Psychollatine, a glucosidic monoterpene indole alkaloid from Psychotria umbellata

Targeted Isolation of Monoterpene Indole Alkaloids from Palicourea sessilis

Phytochemical investigation of the alkaloid extract of Palicourea sessilis by LC-HRMS/MS using molecular networking and an in silico MS/MS fragmentation approach suggested the presence of several new monoterpene indole alkaloids. These compounds were isolated by semipreparative HPLC, and their structures confirmed by means of HRMS, NMR, and ECD measurements as 4-N-methyllyaloside (3), 4-N-methyl-3,4-dehydrostrictosidine (4), 4β-hydroxyisodolichantoside (6), and 4α-hydroxyisodolichantoside (7), as well as the known alkaloids alline (1), N-methyltryptamine (2), isodolichantoside (5), and 5-oxodolichantoside (8). In addition, the acetylcholinesterase inhibitory activity of the compounds was evaluated up to 50 μM.

Toxicological profile and acetylcholinesterase inhibitory potential of Palicourea deflexa, a source of β-carboline alkaloids

Palicourea genus is chemically and taxonomically close to Psychotria genus, a well-known source of neuroactive alkaloids. It has been previously reported the pharmacological potential of these alkaloids in some targets related to the neurodegenerative process. In this context, this study was carried out in order to evaluate the toxic effects and acetylcholinesterase (AChE) inhibitory potential of Palicourea deflexa fraction of total alkaloids (FTA). P. deflexa FTA was analyzed by means of HPLC-DAD and HRMS-ESI. We performed toxicological screening through Fish Embryo Toxicity (FET) test using zebrafish embryo and abnormal developmental phenotypes were recorded daily. For AChE inhibition, zebrafish brains were used as enzymatic source and formation of thiolate dianion of 5,5'-Dithiobis(2-nitrobenzoic acid) (DTNB) was used to monitor acetylthiocholine hydrolysis. Lineaweaver-Burk double reciprocal plots were used to indicate mode of inhibition. Chemical analysis of the P. deflexa FTA allowed the identification of the main compound as harman-3-carboxylic acid. This fraction was evaluated in vivo for its toxicological effect. The zebrafish embryo test indicated that the FTA has a lethal concentration of 50% (LC₅₀)=72.18μg/mL. Further, the FTA was evaluated for its AChE inhibitory profile, demonstrating an inhibitory concentration of 50% (IC₅₀) of 50.65μg/mL. Lineaweaver-Burk double reciprocal plots indicated a mixed mode of inhibition. It is reported for the first time the toxicological and pharmacological profile of the alkaloid fraction of Palicourea deflexa in zebrafish models.

13C-NMR Spectral Data of Alkaloids Isolated from Psychotria Species (Rubiaceae)

The genus Psychotria (Rubiaceae) comprises more than 2000 species, mainly found in tropical and subtropical forests. Several studies have been conducted concerning their chemical compositions, showing that this genus is a potential source of alkaloids. At least 70 indole alkaloids have been identified from this genus so far. This review aimed to compile ¹³C-NMR data of alkaloids isolated from the genus Psychotria as well as describe the main spectral features of different skeletons.

Conformational Preferences of Modified Nucleoside 5-Taurinomethyluridine, τm(5)U Occur at 'wobble' 34th Position in the Anticodon Loop of tRNA

Conformational preferences of hypermodified nucleoside 5-taurinomethyluridine 5'-monophoshate 'p-τm(5)U' (-CH2-NH2(+)-CH2-CH2-SO3(-)) have been investigated using semi-empirical RM1 method. Automated geometry optimization using ab initio molecular orbital HF-SCF (6-31G**) and DFT (B3LYP/6-31G**) calculations have also been made to compare the salient features. The RM1 preferred most stable conformation of 'p-τm(5)U' has been stabilized by hydrogen bonding interactions between O(11a)…HN(8), O1P(34)…HN(8), and O1P(34)…HC(10). Another conformational study of 5-taurinomethyluridine side chain has also been performed in context of anticodon loop bases of E. coli tRNA(Leu). The atom O(11a) of τm(5)U(34) side chain interacts with adenosine (A35) as well as ribose-phosphate backbone which might provide structural stability to the anticodon loop. The glycosyl torsion angle of τm(5)U retains 'anti'-conformation. The solvent accessible surface area calculations revealed the role of τm(5)U in tRNA(Leu) anticodon loop. MD simulation results are found in agreement with RM1 preferred stable structure. The MEPs calculations of τm(5)U(34):G3 model show unique potential tunnels between the hydrogen bond donor and acceptor atoms as compared to τm(5)U(34):A3 model. Thus, these results could pave the way to understand the role of τm(5)U(34) to recognize UUG/UUA codons at atomic level in the mitochondrial disease, MELAS.

