Synthesis and Preliminary Biological Evaluation of Indol-3-yl-oxoacetamides as Potent Cannabinoid Receptor Type 2 Ligands

A small series of indol-3-yl-oxoacetamides was synthesized starting from the literature known N-(adamantan-1-yl)-2-(5-(furan-2-yl)-1-pentyl-1H-indol-3-yl)-2-oxoacetamide (5) by substituting the 1-pentyl-1H-indole subunit. Our preliminary biological evaluation showed that the fluorinated derivative 8 is a potent and selective CB₂ ligand with K_i = 6.2 nM.

Synthesis of (2-mercaptoacetyl)-L-[2-14 C]tryptophan as a selective metallo-β-lactamase inhibitor via [2-14 C]indole based on chiral pool strategy

Metallo-beta-lactamase enzymes make bacteria resistant to a broad range of commonly used beta-lactam antibiotics. Several thiol derivatives of L-amino acids have been shown their inhibitory effects against the metallo-β-lactamase IMP-1. In this study, (2-mercaptoacetyl)-L-tryptophan as a new inhibitor of metallo-β-lactamases labeled with carbon-14 in the 2-position of the indole ring was prepared from [2-¹⁴ C]indole as a key synthetic intermediate based on chiral pool strategy. The overall synthesis was performed in 10 steps with the overall radiochemical yield 3.6% on the basis of the barium [¹⁴ C]carbonate as a starting material.

Crystal structure of vilazodone hydro-chloride methanol monosolvate

In the title compound, C26H28N5O2+·Cl-·CH3OH {systematic name: 4-(2-carbamoyl-1-benzo-furan-5-yl)-1-[4-(5-cyano-1H-indol-3-yl)but-yl]piperazin-1-ium chloride methanol monosolvate}, the protonated piperazine ring adopts a chair conformation. The indole ring plane is nearly perpendicular to the benzo-furan ring system, with a dihedral angle of 85.77 (2)°. In the crystal, the organic cations, Cl- anions and methanol solvent mol-ecules are linked by classical N-H⋯O and N-H⋯Cl hydrogen bonds, and weak C-H⋯O and C-H⋯π inter-actions into a three-dimensional supra-molecular architecture.

Enantioselective Syntheses of (-)-Alloyohimbane and (-)-Yohimbane by an Efficient Enzymatic Desymmetrization Process

Enantioselective syntheses of (-)-alloyohimbane and (-)-yohimbane was accomplished in a convergent manner. The key step involved a modified mild protocol for the enantioselective enzymatic desymmetrization of meso-diacetate. The protocol provided convenient access to an optically active monoacetate in multi-gram scale in high enantiomeric purity. This monoacetate was converted to (-)-alloyohimbane. Reductive amination of the derived aldehyde causes the isomerization leading to the trans-product and allows the synthesis of (-)-yohimbane.

Gut Bacteria and Hydrogen Sulfide: The New Old Players in Circulatory System Homeostasis

Accumulating evidence suggests that gut bacteria play a role in homeostasis of the circulatory system in mammals. First, gut bacteria may affect the nervous control of the circulatory system via the sensory fibres of the enteric nervous system. Second, gut bacteria-derived metabolites may cross the gut-blood barrier and target blood vessels, the heart and other organs involved in the regulation of the circulatory system. A number of studies have shown that hydrogen sulfide (H₂S) is an important biological mediator in the circulatory system. Thus far, research has focused on the effects of H₂S enzymatically produced by cardiovascular tissues. However, some recent evidence indicates that H₂S released in the colon may also contribute to the control of arterial blood pressure. Incidentally, sulfate-reducing bacteria are ubiquitous in mammalian colon, and H₂S is just one among a number of molecules produced by the gut flora. Other gut bacteria-derived compounds that may affect the circulatory system include methane, nitric oxide, carbon monoxide, trimethylamine or indole. In this paper, we review studies that imply a role of gut microbiota and their metabolites, such as H₂S, in circulatory system homeostasis.

Chiral N,N'-Dioxide-Scandium(III) Complex-Catalyzed Asymmetric Friedel-Crafts Alkylation Reaction of ortho-Hydroxybenzyl Alcohols with C3-Substituted N-Protected Indoles

The first Lewis acid catalyzed asymmetric Friedel-Crafts alkylation reaction of ortho-hydroxybenzyl alcohols with C3-substituted indoles is described. A chiral N,N'-dioxide Sc(OTf)₃ complex served not only to promote formation of ortho-quinone methides (o-QMs) in situ but also induced the asymmetry of the reaction. This methodology enables a novel activation of ortho-hydroxybenzyl alcohols, thus affording the desired chiral diarylindol-2-ylmethanes in up to 99 % yield and 99 % ee. A range of functional groups were also tolerated under the mild reaction conditions. Moreover, this strategy gives concise access to enantioenriched indole-fused benzoxocines.

Evaluation of PVP/Au Nanocomposite Fibers as Heterogeneous Catalysts in Indole Synthesis

Electrospun nanocomposite fibers consisting of crosslinked polyvinylpyrrolidone (PVP) chains and gold nanoparticles (Au NPs) were fabricated, starting from highly stable PVP/Au NP colloidal solutions with different NP loadings, followed by thermal treatment. Information on the morphological characteristics of the fibers and of the embedded Au NPs was obtained by electron microscopy. Cylindrical, bead-free fibers were visualized by Scanning Electron Microscopy (SEM) while Transmission Electron Microscopy (TEM) and Energy Diffraction X-ray (EDX) analysis supported the presence of Au NPs within the fibers and gave information on their morphologies and average diameters. These materials were briefly evaluated as heterogeneous catalytic supports for the gold-catalyzed intramolecular cyclisation of 2‑(phenylethynyl)aniline to form 2-phenyl-1H-indole. The performance of the gold catalyst was strongly dependent on the Au NP size, with the system containing the smallest Au NPs being the more effective. Moreover, a slight drop of their catalytic efficiency was observed after three consecutive reaction runs, which was attributed to morphological changes as a consequence of fiber merging.

