[Alstonia scholaris: the structure of the indole alkaloid nareline (author's transl)]

Monoterpenoid indole alkaloids from Alstonia scholaris and their Toxoplasma gondii inhibitory activity

Nine previously unreported various types of monoterpenoid indole alkaloids, together with seven known analogues were isolated from the stem barks of Alstonia scholaris through a silica gel free methodology. The structures of 1-9 were elucidated by spectroscopic data analysis, electronic circular dichroism calculations, and single-crystal X-ray diffraction. Compound 1 is a modified echitamine-type alkaloid with a novel 6/5/5/7/6/6 hetero hexacyclic bridged ring system, and 8 and 9 exist as a zwitterion and trifluoroacetate salt, respectively. The anti-Toxoplasma activity of all isolates on infected Vero cells were evaluated, which revealed that compound 14 at 0.24 μM displayed potent activity. This study expanded the structural diversity of alkaloids of A. scholaris, and presented their potential application in anti-Toxoplasma drug development.

Assessment of Tissue Specific Distribution and Seasonal Variation of Alkaloids in Alstonia scholaris

Alstonia scholaris is a well-known source of alkaloids and widely recognized for therapeutic purposes to treat the ailments in human and livestock. However, the composition and production of alkaloids vary due to tissue specific metabolism and seasonal variation. This study investigated alkaloids in leaves, stems, trunk barks, fruits, and flowers of A. scholaris. The impact of seasonal changes on the production of alkaloids in the leaves of A. scholaris was also investigated. One and two-dimensional Nuclear Magnetic Resonance (NMR) experiments were utilized for the characterization of alkaloids and total eight alkaloids (picrinine, picralinal, akuammidine, 19 S scholaricine, 19,20 E vallesamine, Nb-demethylalstogustine N-Oxide, Nb-demethylalstogustine, and echitamine) were characterized and quantified. Quantitative and multivariate analysis suggested that the alkaloids content is tissue specific, illustrating the effect of plant tissue organization on alkaloidal production in A. scholaris. The results suggest that the best part to obtain alkaloids is trunk barks, since it contains 7 alkaloids. However, the best part for isolating picrinine, picralinal, akuammidine, 19 S scholaricine, and 19,20 E vallesamine is fruit, since it shows highest amount of these alkaloids. Undoubtedly, NMR and statistical methods are very helpful to differentiate the profile of alkaloids in A. scholaris.

Chemical Diversity and Bioactivities of Monoterpene Indole Alkaloids (MIAs) from Six Apocynaceae Genera

By the end of the twentieth century, the interest in natural compounds as probable sources of drugs has declined and was replaced by other strategies such as molecular target-based drug discovery. However, in the recent times, natural compounds regained their position as extremely important source drug leads. Indole-containing compounds are under clinical use which includes vinblastine and vincristine (anticancer), atevirdine (anti-HIV), yohimbine (erectile dysfunction), reserpine (antihypertension), ajmalicine (vascular disorders), ajmaline (anti-arrhythmic), vincamine (vasodilator), etc. Monoterpene Indole Alkaloids (MIAs) deserve the curiosity and attention of researchers due to their chemical diversity and biological activities. These compounds were considered as an impending source of drug-lead. In this review 444 compounds, were identified from six genera belonging to the family Apocynaceae, will be discussed. These genera (Alstonia, Rauvolfia, Kopsia, Ervatamia, and Tabernaemontana, and Rhazya) consist of 400 members and represent 20% of Apocynaceae species. Only 30 (7.5%) species were investigated, whereas the rest are promising to be investigated. Eleven bioactivities, including antibacterial, antifungal, anti-inflammatory and immunosuppressant activities, were reported. Whereas cytotoxic effect represents 47% of the reported activities. Convincingly, the genera selected in this review are a wealthy source for future anticancer drug lead.

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.

Monoterpenoid indole alkaloids from the leaves of Alstonia scholaris and their NF-κB inhibitory activity

Four new monoterpenoid indole alkaloids (MIAs), scholarisines P-S (1-4), and 14 known MIAs (5-18) were isolated from the leaves of Alstonia scholaris (L) R. Br. (Apocynaceae). Their structures were elucidated by analyzing their HRESIMS data and NMR spectroscopic data. All of the isolated MIAs were evaluated for their Nuclear Factor-kappa B (NF-κB) inhibitory activity in HepG2-NF-κB-Luc cells. Among them, five compounds (4, 7, 8, 13 and 16) exhibited significant NF-κB inhibitory activity.

