Alstoscholarisine K, an Antimicrobial Indole from Gall-Induced Leaves of Alstonia scholaris

Copper-Catalyzed Chemoselective O-Arylation of Oxindoles: Access to Cyclic Aryl Carboxyimidates

We have developed a highly efficient base- and additive-free chemoselective CuO-catalyzed strategy for the O-arylation of 2-oxindoles to synthesize 2-phenoxy-3H-indole and 2-phenoxy-1H-indole derivatives in the presence of diaryl iodonium salts. This method offers a variety of O-arylated oxindoles in good to excellent yields under relatively milder reaction conditions. Furthermore, this methodology was extended for the O-arylation of 2-pyridinone and isoindoline-1-one derivatives as well.

Aspertaichamide a, a novel cytotoxic prenylated indole alkaloid possessing a bicyclo[2.2.2]diazaoctane framework from a marine algal-derived endophytic fungus aspergillus taichungensis 299

Filamentous fungi belonging to the genus Aspergillus are prodigious producers of alkaloids, particularly prenylated indole alkaloids, that often exhibit structurally diversified skeletons and potent biological activities. In this study, five prenylated indole alkaloids possessing a bicyclo[2.2.2]diazaoctane core ring system, including a novel derivative, namely aspertaichamide A (1), as well as four known compounds, (+)-stephacidin A (2), sclerotiamide (3), (-)-versicolamide B (4), and (+)-versicolamide B (5), were isolated and identified from A. taichungensis 299, an endophytic fungus obtained from the marine red alga Gelidium amansii. The chemical structures of the compounds were elucidated by comprehensive NMR and HRESIMS spectroscopic analyses. In addition to the previously reported prenylated indole alkaloids, aspertaichamide A (1) was characterized as having an unusual ring structure with the fusion of a 3-pyrrolidone dimethylbenzopyran to the bicyclo[2.2.2]diazaoctane moiety, which was rare in these kinds of compounds. The absolute configuration of 1 was determined by TDDFT-ECD calculations. In vitro cytotoxic assays revealed that the novel compound 1 possessed selective cytotoxic activity against five human tumor cell lines (A549, HeLa, HepG2, HCT-116, and AGS), with IC50 values of 1.7-48.5 μM. Most importantly, compound 1 decreased the viability of AGS cells in a concentration-dependent manner with an IC50 value of 1.7 μM. Further studies indicated that 1 may induce AGS cells programmed cell death via the apoptotic pathway.

Undescribed indole lactones from Alstonia scholaris protecting hepatic cell damage

Six previously undescribed rigidly monoterpenoid indole alkaloids, alstolactines F-K (1-6), were isolated from Alstonia scholaris. Among them, a pair of cage-like epimers, 1 and 2, featuring a rare 6/5/6/6/7 ring system, represent the first example of C5→C20-olide, while compound 3 possesses unique degraded C18 and C19. The structures of the isolates were established by multiple spectroscopic analyses, quantum computational chemistry methods, and X-ray diffraction. Furthermore, the expression levels of proteins including NLRP3, TLR4, P-p65, NF-ĸB, Notch-2, IL-18, P-p38, and p38 in LPS-induced human normal hepatocyte (LO2) cells could be significantly downregulated by compounds 1-6, which showed potent anti-inflammatory bioactivity.

Spirooxindol alkaloids from Voacanga africana: Targeting biofilm of MBLs producing Escherichia coli

Seven rarely spirooxindole alkaloids, voagafricines A-G (1-7) were isolated from the stem barks of Voacanga africana. Their structures were unambiguously elucidated by comprehensive spectroscopic data and electronic circular dichroism (ECD) analyses. 1 and 2 possess a unique indoleone system in conjugation with a 3,4'-decahydroquinoline spiral ring originating from seco-quinolhiddin core of the precursor, furthermore 1 undergo decarburization formed a novel C-3-nor monoterpenoid indole. All isolates were evaluated for their antibacterial activities against MBLs producing Escherichia coli strains. Compounds 1 and 7 were found to be potent inhibitors against E. coli 298 and 140 by targeting biofilm. Possible interaction sites of 1 and 7 with biofilm were preliminarily explored by means of molecular docking.