Palladium(0)-Catalyzed Intermolecular Allylic Dearomatization of Indoles by a Formal [4+2] Cycloaddition Reaction

Bridged indoline derivatives were synthesized by an intermolecular Pd-catalyzed allylic dearomatization reaction of substituted indoles. The reaction between indoles and allyl carbonates bearing a nucleophilic alcohol side-chain proceeds in a cascade fashion, providing bridged indolines in excellent enantioselectivity.

Weak inter-actions in the crystal structures of two indole derivatives

We describe the syntheses and crystal structures of two indole derivatives, namely a second monoclinic polymorph of ethyl 5-chloro-1H-indole-2-carboxyl-ate C11H10ClNO2, (I), and ethyl 5-chloro-3-iodo-1H-indole-2-carboxyl-ate, C11H9ClINO2, (II). In their crystal structures, both compounds form inversion dimers linked by pairs of N-H⋯O hydrogen bonds, which generate R 2 (2)(10) loops. The dimers are linked into double chains in (I) and sheets in (II) by a variety of weak inter-actions, including π-π stacking, C-I⋯π, C-Cl-π inter-actions and I⋯Cl halogen bonds.

Formation of Volatile Tea Constituent Indole During the Oolong Tea Manufacturing Process

Indole is a characteristic volatile constituent in oolong tea. Our previous study indicated that indole was mostly accumulated at the turn over stage of oolong tea manufacturing process. However, formation of indole in tea leaves remains unknown. In this study, one tryptophan synthase α-subunit (TSA) and three tryptophan synthase β-subunits (TSBs) from tea leaves were isolated, cloned, sequenced, and functionally characterized. Combination of CsTSA and CsTSB2 recombinant protein produced in Escherichia coli exhibited the ability of transformation from indole-3-glycerol phosphate to indole. CsTSB2 was highly expressed during the turn over process of oolong tea. Continuous mechanical damage, simulating the turn over process, significantly enhanced the expression level of CsTSB2 and amount of indole. These suggested that accumulation of indole in oolong tea was due to the activation of CsTSB2 by continuous wounding stress from the turn over process. Black teas contain much less indole, although wounding stress is also involved in the manufacturing process. Stable isotope labeling indicated that tea leaf cell disruption from the rolling process of black tea did not lead to the conversion of indole, but terminated the synthesis of indole. Our study provided evidence concerning formation of indole in tea leaves for the first time.

Chlamydia trachomatis Genital Tract Infections: When Host Immune Response and the Microbiome Collide

Genital infections with Chlamydia trachomatis continue to be a major health problem worldwide. While some individuals clear their infection (presumed to be the result of an effective Th1/interferon-γ response), others develop chronic infections and some are prone to repeat infections. In females in particular, chronic asymptomatic infections are common and can lead to pelvic inflammatory disease and infertility. Recent studies suggest that the genital tract microbiota could be a significant factor and explain person-to-person variation in C. trachomatis infections. One hypothesis suggests that C. trachomatis can use its trpBA genes to rescue tryptophan from indole, which is a product of anaerobic members of the genital tract microbiota. Women with particular microbiota types, such as seen in bacterial vaginosis, have increased numbers of anaerobes, and this would enable the chlamydia in these individuals to overcome the host's interferon-γ attempts to eliminate it, resulting in more repeat and/or chronic infections.

Ultrahigh-Performance Liquid Chromatography (UHPLC)-Tandem Mass Spectrometry (MS/MS) Quantification of Nine Target Indoles in Sparkling Wines

An ultrahigh-performance liquid chromatography (UHPLC)-tandem mass spectrometry (MS/MS) method was developed for the simultaneous determination of nine target indoles in sparkling wines. The proposed method requires minimal sample pretreatment, and its performance parameters (accuracy, repeatability, LOD, and matrix effect) indicate that it is suitable for routine analysis. Four indoles were found at detectable levels in commercial Cava samples: 5-methoxytryptophol (5MTL), tryptophan (TRP), tryptophan ethyl ester (TEE), and N-acetylserotonin (NSER). Two of them, NSER and 5MTL, are reported here for the first time in sparkling wines, with values of 0.3-2 and 0.29-29.2 μg/L, respectively. In the same samples, the contents of melatonin (MEL), serotonin (SER), 5-hydroxytryptophan (5-OHTRP), 5-hydroxyindole-3-acetic acid (5OHIA), and 5-methoxy-3-indoleacetic acid (5MIA) were all below the corresponding limits of detection.

Different N-H⋯π inter-actions in two indole derivatives

We describe the syntheses and crystal structures of two indole derivatives, namely 6-isopropyl-3-(2-nitro-1-phenyl-eth-yl)-1H-indole, C19H20N2O2, (I), and 2-(4-meth-oxy-phen-yl)-3-(2-nitro-1-phenyl-eth-yl)-1H-indole, C23H20N2O3, (II); the latter crystallizes with two mol-ecules (A and B) with similar conformations (r.m.s. overlay fit = 0.139 Å) in the asymmetric unit. Despite the presence of O atoms as potential acceptors for classical hydrogen bonds, the dominant inter-molecular inter-action in each crystal is an N-H⋯π bond, which generates chains in (I) and A+A and B+B inversion dimers in (II). A different aromatic ring acts as the acceptor in each case. The packing is consolidated by C-H⋯π inter-actions in each case but aromatic π-π stacking inter-actions are absent.

