Indole Core Research Articles

Establishment of Broad-Specificity Monoclonal Antibody-Based Immunoassay for Rapid Detection of Indole-Type and Indazole-Type Synthetic Cannabinoids and Metabolites.

Synthetic cannabinoids (SCs) have emerged as one of the most severely abused categories of new psychoactive substances (NPS), exacerbating the global drug problem and posing significant threats to public health. Presently, a class of new amide-type SCs featuring an indazole or indole core has been identified in numerous cases of illegal drug use, but there is still a lack of comprehensive analysis methods of SC detection. Herein, monoclonal antibodies (mAbs) 2E4 and AE6 targeting 36 indole-type and indazole-type SCs and their metabolites with IC50 ranging from 0.14 to 85.28 ng/mL were prepared and the molecular mechanism of antibody recognition was elaborated. We established the indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and gold immunochromatography assay (GICA) based on mAbs 2E4 and AE6 to detect indazole-type and indole-type SCs in urine and hair samples. Under optimal conditions, the proposed method detected ADB-BUTINACA (an indazole-type SC) with limits of detection (LODs) of 0.11 ng/mL for urine and 0.024 ng/mg for hair by ic-ELISA, and 1.02 ng/mL for urine and 0.046 ng/mg for hair by GICA; the LODs of 4F-MDMB-BUTICA (an indole-type SC) detection was 0.036 ng/mL for urine and 0.012 ng/mg for hair by ic-ELISA, and 0.54 ng/mL for urine and 0.03 ng/mg for hair by GICA. Collectively, our study provides a comprehensive foundation for the rapid screening and quantitation of SC derivatives in biological samples.

Synthesis, Analytical Characterization, and Human CB1 Receptor Binding Studies of the Chloroindole Analogues of the Synthetic Cannabinoid MDMB-CHMICA

Synthetic cannabinoids (SCs) are one of the largest groups of new psychoactive substances (NPSs). However, the relationship between their chemical structure and the affinity to human CB1 receptors (hCB1), which mediates their psychotropic activity, is not well understood. Herein, the synthesis of the 2-, 4-, 5-, 6- and 7-chloroindole analogues of the synthetic cannabimimetic MDMB-CHMICA, along with their analytical characterization via ultraviolet–visible (UV/VIS), infrared (IR), nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry, is described. Furthermore, all five derivatives of MDMB-CHMICA were analyzed for their hCB1 binding affinities. Chlorination at position 4 and 5 of the indole core reduced the binding affinity compared to MDMB-CHMICA, while the test compounds chlorinated in positions 2, 6, and 7 largely retained their binding affinities relative to the non-chlorinated parent compound.

Organocatalytic Asymmetric [3 + 2] Cyclization: Enantioselective Synthesis of α-Indolyl Pyrrolo[1,2-a]indole Scaffolds.

A novel asymmetric [3 + 2] cyclization of α-indolyl propargylic alcohols with 3-alkyl-1H-indoles via chiral phosphoric acid catalysis has been established. This strategy allowed the synthesis of chiral α-indolyl pyrrolo[1,2-a]indole derivatives with high yields (up to 91%) and excellent enantioselectivities (up to 99% ee), facilitating both the reaction activity and enantioselectivity by using the solvent of CH3CFCl2. Significantly, this protocol will provide an effective synthetic approach for constructing enantioenriched α-indolyl pyrrolo[1,2-a]indole cores of antimalarial natural product isoborreverine analogues.

Novel Pyrazino[1,2-a]indole-1,3(2H,4H)-dione Derivatives Targeting the Replication of Flaviviridae Viruses: Structural and Mechanistic Insights.

