Aspidosperma species: A review of their chemistry and biological activities

Selectivity Rules for the Dearomative (3+2) Annulation Reaction Between Substituted Indoles and Oxyallyl Cations

We report a collection of "selectivity rules" for the dearomative (3+2) annulation reaction between substituted indoles and oxyallyl cations. The application of these rules enables us to synthesize four different regioisomeric permutations of the annulation products in a stereoselective fashion. We demonstrated that these products could be further transformed into hexahydro- and tetrahydrocarbazoles by nucleophile-intercepted Beckmann fragmentation (NuBFr) and Beckmann fragmentation (BFr).

Regioselective cyclocondensations with thiobarbituric acid: spirocyclic and azocine products, X-ray characterization, and antioxidant evaluation

Multicomponent cyclocondensations of 5-amino-3-methyl-1-phenyl-1H-pyrazole (AMPZ), thiobarbituric acid, and p-formaldehyde under conventional thermal heating or ultrasonic irradiation were studied. Treatment of the reaction mixture in ethanol in an ultrasonic bath for 3 h produced azocine compound 4b, while the same mixture in ethanol under reflux conditions for 15 h produced spiro compound 4a. This work encompasses intricate experimental details, X-ray diffraction measurements, and multifaceted computational analyses employing methods such as the density functional theory and Hirshfeld surface analysis. Crystallographic investigations revealed the molecular structure of the compound and clarified its interactions involving hydrogen bonds and weak intermolecular forces. This article describes the synthesis and characterization of a novel spirocyclic compound. The study also evaluated the antioxidant potential in vitro using the DPPH and ABTS methods. The results showed that these compounds showed the best free radical scavenging ability, even in very small amounts, and that even at very low concentrations, these compounds showed excellent radical scavenging potential. Surprisingly, these compounds exhibited strong (ABTS+) radical scavenging activities, mainly attributed to the HAT mechanism, indicating their potential as therapeutic agents. Facile multipurpose, three-component selective procedures for new spiroheterocycles have been proposed, presenting intriguing perspectives in the field of medicine, particularly in the field of antioxidants. The geometric values of the computationally optimized structure were calculated using the density functional theory in LC-BLYP/6-31(d), aligned with the X-ray diffraction data, reinforcing the precision of our findings.

Cyclic Imines and Their Salts as Universal Precursors in the Synthesis of Nitrogen-Containing Alkaloids

Alkaloids are predominantly nitrogen-containing heterocyclic compounds that are usually isolated from plants, and sometimes from insects or animals. Alkaloids are one of the most important types of natural products due to their diverse biological activities and potential applications in modern medicine. Cyclic imines were chosen as starting compounds for the synthesis of alkaloids due to their high synthetic potential. Thus, this review summarizes the achievements in the synthesis of various alkaloids from cyclic imines, paying special attention to stereoselective methods used for their preparation. Information on the biological activity of some alkaloids, their application and occurrence in natural objects is presented. Synthesis methods are classified based on the type of alkaloid obtained.

Asymmetric Formal Total Syntheses of (+)- and (-)-Limaspermidine from Chirally Resolved 2-Pyrone Diels-Alder Cycloadducts via Aromatic C-H Amidation and Imino-Diels-Alder Reaction

A new asymmetric synthetic route to (+)- and (-)-limaspermidine was devised, starting with chirally resolved enantiomerically pure 2-pyrone Diels-Alder cycloadducts. This route utilizes intramolecular Pd-catalyzed aromatic C-H amidation and imino-Diels-Alder reactions to construct the key indoline and indolizidine subunits onto the central cyclohexane core, allowing the straightforward formal total syntheses of both (+)- and (-)-limaspermidine.

Total Synthesis of Quebrachamine and Kopsiyunnanine D

The total syntheses of (±)-quebrachamine and (±)-kopsiyunnanine D are reported. Key transformations include an intermolecular Horner-Wadsworth-Emmons olefination to merge the two fragments convergently and an intramolecular Mitsunobu reaction to introduce the synthetically challenging nine-membered azonane ring efficiently.

Aza-Achmatowicz rearrangement coupled with intermolecular aza-Friedel-Crafts enables total syntheses of uleine and aspidosperma alkaloids

Aspidosperma and uleine alkaloids belong to the large family of monoterpene indole alkaloids with diverse biological activities and thus have attracted extensive synthetic interest. Reported is the development of a new synthetic strategy that allows direct C3-C2' linkage of indoles with functionalized 2-hydroxypiperidines to construct the core common to all aspidoserma and uleine alkaloids. Such indole-piperidine linkage is enabled by coupling aza-Achmatowicz rearrangement (AAR) with indoles via an intermolecular aza-Friedel-Crafts (iAFC) reaction. This AAR-iAFC reaction proceeds under mild acidic conditions with wide tolerance of functional groups (33 examples). The synthetic application of the AAR-iAFC method was demonstrated with collective total syntheses of 3 uleine-type and 6 aspidosperma alkaloids: (+)-3-epi-N-nor-dasycarpidone, (+)-3-epi-dasycarpidone, (+)-3-epi-uleine, 1,2-didehydropseudoaspidospermidine, 1,2-dehydroaspidospermidine, vincadifformine, winchinine B, aspidospermidine, and N-acetylaspidospermidine. We expect that this AAR-iAFC strategy is applicable to other monoterpene indole alkaloids with the C3-C2' linkage of indoles and piperidines.