New Lupanes from Alstonia scholaris Reducing Uric Acid Level

Twelve lupanes including three new compounds named alstoscholarilups A-C (1: -3: ) were isolated from the leaves of Alstonia scholaris. Their structures were elucidated by spectroscopic analysis and ECD calculation. Structurally, compound 1: with a rare A ring-seco skeleton formed lactone and degraded C-3, while 2: with a 28-nor and 3: with a 29-nor-lupane skeleton supported the phytochemical diversity and novelty of the plant. Pharmacologically, compounds 4, 7: , and 10: reduced the serum uric acid (UA) levels of mice significantly.

Alscholarines A and B, two rearranged monoterpene indole alkaloids from Alstonia scholaris

Alscholarines A and B (1 and 2), two unprecedented rearranged monoterpene indole alkaloids, were isolated from Alstonia scholaris. Alscholarine A (1) features an imidazole ring fused with a rearranged vallesamine-type alkaloid possessing an unparalleled 6/5/6/6 tetracyclic skeleton through an unprecedented C7-C-19 connectivity. Alscholarine B (2), incorporating an unusual 7-oxa-1-azabicyclo[3.2.1]octane moiety, represents a unique rearranged vallesamine-type alkaloid with a 6/5/6/6/5 ring system via an unprecedented C-6-C-20 connectivity. Their structures were established by spectroscopic analysis, X-ray crystallography, and quantum-chemical calculations. Their plausible biosynthetic pathways were proposed. The vasorelaxant and anti-inflammatory activities of them were also evaluated. Compounds 1-3 showed moderate vasorelaxant activities.

Ormosianines A-P, Structurally Diverse Quinolizidine Alkaloids with AChE Inhibitory Effects from Ormosia yunnanensis

Sixteen new quinolizidine alkaloids (QAs), named ormosianines A-P (1-16), and 18 known congeners (17-34) were isolated from the stems and leaves of Ormosia yunnanensis. The structures were elucidated based on spectroscopic analyses and electron circular dichroism (ECD) calculations. Structurally, ormosianines A (1) and B (2) are the first examples of cytisine and Ormosia-type alkaloids with the cleavage of the piperidine ring. Results of the acetylcholinesterase (AChE) inhibitory assay revealed that the pentacycline Ormosia-type QAs, including 1, 16, 24, and 27-29, are good AChE inhibitors. Ormosianine A (1) exhibited more potent AChE inhibitory activity with an IC50 value of 1.55 μM. Molecular docking revealed that 1 might bind to the protein 1DX4, forming two hydrogen bonds with residues SER-238 and HIS-480.

Structurally diverse monoterpene indole alkaloids with vasorelaxant activities from the branches of Alstonia scholaris

Seven undescribed monoterpene indole alkaloids alstoscholarinines A‒G, along with nineteen known alkaloids, were isolated from the branches of Alstonia scholaris (L.) R. Br. The isolated alkaloids were classified into ten framework types. The structures of the undescribed alkaloids were elucidated by extensive spectroscopic analysis, ECD calculation, and single-crystal X-ray diffraction analysis. Alstoscholarinine A is an unreported and unusual monoterpene indole alkaloid incorporating three nitrogen atoms, characterized by a compact 6/5/6/6/6/5 hexacyclic system bearing a piperidine ring and a unique oxazolidine ring. Alstoscholarinine B represents the first naturally C-17 nor-isositsirikine-type alkaloid. Plausible biosynthetic pathways of alstoscholarinines A and B were proposed. All isolates were evaluated for their vasorelaxant activities against phenylephrine-induced contraction of rat mesenteric arteries. Among them, seven alkaloids showed significant vasorelaxant activities with EC₅₀ values less than 10 μM. Importantly, the akuammicine-type alkaloids in this study showed much better vasorelaxant activities than other framework type alkaloids, indicating that this type of alkaloid may be a valuable source for the discovery of vasodilators. A preliminary structure-activity relationship for vasorelaxant activities of the isolated akuammicine-type alkaloids is also discussed.