Infections with Flaviviridae viruses, such as hepatitis C (HCV), dengue (DENV), and yellow fever (YFV) viruses, are major public health problems worldwide. In the case of HCV, treatment is associated with drug resistance and high costs, while there is no clinically approved therapy for DENV and YFV. Consequently, there is still a need for new chemotherapies with alternative modes of action. We have previously identified novel 2-hydroxypyrazino[1,2-a]indole-1,3(2H,4H)-diones as metal-chelating inhibitors targeting HCV RNA replication. Here, by utilizing a structure-based approach, we rationally designed a second series of compounds by introducing various substituents at the indole core structure and at the imidic nitrogen, to improve specificity against the RNA-dependent RNA polymerase (RdRp). The resulting derivatives were evaluated for their potency against HCV genotype 1b, DENV2, and YFV-17D using stable replicon cell lines. The most favorable substitution was nitro at position 6 of the indole ring (compound 36), conferring EC50 1.6 μM against HCV 1b and 2.57 μΜ against HCV 1a, with a high selectivity index. Compound 52, carrying the acetohydroxamic acid functionality (-CH2CONHOH) on the imidic nitrogen, and compound 78, the methyl-substituted molecule at the position 4 indolediketopiperazine counterpart, were the most effective against DENV and YFV, respectively. Interestingly, compound 36 had a high genetic barrier to resistance and only one resistance mutation was detected, T181I in NS5B, suggesting that the compound target HCV RdRp is in accordance with our predicted model.

Synthesis and Biological Evaluations of Granulatamide B and its Structural Analogues.

While granulatamides A and B have been previously isolated, their biological activities have been only partially examined. The aim of this study was to synthesize granulatamide B (4b), a tryptamine-derivative naturally occurring in Eunicella coral species, using the well-known procedure of Sun and Fürstner and its 12 structural analogues by modifying the side chain, which differs in length, degree of saturation as well as number and conjugation of double bonds. The prepared library of compounds underwent comprehensive assessment for their biological activities, encompassing antioxidative, antiproliferative, and antibacterial properties, in addition to in vivo toxicity evaluation using a Zebrafish model. Compound 4i, which consists of a retinoic acid moiety, exhibited the strongest scavenging activity against ABTS radicals (IC50 = 36 ± 2 μM). In addition, 4b and some of the analogues (4a, 4c and 4i), mostly containing an unsaturated chain and conjugated double bonds, showed moderate but non-selective activity with certain IC50 values in the range of 20-40 μM. In contrast, the analogue 4l, a derivative of alpha-linolenic acid, was the least toxic towards normal cell lines. Moreover, 4b was also highly active against Gram-positive Bacillus subtilis with an MIC of 125 μM. Nevertheless, both 4b and 4i, known for the best-observed effects, caused remarkable developmental abnormalities in the zebrafish model Danio rerio. Since modification of the side chain did not significantly alter the change in biological activities compared to the parent compound, granulatamide B (4b), the substitution of the indole ring needs to be considered. Our group is currently carrying out new syntheses focusing on the functionalization of the indole core.

Synthesis of Bridged Bicyclic Systems peri‐Annulated to the Indole Ring: Tropane‐Fused Indoles

AbstractYtterbium triflate catalysed domino reaction of (3‐formyl‐4‐indolyl)‐derived donor‐acceptor cyclopropane with primary amines provides a simple approach to an unprecedented tetracyclic skeleton in which tropane system is peri‐annulated with an indole core. This process involves the formation of an imine and its (3+2)‐cross‐cycloaddition with donor‐acceptor cyclopropane moiety, yielding tropane‐fused indole core under mild reaction conditions. These products are of significant interest for pharmacology as potential hybrid molecules with a dual mode of action.

One‐Pot Gold/Acid‐Catalyzed Synthesis of Indolo[1,2‐a]quinolin‐5(6H)‐ones from 1‐(2‐Ethynylphenyl)‐1H‐indoles

AbstractWe present a method for the synthesis of substituted indolo[1,2‐a]quinoline‐5(6H)‐ones starting from 1‐(2‐ethynylphenyl)‐1H‐indoles. The transformation involves gold‐catalyzed oxidation of the triple bond followed by acid‐promoted intramolecular cyclization at the indole C2 position. Demonstrating noteworthy versatility, the reaction tolerates a wide array of substituents on the indole core and proceeds in good to excellent yields (up to 93 %).

Halogenated 9H-Indeno[1,2-b]Pyrazine-2,3-Dicarbonitrile End Groups Based Asymmetric Non-Fullerene Acceptors for Green Solvent-Processable, Additive-Free, and Stable Organic Solar Cells.

