Melohenines A and B, Two Unprecedented Alkaloids from Melodinus henryi

Biomimetic Synthesis of Biologically Active Natural Products: An Updated Review

BACKGROUND

Natural products have optical activities with unusual structural characteristics or specific stereoselectivity, mostly including spiro-ring systems or quaternary carbon atoms. Expensive and time-consuming methods for natural product purification, especially natural products with bioactive properties, have encouraged chemists to synthesize those compounds in laboratories. Due to their significant role in drug discovery and chemical biology, natural products have become a major area of synthetic organic chemistry. Most medicinal ingredients available today are healing agents derived from natural resources, such as plants, herbs, and other natural products.

METHODS

Materials were compiled using the three databases of ScienceDirect, PubMed, and Google Scholar. For this study, only English-language publications have been evaluated based on their titles, abstracts, and full texts.

RESULTS

Developing bioactive compounds and drugs from natural products has remained challenging despite recent advances. A major challenge is not whether a target can be synthesized but how to do so efficiently and practically. Nature has the ability to create molecules in a delicate but effective manner. A convenient method is to imitate the biogenesis of natural products from microbes, plants, or animals for synthesizing natural products. Inspired by the mechanisms occurring in the nature, synthetic strategies facilitate laboratory synthesis of natural compounds with complicated structures.

CONCLUSION

In this review, we have elaborated on the recent syntheses of natural products conducted since 2008 and provided an updated outline of this area of research (Covering 2008-2022) using bioinspired methods, including Diels-Alder dimerization, photocycloaddition, cyclization, and oxidative and radical reactions, which will provide an easy access to precursors for biomimetic reactions. This study presents a unified method for synthesizing bioactive skeletal products.

Chemical constituents and anti-inflammatory activity of the total alkaloid extract from Melodinus cochinchinensis (Lour.) Merr. and its inhibition of the NF-κB and MAPK signaling pathways

BACKGROUND

Melodinus cochinchinensis (Lour.) Merr. is a medicinal plant, which is used as a folk medicine for treating meningitis and fractures. However, the anti-inflammatory activity of total alkaloid extract from M. cochinchinensis (MCTA) and its molecular mechanism are still not studied.

PURPOSE

The aim of this study is to investigate the main chemical constituents of MCTA and explore its anti-inflammatory potential in both in vitro and in vivo assessments.

METHODS

UHPLC-ESI-HRMS/MS was applied to analyze the chemical profiling. The anti-inflammatory efficacy of MCTA was evaluated on lipopolysaccharide (LPS) induced RAW 264.7 cells and two common inflammation models in mice. The production of pro-inflammatory mediator and cytokine was tested using the ELISA method. The pathological change was analyzed by histological assessment. The expression of NF-κB, MAPKs and PPAR-γ proteins was evaluated using western blot analysis.

RESULTS

A total of 21 monoterpenoid indole alkaloids (MIAs) were characterized by UHPLC-ESI-HRMS/MS. Aspidospermine- and quinolone-type alkaloids were found to be the major compounds. MCTA significantly decreased the production of NO, IL-1β, IL-6 and TNF-α in LPS-induced RAW 264.7 macrophages. MCTA significantly inhibited the phosphorylation of ERK1/2, JNK and p38 MAPK, suppressed the NF-κB transcriptional activation and improved the PPAR-γ expression. Moreover, the in vivo experiment exhibited that MCTA pretreatment markedly alleviated the xylene-induced ear edema and carrageenan-induced paw edema in mice and decreased the IL-1β, IL-6 and TNF-α expressions.

CONCLUSION

MCTA is rich in MIAs and exhibited a significant inhibitory effect on the production proinflammatory cytokines. The mechanism might be related to the inhibition of activation of NF-κB and MAPK pathways.