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.

Loganin and secologanin derived tryptamine-iridoid alkaloids from Palicourea crocea and Palicourea padifolia (Rubiaceae)

During comparative analysis on Palicourea species from Costa Rica, two unusual loganin derived tryptamine-iridoid alkaloids were isolated from an accession of Palicourea crocea. Besides the already known brachycerine (2), palicroceaine (1) features a novel hexacyclic backbone. A second provenance, however, yielded strictosidinic acid (3), belonging to the more common secologanin derived tryptamine-iridoid alkaloids, such as those found in Palicourea padifolia. From this species, strictosidine (4), lyaloside (5) and its derivative (E)-O-(6')-(4″-hydroxy-3″,5″-dimethoxy)-cinnamoyl lyaloside (6) could be isolated. A herbarium specimen-based screening was performed, indicating some degree of regional differentiation in alkaloid content and biosynthetic pathways within the widespread and variable Pal. crocea. It further shows its differentiation from the related strictosidine containing Palicourea croceoides. The occurrence of loganin derived tryptamine-iridoid alkaloids in Pal. crocea, Psychotria brachyceras and Psychotria brachypoda, all putatively unrelated members of the Palicourea s.l. clade, is a noteworthy exception within the genus, otherwise largely characterized by secologanin-derived tryptamine-iridoid alkaloids.

Silver-catalysed reactions of alkynes: recent advances

Silver is a less expensive noble metal. Superior alkynophilicity due to π-coordination with the carbon-carbon triple bond makes silver salts ideal catalysts for alkyne-based organic reactions. This review highlights the progress in alkyne chemistry via silver catalysis primarily over the past five years (ca. 2010-2014). The discussion is developed in terms of the bond type formed with the acetylenic carbon (i.e., C-C, C-N, C-O, C-Halo, C-P and C-B). Compared with other coinage metals such as Au and Cu, silver catalysis is frequently observed to be unique. This critical review clearly indicates that silver catalysis provides a significant impetus to the rapid evolution of alkyne-based organic reactions, such as alkynylation, hydrofunctionalization, cycloaddition, cycloisomerization, and cascade reactions.

Conformational preferences of modified nucleoside N(4)-acetylcytidine, ac4C occur at "wobble" 34th position in the anticodon loop of tRNA

Conformational preferences of modified nucleoside, N(4)-acetylcytidine, ac(4)C have been investigated using quantum chemical semi-empirical RM1 method. Automated geometry optimization using PM3 method along with ab initio methods HF SCF (6-31G**), and density functional theory (DFT; B3LYP/6-31G**) have also been made to compare the salient features. The most stable conformation of N(4)-acetyl group of ac(4)C prefers "proximal" orientation. This conformation is stabilized by intramolecular hydrogen bonding between O(7)···HC(5), O(2)···HC2', and O4'···HC(6). The "proximal" conformation of N(4)-acetyl group has also been observed in another conformational study of anticodon loop of E. coli elongator tRNA(Met). The solvent accessible surface area (SASA) calculations revealed the role of ac(4)C in anticodon loop. The explicit molecular dynamics simulation study also shows the "proximal" orientation of N(4)-acetyl group. The predicted "proximal" conformation would allow ac(4)C to interact with third base of codon AUG/AUA whereas the 'distal' orientation of N(4)-acetyl cytidine side-chain prevents such interactions. Single point energy calculation studies of various models of anticodon-codon bases revealed that the models ac(4)C(34)(Proximal):G3, and ac(4)C(34)(Proximal):A3 are energetically more stable as compared to models ac(4)C(34)(Distal):G3, and ac(4)C(34)(Distal):A3, respectively. MEPs calculations showed the unique potential tunnels between the hydrogen bond donor-acceptor atoms of ac(4)C(34)(Proximal):G3/A3 base pairs suggesting role of ac(4)C in recognition of third letter of codons AUG/AUA. The "distal" conformation of ac(4)C might prevent misreading of AUA codon. Hence, this study could be useful to understand the role of ac(4)C in the tertiary structure folding of tRNA as well as in the proper recognition of codons during protein biosynthesis process.

