Alkaloids from flowers of Erythrina corallodendron

Two new Erythrina alkaloids, 10-oxo-erythrinine (1) erythrinine N-oxide (2) together with 23 known ones were obtained from the flowers of Erythrina corallodendron. The structures were determined based on analysis of their spectroscopic data. All compounds were first isolated from plants of Erythrina corallodendron.     

Studies of Erythrina alkaloids: VII—13C NMR spectral studies of some Erythina alkaloids

A variety of alkaloids have been isolated from the seeds of a range of Erythrina species, including dienoid, alkenoid and lactonic derivatives. The ¹³C NMR spectra of these compounds have been assigned by internal comparisons within this series of related compounds and also by the use of model compounds.     

Intramolecular [4+2] cycloaddition reactions of enamines and enamides

An attempt to utilize a new strategy for alkaloid synthesis which features the intramolecular [4+2] cycloaddition of enamines and enamides for the construction of the tetracyclic spiroamine skeleton characteristic of the Erythrina alkaloids was unsuccessful, unexpectedly giving a bridged cycloadduct rather than a fused one.     

An overview of techniques and strategies for isolation of flavonoids from the genus Erythrina

Plants in the genus Erythrina is a potential source of chemical constituents, one of which is flavonoids, which have diverse bioactivities. To date, literature on the flavonoids from the genus Erythrina has only highlighted the phytochemical aspects, so this review article will discuss isolation techniques and strategies for the first time. More than 420 flavonoids have been reported in the Erythrina genus, which are grouped into 17 categories. These flavonoid compounds were obtained through isolation techniques and strategies using polar, semi-polar, and non-polar solvents. Various chromatographic techniques have been developed to isolate flavonoids using column flash chromatography, quick column chromatography, centrifugally accelerated thin-layer chromatography, radial chromatography, medium-pressure column chromatography, semi-preparative high-performance liquid chromatography, and preparative high-performance liquid chromatography. Chromatographic processes for isolating flavonoids can be optimized using multivariate statistical applications such as response surface methodology with central composite design, Box–Behnken design, Doehlert design, and mixture design.     

Three new dibromopyrrole alkaloids from the South China Sea sponge Agelas nemoechinata

Three new dibromopyrrole alkaloids, 9-N-methylcylindradine A (1), 1-N-methylugibohlin (2), nemoechine H (3), together with one known dibromopyrrole alkaloid N-methyldibromoisophakellin (4) were isolated from the South China Sea sponge Agelas nemoechinata. Their structures were elucidated by comprehensive spectroscopic methods including HRESIMS and NMR, and the absolute configuration of compound 1 was further confirmed by comparison of optical rotation. Compound 3 exhibited moderate cytotoxic activity against K562 and L-02 with IC₅₀ values of 6.1 μM and 12.3 μM, respectively.     

Oxidative Dearomatization of 4,5,6,7‐Tetrahydro‐1H‐indoles Obtained by Metal‐ and Solvent‐Free Thermal 5‐endo‐dig Cyclization: The Route to Erythrina and Lycorine Alkaloids

A facile one‐pot approach based on a thermally induced metal‐ and solvent‐free 5‐endo‐dig cyclization reaction of the amino propargylic alcohols in combination with Dess–Martin periodinane‐promoted oxidative dearomatization of 4,5,6,7‐tetrahydroindole intermediates provides an efficient and robust access to 5,6‐dihydro‐1H‐indol‐2(4H)ones. Green, relatively mild and operationally simple characteristics of the synthetic sequence are the major advantages, which greatly amplify the developed methodology. The utility of obtained indolones as unified key precursors is demonstrated by the application of these products to the formal total syntheses of a whole pleiad of Erythrina‐ and Lycorine‐type alkaloids, namely (±)‐erysotramidine, (±)‐erysotrine, (±)‐erythravine, (±)‐γ‐lycorane, and abnormal erythrinanes (±)‐coccoline and (±)‐coccuvinine.     

Late stages in the biosynthesis of abnormal erythrina alkaloids

The incorporation of (±)-, N-norprotosinomenine, N-nor-orientaline, N-nor-reticuline, norlaudanosoline, protosinomenine, and N-[2-(3-hydroxy-4-methoxyphenyl)ethyl]-2-(4-hydroxyphenyl) ethylamine into coccuvine has been studied, and the specific utilisation of the (±)-norprotosinomenine demonstrated. A double labelling experiment with (±)-[1-³H,4'-methoxy-¹⁴C]-N-norprotosinomenine showed that the 4'-O-Me group of the precursor is retained in the bioconversion and the erythrinan ring system is not formed by addition of secondary amino function onto an ortho-quinone system. Feeding of (±)-[1-³H, 7-methoxy-¹⁴C]norprotosinomenine established that O-demethylation is the terminal step in the biosynthesis of coccuvine. Feeding of labelled abnormal Erythrina alkaloids revealed that isococculidine is converted into coccoline via coccuvinine and isococculine into coccolinine via coccuvine.     