Spiroleiferthione A and Oleiferthione A: Two Unusual Isothiocyanate-Derived Thioketone Alkaloids from Moringa oleifera Lam. Seeds

Spiroleiferthione A (1), with a 2-thiohydantoin a heterocyclic spiro skeleton, and oleiferthione A (2), an imidazole-2-thione derivative, were isolated from the aqueous extract of Moringa oleifera Lam. seeds. The unprecedented structures of 1 and 2 were elucidated by extensive spectroscopic data, X-ray diffraction, and gauge-independent atomic orbital (GIAO) NMR calculation, as well as electronic circular dichroism (ECD) calculation. The structures of 1 and 2 were determined to be (5R,7R,8S)-8-hydroxy-3-(4′-hydroxybenzyl)-7-methyl-2-thioxo-6-oxa-1, 3-diazaspiro [4.4] nonan-4-one, and 1-(4′-hydroxybenzyl)-4,5-dimethyl-1,3-dihydro-2H-imidazole-2-thione, respectively. Biosynthetic pathways for 1 and 2 have been proposed. Compounds 1 and 2 are considered to have originated from isothiocyanate and then undergone a series of oxidation and cyclization reactions to form 1 and 2. Compounds 1 and 2 demonstrated weak inhibition rates of NO production, 42.81 ± 1.56% and 33.53 ± 2.34%, respectively, at a concentration of 50 μM. Additionally, Spiroleiferthione A demonstrated moderate inhibitory activity against high glucose-induced human renal mesangial cell proliferation in a dosage-dependent manner. A wider range of biological activities, and the diabetic nephropathy protective activity of Compound 1 in vivo and its mechanism of action, need further investigation after the sufficient enrichment of Compound 1 or total synthesis.

Significant anti-inflammatory aziridine-containing indole alkaloids from the Chinese medicinal plant Alstonia scholaris

Two unique windmill-like aziridine-containing indole alkaloids, possessing an unprecedented 6/5/5/6/6/5/3 rigid ring system and an unusual azabicyclo[3.1.0]hexane core, were isolated from Alstonia scholaris. Their structures were established by spectroscopy, X-ray diffraction, and electronic circular dichroism calculations. The novel compounds exhibited significant anti-inflammatory bioactivity in vitro and alleviated LPS-induced acute lung injury in mice.

Antimicrobial indole alkaloids from Tabernaemontana corymbosa

Four unreported monoterpene indole alkaloids, tabernaecorymines B-E (1-4), together with twenty-one known indole alkaloids (5-25) were obtained from the stem bark of Tabernaemontana corymbosa. Their structures and absolute configurations were elucidated by extensive spectroscopy, quantum chemical calculations, DP4+ probability analyses and Mo₂(OAc)₄-induced electronic circular dichroism experiment. The antibacterial and antifungal activities of these compounds were evaluated and some of them showed significant activity against Staphylococcus aureus,Bacillus subtilis, Streptococcus dysgalactiae and Candida albicans.

Exploration of the Main Antibiofilm Substance of Lactobacillus plantarum ATCC 14917 and Its Effect against Streptococcus mutans

Dental plaque, a complex biofilm system established by cariogenic bacteria such as Streptococcus mutans (S. mutans), is the initiator of dental caries. Studies have found that the cell-free supernatant (CFS) of Lactobacilli could inhibit S. mutans biofilm formation. However, the main antibiofilm substance of the Lactobacilli CFS that acts against S. mutans is unclear. The present study found that the CFS of Lactobacillus plantarum (L. plantarum) ATCC 14917 had the strongest antibiofilm effect among the five tested oral Lactobacilli. Further bioassay-guided isolation was performed to identify the main antibiofilm substance. The antibiofilm effect of the end product, named 1-1-4-3, was observed and the structure of it was elucidated by using Q-TOF MS, 2D NMR and HPLC. The results showed that several components in the CFS had an antibiofilm effect; however, the effect of 1-1-4-3 was the strongest, as it could reduce the generation of exopolysaccharides and make the biofilm looser and thinner. After structure elucidation and validation, 1-1-4-3 was identified as a mixture of lactic acid (LA) and valine. Additionally, LA was shown to be the main antibiofilm substance in 1-1-4-3. In summary, this study found that the antibiofilm effect of the L. plantarum CFS against S. mutans was attributable to the comprehensive effect of multiple components, among which LA played a dominant role.