The microbiota-derived metabolite indole decreases mucosal inflammation and injury in a murine model of NSAID enteropathy

Non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most frequently used classes of medications in the world. Unfortunately, NSAIDs induce an enteropathy associated with high morbidity and mortality. Although the pathophysiology of this condition involves the interaction of the gut epithelium, microbiota, and NSAIDs, the precise mechanisms by which microbiota influence NSAID enteropathy are unclear. One possible mechanism is that the microbiota may attenuate the severity of disease by specific metabolite-mediated regulation of host inflammation and injury. The microbiota-derived tryptophan-metabolite indole is abundant in the healthy mammalian gut and positively influences intestinal health. We thus examined the effects of indole administration on NSAID enteropathy. Mice (n = 5 per group) were treated once daily for 7 days with an NSAID (indomethacin; 5 mg/kg), indole (20 mg/kg), indomethacin plus indole, or vehicle only (control). Outcomes compared among groups included: microscopic pathology; fecal calprotectin concentration; proportion of neutrophils in the spleen and mesenteric lymph nodes; fecal microbiota composition and diversity; small intestinal mucosal transcriptome; and, fecal tryptophan metabolites. Co-administration of indole with indomethacin: significantly reduced mucosal pathology scores, fecal calprotectin concentrations, and neutrophilic infiltration of the spleen and mesenteric lymph nodes induced by indomethacin; modulated NSAID-induced perturbation of the microbiota, fecal metabolites, and inferred metagenome; and, abrogated a pro-inflammatory gene expression profile in the small intestinal mucosa induced by indomethacin. The microbiota-derived metabolite indole attenuated multiple deleterious effects of NSAID enteropathy, including modulating inflammation mediated by innate immune responses and altering indomethacin-induced shift of the microbiota.

Concentrations of thiocyanate and goitrin in human plasma, their precursor concentrations in brassica vegetables, and associated potential risk for hypothyroidism

Brassica vegetables are common components of the diet and have beneficial as well as potentially adverse health effects. Following enzymatic breakdown, some glucosinolates in brassica vegetables produce sulforaphane, phenethyl, and indolylic isothiocyanates that possess anticarcinogenic activity. In contrast, progoitrin and indolylic glucosinolates degrade to goitrin and thiocyanate, respectively, and may decrease thyroid hormone production. Radioiodine uptake to the thyroid is inhibited by 194 μmol of goitrin, but not by 77 μmol of goitrin. Collards, Brussels sprouts, and some Russian kale (Brassica napus) contain sufficient goitrin to potentially decrease iodine uptake by the thyroid. However, turnip tops, commercial broccoli, broccoli rabe, and kale belonging to Brassica oleracae contain less than 10 μmol of goitrin per 100-g serving and can be considered of minimal risk. Using sulforaphane plasma levels following glucoraphanin ingestion as a surrogate for thiocyanate plasma concentrations after indole glucosinolate ingestion, the maximum thiocyanate contribution from indole glucosinolate degradation is estimated to be 10 μM, which is significantly lower than background plasma thiocyanate concentrations (40-69 μM). Thiocyanate generated from consumption of indole glucosinolate can be assumed to have minimal adverse risks for thyroid health.

Crystal structure of 3-{5-[3-(4-fluoro-phen-yl)-1-isopropyl-1H-indol-2-yl]-1H-pyrazol-1-yl}indolin-2-one ethanol monosolvate

The title indolin-2-one compound, C28H23FN4O·C2H6O, crystallizes as a 1:1 ethanol solvate. The ethanol mol-ecule is disordered over two positions with refined site occupancies of 0.560 (14) and 0.440 (14). The pyrazole ring makes dihedral angles of 84.16 (10) and 85.33 (9)° with the indolin-2-one and indole rings, respectively, whereas the dihedral angle between indolin-2-one and indole rings is 57.30 (7)°. In the crystal, the components are linked by N-H⋯O and O-H⋯O hydrogen bonds, forming an inversion mol-ecule-solvate 2:2 dimer with R 4 (4)(12) ring motifs. The crystal structure is consolidated by π-π inter-action between pairs of inversion-related indolin-2-one rings [inter-planar spacing = 3.599 (2) Å].

Crystal structures of four indole derivatives with a phenyl substituent at the 2-position and a carbonyl group at the 3-position: the C(6) N-H⋯O chain remains the same, but the weak reinforcing inter-actions are different

We describe the crystal structures of four indole derivatives with a phenyl ring at the 2-position and different carbonyl-linked substituents at the 3-position, namely 1-(2-phenyl-1H-indol-3-yl)ethanone, C16H13NO, (I), 2-cyclo-hexyl-1-(2-phenyl-1H-indol-3-yl)ethanone, C22H23NO, (II), 3,3-dimethyl-1-(2-phenyl-1H-indol-3-yl)butan-1-one, C20H21NO, (III), and 3-benzoyl-2-phenyl-1H-indole, C21H15NO, (IV). In each case, the carbonyl-group O atom lies close to the indole-ring plane and points towards the benzene ring. The dihedral angles between the indole ring system and 2-phenyl ring for these structures are clustered in a narrow range around 65°. The dominant inter-molecular inter-action in each case is an N-H⋯O hydrogen bond, which generates a C(6) chain, although each structure possesses a different crystal symmetry. The C(6) chains are consolidated by different (C-H⋯O, C-H⋯π and π-π stacking) weak inter-actions, with little consistency between the structures.

Novel indole-based melatonin analogues substituted with triazole, thiadiazole and carbothioamides: studies on their antioxidant, chemopreventive and cytotoxic activities

Melatonin (MLT) is a well-known free-radical scavenger, involving in the prevention of cellular damage that can lead to cancer, ageing and a variety of neurodegenerative diseases. Research on MLT-related compounds has been required to optimise the maximum pharmaceutical activity with the lowest side effects. In our ongoing research, we have synthesized new indole-based MLT analogues as potential antioxidant agents by modifying the MLT molecule. In this study, we build on previous findings, through the synthesis, characterization and in vitro antioxidant profiling of a series of new indole-based MLT analogues which possess triazole, thiadiazole and carbothioamides on the third position on the indole ring. In vitro antioxidant activity was investigated by evaluating their reducing effect against oxidation of a redox sensitive fluorescent probe and their radical scavenging activity was assessed via the DPPH assay. In addition, in vitro cytotoxic effects of newly synthesized compounds were investigated in CHO-K1 cells using the MTT assay.