A new erythrinan N-oxide alkaloid from Erythrina stricta

This phytochemical study of stems and leaves of Erythrina stricta led to the isolation of twenty-three alkaloids, one of them previously unreported, 11β-hydroxyerythratidine N-oxide. Their structures were elucidated on the basis of extensive 1D and 2D NMR spectroscopic analyses including HSQC, HMBC, ¹H–¹H COSY, NOESY, as well as HRESIMS data in addition to comparison with reports in the literature.     

A formal asymmetric synthesis of both enantiomers of the Erythrina alkaloid 3-demethoxyerythratidinone

A formal asymmetric synthesis of both enantiomers of the Erythrina alkaloid 3-demethoxyerythratidinone is reported through the application of a highly functionalised lactam template as an N-acyliminium precursor.     

Optimization of Pressurized Liquid Extraction of Lycopodiaceae Alkaloids Obtained from Two Lycopodium Species

Alkaloids of the Lycopodiaceae family are of great interest to researchers due to their numerous properties and wide applications in medicine. They play a very important role mainly due to their potent antioxidant, antidepressant effects and a reversible ability to inhibit acetylcholinesterase (AChE) enzyme activity. This property is of immense importance due to the growing problem of an increasing number of patients with neurodegenerative diseases in developed countries and a lack of effective and efficient treatment for them. Numerous studies have shown that Lycopodiaceae alkaloids are a rich source of AChE inhibitors. In the obtaining of new therapeutic phytochemicals from plant material, the extraction process and its efficiency is crucial. Therefore, the aim of this work was to optimize the conditions of modern PLE to obtain bioactive alkaloids from two Lycopodium species: L. clavatum L. and L. annotinum L. Five different solvents of different polarity were used for prepared plant extracts in order to compare the alkaloid content in and thereby effectiveness of the entire extraction. PLE parameters were used based on multiple studies conducted that gave the highest alkaloids recovery. Crude extracts were purified using solid-phase extraction (SPE) on Oasis HLB cartridge and examined by HPLC/ESI-QTOF–MS of the highly abundant alkaloids. To the best of our knowledge, this is the first time such high recoveries have been obtained for known Lycopodiaceae alkaloids. The best extraction results of alkaloid-lycopodine were detected in the dichloromethane extract from L. clavatum, where the yield exceeded 45%. The high recovery of annotinine above 40% presented in L. annotinum was noticed in dichloromethane and ethyl acetate extracts. Moreover, chromatograms were obtained with all isolated alkaloids and the best separation and quality of the bands in methanolic extracts. Interestingly, no alkaloid amounts were detected in cyclohexane extracts belonging to the non-polar solvent. These results could be helpful for understanding and optimizing the best conditions for isolating potent AChE inhibitors.     

Synthetic Studies on Erythrina Alkaloids: Formal Total Synthesis of (+)-3-Demethoxyerythratidinone

A formal asymmetric synthesis of (+)-3-demethoxyerythratidinone (1) is reported using the key intermediate 3 as the starting material, which is available from L-malic acid by a known method.

Structure Elucidation and Cholinesterase Inhibition Activity of Two New Minor Amaryllidaceae Alkaloids

Two new minor Amaryllidaceae alkaloids were isolated from Hippeastrum × hybridum cv. Ferrari and Narcissus pseudonarcissus cv. Carlton. The chemical structures were identified by various spectroscopic (one- and two-dimensional (1D and 2D) NMR, circular dichroism (CD), high-resolution mass spectrometry (HRMS) and by comparison with literature data of similar compounds. Both isolated alkaloids were screened for their human acetylcholinesterase (hAChE) and butyrylcholinesterase (hBuChE) inhibition activity. One of the new compounds, a heterodimer alkaloid of narcikachnine-type, named narciabduliine (2), showed balanced inhibition potency for both studied enzymes, with IC₅₀ values of 3.29 ± 0.73 µM for hAChE and 3.44 ± 0.02 µM for hBuChE. The accommodation of 2 into the active sites of respective enzymes was predicted using molecular modeling simulation.     