Absolute configuration study of a new dimeric indole alkaloid from the leaves and twigs of Psychotria henryi

From the leaves and twigs of Psychotria henryi, a new dimeric indole alkaloid, named psychohenin, was isolated, whose structure was elucidated on the basis of extensive spectroscopic analysis. The absolute configuration of psychohenin was determined by a single-crystal X-ray diffraction study using a mirror Cu Kα radiation.

Indole alkaloids of Psychotria as multifunctional cholinesterases and monoamine oxidases inhibitors

Thirteen Psychotria alkaloids were evaluated regarding their interactions with acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and monoamine oxidases A and B (MAO-A and MAO-B), which are enzymatic targets related with neurodegenerative diseases. Two quaternary β-carboline alkaloids, prunifoleine and 14-oxoprunifoleine, inhibited AChE, BChE and MAO-A with IC(50) values corresponding to 10 and 3.39 μM for AChE, 100 and 11 μM for BChE, and 7.41 and 6.92 μM for MAO-A, respectively. Both compounds seem to behave as noncompetitive AChE inhibitors and time-dependent MAO-A inhibitors. In addition, the monoterpene indole alkaloids (MIAs) angustine, vallesiachotamine lactone, E-vallesiachotamine and Z-vallesiachotamine inhibited BChE and MAO-A with IC(50) values ranging from 3.47 to 14 μM for BChE inhibition and from 0.85 to 2.14 μM for MAO-A inhibition. Among the tested MIAs, angustine is able to inhibit MAO-A in a reversible and competitive way while the three vallesiachotamine-like alkaloids display a time-dependent inhibition on this target. Docking calculations were performed in order to understand the binding mode between the most active ligands and the selected targets. Taken together, our findings established molecular details of AChE, BChE and MAO-A inhibition by quaternary β-carboline alkaloids and MIAs from Psychotria, suggesting these secondary metabolites are scaffolds for the development of multifunctional compounds against neurodegeneration.

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.

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.

Structure elucidation and NMR assignments of two unusual monoterpene indole alkaloids from Psychotria stachyoides

Two unusual monoterpene indole alkaloids, stachyoside (1) and nor-methyl-23-oxo-correantoside (2), have been isolated from the aerial parts of Psychotria stachyoides. The structural elucidation of both compounds was performed by the aid of HRESIMS, FT-IR, and 1D- and 2D-NMR techniques including COSY, HSQC, HMBC, and NOESY.

Monoamine levels in rat striatum after acute intraperitoneal injection of strictosidinic acid isolated from Psychotria myriantha Mull. Arg. (Rubiaceae)

Strictosidinic acid 10mg/kg, isolated from Psychotria myriantha leaves, were administered intraperitoneally to Wistar male rats (n=5-6). After 60 minutes, striatum was dissected, homogenized and injected onto HPLC-ED chromatographic system. It was observed a 28.7% reduction in the 5-HT levels followed up by an increase of 5-HIAA levels (29.4%). Furthermore there was a decrease of 8.0% in DA levels and an increase in the levels of metabolites DOPAC (21.5%) and HVA (52.5%). The results indicate that strictosidinic acid has a promising effect in the central nervous system, justifying more studies about the central actions of Psychotria compounds.

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.

Bioactive Alkaloids from South American Psychotria and Related Species

Many important molecules have been discovered from tropical and sub-tropical plant biodiversity. However, the largest part of the chemical profile of such biodiversity remains unknown. Combining ethnopharmacological and chemotaxonomical investigation can be a good strategy in bioactive compound discovery. South American Psychotria species studied by this approach proved to be a rich source of new bioactive alkaloids, some of which bear unique chemical skeletons.