Melodinines Y1–Y4, four monoterpene indole alkaloids from Melodinus henryi

Melodinines Y₁–Y₄ (1–4), four undescribed alkaloids were isolated from Melodinus henryi. Their structures were elucidated by extensive NMR, mass spectroscopic analyses, theoretical NMR and electronic circular dichroism (ECD) calculations. Compounds 1 and 2 are the first examples of bisindole alkaloids possessing an eburnamine–leuconoxine combination. Compound 3 is a rare 2,3-seco pleiocarpamine type monoterpene indole alkaloid. Compound 1 showed cytotoxic activities against six human cancer cell lines with IC₅₀ values of 0.5–15.2 μM.

Monoterpenoid indole alkaloids from Melodinus henryi

Acute and Sub-Acute Toxicological Evaluations of Bioactive Alkaloidal Extract from Melodinus henryi and Their Main Chemical Constituents

Melodinus henryi is a good source of terpenoid indole alkaloids, and traditionally used as a folk medicine in the treatment of meningitis and fracture. In order to further exploit their potential uses, its anti-inflammatory and immunosuppressive activities, safety evaluations and chemical profiles have been illustrated. Compared to the crude methanol extract from M. henryi and its non-alkaloidal fraction, the total alkaloidal fraction (MHTA) had the strongest anti-inflammatory and immunosuppressive activities. In the acute oral toxicity assay, the half lethal dose (LD50) of MHTA was more than 2000 mg/kg. The sub-acute toxicity assay for consecutive 28 days exhibited MHTA at a lower concentrations of less than 500 mg/kg might be regarded as safe, and might damage spleen, liver, kidney, and heart when the dose is higher than 1000 mg/kg. In addition, a phytochemical investigation on MHTA led to the isolation of 15 monoterpenoid indole alkaloids. Thus, in regard with the potent side effects of MHTA, it should be used with caution in the development of phytomedicine.

Cytotoxic aspidosperma-type alkaloids from Melodinus suaveolens

Four new aspidosperma-type alkaloids, melosuavines J-M (1-4) were isolated from the leaves of Melodinus suaveolens. Their structures with absolute configurations were elucidated by extensive HRESIMS and NMR spectroscopic analysis, as well as ECD calculations and Mosher's method. Their cytotoxic activities against four human cancer cell lines were also evaluated.

Monoterpenoid indole alkaloids from the stems of Kopsia officinalis

Five new indole alkaloids, kopsiofficines H-L (1-5), along with fourteen known alkaloids (6-19) were isolated from the stems of Kopsia officinalis. Their structures were elucidated by extensive NMR, mass spectroscopic analyses and comparison to the reported data. All the isolated compounds were evaluated their anti-inflammatory activities by inhibiting IL-1β, PGE2 and TNF-α secretion in lipopolysaccharide (LPS)-activated RAW264.7 cells. Compounds 2, 3, 6, 7, 11, 12, 15, and 17 show significant anti-inflammatory activities. These results demonstrate pharmacodynamic substance basis of these folkloric claims.

Melognine, a novel monoterpenoid indole alkaloid from Melodinus fusiformis that induce apoptosis in BT549 cells

A novel monoterpenoid indole alkaloid, melognine (1) possessing an unprecedented skeleton with a 6/6/5/5/6/6 hexatomic rearranged ring system was isolated from the stems of Melodinus fusiformis. The structure with absolute configuration of 1 was established by extensive spectroscopic analyses and quantum ECD calculations. Melognine showed significant cytotoxicity on human breast cancer BT549 cells with an IC₅₀ value of 1.49 μM by MTT assay. Further mechanism of action study indicated that melognine demonstrated the ability to induce apoptosis by activation of caspase-3 and p53, and downregulation of Bcl-2 in BT549 cells.