Non-fullerene acceptors (NFAs) significantly enhance photovoltaic performance in organic solar cells (OSCs) using halogenated solvents and additives. However, these solvents are environmentally detrimental and unsuitable for industrial-scale production, and the issue of OSCs' poor long-term stability persists. This report introduces eight asymmetric NFAs (IPCnF-BBO-IC2F, IPCnF-BBO-IC2Cl, IPCnCl-BBO-IC2F, and IPCnCl-BBO-IC2Cl, where n = 1 and 2). These NFAs comprise a 12,13-bis(2-butyloctyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2'',3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno-[3,2-b]indole (BBO) core. One end of the core attaches to a mono- or di-halogenated 9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile (IPC) end group (IPC1F, IPC1Cl, IPC2F, or IPC2Cl), while the other end connects to a 2-(5,6-dihalo-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC) end group (IC2F or IC2Cl). The optical and electronic properties of these NFAs can be finely tuned by controlling the number of halogen atoms. Crucially, these NFAs demonstrate excellent compatibility with PM6 even in o-xylene, facilitating the production of additive-free OSCs. The di-halogenated IPC-based NFAs outperform their mono-halogenated counterparts in photovoltaic performance within OSCs. Remarkably, the di-halogenated IPC-based NFAs maintain 94‒98% of their initial PCEs over 2000 h in air without encapsulation, indicating superior long-term device stability. These findings imply that the integration of di-halogenated IPCs in asymmetric NFA design offers a promising route to efficient, stable OSCs manufactured through environmentally friendly processes.

Insights into the metabolism of CH-PIATA - a novel synthetic cannabinoid featuring an acetamide linker.

The recent change from the popular carboxamide to an acetamide (ATA) linker scaffold in synthetic cannabinoid receptor agonists (SCRAs) can be interpreted as an attempt to circumvent legal regulations, setting new analytical challenges. Metabolites of N-cyclohexyl-2-(1-pentyl-1H-indol-3-yl)acetamide: CH-PIATA, the second ATA type SCRA detected in the EU, were investigated in urine and serum samples by LC-HRMS-MS and LC-MS-MS. Two different in vitro models: a pHLM assay and HepG2-cells as well as an in silico prediction by GLORYx freeware assisted in metabolite formation/identification. CH-PIATA was extensively metabolized, leading to metabolites formed primarily by mono- and dihydroxylation. For urine and serum specimens, monohydroxylation at the indole core or the methylene spacer of the acetamide linker (M1.8), carboxylic acid formation at the N-pentyl side chain (M3.1), and degradation of the latter leading to a tentatively identified N-propionic acid metabolite (M5.1) are suggested as reliable markers for substance intake. The N-propionic acid metabolite could not be confirmed in the in vitro assays as it includes multiple consecutive metabolic reactions. Furthermore, CH-PIATA could be detected as parent substance in blood samples, but not in urine. Both in vitro assays and the in silico tool proved suitable for predicting metabolites of CH-PIATA. Considering effort and costs, pHLM incubations seem to be more effective for metabolite prediction in forensic toxicology. The highlighted phase I metabolites serve as reliable urinary targets for confirming CH-PIATA use. The in silico approach is advantageous when reference material is unavailable.

Copper–Catalyzed Construction of the Indole Core: Recent Advancements

AbstractIndoles are one of the most important heterocycles because of their widespread occurrence in bioactive natural products, synthetic drugs and organic materials. Therefore, development of efficient strategies for synthesizing functionalized indoles has been of great importance in organic synthesis. Copper, being a transition metal, meet the goal due to its low toxicity, high catalytic activity and cost‐effectiveness. In this review, we focus on last five year (2019–2023) advancement in copper‐catalyzed annulations for the construction of indole core involving various N‐containing substrates, which include anilines, o‐alkynylanilines, o‐aminophenylpropynols, o‐alkynylnitroarenes, o‐nitrochalcones, azidoalkynes, isonitriles, nitriles, enamines, imines, etc. Mechanistic aspects of the reactions have also been highlighted for better understanding of the reaction pathways.

