Turbinatine, a potential key intermediate in the biosynthesis of corynanthean-type indole alkaloids

Molecular Networking Reveals Serpentinine-Related Bisindole Alkaloids from Picralima nitida, a Previously Well-Investigated Species

Five new monoterpene indole alkaloids (1-5), including four serpentinine-related bisindoles and one alstonine derivative monomer, have been isolated from the aerial parts of Picralima nitida. Their structures were elucidated by analysis of their HRMS and NMR spectroscopic data, and their absolute configurations were deduced from the comparison of experimental and simulated ECD spectra. In addition, two known compounds (6 and 7), previously undescribed from P. nitida, have also been purified. The compound isolation workflow was guided by a molecular networking-based dereplication strategy. Twenty-three compounds were dereplicated from the EtOH extract of P. nitida and fractions network and were assigned various levels of identification confidence. The antiparasitic activities against Plasmodium falciparum as well as the cytotoxic activity against the MRC-5 cell line were determined for compounds 1-7.

Mappianines A-E, structurally diverse monoterpenoid indole alkaloids from Mappianthus iodoides

Five previously undescribed monoterpenoid indole alkaloids, mappianines A-E, along with twelve known analogues, were isolated from the stems of Mappianthus iodoides Hand.-Mazz. Their structures and absolute configurations were determined by spectroscopic analysis, single-crystal X-ray diffraction, and ECD calculations. The plausible biogenetic pathway of mappianine A was proposed. All the isolated compounds were evaluated for their cytotoxic effects on MGC-803, Bel-7404, A549, NCI-H460, and HepG2 cancer cell lines. Mappianine B, tetrahydroalstonine, β-carbolin-1-one, and 1,2,3,4-tetrahydronorharman-1-one displayed moderate cytotoxicity against all cell lines tested, with IC₅₀ values ranging from 5.19 to 42.86 μM.

ESI-MS/MS of expanded porphyrins: a look into their structure and aromaticity

Electrospray mass spectrometry/mass spectrometry was used to investigate the gas-phase properties of protonated expanded porphyrins, in order to correlate those with their structure and conformation. We have selected five expanded meso-pentafluorophenyl porphyrins, respectively, a pair of oxidized/reduced fused pentaphyrins (22 and 24 π electrons), a pair of oxidized/reduced regular hexaphyrins (26 and 28 π electrons) and a regular doubly N-fused hexaphyrin (28 π electrons). The gas-phase behavior of the protonated species of oxidized and reduced expanded porphyrins is different. The oxidized species (aromatic Hückel systems) fragment more extensively, mainly by the loss of two HF molecules. The reduced species (Möbius aromatic or Möbius-like aromatic systems) fragment less than their oxidized counterparts because of their increased flexibility. The protonated regular doubly fused hexaphyrin (non-aromatic Hückel system) shows the least fragmentation even at higher collision energies. In general, cyclization through losses of HF molecules decreases from the aromatic Hückel systems to Möbius aromatic or Möbius-like aromatic systems to non-aromatic Hückel systems and is related to an increase in conformational distortion. Copyright © 2016 John Wiley & Sons, Ltd.

Indole Alkaloids from Vinca major and V. minor Growing in Turkey

A new indole alkaloid, 11-hydroxypolyneuridine, was isolated from Vinca major subsp. major L. and the known indole alkaloids vallesiachotamine and isovallesiachotamine from Vinca minor L. This is the first report on the alkaloids of both Vinca species growing in Turkey; vallesiachotamine and isovallesiachotamine were isolated from a Vinca species for the first time. V. minor may be considered as a new source for these two alkaloids due to their occurrence in high amount in the aerial parts of the plant. The alkaloid extracts of the two Vinca species were found to have high lipid peroxidation inhibitory and DPPH radical scavenging activities. Anticholinesterase activity of the extracts was also very strong.