Monoterpenoid Indole Alkaloids from Inadequately Dried Leaves of Alstonia scholaris

Six new indole alkaloids, named alstoniascholarines L-Q (1-6), together with nineteen known analogues were isolated from the inadequately dried leaves of Alstonia scholaris. Their structures were elucidated on the basis of extensive analysis of spectroscopic data and by comparison of their physical and spectroscopic data with the literature values. In addition, the new alkaloids were tested for their cytotoxic and neurite outgrowth-promoting activities.

Access to the akuammiline family of alkaloids: total synthesis of (+)-scholarisine A

The planning and implementation of an enantioselective total synthesis of (+)-scholarisine A is presented. Key tactics employed include a novel cyclization, consisting of a nitrile reduction coupled with concomitant addition of the resultant amine to an epoxide; a modified Fischer indolization; an oxidative lactonization of a diol in the presence of an indole ring; and a late-stage cyclization to complete the caged ring scaffold. The development of a possible "retro-biosynthetic" approach to other members of the akuammiline alkaloid family is also described.

A Review of the Ethnobotany and Pharmacological Importance of Alstonia boonei De Wild (Apocynaceae)

Alstonia boonei De Wild is a herbal medicinal plant of West African origin, popularly known as God's tree or "Onyame dua". Within West Africa, it is considered as sacred in some forest communities; consequently the plant parts are not eaten. The plant parts have been traditionally used for its antimalarial, aphrodisiac, antidiabetic, antimicrobial, and antipyretic activities, which have also been proved scientifically. The plant parts are rich in various bioactive compounds such as echitamidine, Nα-formylechitamidine, boonein, loganin, lupeol, ursolic acid, and β-amyrin among which the alkaloids and triterpenoids form a major portion. The present paper aims at investigating the main research undertaken on the plant in order to provide sufficient baseline information for future work and for commercial exploitation.

A cage-monoterpene indole alkaloid from Alstonia scholaris

An unprecedented cage-like alkaloid, scholarisine A was isolated from the leaves of Alstonia scholaris and its structure determined on the basis of 1D and 2D NMR, FTIR, UV, and high-resolution mass spectroscopic data. This alkaloid might be derived from picrinine via oxygenation, rearrangement, and lactonization.

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.

New indole alkaloids from the bark of Alstonia scholaris

A new indole alkaloid, akuammiginone (1), and a new glycosidic indole alkaloid, echitamidine-N-oxide 19-O-beta-d-glucopyranoside (2), together with the five known alkaloids, echitaminic acid (3), echitamidine N-oxide (4), N(b)-demethylalstogustine N-oxide (5), akuammicine N-oxide (6), and N(b)-demethylalstogustine (7), were isolated from the trunk bark of Alstonia scholaris collected in Timor, Indonesia. The structures of all compounds were elucidated by spectroscopic methods. This is the first report of compounds 3-5and 7 in A. scholaris. Some NMR assignments of the known compounds were revised.

Studying Chemistry of Heterocyclic Compounds —Some Rearrangement Reactions of Indoles and the Related Compounds—

Indole alkaloids are one of the most interesting research fields. The chemistry of monoterpenoid indole alkaloids, in particular, offers many skeletal rearrangement reactions including terpenoid rearrangements. The author describes those compounds encountered or connected with in his research, including iridoids, indole alkaloids, adamantanes found in nature, and oxyindoles that are correlated with rearrangements.

New indole alkaloids from Alstonia macrophylla

Ten new indole alkaloids, alstomaline (1), 10,11-dimethoxynareline (2), alstohentine (3), alstomicine (4), 16-hydroxyalstonisine (5), 16-hydroxyalstonal (6), 16-hydroxy-N(4)-demethylalstophyllal oxindole (7), alstophyllal (8), 6-oxoalstophylline (9), and 6-oxoalstophyllal (10), in addition to 21 other known ones, were obtained from the leaf extract of the Malayan Alstonia macrophylla. The structures were determined using NMR and MS analysis.