Crystal structure of 2-[2-phenyl-1-(phenyl-sulfon-yl)eth-yl]-1-phenyl-sulfonyl-1H-indole

In the title compound, C28H23NO4S2, the indole ring system (r.m.s. deviation = 0.007 Å) subtends dihedral angles of 78.69 (13) and 38.97 (13)° with the planes of the N- and C-bonded sulfonyl-benzene rings, respectively, and these two benzene rings are inclined to each other at an angle of 65.45 (16)°. The methyl-ene-linked phenyl ring is twisted at an angle of 81.80 (13)° from the indole ring. The mol-ecular structure features two short intra-molecular C-H⋯O contacts, which both generate S(6) rings. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds and C-H⋯π inter-actions, generating a three-dimensional network.

Crystal structure of 4-({(1E,2E)-3-[3-(4-fluoro-phen-yl)-1-isopropyl-1H-indol-2-yl]allyl-idene}amino)-1H-1,2,4-triazole-5(4H)-thione

The asymmetric unit of the titled compound, C22H20FN5S, comprises two independent mol-ecules (A and B), both of which have a trans conformation with respect to the methene C=C [1.342 (2) and 1.335 (2) Å] and the acyclic N=C [1.283 (2) and 1.281 (2) Å] bonds. In mol-ecule A, the triazole ring makes dihedral angles of 55.01 (12) and 18.17 (9)° with the benzene and indole rings, respectively. The corresponding dihedral angles for mol-ecule B are 54.54 (11) and 14.60 (10)°, respectively. In the crystal, mol-ecules are consolidated into -A-B-A-B- chains along [010] via N-H⋯N hydrogen bonds. The chains are further linked into layers parallel to the ac plane via π-π inter-actions involving inversion-related triazole rings [centroid-centroid distances = 3.3436 (11)-3.4792 (13) Å].

Role of the Gut Microbiome in Uremia: A Potential Therapeutic Target

Also known as the "second human genome," the gut microbiome plays important roles in both the maintenance of health and the pathogenesis of disease. The symbiotic relationship between host and microbiome is disturbed due to the proliferation of dysbiotic bacteria in patients with chronic kidney disease (CKD). Fermentation of protein and amino acids by gut bacteria generates excess amounts of potentially toxic compounds such as ammonia, amines, thiols, phenols, and indoles, but the generation of short-chain fatty acids is reduced. Impaired intestinal barrier function in patients with CKD permits translocation of gut-derived uremic toxins into the systemic circulation, contributing to the progression of CKD, cardiovascular disease, insulin resistance, and protein-energy wasting. The field of microbiome research is still nascent, but is evolving rapidly. Establishing symbiosis to treat uremic syndrome is a novel concept, but if proved effective, it will have a significant impact on the management of patients with CKD.

Crystal structure of 3-(2-nitro-phen-yl)-1-(1-phenyl-sulfonyl-1H-indol-3-yl)propan-1-one

In the title compound, C₂₃H₁₈N₂O₅S, the phenyl and benzene rings subtend dihedral angles of 78.18 (10) and 30.18 (9)°, respectively, with the indole ring system (r.m.s. deviation = 0.022 Å). The crystal structure features weak C—H⋯O and C—H⋯π inter­actions, which link the mol­ecules into a three-dimensional network.

Crystal structure of 4-({(1E,2E)-3-[3-(4-fluoro-phen-yl)-1-isopropyl-1H-indol-2-yl]allyl-idene}amino)-5-methyl-1H-1,2,4-triazole-5(4H)-thione

The title compound, C23H22FN5S, exists in a trans conformation with respect to the methene C=C and the acyclic N=C bonds. The 1,2,4-triazole-5(4H)-thione ring makes dihedral angles of 88.66 (9) and 84.51 (10)°, respectively, with the indole and benzene rings. In the crystal, mol-ecules are linked by pairs of N-H⋯S hydrogen bonds, forming inversion dimers with an R 2 (2)(8) ring motif. The dimers are linked via C-H⋯π inter-actions, forming chains along [1-10]. The chains are linked via π-π inter-actions involving inversion-related triazole rings [centroid-centroid distance = 3.4340 (13) Å], forming layers parallel to the ab plane.

Crystal structure of 3'-(1H-indole-3-carbon-yl)-1'-methyl-2-oxo-4'-(4-oxo-4H-chromen-3-yl)spiro-[indoline-3,2'-pyrrolidine]-3'-carbo-nitrile

In the title compound, C₃₁H₂₂N₄O₄, the pyrrolidine ring adopts a twist conformation on the N—CH₂ bond. The indolin-2-one and the 1H-indole rings are nearly planar (r.m.s. deviations = 0.06 and 0.011 Å, respectively) and are inclined to one another by 34.19 (9)°. The chromene ring system is also nearly planar (r.m.s. deviation = 0.029 Å). It is almost normal to the 1H-indole ring system, with a dihedral angle of 88.71 (8)°, and is inclined to the indolin-2-one ring system by 72.76 (8)°. In the crystal, mol­ecules are linked via N—H⋯O hydrogen bonds, forming slabs parallel to (10-1). The slabs are linked by C—H⋯O hydrogen bonds, forming a three-dimensional structure.

Synthesis of quinoline-3-carboxylates by a Rh(II)-catalyzed cyclopropanation-ring expansion reaction of indoles with halodiazoacetates

In this letter, we report a novel synthesis of ethyl quinoline-3-carboxylates from reactions between a series of indoles and halodiazoacetates. The formation of the quinoline structure is probably the result of a cyclopropanation at the 2- and 3-positions of the indole followed by ring-opening of the cyclopropane and elimination of H–X.