New aporphine alkaloids with selective cytotoxicity against glioma stem cells from Thalictrum foetidum

Seven new isoquinoline alkaloids, 9-(2'-formyl-5', 6'-dimethoxyphenoxy)-1, 2, 3, 10-tetramethoxy dehydroaporphine (1), 9-(2'-formyl-5', 6'-dimethoxyphenoxy)-1, 2, 3, 10-tetramethoxy oxoaporphine (2), 3-methoxy-2'-formyl oxohernandalin (3), (-)-9-(2'-methoxycarbonyl-5', 6'-dimethoxyphenoxy)-1, 2, 3, 10-tetramethoxy aporphine (4), (-)-2'-methoxycarbonyl thaliadin (5), (-)-9-(2'-methoxyethyl-5', 6'-dimethoxyphenoxy)-1, 2, 3, 10-tetramethoxy aporphine (6), (-)-3-methoxy hydroxyhernandalinol (7), together with six known isoquinoline alkaloids (8-13) were isolated from the roots of Thalictrum foetidum. Their structures were elucidated by extensive spectroscopic measurements. Compounds 1 and 2 showed significant selective cytotoxicity against glioma stem cells (GSC-3^# and GSC-18^#) with IC₅₀ values ranging from 2.36 to 5.37 μg·mL^-1.

Hunterines A-C, Three Unusual Monoterpenoid Indole Alkaloids from Hunteria zeylanica

Three new monoterpenoid indole alkaloids (MIAs), hunterines A-C (1-3), were isolated from Hunteria zeylanica. Compound 1 possesses a unique skeleton with an unprecedented azabicyclo[4.3.1]decane ring system. Compounds 2 and 3 are a pair of epimeric vobasinylindole alkaloid heterodimers. Their structures including absolute configurations were established by spectroscopic analyses, X-ray diffraction, computational calculation, and the modified Mosher's method. Plausible biogenetic pathways of 1-3 were also proposed. Alkaloid 1 showed moderate cytotoxic activity against the HepG2 cell line.

Alkaloids from Melodinus henryi with anti-inflammatory activity

One new quinolinic scandine-type monoterpeniod alkaloid, 3-oxo-scandine (1), as well as seven known ones (2-8), was isolated from the roots of Melodinus henryi. Their structures were elucidated by extensive spectroscopic analysis. All of the compounds were prepared and evaluated for their anti-inflammatory activities by measuring the inhibitory activity of nitric oxide (NO) in vitro in RAW 264.7 mouse peritoneal macrophages. Compounds 6 and 7 showed significant activities with IC₅₀ values of 8.54 and 5.19 μM, respectively.

Cytotoxic aspidosperma-type alkaloids from Melodinus axillaris

One new aspidosperma-type alkaloid, melotenine A (1), together with five known ones (2-6), was isolated from the leaves of Melodinus axillaris. Their structures were elucidated by detailed spectroscopic analysis and quantum chemical ECD calculation. The isolated aspidosperma-type alkaloids were evaluated for their cytotoxicity against four human cancer cell lines and melotenine A showed significant cytotoxicity against all cells with IC₅₀ values ranging from 0.6 to 1.5 μM.

Hybrid isoquinolines from Thalictrum foetidum: a new type of aporphine inhibiting Staphylococcus aureus by combined mechanisms

Thalfoetines A–D (1–4), unique hybrid aporphine alkaloids with a C-7 aromatic unit formed by a new C–C bond linking two building blocks, were isolated from Thalictrum foetidum.

Novel nor-monoterpenoid indole alkaloids inhibiting glioma stem cells from fruits of Alstonia scholaris

BACKGROUND

Glioblastoma multiforme (GBM) is a highly aggressive and frequently recurrent malignant brain tumor, and to date, the clinically effective drugs against GBM remain scarce. Natural products play an important role in drug discovery, and might be the resource of antitumor agents for GSCs. Alstonia scholaris (L.) R. Br. is rich in monoterpenoid indole alkaloids (MIAs) and used extensively for treatment of tumor in the traditional medicine system of Asia.

PURPOSE

To search for new MIAs with antitumor activity against glioma stem cells from clinical patients and explore their mechanism.