Monoamine oxidase inhibition by monoterpene indole alkaloids and fractions obtained from Psychotria suterella and Psychotria laciniata

Alkaloid fractions of Psychotria suterella (SAE) and Psychotria laciniata (LAE) as well as two monoterpene indole alkaloids (MIAs) isolated from these fractions were evaluated against monoamine oxidases (MAO-A and -B) obtained from rat brain mitochondria. SAE and LAE were analysed by HPLC-PDA and UHPLC/HR-TOF-MS leading to the identification of the compounds 1, 2, 3 and 4, whose identity was confirmed by NMR analyses. Furthermore, SAE and LAE were submitted to the enzymatic assays, showing a strong activity against MAO-A, characterized by IC(50) values of 1.37 ± 1.05 and 2.02 ± 1.08 μg/mL, respectively. Both extracts were also able to inhibit MAO-B, but in higher concentrations. In a next step, SAE and LAE were fractionated by RP-MPLC affording three and four major fractions, respectively. The RP-MPLC fractions were subsequently tested against MAO-A and -B. The RP-MPLC fractions SAE-F3 and LAE-F4 displayed a strong inhibition against MAO-A with IC(50) values of 0.57 ± 1.12 and 1.05 ± 1.15 μg/mL, respectively. The MIAs 1 and 2 also inhibited MAO-A (IC(50) of 50.04 ± 1.09 and 132.5 ± 1.33 μg/mL, respectively) and -B (IC(50) of 306.6 ± 1.40 and 162.8 ± 1.26 μg/mL, respectively), but in higher concentrations when compared with the fractions. This is the first work describing the effects of MIAs found in neotropical species of Psychotria on MAO activity. The results suggest that species belonging to this genus could consist of an interesting source in the search for new MAO inhibitors.

Antinociceptive and anti-inflammatory effects of octacosanol from the leaves of Sabicea grisea var. grisea in mice

Sabicea species are used in the Amazon for treatment of fever and malaria, which suggests that its chemical constituents may have some effect on pain and inflammation. Phytochemical analysis of the hexane fraction obtained from the crude ethanol extract from Sabicea grisea var. grisea Cham. & Schltdl (Rubiaceae), an endemic plant in Brazil, resulted in the isolation of octacosanol. This study investigated the antinociceptive and anti-inflammatory effects of the octacosanol in different experimental models. The crude ethanolic extract and hexane fraction obtained from the leaves of S. grisea produced an inhibition of acetic acid-induced pain. Moreover, octacosanol isolated from the hexane fraction produced a significant inhibition of pain response elicited by acetic acid. Pre-treatment with yohimbine, an alpha 2-adrenergic receptor antagonist, notably reversed the antinociceptive activity induced by octacosanol in the abdominal constriction test. Furthermore, mice treated with octacosanol did not exhibit any behavioral alteration during the hot plate and rota-rod tests, indicating non-participation of the supraspinal components in the modulation of pain by octacosanol with no motor abnormality. In the formalin test, octacosanol did not inhibit the licking time in first phase (neurogenic pain), but significantly inhibited the licking time in second phase (inflammatory pain) of mice. The anti-inflammatory effect of octacosanol was evaluated using carrageenan-induced pleurisy. The octacosanol significantly reduced the total leukocyte count and neutrophils influx, as well as TNF-α levels in the carrageenan-induced pleurisy. This study revealed that the mechanism responsible for the antinociceptive and anti-inflammatory effects of the octacosanol appears to be partly associated with an inhibition of alpha 2-adrenergic transmission and an inhibition of pathways dependent on pro-inflammatory cytokines. Finally, these results demonstrated that the octacosanol from the leaves of S. grisea possesses antinociceptive and anti-inflammatory activities, which could be of relevance for the pharmacological control of pain and inflammatory processes.