Crystal structure of dimethyl 3,3'-[(4-fluoro-phen-yl)methyl-ene]bis-(1H-indole-2-carboxyl-ate)

In the title compound, the two indole ring systems are approximately perpendicular to one another, with a dihedral angle between their planes of 84.0 (5)°.

In the title compound, C₂₇H₂₁FN₂O₄, the mean planes of the indole ring systems (r.m.s. deviations = 0.0263 and 0.0160 Å) are approximately perpendic­ular to one another, making a dihedral angle of 84.0 (5)°; the fluoro­benzene ring is twisted with respect to the mean planes of the two indole ring systems at 89.5 (5) and 84.6 (3)°. In the crystal, pairs of N—H⋯O hydrogen bonds link the mol­ecules into inversion dimers, which are further linked by N—H⋯O hydrogen bonds into supra­molecular chains propagated along the b-axis direction. Weak C—H⋯π inter­actions are observed between neighbouring chains.

Design, Synthesis, and Biological Evaluation of Indole Biphenylcarboxylic Acids as PPARγ Antagonists

The thiazolidinediones (TZD) typified by rosiglitazone are the only approved therapeutics targeting PPARγ for the treatment of type-2 diabetes (T2DM). Unfortunately, despite robust insulin sensitizing properties, they are accompanied by a number of severe side effects including congestive heart failure, edema, weight gain, and osteoporosis. We recently identified PPARγ antagonists that bind reversibly with high affinity but do not induce transactivation of the receptor, yet they act as insulin sensitizers in mouse models of diabetes (SR1664).1 This Letter details our synthetic exploration around this novel series of PPARγ antagonists based on an N-biphenylmethylindole scaffold. Structure-activity relationship studies led to the identification of compound 46 as a high affinity PPARγ antagonist that exhibits antidiabetic properties following oral administration in diet-induced obese mice.

Indole - the scent of a healthy 'inner soil'

Tryptophan is an essential amino acid with an indole nucleus. Humans cannot produce this amino acid themselves, but must obtain it through their diet. Much attention is currently paid to the wide physiological and clinical implications of the tryptophan-derived substances, serotonin and kynurenines, generated by human enzymes following the intestinal absorption of tryptophan. However, even before being absorbed, several microbial metabolites of tryptophan are formed, mainly from ‘malabsorbed’ (incompletely digested) proteins within the colon. The normal smell of human faeces is largely due to indole, one of the major metabolites. Recent studies indicate that this foul-smelling substance is also of utmost importance for our health.

Does Enzymatic Hydrolysis of Glycosidically Bound Volatile Compounds Really Contribute to the Formation of Volatile Compounds During the Oolong Tea Manufacturing Process?

It was generally thought that aroma of oolong tea resulted from hydrolysis of glycosidically bound volatiles (GBVs). In this study, most GBVs showed no reduction during the oolong tea manufacturing process. β-Glycosidases either at protein or gene level were not activated during the manufacturing process. Subcellular localization of β-primeverosidase provided evidence that β-primeverosidase was located in the leaf cell wall. The cell wall remained intact during the enzyme-active manufacturing process. After the leaf cell disruption, GBV content was reduced. These findings reveal that, during the enzyme-active process of oolong tea, nondisruption of the leaf cell walls resulted in impossibility of interaction of GBVs and β-glycosidases. Indole, jasmine lactone, and trans-nerolidol were characteristic volatiles produced from the manufacturing process. Interestingly, the contents of the three volatiles was reduced after the leaf cell disruption, suggesting that mechanical damage with the cell disruption, which is similar to black tea manufacturing, did not induce accumulation of the three volatiles. In addition, 11 volatiles with flavor dilution factor ≥4(4) were identified as relatively potent odorants in the oolong tea. These results suggest that enzymatic hydrolysis of GBVs was not involved in the formation of volatiles of oolong tea, and some characteristic volatiles with potent odorants were produced from the manufacturing process.

Synthesis of bis(indolyl)methanes Catalyzed by Triethylborane

Triethylborane (TEB) was found to be a mild, efficient, and acid catalyst in electrophilic substitution reaction of indoles with aldehydes compounds to afford the corresponding bis(indolyl)methanes. Vibrindole A (5) and bis(indolyl)methanes derivatives 16 and 18 were synthesized using this methodology. Compound 16 is an intermediary in the synthesis of the natural bisindoles arsindoline B (2) and streptindole (6). The structure of vibrindole A (5) was unequivocally confirmed by a single crystal X-ray diffraction analysis.

A Practical, Multi-gram Synthesis of (±)-Herbindole A, (±)-Herbindole B, and (±)-Herbindole C from a Common Intermediate via 6,7-Indole Aryne Cycloaddition and Pd(0)-Catalyzed Cross-Coupling Reactions

A practical, multi-gram 10-step synthesis of racemic herbindole A, B, and C from a common intermediate is described. The key step features a remarkably regioselective C-7 metal-halogen exchange and elimination from a Bartoli-generated N-t-butyldimethylsilyl-4,6,7-tribromo-5-methylindole scaffold to afford the 6,7-indole aryne. Cycloaddition with cyclopentadiene, oxidative cleavage, and Fujimoto reduction gave a common intermediate from which all three herbindoles were readily derived. A final Pd(0)-catalyzed Negishi and Stille cross-coupling reaction at the C-4 bromide afforded each of the herbindoles on a multigram scale.

Electrophilic Carbonyl Activation: Competing Condensative Cyclizations of Tryptamine Derivatives

A series of tryptamine derived bisindole substrates were subject to electrophilic activation of the functional grouping at their alpha-nitrogen in the form of iminium ions to enable cyclization onto the sterically hindered indole substructure. Our observations regarding divergent cyclization outcomes using electronically distinct bisindole substrates are described. Surprising preference for Friedel-Crafts alkylation reaction and evidence for an intriguing reversible spirocyclization are discussed.