Synthesis of Functionalized Hexahydrocarbazoles by Beckmann Elimination and Nucleophile-Intercepted Beckmann Fragmentation

The Beckmann elimination and nucleophile-intercepted Beckmann fragmentation (NuBFr) of oximes starting from regioisomeric indolinyl bicyclic ketones lead to products that are subjected to further synthetic manipulations and ultimately result in the stereospecific formation of densely functionalized hexahydrocarbazoles. The Pd-catalyzed Suzuki-Miyaura cross-coupling reaction of a key alkenyl bromide intermediate with various boronic acids gives arylated products.

The traditional use of native Brazilian plants for male sexual dysfunction: Evidence from ethnomedicinal applications, animal models, and possible mechanisms of action

ETHNOPHARMACOLOGICAL RELEVANCE

Sexual dysfunction is a multifactorial health condition characterized by distressing disturbances in the sexual response and libido, leading to an inability to maintain penile erection and achieve pleasure. Considering the huge Brazilian biodiversity, many plants are traditionally used for aphrodisiac purposes. However, the use of native medicinal plants as sexual boosters in Brazil has been poorly studied.

AIM OF THE STUDY

This review focuses on the composition, pharmacology, and results of experimental trials of the main native plants used in Brazilian folk medicine with alleged aphrodisiac effects. We aimed to provide a state-of-the-art reference for research on herbs for the treatment of male sexual dysfunction by summarizing and discussing the main studies found.

MATERIALS AND METHODS

The relevant information was collected by searching keywords (aphrodisiac, sexual tonic, sexual stimulant, sexual vigor stimulant, sexual impotency, erectile dysfunction, etc.) from books containing primary surveys conducted in the original communities and bibliographic surveys prepared by authors linked to the national academic and scientific environment edited in Brazil. Preclinical and clinical studies of the compiled plant species were performed using scientific databases (Scopus, PubMed, SciELO, and SciFinder).

RESULTS

Seventy-four plant species belonging to 44 families used in Brazil to treat sexual dysfunction were compiled from ethnopharmacological literature. Fourteen plants, including Pfaffia glomerata (Spreng.) Pedersen, Aspidosperma quebracho-blanco Schltdl., Anemopaegma arvense (Vell.) Stellfeld ex de Souza, Mimosa pudica L., Heteropterys tomentosa A. Juss., Trichilia catigua A. Juss., and Turnera diffusa Willd. ex Schult. were pharmacologically studied to confirm these therapeutic properties. Probable modes of action include antioxidant and androgenic activities, inhibition of the PDE5 enzyme, increase in NO levels, and activation of dopaminergic and noradrenergic pathways. In addition, several different species popularly known as "catuaba" were identified, leading to adulterations and controversial effects.

CONCLUSION

The overall results of the present review of Brazilian folk literature reveal that Brazil has a long tradition of using plants with potential aphrodisiac effects. However, further research is required to identify, characterize, and standardize the active ingredients and herbal preparations used in aphrodisiacs.

A Homo-Mannich Reaction Strategy Enables Collective Access to Ibophyllidine, Aspidosperma, Kopsia, and Melodinus Alkaloids

We report here a homo-Mannich reaction of cyclopropanol with an iminium ion, generated by an asymmetric allylic dearomatization of indole, to construct a tricyclic hydrocarbazole core, which is shared by a variety of monoterpenoid indole alkaloids across families. Through this approach, an all-carbon quaternary stereogenic center as well as an allyl and a ketone group were installed. Using this functionalized hydrocarbazole as the structural platform, D ring and E rings of different sizes (i.e., five-, six-, and seven-membered) were successively or simultaneously assembled, leading to a collective asymmetric synthesis of seven alkaloids belonging to the ibophyllidine, Aspidosperma, Kopsia, and Melodinus alkaloid families.

A Modular Synthesis of the Rhazinilam Family of Alkaloids and Analogs Thereof

A short, modular strategy for synthesizing three representative alkaloids of the (±)-rhazinilam family and 10 non-natural analogs is described. The protocol involves a radical addition/cyclization cascade reaction that assembles the tetrahydroindolizine system decorated with appropriate groups for a subsequent Pd-mediated cyclization, which generates the nine-membered lactam.