Alkaloids from Hippeastrum morelianum Lem. (Amaryllidaceae)

The Amaryllidaceae family has proven to be a rich source of active molecules. As part of an ongoing project, we report a phytochemical study of Hippeastrum morelianum (Amaryllidaceae), from which we have isolated two homolycorine-type alkaloids, the new 2α,7-dimethoxyhomolycorine (1) and the poorly described candimine (2), as well as six known alkaloids: tazettine, pretazettine, 3-epimacronine, haemanthamine, hamayne and trisphaeridine. For reference purposes, the NMR of the isolated compounds was unequivocally described, based on 2D NMR measurements including (1)H-(1)H COSY, (1)H-(1)H NOESY, HSQC and HMBC.

An unprecedented neolignan skeleton from Chimarrhis turbinata

A lignan with a new skeleton named chimarrhinin (1) was isolated from an extract of the leaves of Chimarrhis turbinata, a Rubiaceae plant species. (13)C NMR spectrometric techniques including 1D and 2D experiments and HRESIMS provided unequivocal structural confirmation of this new C(6).C(3) skeleton type. The relative configuration of 1 was established by 2D (1)H-H analysis and J couplings, while its conformation was evaluated through molecular modeling using the RM1 semiempirical method, with the aid of coupling constants obtained by NMR analysis. The antioxidant activity of the new derivative 1 and two known and previously isolated phenolic derivatives (2 and 3) was investigated. An IC(50) value of 7.50 ± 0.5 μmol L(-1) was obtained for the new derivative 1, while 2 and 3 showed IC(50) values of 18.60 ± 0.4 and 18.50 ± 0.6 μmol, respectively.

Characterization of the conformational ensemble from bioactive N-acylhydrazone derivatives

The search for bioactive conformations from prototypes is mostly referenced on crystallographic ligand-receptor complexes, in which the molecule conformation is already caged inside its binding site. However, the complexation process is a thermodynamic event depending on both complexed and uncomplexed states. As ligand affinity originates from such equilibrium, the development of novel computational models capable of supplying data on ligand dynamics in biological solutions is potentially applicable in more efficient methods for prediction of compounds binding and affinity. In this context, the current work employs a series of molecular dynamics simulations on three N-acylhydrazone derivatives, already shown to present promising cardioinotropic and vasodilatory activities, in order to obtain a precise characterization of each compound conformational ensemble in aqueous solutions, instead of a single minimum energy conformation. Consequently, we were able to observe the influence of each functional group of the studied molecules on the conformation of the entire compounds and thus on the exposure of functional groups that might potentially bind to target receptors. Additionally, the differences between the molecules conformational behavior were characterized, supporting a spatial and temporal image of each ligand, which may be potentially correlated to their biological activities. So in the context of conformational selection, such strategy may represent a useful methodology to contribute in the choice of ligands conformations for both 3D-QSAR and docking calculations.

Psychollatine, a glucosidic monoterpene indole alkaloid from Psychotria umbellata

A monoterpene indole alkaloid, psychollatine ( 1), was isolated from Psychotria umbellata leaves. Its structure was characterized by interpretation of spectroscopic data and by comparison of its NMR data with those of croceaine A ( 2) from Palicourea crocea. The configuration of psychollatine ( 1) was established by NOE difference and circular dichroism (CD) techniques, while its conformation was evaluated through molecular modeling studies and NMR coupling constants.

Unique monoterpenoid indole alkaloids from Alstonia scholaris

[structure: see text] A pair of geometrically isomeric monoterpenoid indole alkaloids with a skeleton rearrangement and two additional carbons, named (19,20) E-alstoscholarine (1) and (19,20) Z-alstoscholarine (2), were obtained from the leaf extract of Alstonia scholaris. Their structures were elucidated on the basis of spectroscopic methods and then confirmed by X-ray crystal diffraction. The biogenesis of these compounds was also proposed.