Crystal structure of methyl (2Z)-3-(4-chloro-phen-yl)-2-[(3-methyl-1H-indol-1-yl)meth-yl]prop-2-enoate

In the title indole derivative, C20H18ClNO2, the chloro-phenyl ring is almost perpendicular to the indole moiety, making a dihedral angle of 87.6 (1)°. The mol-ecular packing is stabilized by C-H⋯π inter-actions, which form a C(9) chain motif along [10-1]. In addition, there are weak π-π inter-actions [centroid-centroid distance 3.851 (1) Å] between the chains, involving inversion-related chloro-phenyl rings.

Crystal structures of four indole derivatives as possible cannabinoid allosteric antagonists

The crystal structures of four indole derivatives with various substituents at the 2-, 3- and 5-positions of the ring system are described, namely, ethyl 3-(5-chloro-2-phenyl-1H-indol-3-yl)-3-phenyl-propano-ate, C25H22ClNO2, (I), 2-bromo-3-(2-nitro-1-phenyl-eth-yl)-1H-indole, C16H13BrN2O2, (II), 5-meth-oxy-3-(2-nitro-1-phenyl-eth-yl)-2-phenyl-1H-indole, C23H20N2O3, (III), and 5-chloro-3-(2-nitro-1-phenyl-eth-yl)-2-phenyl-1H-indole, C22H17ClN2O2, (IV). The dominant inter-molecular inter-action in each case is an N-H⋯O hydrogen bond, which generates either chains or inversion dimers. Weak C-H⋯O, C-H⋯π and π-π inter-actions occur in these structures but there is no consistent pattern amongst them. Two of these compounds act as modest enhancers of CB1 cannabanoid signalling and two are inactive.

Plant strengtheners enhance parasitoid attraction to herbivore-damaged cotton via qualitative and quantitative changes in induced volatiles

BACKGROUND

Herbivore-damaged plants release a blend of volatile organic compounds (VOCs) that differs from undamaged plants. These induced changes are known to attract the natural enemies of the herbivores and therefore are expected to be important determinants of the effectiveness of biological control in agriculture. One way of boosting this phenomenon is the application of plant strengtheners, which has been shown to enhance parasitoid attraction in maize. It is unclear whether this is also the case for other important crops.

RESULTS

The plant strengtheners BTH [benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester] and laminarin were applied to cotton plants, and the effects on volatile releases and the attraction of three hymenopteran parasitoids, Cotesia marginiventris, Campoletis sonorensis and Microplitis rufiventris, were studied. After treated and untreated plants were induced by real or simulated caterpillar feeding, it was found that BTH treatment increased the attraction of the parasitoids, whereas laminarin had no significant effect. BTH treatment selectively increased the release of two homoterpenes and reduced the emission of indole, the latter of which had been shown to interfere with parasitoid attraction in earlier studies. Canonical variate analyses of the data show that the parasitoid responses were dependent on the quality rather than the quantity of volatile emission in this tritrophic interaction.

CONCLUSION

Overall, these results strengthen the emerging paradigm that induction of plant defences with chemical elicitors such as BTH could provide a sustainable and environmentally friendly strategy for biological control of pests by enhancing the attractiveness of cultivated plants to natural enemies of insect herbivores.

Crystal structure of rac-(3a'R,9a'R)-3a'-(indol-3-yl)-1',2',3',3a',4',9a'-hexa-hydro-spiro-[cyclo-pentane-1,9'-penta-leno[1,2-b]indole] p-xylene hemisolvate

The title compound, C26H26N2·0.5C8H10, is the first reported characterized 2:2 product from acid-catalyzed condensation of indole with cyclo-penta-none and no other 2:2 products were observed. Recrystallization from p-xylene gave the title hemisolvate with the p-xylene mol-ecule located about an inversion center. The terminal penta-lene ring is envelope-flap disordered at the C atom farthest from the skeletal indole unit, with a refined occupancy ratio of 0.819 (4):0.181 (4). The major component has this C atom bent away from the spiro-fused cyclo-pentane ring. In the crystal, mol-ecules are connected by N-H⋯π inter-actions, forming chains along [100], and N-H⋯π and C-H⋯π inter-actions, forming chains along [001], which results in the formation of slabs parallel to (010).

Indole-based hydrazide-hydrazones and 4-thiazolidinones: synthesis and evaluation as antitubercular and anticancer agents

A new series of indolylhydrazones (6) and indole-based 4-thiazolidinones (7, 8) have been designed, synthesized and screened for in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv. 4-Thiazolidinone derivatives 7g-7j, 8g, 8h and 8j displayed notable antituberculosis (anti-TB) activity showing 99% inhibition at MIC values ranging from 6.25 to 25.0 µg/ml. Compounds 7g, 7h, 7i, 8h and 8j demonstrated anti-TB activity at concentrations 10-fold lower than those cytotoxic for the mammalian cell lines. The indolylhydrazone derivative 6b has also been evaluated for antiproliferative activity against human cancer cell lines at the National Cancer Institute (USA). Compound 6b showed an interesting anticancer profile against different human tumor-derived cell lines at sub-micromolar concentrations with obvious selectivity toward colon cancer cell line COLO 205.

Crystal structure of ethyl 1',1''-dimethyl-2'',3-dioxo-3H-di-spiro-[benzo[b]thio-phene-2,3'-pyrrolidine-2',3''-indoline]-4'-carboxyl-ate

In the title compound, C23H22N2O4S, the pyrrolidine ring has an envelope conformation with the spiro C atom, shared with the indoline ring system, as the flap. The mean planes of the benzo-thio-phene and indoline ring systems are inclined to the mean plane of the pyrrolidine ring by 88.81 (8) and 79.48 (8)°, respectively, and to each other by 68.12 (5)°. In the crystal, mol-ecules are linked via C-H⋯O hydrogen bonds, forming chains propagating along [001].