Polycyclic pyrroloindoline-containing natural products with a unique 3-heptyl-2a,4a-diazapentaleno[1,6-ab]indene core isolated from Alstonia scholaris.

Alscholarine C (1), featuring an unprecedented pyrroloindoline-containing natural product (PiNP) with a 6/5/5/5 tetracyclic carbon skeleton, and four known PiNPs (2-5), namely demethylalstoscholarinine E (2), Nb-demethylechitamine (3), winphylline A (4), and echitamine (5), were isolated from Alstonia scholaris. Compound 1 was characterized by a hexahydropyrrolo[2,3-b] indole (HPI) core fused to a unique 4-heptylimidazolidine motif, forming an unparalleled 3-heptyl-2a,4a-diazapentaleno[1,6-ab]indene ring system. Their structures were established by spectroscopic analysis, quantum-chemical calculated 13C NMR data with DP4+ probability analyses, and ECD calculations and comparison. A plausible biosynthetic pathway of 1 was proposed. Compound 1 exhibited potential anti-inflammatory activity against LPS-stimulated NO production in RAW264.7 cells.

The Discovery of Indole-2-carboxylic Acid Derivatives as Novel HIV-1 Integrase Strand Transfer Inhibitors.

As an important antiviral target, HIV-1 integrase plays a key role in the viral life cycle, and five integrase strand transfer inhibitors (INSTIs) have been approved for the treatment of HIV-1 infections so far. However, similar to other clinically used antiviral drugs, resistance-causing mutations have appeared, which have impaired the efficacy of INSTIs. In the current study, to identify novel integrase inhibitors, a set of molecular docking-based virtual screenings were performed, and indole-2-carboxylic acid was developed as a potent INSTI scaffold. Indole-2-carboxylic acid derivative 3 was proved to effectively inhibit the strand transfer of HIV-1 integrase, and binding conformation analysis showed that the indole core and C2 carboxyl group obviously chelated the two Mg2+ ions within the active site of integrase. Further structural optimizations on compound 3 provided the derivative 20a, which markedly increased the integrase inhibitory effect, with an IC50 value of 0.13 μM. Binding mode analysis revealed that the introduction of a long branch on C3 of the indole core improved the interaction with the hydrophobic cavity near the active site of integrase, indicating that indole-2-carboxylic acid is a promising scaffold for the development of integrase inhibitors.

Electrochemical Oxidation of Indoles to Access Tryptanthrins at Room Temperature

AbstractAn electrooxidative reconstruction of the indole core under ambient conditions is reported, resulting in the construction of tryptanthrins. This electrochemical strategy simplifies molecular skeleton‐hopping by employing commercially available NH‐indole feedstock as the starting materials. Furthermore, the synthetic value of this skeletal reconstruction was demonstrated by divergent further transformations. A preliminary mechanistic investigation involving control experiments and cyclovoltammetric studies showed the indispensability of electricity, as well as the importance of oxygen and TEMPO, thereby revealing a possible reaction pathway.

Acetoxy Group-Directed Regioselective C2 Alkenylation of Indoles via Pd-Ag Bimetallic Catalysis.

Regioselective C-H functionalizations of indoles reported to date with directing groups at C3 mainly rely on functional groups that are linked to the indole via C-C bonds. However, groups that are linked to the indole core by C-X linkages are also attractive due to the possibility of further modifications of the C-X bond. Herein, we report a 3-acetoxy directing group for the regioselective C2 alkenylation of indoles via a C-H activation-based, cross-dehydrogenative, oxidative Heck-type reaction. The reaction is catalyzed by Pd(II) and Ag(I) with stoichiometric Cu(II) as the oxidant and provides the 2-alkenylated indoles in yields of 52-84%. The reaction conditions are compatible with several functional groups at different positions as well as different N-protecting groups or free NH groups on the indole core. With respect to the alkene coupling partners, the reactions are successful with acrylates, vinyl sulfates, and phosphates. Specifically designed experiments, as well as density functional theory (DFT) computational studies, reveal that a heterodinuclear [Pd(μ-OAc)3Ag] bimetallic species is the actual catalyst responsible for the C-H alkenylation. A mechanistic path involving this catalytic species was also found to be favorable over other possible pathways for explaining the observed regioselectivity through DFT studies.