Chemical Synthesis and Biological Activities of Amaryllidaceae Alkaloid Norbelladine Derivatives and Precursors

Amaryllidaceae alkaloids (AAs) are a structurally diverse family of alkaloids recognized for their many therapeutic properties, such as antiviral, anti-cholinesterase, and anticancer properties. Norbelladine and its derivatives, whose biological properties are poorly studied, are key intermediates required for the biosynthesis of all ~650 reported AAs. To gain insight into their therapeutic potential, we synthesized a series of O-methylated norbelladine-type alkaloids and evaluated their cytotoxic effects on two types of cancer cell lines, their antiviral effects against the dengue virus (DENV) and the human immunodeficiency virus 1 (HIV-1), and their anti-Alzheimer’s disease (anti-cholinesterase and -prolyl oligopeptidase) properties. In monocytic leukemia cells, norcraugsodine was highly cytotoxic (CC₅₀ = 27.0 μM), while norbelladine was the most cytotoxic to hepatocarcinoma cells (CC₅₀ = 72.6 μM). HIV-1 infection was impaired only at cytotoxic concentrations of the compounds. The 3,4-dihydroxybenzaldehyde (selectivity index (SI) = 7.2), 3′,4′-O-dimethylnorbelladine (SI = 4.8), 4′-O-methylnorbelladine (SI > 4.9), 3′-O-methylnorbelladine (SI > 4.5), and norcraugsodine (SI = 3.2) reduced the number of DENV-infected cells with EC₅₀ values ranging from 24.1 to 44.9 μM. The O-methylation of norcraugsodine abolished its anti-DENV potential. Norbelladine and its O-methylated forms also displayed butyrylcholinesterase-inhibition properties (IC₅₀ values ranging from 26.1 to 91.6 μM). Altogether, the results provided hints of the structure–activity relationship of norbelladine-type alkaloids, which is important knowledge for the development of new inhibitors of DENV and butyrylcholinesterase.     

Completion of the Total Synthesis of Several Bioactive Sarpagine/Macroline Alkaloids including the Important NF-κB Inhibitor N4-Methyltalpinine

The unification of the general synthetic strategy regarding the important and emerging group of C-19 methyl-substituted sarpagine/macroline alkaloids has culminated in the completion of the total synthesis of several bioactive alkaloids. Key transformations include an ACE-Cl mediated late-stage N(4)-demethylation and an anhydrous acid-mediated intramolecular quaternary hemiaminal formation between a tertiary amine and an aldehyde function to allow efficient access to several biologically important alkaloids from this group. Herein, the enantiospecific total synthesis of the first known sarpagine/macroline alkaloid with NF-κB inhibitory activity, N(4)-methyltalpinine (as a chloride salt), as well as the anticancer alkaloids talpinine, O-acetyltalpinine, and macrocarpines F–G, are described.     

Chabamides F and G, two novel dimeric alkaloids from the roots of piper chaba hunter

Two new dimeric alkaloids, chabamide F (1) and chabamide G (2), containing pyrrolidine rings, were isolated from the roots of piper chaba hunter. The structures of 1 and 2 were established on the basis of spectroscopic data, especially 2D NMR and mass spectral data.     

Asperflaloids A and B from Aspergillus flavipes DZ-3, an Endophytic Fungus of Eucommia ulmoides Oliver

The fungus strain DZ-3 was isolated from twigs of the well-known medicinal plant Eucommia ulmoides Oliver and identified as Aspergillus flavipes. Two new alkaloids, named asperflaloids A and B (1 and 2), together with 10 known compounds (3–12) were obtained from the EtOAc extract of the strain. Interestingly, the alkaloids 1–4 with different frameworks are characterized by the presence of the same anthranilic acid residue. The structures were established by detailed analyses of the spectroscopic data. The absolute configuration of asperflaloids A and B was resolved by quantum chemistry calculation. All compounds were screened for their inhibitions against α-glucosidase and the antioxidant capacities. The results were that compound 3 had an IC₅₀ value of 750.8 μM toward α-glucosidase, and the phenol compounds 7 and 8 exhibited potent antioxidant capacities with IC₅₀ values 14.4 and 27.1 μM respectively.     

An experimental design approach to obtain canthinone alkaloid-enriched extracts from Simaba aff. paraensis

The species of the genus Simaba (Simaroubaceae) are found in almost all Brazil and they are used by local population for the treatment of ulcers and malaria. The genus is characterized by the presence of quassinoids and canthinone alkaloids. There is a great interest in canthinones due to important biological activities associated with this class of alkaloids. In this study, methods were developed for obtaining enriched fractions of canthinone alkaloids from Simaba aff. paraensis using experimental factorial design analyzed by gas chromatography. Three alkaloids were detected: canthin-6-one, 4,5-dimethoxycanthin-6-one and the major 9-methoxycanthin-6-one. Within the experimental domain, factorial designs 2² helped establish the minimum amount of solvent and minimum time necessary to obtain extracts enriched in canthinone alkaloids from S. aff. paraensis barks by two extraction methods. These results represent a reduction in costs for obtaining canthinone alkaloids described for the first time in S. aff. paraensis.