METHODS

Compounds were obtained from the fruits of A. scholaris by chromatographic separation, including silica gel, Sephadex LH-20 and recrystallization. Their structures were elucidated by the use of UV, IR, NMR and MS spectra. The antitumor activity of the compounds against the glioma stem cells (GSC-3#, GSC-12#, GSC-18#) were investigated by phenotypic screening and MTS assays. Cell proliferation assay by BrdU immunofluorescence staining, and apoptosis assay by cleaved-caspase-3 immunofluorescence staining and real-time PCR assay. The soft-agar clonal formation assay was performed to determine the antitumor efficacy of the compounds in vitro.

RESULTS

Two new nor-monoterpenoid indole alkaloids were isolated from the fruits of A. scholaris. They exhibited selective antitumor activity against glioma stem cells (GSC-3#, GSC-12#, GSC-18#) with IC₅₀ values of 15-25 µg/ml. Furthermore, they inhibited GSCs proliferation, induced GSCs apoptosis by increasing the expression of TNF-α and cleavage of caspase-3, and significantly damaged colony forming capacity of GSCs.

CONCLUSION

New nor-monoterpenoid indole alkaloids from the fruits of A. scholaris provide new type promising molecule for the selective killing of human glioma stem cells.

Antibacterial Indole Alkaloids with Complex Heterocycles from Voacanga africana

Voacafricines A and B, two unique monoterpenoid indole alkaloids each bearing five fused heterocycles, were obtained from the fruits of Voacanga africana. Their structures were elucidated by extensive spectroscopic methods and computational studies. A plausible biogenetic pathway was proposed from a common precursor, 19- epi-voacristine. Both compounds exhibited potent activity against Staphylococcus aureus and Salmonella typhi, and their activities were superior to those of the well-known antibacterial drugs berberine and fibrauretine.

Pd(ii)-Catalyzed oxidative dearomatization of indoles: substrate-controlled synthesis of indolines and indolones

A Pd(ii)-catalyzed oxidative dearomatization of indoles provides a straightforward access to diverse fused indolines and indolones bearing C2-oxygenated quaternary stereocenters.

Melaxillines A and B, monoterpenoid indole alkaloids from Melodinus axillaris

Two new monoterpenoid indole alkaloids, melaxillines A (1) and B (2), together with four known alkaloids (3-6), were isolated from the roots of Melodinus axillaris. The structures were determined by extensive spectroscopic methods, including 1D and 2D-NMR spectroscopy, high resolution mass spectrometric data, and by comparison to literature data. New compounds 1-2 might be derived from a common precursor (3) by proposing their biogenetic route, and compound 1 represents the first Melodinus alkaloid featuring an ethyl acetate group skeleton at C-18. The anti-inflammatory effects of all the isolated compounds were evaluated by measuring the inhibitory ratios of β-glucuronidase release in rat polymorphonuclear leukocytes (PMNs) induced by platelet-activating factor. Compounds 1-4 showed significant anti-inflammatory activities with IC₅₀ values ranging from 1.51 to 21.56μM, respectively.

Melokhanines A-J, Bioactive Monoterpenoid Indole Alkaloids with Diverse Skeletons from Melodinus khasianus

The new melokhanines A-J (1-10) and 22 known (11-32) alkaloids were isolated from the twigs and leaves of Melodinus khasianus. The new compounds and their absolute configurations were elucidated by extensive analysis of spectroscopic, X-ray diffraction, and computational data. Melokhanine A (1), composed of a hydroxyindolinone linked to an octahydrofuro[2,3-b]pyridine moiety, is an unprecedented monoterpenoid indole alkaloid. Melokhanines B-H (2-8) possess a new 6/5/5/6/6 pentacyclic indole alkaloid skeleton. Alkaloids 1-16, 25-27, 31, and 32 showed the best antibacterial activity against Pseudomonas aeruginosa (MIC range 2-22 μM). Among the seven dermatophytes tested, compound 1 showed significant inhibitory activity against Microsporum canis, M. ferrugineum, and Trichophyton ajelloi (MIC range 38-150 μM), i.e., half the efficacy of the positive control, griseofulvin.