Crystal structure of methyl (E)-2-(1-methyl-2-oxoindolin-3-yl-idene)acetate

The title compound, C12H11NO3, is essentially planar, with the mean plane of the acetate side chain [-C-C(=O)-O-C] being inclined to the mean plane of the indole ring system by 12.49 (7)°. The five- and six-membered rings of the indole group are almost coplanar, making a dihedral angle of 1.76 (8)°. The conformation about the C=C bond is E and there is an intra-molecular C-H⋯O hydrogen bond present. In the crystal, mol-ecules are linked by pairs of C-H⋯O hydrogen bonds forming inversion dimers, with an R 2 (2)(16) ring motif. The dimers are linked by a second pair of C-H⋯O hydrogen bonds, enclosing R 2 (2)(16) ring motifs, forming ribbons lying parallel to (-114). The ribbons are linked via C-H⋯π inter-actions, forming a three-dimensional structure.

Novel approaches in selective tryptophan isotope labeling by using Escherichia coli overexpression media

NMR-based investigations of large protein complexes require optimized isotopic labeling schemes. We report new methods to introduce stable isotopes into tryptophan residues; these are fine-tuned to the requirements of the particular protein NMR experiment. Selective backbone labeling was performed by using a new α-ketoacid precursor as an additive in cell-based overexpression media. Additionally, we developed synthetic routes to certain isotopologues of indole with (13)C-(1)H spin systems surrounded by (12)C and (2)H. The corresponding proteins, overexpressed in the presence of these precursor compounds, can be effectively analyzed for conformational changes in tryptophan residues in response to external stimuli, such as interaction with other proteins or small molecules.

Crystal structure of (2-bromo-methyl-1-phenyl-sulfonyl-1H-indol-3-yl)(phen-yl)methanone

In the title compound, C₂₂H₁₆BrNO₃S, the phenyl rings make dihedral angles of 84.81 (16) and 61.67 (17)° with the indole ring system (r.m.s. deviation = 0.012 Å), while the phenyl rings are inclined to one another by 69.5 (2)°. The mol­ecular structure is stabilized by weak intra­molecular C—H⋯O hydrogen bonds. The sulfonyl S atom has a distorted tetra­hedral configuration. In the crystal, there are no significant inter­molecular inter­actions present.

3He NMR studies on helium-pyrrole, helium-indole, and helium-carbazole systems: a new tool for following chemistry of heterocyclic compounds

The (3)He nuclear magnetic shieldings were calculated for free helium atom and He-pyrrole, He-indole, and He-carbazole complexes. Several levels of theory, including Hartree-Fock (HF), Second-order Møller-Plesset Perturbation Theory (MP2), and Density Functional Theory (DFT) (VSXC, M062X, APFD, BHandHLYP, and mPW1PW91), combined with polarization-consistent pcS-2 and aug-pcS-2 basis sets were employed. Gauge-including atomic orbital (GIAO) calculated (3)He nuclear magnetic shieldings reproduced accurately previously reported theoretical values for helium gas. (3)He nuclear magnetic shieldings and energy changes as result of single helium atom approaching to the five-membered ring of pyrrole, indole, and carbazole were tested. It was observed that (3)He NMR parameters of single helium atom, calculated at various levels of theory (HF, MP2, and DFT) are sensitive to the presence of heteroatomic rings. The helium atom was insensitive to the studied molecules at distances above 5 Å. Our results, obtained with BHandHLYP method, predicted fairly accurately the He-pyrrole plane separation of 3.15 Å (close to 3.24 Å, calculated by MP2) and yielded a sizable (3)He NMR chemical shift (about -1.5 ppm). The changes of calculated nucleus-independent chemical shifts (NICS) with the distance above the rings showed a very similar pattern to helium-3 NMR chemical shift. The ring currents above the five-membered rings were seen by helium magnetic probe to about 5 Å above the ring planes verified by the calculated NICS index.

Crystal structure of dimethyl 3,3'-[(3-fluoro-phenyl)methyl-ene]bis-(1H-indole-2-carboxyl-ate)

In the title compound, the two indole ring systems are approximately perpendicular to one another, making a dihedral angle of 87.8 (5)°. In the crystal, pairs of N—H⋯O hydrogen bonds link the mol­ecules into the inversion dimers, which are further linked by N—H⋯O hydrogen bonds into supra­molecular chains propagating along the b-axis direction.

In the title compound, C₂₇H₂₁FN₂O₄, the mean planes of the two indole ring systems (r.m.s. deviations = 0.0166 and 0.0086 Å) are approximately perpendic­ular to one another, making a dihedral angle of 87.8 (5)°; the fluorobenzene ring is twisted with respect to the mean planes of the two indole ring systems at 82.7 (5) and 85.5 (3)°. In the crystal, pairs of N—H⋯O hydrogen bonds link the mol­ecules into the inversion dimers, which are further linked by N—H⋯O hydrogen bonds into supra­molecular chains propagating along the b-axis direction. Weak C—H⋯π inter­actions are observed between neighbouring chains.

Design, synthesis, and biological activity of oxime ether strobilurin derivatives containing indole moiety as novel fungicide

Twenty-one novel oxime ether strobilurins containing indole moiety, which employed an indole group to stabilize the E-styryl group in Enoxastrobin, were designed and synthesized. The biological assay indicated that most compounds exhibited potent fungicidal activities. The structure-activity relationship study demonstrated that the synthesized methyl 3-methoxypropenoate oxime ethers 7b-e exhibited remarkably high activities among all the synthesized oxime ether compounds 7. Moreover, the fungicidal activities of methyl α-(methoxyimino)benzeneacetate oxime ethers compounds 7f-i and N-methoxy-carbamic acid methyl esters compounds 7j-m showed significant differences compared to the corresponding products of ammonolysis.