Anxiolytic effects of erythrinian alkaloids from Erythrina mulungu

One new erythrinian alkaloid derivative, (+)-11alpha-hydroxyerythravine (1), and the known (+)-erythravine (2) and (+)-alpha-hydroxyerysotrine (3) were isolated from the flowers of Erythrina mulungu. Their structures were determined by spectroscopic/spectrometric data interpretation of 1H, 13C, and 2D NMR and MS experiments. The relative configuration was established by NOESY analysis, while the conformation adopted by these molecules was evaluated through molecular modeling studies and coupling constants obtained by NMR analysis. Furthermore, the anxiolytic effects of the E. mulungu aqueous alcoholic crude extract and of the purified alkaloids were evaluated using the elevated T-maze test.

The absolute configuration of 1-(3',4'-dihydroxycinnamoyl)cyclopentane-2,3-diol from the amazonian tree Chimarrhis turbinata

An antioxidant, 1-(3',4'-dihydroxycinnamoyl)cyclopentane-2,3-diol [or (E)-2,3-dihydroxycyclopentyl-3-(3',4'-dihydroxyphenyl)acrylate (1)], and two known trans- and cis-chlorogenic acid methyl esters were isolated from the ethanolic extract of the leaves of Chimarrhis turbinata. The relative configuration of 1 was determined by NMR and by comparison of the circular dichroic spectrum (CD) with those of the enantiomers of synthetic 3',4'-dimethoxycinnamoyl analogues. The absolute configuration of one of the synthetic enantiomers was determined using the CD exciton chirality method. This established the structure of naturally occurring 1 as (E)-2,3-dihydroxycyclopentyl-3-(3',4'-dihydroxyphenyl)acrylate.

Simple indole alkaloids and those with a non-rearranged monoterpenoid unit

This review covers newly isolated simple indole alkaloids, structure determinations, total syntheses and biological activities reported in the literature in 2003.

NMR spectroscopic, mass spectroscopic, X-ray crystallographic, and theoretical studies of molecular mechanics of natural products: farformolide B and sesamin

Two natural products, farformolide B and sesamin were isolated from Farfugium japonicum and Cinnamomum kanehirae, respectively. The structures of the two natural products, including their relative stereochemistry, were elucidated using spectroscopic data and theoretical calculations. The molecule 1 (farformolide B) is newly recognized by X-ray crystallography. The two compounds were also investigated by a theoretical analysis using the B3LYP/6-31G* method of the Gaussian 03 package program. The theoretical results were supplemented by experimental data to determine the optimal geometric structures of the two compounds. The calculated molecular mechanics were found to compare well with the experimental data. Several important thermodynamic properties of the two products, including ionization potentials, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, energy gaps, heat of formation, atomization energies, and vibration frequencies, were also calculated. The study also provided a good understanding of the stereochemical structure and thermodynamic properties of the two molecules.

Indole glucoalkaloids from Chimarrhis turbinata and their evaluation as antioxidant agents and acetylcholinesterase inhibitors

As part of our study on bioactive agents from Brazilian rainforest plants, two new glucoalkaloids, 3,4-dehydro-strictosidine (1) and 3,4-dehydro-strictosidinic acid (2), were isolated from Chimarrhis turbinata, along with seven known glucoalkaloids, cordifoline (3), strictosidinic acid (4), strictosidine (5), 5 alpha-carboxystrictosidine (6), turbinatine (7), desoxycordifoline (8), and harman-3-carboxylic acid (9). The structures of the new alkaloids were established on the basis of comprehensive spectral analysis, mainly 1D and 2D NMR experiments, as well as high-resolution HRESIMS. Alkaloid 3 showed strong free-radical scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) as well as pronounced antioxidant activity evidenced by redox properties measured by ElCD-HPLC. Additionally, alkaloids 1-9 were submitted to TLC screening for acetylcholinesterase inhibitors. Both 7 and 8 were shown to be moderate acetylcholinesterase inhibitors at a concentration of 0.1 and 1.0 microM, respectively. In an in vitro rat brain assay, 7 showed moderate activity (IC(50) 1.86 microM), compared to the standard compound, galanthamine (IC(50) 0.92 microM).