Two new compounds from Melodinus suaveolens

Two new compounds, 19-hydroxy-melodinine K (1) and melodiside (2), and 25 known compounds were isolated from leaves and twigs of Melodinus suaveolens. Their structures were elucidated based on 1- and 2-D NMR, FTIR, UV and MS spectroscopic data. 19-hydroxy-melodinine K showed cytotoxic activity against MDA-MB-231 breast, BCG-823 gastric, SW480 colon and Hela cancer cells.

Fusiformines A and B: new indole alkaloids from Melodinus fusiformis

Fusiformines A (1) and B (2), two new monoterpenoid indole alkaloids, were isolated from the twigs and leaves of Melodinus fusiformis. Their structures were established by extensive spectroscopic techniques, including 2D NMR spectroscopy and mass spectrometry.

Aspidosperma-type Alkaloids from Melodinus Suaveolens

Three new aspidosperma-type alkaloids, 3-oxo-11-hydroxytabersonine (2), 11-hydroxytabersonine N-oxide (3) and 11-methoxytabersonine N-oxide (4), along with three known ones were isolated from the twigs and leaves of Melodinus suaveolens. The structures of the new compounds were elucidated by using spectroscopic methods, and circular dichroism experiments. The known compounds were identified by comparing their spectroscopic data with those reported in the literature.

Six new alkaloids from Melodinus henryi

A total of six new alkaloids, melodinhenines A-F (1-6), were isolated from Melodinus henryi. Melodinhenines A and B are new eburnan-vindolinine-type bisindole alkaloids and melodinhenines C-F are new quinolinic melodinus alkaloids. Their structures were elucidated through extensive spectroscopic methods including 2D NMR and HRESIMS analyses. The absolute configuration of 1 and 2 was determined using ECD exciton chirality method. To the best of our knowledge, this is the first report on the determination of the absolute configuration of eburnan-vindolinine-type bisindole alkaloid using this method.

Two New Alkaloids from Melodinus suaveolens

Two new Melodinus-type alkaloids, 15 β-hydroxy-14,15-dihydroscandine (1) and 14,15-dihydroscandine (2), together with 6 known ones were isolated from Melodinus suaveolens. The structures of the new compounds were identified from spectroscopic (NMR, UV, IR, CD) and mass spectrometric data and Mosher's method. The new compounds exhibited significant, dose-dependent inhibition of the production of lipopolysaccharide (LPS)-induced NO, IL-6 and IL-8 in mice macrophages.

Alkaloids from Melodinus yunnanensis

Ten monoterpenoid indole alkaloids, namely meloyine, 19S-methoxytubotaiwine N₄-oxide, 16,19-epoxy-Δ¹⁴-vincanol, 14β-hydroxymeloyunine, meloyunine, Δ¹⁴-vincamenine N₄-oxide, 16β,21β-epoxy-vincadine, 14β,15β-20S-quebrachamine, 3-oxo-voaphylline, 2α,7α-dihydroxy-dihydrovoaphylline, and 32 known alkaloids were isolated from leaves and twigs of Melodinus yunnanensis. Their structures were elucidated based on 1- and 2-D NMR, FTIR, UV, and MS spectroscopic data. Meloyine I showed weak cytotoxic activity against four human cancer cell lines: MCF-7 breast cancer, SMMC-7721 hepatocellular carcinoma, HL-60 myeloid leukemia, and A-549 lung cancer.

Melodinines M-U, cytotoxic alkaloids from Melodinus suaveolens

Nine new alkaloids, melodinines M-U (1-9), and 11 known alkaloids were isolated from Melodinus suaveolens. The new structures were elucidated by extensive NMR and mass spectroscopic analyses and comparison to known compounds. All compounds were evaluated for their cytotoxicity against five human cancer cell lines. Compounds 6, 11, and 16 showed significant cytotoxicity.