Design, Synthesis, and Biological Evaluation of 1-(thiophen-2-yl)-9H-pyrido[3,4-b]indole Derivatives as Anti-HIV-1 Agents

A novel series of 1-(thiophen-2-yl)-9H-pyrido [3,4-b]indole derivatives were synthesized using DL-tryptophan as starting material. All the compounds were characterized by spectral analysis such as (1) H NMR, Mass, IR, elemental analysis and evaluated for inhibitory potency against HIV-1 replication. Among the reported analogues, compound 7g exhibited significant anti-HIV activity with EC(50) 0.53 μm and selectivity index 483; compounds 7e, 7i, and 7o displayed moderate activity with EC(50) 3.8, 3.8, and 2.8 μm and selectivity index >105, >105, and 3.85, respectively. Interestingly, compound 7g inhibited p24 antigen expression in acute HIV-1(IIIB) infected cell line C8166 with EC50 1.1 μm. In this study, we also reported the Lipinski rule of 5 parameters, predicted toxicity profile, drug-likeness, and drug score of the synthesized analogues.

Crystal structure of dimethyl 3,3'-[(3-nitro-phen-yl)methyl-ene]bis-(1H-indole-2-carboxyl-ate) ethanol monosolvate

In the title compound, C27H21N3O6·C2H5OH, the indole ring systems are approximately perpendicular to each other, with a dihedral angle of 89.3 (5)°; the plane of the benzene ring is oriented with respect to the indole ring systems at 49.9 (5) and 73.4 (3)°. In the crystal, mol-ecules are linked by N-H⋯O and O-H⋯O hydrogen bonds and weak C-H⋯π inter-actions into a three-dimensional supra-molecular architecture. A void of 33.0 (7) Å(3) is observed in the crystal structure. The solvent ethanol molecule acts as a donor, forming an O-H⋯O hydrogen bond, reinforcing the framework structure.

Phosphodiesterase DosP increases persistence by reducing cAMP which reduces the signal indole

Persisters are bacteria that are highly tolerant to antibiotics due to their dormant state and are of clinical significance owing to their role in infections. Given that the population of persisters increases in biofilms and that cyclic diguanylate (c-di-GMP) is an intracellular signal that increases biofilm formation, we sought to determine whether c-di-GMP has a role in bacterial persistence. By examining the effect of 30 genes from Escherichia coli, including diguanylate cyclases that synthesize c-di-GMP and phosphodiesterases that breakdown c-di-GMP, we determined that DosP (direct oxygen sensing phosphodiesterase) increases persistence by over a thousand fold. Using both transcriptomic and proteomic approaches, we determined that DosP increases persistence by decreasing tryptophanase activity and thus indole. Corroborating this effect, addition of indole reduced persistence. Despite the role of DosP as a c-di-GMP phosphodiesterase, the decrease in tryptophanase activity was found to be a result of cyclic adenosine monophosphate (cAMP) phosphodiesterase activity. Corroborating this result, the reduction of cAMP via CpdA, a cAMP-specific phosphodiesterase, increased persistence and reduced indole levels similarly to DosP. Therefore, phosphodiesterase DosP increases persistence by reducing the interkingdom signal indole via reduction of the global regulator cAMP.

Concise and enantioselective total synthesis of (-)-mehranine, (-)-methylenebismehranine, and related Aspidosperma alkaloids

We report an efficient and highly stereoselective strategy for the synthesis of Aspidosperma alkaloids based on the transannular cyclization of a chiral lactam precursor. Three new stereocenters are formed in this key step with excellent diastereoselectivity due to the conformational bias of the cyclization precursor, leading to a versatile pentacyclic intermediate. A subsequent stereoselective epoxidation followed by a mild formamide reduction enabled the first total synthesis of the Aspidosperma alkaloids (-)-mehranine and (+)-(6S,7S)-dihydroxy-N-methylaspidospermidine. A late-stage dimerization of (-)-mehranine mediated by scandium trifluoromethanesulfonate completed the first total synthesis of (-)-methylenebismehranine.

Crystal structure of dimethyl 3,3'-[(4-chloro-phen-yl)methyl-ene]bis-(1H-indole-2-carboxyl-ate)

In the crystal, mol­ecules are linked by N—H⋯O hydrogen bonds, forming inversion dimers, which are linked by a further N—H⋯O hydrogen bond, forming chains along [100]. There are intra- and inter­molecular C—H⋯π inter­actions present, the latter linking the chains to form a three-dimensional supra­molecular structure.

In the title compound, C₂₇H₂₁ClN₂O₄, the mean planes of the two indole ring systems (r.m.s. deviations = 0.021 and 0.024 Å) are approximately perpendicular to one another, with a dihedral angle of 79.54 (12)°. The benzene ring is twisted with respect to the mean planes of the two indole ring systems at angles of 80.14 (15) and 86.30 (15)°. In the crystal, mol­ecules are linked by N—H⋯O hydrogen bonds, forming inversion dimers with an R²₂(18) ring motif. The dimers are linked by a further N—H⋯O hydrogen bond, forming chains along [100]. There are intra- and inter­molecular C—H⋯π inter­actions present, the latter linking the chains to form a three-dimensional supra­molecular structure.

Measurement of boar taint in porcine fat using a high-throughput gas chromatography-mass spectrometry protocol

This work outlines an optimized gas chromatrography-mass spectrometry (GC-MS) based protocol for screening of the presence of the three boar-taint-producing compounds indole, skatole (3-methylindole), and androstenone (5α-androst-16-en-3-one) in porcine fat. The study shows that an accuracy suitable for sample screening can be achieved even when speed and ease of sample handling is prioritized and without the use of internal standards. The method provides levels of detection of 82 ng/g for indole, 97 ng/g for skatole, and 623 ng/g for androstenone (in a 2 g natural backfat matrix). A least-squares approach of predicting the sample analyte mass from instrument response is shown to have prediction errors (root-mean-square error) of 96 ng/g for indole, 94 ng/g for skatole, and 331.3 ng/g for androstenone. The method is intended for discrimination of samples in risk groups, and a scheme is proposed to turn the GC-MS response of the boar-taint analytes into risk classes.