on the antiviral activity of β-carboline and tetrahydro-β-carboline derivatives, using (1S,3S)-1-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carbohydrazide (1) as a lead compound, series of novel tetrahydro-β-carboline derivatives containing acylhydrazone moiety were designed, synthesized, and first evaluated for their biological activities. Most of these compounds exhibited excellent antiviral activity both in vitro and in vivo. The in vivo inactivation, curative, and protection activities of compounds 8, 9, 12, 16, 28, 29, and 30 were much higher than that of ribavirin (37.6%, 39.4%, and 37.9% at 500 μg/mL) and the lead compound (40.0%, 42.3%, and 39.6% at 500 μg/mL). Especially, the in vitro and in vivo activities of compound 16 (36.9%, 33.6%, 30.2%, and 35.8%) at 100 μg/mL, which were very close to that of ribavirin (40.0% for in vitro activity) at 500 μg/mL. Compounds 9 and 29 were chosen for the field trials of antiviral efficacy against TMV (tobacco mosaic virus); the results exhibited that both compounds, especially compound 29, showed better activities than control plant virus inhibitors. At the same time, the fungicidal results showed that compounds 6, 9, and 11 exhibited good fungicidal activities against 14 kinds of phytopathogens. Additionally, compounds 3 and 23 exhibited moderate insecticidal activity against the four tested species of insects.

Inhibitory effect of a callophycin A derivative on iNOS expression via inhibition of Akt in lipopolysaccharide-stimulated RAW 264.7 cells

In previous studies, (R)-2-isobutyl 3-methyl 3,4-dihydro-1H-pyrido[3,4-b]indole-2,3(9H)-dicarboxylate (1), a callophycin A derivative, was found to strongly inhibit nitrite production in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells, while (R)- or (S)-callophycin A showed only weak inhibition. We currently report additional studies to define the mechanisms underlying the inhibitory action of 1. Expression of inducible nitric oxide synthase (iNOS) was reduced at both protein and mRNA levels. Major upstream signaling molecules and transcription factors regulating iNOS expression were examined, but it was found that 1 did not affect the phosphorylated and total protein levels of p38 mitogen-activated protein kinase (p38 MAPK), Jun N-terminal kinase (JNK), extracellular signal-regulated kinase 1/2 (ERK1/2), and signal transducer and activator of transcription 1 (STAT1), nor did it mediate the degradation of the inhibitor of nuclear factor-κB α-isoform (IκBα). However, starting at early time points, 1 consistently inhibited the phosphorylation of protein kinase B/Akt at serine 473. In addition, 1 suppressed the protein expression of octamer-binding transcription factor-2 (Oct-2) and the expression of microRNA 155 (miR-155). In sum, compound 1 inhibits LPS-induced nitrite production by a unique and complex mechanism. Reduction of iNOS expression is accompanied by inhibition of Akt activation, Oct-2 protein expression, and miR-155 expression.

Synthesis and evaluation of new β-carboline-3-(4-benzylidene)-4H-oxazol-5-one derivatives as antitumor agents

In the present work, we report the synthesis and in vitro anticancer and antimicrobial activity evaluation of a new series of 1-substituted-β-carboline derivatives bearing a 4-benzylidene-4H-oxazol-5-one unity at C-3. The compound 2-[1-(4-methoxyphenyl)-9H-β-carbolin-3-yl]-4-(benzylidene)-4H-oxazol-5-one (11) was the most active derivative, exhibiting a potent cytotoxic activity against glioma (U251), prostate (PC-3) and ovarian (OVCAR-03) cancer cell lines with IC₅₀ values of 0.48, 1.50 and 1.07 µM, respectively. An in silico study of the ADME properties of the novel synthesized β-carboline derivatives was also performed.