Isolation and biological activity of azocine and azocane alkaloids

Thousands of known alkaloids contain a nitrogen (N) heterocycle. While five-, six- and seven-membered N-heterocycles (ie: pyrroles, imidazoles, indoles, pyridines and azepines and their saturated variants) are common, those with an eight-membered N-heterocycle are comparatively rare. This review discusses the structure and bioactivity of alkaloids that contain an azocine (or saturated azocane) ring, and the array of sources whence they originate.

The toxicity of Aspidosperma subincanum to MCF7 cells is related to modulation of oxidative status and proinflammatory pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Cancer is an inflammatory disease because carcinogenesis and tumor progression depend on intrinsic and extrinsic inflammatory pathways. Although species of the genus Aspidosperma are widely used to treat tumors, and there is ethnopharmacological evidence for traditional use of the species A. subincanum as an anti-inflammatory agent, its antineoplastic potential is unknown.

AIM OF THE STUDY

To evaluate toxic effects of the indole alkaloid-rich fraction (IAF) of A. subincanum on the MCF7 cell line and identify some of the anti-inflammatory mechanisms involved.

MATERIALS AND METHODS

Chromatographic analyses were performed by ultra-high-performance liquid chromatography with electrospray ionization mass spectrometry, and cytotoxic and antiproliferative effects of IAF were verified by MTT and clonogenic assays. Cell cycle alterations were analyzed by measuring DNA content, while propidium iodide and acridine orange staining was performed to determine the type of induced cell death. The expression of apoptosis markers and proteins involved in cell proliferation and survival pathways was analyzed by immunoblotting, RT-qPCR, and ELISAs. Interference with redox status was investigated using a DCFH-DA probe and by measuring catalase activity.

RESULTS

Chromatographic analyses showed that IAF is a complex mixture containing indole alkaloids. IAF selectively exerted toxic and antiproliferative effects, elevating the Bax/Bcl-xL ratio and inducing apoptosis in MCF7 cells. IAF decreased intracellular reactive oxygen species levels and increased catalase activity, while reducing the IL-8 level and suppressing COX-2 expression.

CONCLUSIONS

IAF induces apoptosis in MCF7 cells by suppressing COX-2 expression while reducing IL-8 levels and intracellular content of reactive oxygen species.

Application of the metabolomics approach to the discovery of active compounds from Brazilian trees against resistant human melanoma cells

INTRODUCTION

The chemical diversity of plants plays an essential role in the development of new drugs. However, new bioactive compound identification and isolation are challenging due to the complexity and time-consuming nature of the traditional process. Recently, alternative strategies have become popular, such as the statistical approach to correlate compounds with biological activities, overcoming bottlenecks in bioactive natural product research.

OBJECTIVE

We aimed to determine bioactive compounds against resistant human melanoma cells from leaves of Aspidosperma subincanum, Copaifera langsdorffii, Coussarea hydrangeifolia, Guarea guidonea and Tapirira guianensis, using a metabolomics approach.

MATERIAL AND METHODS

The extracts and fractions were obtained by accelerated solvent extraction (ASE) and tested against resistant melanoma cells SK-MEL-28 and SK-MEL-103. Chemical analysis was performed by high-performance diode array detector tandem mass spectrometry (HPLC-DAD-MS/MS). Chemical and biological data were analysed through univariate and multivariate analysis.

RESULTS

The species present high chemical diversity, including indole alkaloids, glycosylated flavonoids, galloylquinic acid derivatives, cinnamic acid derivatives, and terpenes. The ASE fractionation separated the compounds according to the physicochemical properties; only C. langsdorffii and T. guianensis extracts were active. Both results from the chemical profile and the biological assay were treated using a metabolomics approach to identify the contribution of different classes of secondary metabolites in the viability of human melanoma cells. The analyses showed the metabolites from C. langsdorffii and T. guianensis, such as polyphenols and terpenes, were the main compounds correlated with the biological response.

CONCLUSION

These findings afford alternative pathways that are trustworthy and less time-consuming to identify new bioactive compounds against multidrug-resistant human melanoma cells.

Synthesis of Hydrocarbazole Derivatives by Oxidative Dearomative Cyclization of Diarylamines Using a Hypervalent Iodine Reagent

Hydrocarbazole derivatives bearing a quaternary stereogenic center at C4a were synthesized by means of intramolecular oxidative dearomatization of diarylamines using hypervalent iodine in moderate to good yields. The hydrocarbazole bearing a cyclohexadienone moiety was further converted into the tetracyclic skeletons of Aspidosperma and akuammiline-type alkaloids via regioselective aza-Michael reaction at C4 and at C9a, respectively.