N, N-dimethyltryptamine forms oxygenated metabolites via CYP2D6 - an in vitro investigation

N, N-dimethyltryptamine (DMT) is a psychedelic compound that has shown potential in the treatment of depression. Aside from the primary role of monoamine oxidase A (MAO-A) in DMT metabolism, the metabolic pathways are poorly understood. Increasing this understanding is an essential aspect of ensuring safe and efficacious use of DMT. This work aimed to investigate the cytochrome 450 (CYP) mediated metabolism of DMT by incubating DMT with recombinant human CYP enzymes and human liver microsomes (HLM) followed by analysis using high-resolution mass spectrometry for metabolite identification. DMT was rapidly metabolised by CYP2D6, while stable with all other investigated CYP enzymes. The metabolism of DMT in HLM was reduced after inclusion of harmine and SKF-525A whereas quinidine did not affect the metabolic rate, likely due to MAO-A residues present in HLM. Analysis of the CYP2D6 incubates showed formation of mono-, di- and tri-oxygenated metabolites, likely as a result of hydroxylation on the indole core. More research is needed to investigate the role of this metabolic pathway in vivo and any pharmacological activity of the proposed metabolites. Our findings may impact on safety issues following intake of ayahuasca in slow CYP2D6 metabolizers or with concomitant use of CYP2D6 inhibitors.

Semicarbazides carrying indole core: Synthesis, cytotoxicity evaluation against human breast cancer cell lines, and molecular modeling studies.

In this paper, we report the synthesis and cytotoxicity evaluation of novel indole-carrying semicarbazide derivatives (IS1-IS15). The target molecules were obtained by the reaction of aryl/alkyl isocyanates with 1H-indole-2-carbohydrazide that was in-house synthesized from 1H-indole-2-carboxylic acid. Following structural characterization by 1H NMR, 13C NMR, and HRMS, IS1-IS15 were investigated for their cytotoxic activity against human breast cancer cell lines, MCF-7 and MDA-MB-231. According to the data obtained from the MTT assay, phenyl ring with a lipophilic group at its para-position and alkyl moiety were preferential substituents on the indole-semicarbazide scaffold for antiproliferative activity. The effect of IS12 (N-(4-chloro-3-(trifluoromethyl)phenyl)-2-(1H-indole-2-carbonyl)hydrazine-1-carboxamide), the compound that demonstrated remarkable antiproliferative activity on both cell lines, was also evaluated on the apoptotic pathway. Moreover, the calculation of critical descriptors constituting drug-likeness confirmed the position of the selected compounds in the anticancer drug development process. Finally, molecular docking studies suggested the inhibition of tubulin polymerization as the potential activity mechanism of this class of molecules.

In vitro cannabinoid receptor activity, metabolism, and detection in seized samples of CH-PIATA, a new indole-3-acetamide synthetic cannabinoid.

The rapidly evolving synthetic cannabinoid receptor agonist (SCRA) market poses significant challenges for forensic scientists. Since the enactment of a generic ban in China, a variety of new compounds have emerged capable of evading the legislation by carrying new structural features. One recent example of a SCRA with new linker and head moieties is CH-PIATA (CH-PIACA, CHX-PIATA, CHX-PIACA). CH-PIATA bears an additional methylene spacer in the linker moiety between the indole core and the traditional carbonyl component of the linker. This study describes detections in 2022 of this new SCRA in the United States, Belgium, and Scottish prisons. CH-PIATA was detected once in a seized powder by Belgian customs and 12 times in Scottish prisons in infused papers or resin. The metabolites of CH-PIATA were investigated via in vitro human liver microsome (HLM) incubations and eight metabolites were identified, dominated by oxidative biotransformations. A blood sample from the United States was confirmed to contain a mixture of SCRAs including CH-PIATA via presence of the parent and at least five of the metabolites identified from HLM incubations. Furthermore, this paper evaluates the intrinsic in vitro cannabinoid 1 and 2 (CB1 and CB2) receptor activation potential of CH-PIATA reference material and the powder seized by Belgian customs by means of β-arrestin 2 recruitment assays. Both the reference and the seized powder showed a weak activity at both CB receptors with signs of antagonism found. Based on these results, the expected harm potential of this newly emerging substance remains limited.