Dimeric benzylisoquinoline alkaloids from Thalictrum delavayi and their biological activities

A phytochemical investigation of the whole plants of T. delavayi led to the isolation of five new dimeric benzylisoquinoline alkaloids, thalidelavines A-E (1-5), together with six known congeners (6-11). The structures and absolute configurations of new compounds were established based on analyses of spectroscopic data, ECD calculations, and single crystal X-ray crystallography. Thalidelavines A-E (1-5) were structurally complex bisbenzylisoquinoline alkaloids with various configurations. These isolated alkaloids were evaluated for their cytotoxic and immunosuppressive effects. Among them, both 9 and 10 displayed significant cytotoxicities against T98G cell lines with an IC₅₀ value of 2.1 μM, compared with the positive CPT-11 (IC₅₀ = 3.0 μM). In addition, 5-7 showed remarkable immunosuppressive effects. These findings not only enrich the structural diversity of bisbenzylisoquinoline alkaloids, but also provide potential candidates for the further development of the antitumor and immunosuppressive agents.

Survey of natural products reported by Asian research groups in 2021

The new natural products reported in 2021 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2021 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

A review on natural products with cage-like structure

Natural products with diverse structures and significant biological activities are essential sources of drug lead compounds, and play an important role in the research and development of innovative drugs. Cage-like compounds have various structures and are widely distributed in nature, especially caged xanthones isolated from Garcinia genus, paeoniflorin and its derivatives isolated from Paeonia lactiflora Pall, tetrodotoxin (TTX) and its derivatives, and so on. In recent years, the development and utilization of cage-like compounds have been a research hotspot in chemistry, biology and other fields due to their special structures and remarkable biological activities. In this review, we mainly summarized the cage-like compounds with various structures found and isolated from natural drugs since 1956, summarized its broad biological activities, and introduced the progress in the biosynthesis of some compounds, so as to provide a reference for the discovery of more novel compounds, and the development and application of innovative drugs.

Anti-hyperuricemic bioactivity of Alstonia scholaris and its bioactive triterpenoids in vivo and in vitro

ETHNOPHARMACOLOGY RELEVANCE

One folk use of Alstonia scholaris (L.) R. Br. in "Dai" ethno-medicine system is to treat gouty arthritis, which might be caused by hyperuricemia, but anti-hyperuricemic investigation of A. scholaris were rarely reported.

AIM OF THE STUDY

To verify anti-hyperuricemic property of A. scholaris, and explore its bioactive compounds in vivo and in vitro.

MATERIALS AND METHODS

The anti-hyperuricemic bioactivity of the non-alkaloids fraction and compounds were evaluated with potassium oxonate (PO) induced hyperuricemia mice model in vivo, and monosodium urate (MSU) induced human renal tubular epithelial cells (HK-2) was selected to test in vitro, respectively, with benzobromarone as the positive control. 11 triterpenoids were isolated by phytochemical methods and their structures were elucidated by spectroscopic analysis and ECD calculation.

RESULTS

The non-alkaloids fraction of A. scholaris decreased the serum uric acid (UA) level in mice model significantly at the doses of 100 mg/kg and 200 mg/kg, and then nine ursane- and two oleanane-triterpenoids including four new compounds (1-3 and 10) were isolated from the bioactive fraction, in which compounds 1, 4, 5, 6 and 10 exhibited better anti-hyperuricemic tendency in vitro by promoting the excretion of UA in MSU-induced HK-2 cell model at a concentration of 5 μM. Furthermore, compounds 1 and 4 were proved to reduce the serum UA level in mice significantly at 5 mg/kg in vivo.

CONCLUSIONS

The results supported the traditional use of A. scholaris in treating gouty arthritis, and also provided new bioactive triterpenoids for further chemical and pharmacological investigation.

Monoterpene indole N-oxide alkaloids from Tabernaemontana corymbosa and their antimicrobial activity

Tabernaemontana corymbosa is a traditional folk medicine. In our research, six monoterpene indole N-oxide alkaloids and their parent alkaloids were obtained from the stem bark of T. corymbosa, including seven new alkaloids (1-7) and five known alkaloids (8-12). Their structures and absolute configurations were elucidated by extensive spectroscopy, quantum chemical calculations, and DP4+ probability analyses. The antimicrobial activity of the obtained compounds was evaluated, among which alkaloids 4, 8, 12 showed significant antimicrobial activity against Staphylococcus aureus with an MIC value of 6.25 μg/mL, while alkaloids 11, 12 showed moderate antimicrobial activity against Bacillus subtilis with an MIC value of 25 μg/mL.

Hot off the press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as chlorahupetone A from Chloranthus henryi var. hupehensis.