Diversification of Nucleophile-Intercepted Beckmann Fragmentation Products and Related Density Functional Theory Studies

The nucleophile-intercepted Beckmann fragmentation (NuBFr) has the potential to be broadly applicable to the synthesis of indoline alkaloid-based natural products. However, the reaction has not been widely adopted, in part, because of limitations associated with the availability of appropriate promoter-Nu reagents. We have devised a stereospecific Ag(I)-promoted reaction for functionalizing NuBFr products to give novel compositions of matter that may be useful in synthesis and medicinal chemistry. With unhindered amine nucleophiles, structurally unique [2.2.2]-bicycloamidines are generated. We also disclose for the first time detailed density functional theory studies, which shed light on the mechanism of the NuBFr and Ag-promoted substitution reaction that supports an unusual aziridinium ion as a key intermediate.

Unraveling the leaf-dropping behavior behind bat folivory: do bats use biological control against roost parasites?

Folivory in bats, the behavior of chewing bites of leaves to extract the liquid portion and discard the fiber as oral pellets, is seen as a strategy that might provide vitamins, micronutrients and proteins not always available in fruits, and even secondary metabolites (hormonal precursors) that stimulate/inhibit reproductive processes. While examining chewed leaves, we noticed an important amount of completely intact leaves below the roosts of Artibeus amplus and Artibeus lituratus, and decided to systematically quantify them during a year. We recovered 639 intact leaves from six plant species and found that both species are constantly feeding on leaves, but invariably leaving 26–78% of these intact, dropping them on the floor just below their roosting sites. These large proportions of dropped, intact leaves suggest a completely different, novel, non-nutritional use by bats. Several studies in birds have revealed that fresh leaves are effectively used in nests to control diverse organisms that include blood suckling ectoparasites, protozoans, fungus and bacteria. We report for the first time this biological control behavior performed by bats by selecting, bringing and dropping intact leaves below their roosting sites. The chemical properties of the leaves need to be investigated to reveal those active components against specific pathogens.

In vitro antileishmanial activity of leaf and stem extracts of seven Brazilian plant species

ETHNOPHARMACOLOGICAL RELEVANCE

Leishmaniasis is a parasitic disease that affects people all over the world. The number of cases of leishmaniasis is increasing and the drugs used for its treatment are toxic and not always effective. The recognition of the global nature of this disease and its direct or indirect effects on health economics and actions focuses attention on the development of new therapeutic options. In Brazil, this parasitic disease is endemic in many regions. The plants used by the population against leishmaniasis can be good starting points in the search of new lead compounds for antileishmanial drugs.

AIM OF THE STUDY

The aim of the present study was to investigate the antileishmanial activity of extracts from leaves and stems of seven Brazilian plant species used by the population to treat leishmaniasis, and symptoms that might be related to Leishmania infections.

MATERIALS AND METHODS

Twenty two extracts from seven plants belonging to five different botanical families were prepared by different methods and evaluated for their effect on the viability of promastigote forms of Leishmania infantum (MHOM/BR/1967/BH46) using the resazurin-based colorimetric assay. The extracts were considered active when they inhibited the growth of promastigotes in a percentage greater than or equal to 50% at 100 and 200 µg/mL. The active samples were further investigated to determine IC₅₀, CC₅₀ and SI values against promastigote forms of L. infantum. The active and non-cytotoxic extracts (SI> 10) were evaluated against amastigote forms of L. infantum. In addition, the active extracts against the amastigote forms were analyzed by TLC and HPLC, while the EtOAc extract of stems from Aspidosperma tomentosum was also evaluated by GC/MS.

RESULTS

Among the twenty two extracts evaluated, two were considered active against L. infantum. The EtOH extract of leaves from Dyospiros hispida (IC₅₀ 55.48 ± 2.77 µg/mL and IC₅₀ 80.63 ± 13.17 µg/mL, respectively) and the EtOAc extract of stems from Aspidosperma tomentosum (IC₅₀ 9.70 ± 2.82 µg/mL and IC₅₀ 15.88 ± 1.53 µg/mL, respectively) inhibited significantly the growth of promastigote and amastigote forms of L. infantum. Some extracts, although active in the initial screening, were considered toxic since the SI was lower than 10. In TLC and HPLC analysis the leaf extract of Dyospiros hispida showed the presence of anthraquinones, terpenes and saponins, and in the EtOAc extract of stems from Aspidosperma tomentosum alkaloids and flavonoids were detected. In addition, in the latter extract the indole alkaloids uleine and dasycarpidone could be identified by GC/MS.

CONCLUSIONS

The ethnopharmacological data of Aspidosperma tomentosum and Dyospiros hispida in part support the results found in the biological models used. Extracts of Aspidosperma tomentosum and Dyospiros hispida presented promising results against L. infantum.