Expansion of a Synthesized Library of N-Benzyl Sulfonamides Derived from an Indole Core to Target Pancreatic Cancer.

In an effort to further investigate previously observed activity of indolyl sulfonamides towards pancreatic cancer cell lines, a library of 44 compounds has been synthesized. The biological activity of the compounds has been determined using two different screening assay techniques against 7 pancreatic cancer cell lines and 9 non-pancreatic cancer cell lines. In the first assay, the cytotoxicity of the compounds was evaluated using a traditional (48 hour compound exposure) method. An in silico investigation was conducted to determine if the compounds might be inducing cell death by inhibiting the S100A2-p53 protein-protein interaction. In the second assay, the potential role of the compounds as metabolic inhibitors of ATP production was evaluated using a rapid screening (1-2 hour compound exposure) method. IC50 values of the hit compounds were obtained and four compounds displayed sub-micromolar potency against PANC-1 cells. The investigation has provided several compounds that display selective in vitro activity toward pancreatic cancer that warrant further development.

Hexafluoroisopropanol (HFIP) as a Multifunctional Agent in Gold-Catalyzed Cycloisomerizations and Sequential Transformations

Despite the unique position of gold catalysis in contemporary organic synthesis, this area of research is notorious for requiring activators and/or additives that enable catalysis by generating cationic forms of gold catalysts. Cycloisomerization reactions occupy a significant portion of the gold-catalyzed reaction space, while they represent a diverse family of reactions that are frequently utilized in synthesis. Herein, hexafluoroisopropanol (HFIP) is shown to be a uniquely simple tool for gold-catalyzed cycloisomerizations, rendering the use of external activators obsolete and leading to highly active catalytic systems with ppm levels of catalyst loading in certain cases. HFIP assumes a dual role as a solvent and an activator, operating via the dynamic activation of the Au–Cl bond through hydrogen bonding, which initiates the catalytic cycle. This special mode of catalysis can enable efficient and scalable cyclization reactions of propargylamides and ynoic acids with simple [AuCl(L)] complexes. A thorough screening of ancillary ligands and counter anions has been performed, establishing this methodology as an alternative to elaborate ligand/catalyst design and to the use of activators. Additionally, this concept is applied in C–C bond-forming cycloisomerization reactions leading to 2H-chromenes and to the design of catalytic systems for sequential or one-pot transformations leading to activated ketoesters, a functionalized N-heterocyclic carbene (NHC) precursor salt, and a compound bearing the bioactive indole core, among others. Importantly, through mechanistic investigations, including a “snapshot” of the species of interest in the solid state, we were able to unambiguously detect the key H-bonding interaction between HFIP and the gold catalyst, shedding light on the intermolecular mode of activation that enables catalysis. In the cases examined herein, HFIP is not only an excellent solvent but also a potent activator and a valuable synthetic handle when incorporated into functional groups of products.

Efficient synthesis of 5-aryl-5H-pyrido[2′,1′:2,3]imidazo[4,5-b]indoles by double C[sbnd]N coupling reactions using HKUST-1 as recyclable heterogeneous catalyst under air

Fluorescent active small compounds containing 5H-pyrido[2′,1:2,3]imidazo[4,5-b]indole core could be successfully synthesized by double CN coupling reaction from 3-iodo-2-(2-bromophenyl)imidazo[1,2-a]pyridine with different amines in high yields under air atmosphere. HKUST-1 was found to be the most suitable heterogeneous catalyst for this transformation. Interestingly, HKUST-1 catalyst (∼12 mol% Cu loading for each reaction) showed highly active, robust, and recyclable properties with the tolerance of broad substrate scope. Remarkably, the mechanism for the CN coupling reaction undergoing Cu1+/ Cu3+ catalytic cycle was proposed from several observed important evidence. Cu2+ sites in the node of HKUST-1 structure could be reduced to Cu1+ which initiated the formation of radical amine species. This method may give potential applications in the pharmaceutical and fine chemical industries.