An O-to-N intramolecular acyl migration in C19-diterpenoid alkaloids

The O-acyl group at C-1 of two C₁₉-diterpenoid alkaloids 2 and 5 was transferred to the secondary amine nitrogen to form amides 3 and 6 in the basic condition. This kind of O-to-N intramolecular acyl migration could be caused by the near distance between the nucleophilic nitrogen atom and the carbonyl group of the ester at C-1 in the C₁₉-diterpenoid alkaloids, which is consistent with the conformation of rings A and E in the C₁₉-diterpenoid alkaloids.     

A fragmentation study on four C19-diterpenoid alkaloids by electrospray ionization ion-trap time-of-flight tandem mass spectrometry

High-resolution electrospray ionization ion-trap time-of-flight tandem mass spectrometry (HR-ESI-IT-TOF-MSⁿ) in positive-ion mode was used to determine the accurate masses and fragmentation pathways of four C₁₉-diterpenoid alkaloids, aconitine (1), yunnaconitine (2), crassicauline A (3), and benzoylmesaconine (4). The [M+H]⁺ ions of compounds 1–4 were readily observed in conventional single-stage mass spectrometry. Based on the MS^1–6 analyses, detailed fragmentation rules of the four compounds were proposed. The neutral losses of AcOH, MeOH, H₂O, CO, C₂H₄, PhCOOH and p-OMePhCOOH segments were the characteristic eliminations from the precursor ions due to the presence of acetyl, methoxyl, hydroxyl, N-ethyl, benzoyl and p-methoxyl-benzoyl units in the structures. Benefited from the high resolution of the mass analyzer, the loss of 28 Da corresponding to CO or CH₄ segment in product ions was unambiguously distinguished. The losing sequence of the main substituent groups was summarized as: C(8)-acetyl>C(16)-methotyl>C(15)-hydroxyl>C(6)-methoxyl>C(1)-methoxyl/C(3)-hydroxyl>C(18)-methoxyl>>C(13)-hydroxyl. The sequential loss of (16)-methoxyl moiety and CO (generating from enol–ketone tautomerism) groups could be recognized as the characteristic eliminations for the compounds with C(16)-methoxyl and C(15)-hydroxyl groups simultaneously. The application of HR-ESI-IT-TOF-MSⁿ technique to investigate the fragmentation of C₁₉-diterpenoid alkaloids provided useful information to understand their fragmentation behaviors.     

Four new C19-diterpenoid alkaloids from the roots of Aconitum ouvrardianum

Four new C₁₉-diterpenoid alkaloids, 3-dehydroxyl-lipoindaconitine (1), 8-dehydroxyl-bikhaconine (2), 19R-acetonyl-talatisamine (3), and 16-hydroxyl-vilmorisine (4), were isolated from the roots of Aconitum ouvrardianum. Their structures were elucidated by spectral analyses, including ESI-MS, HR-ESI-MS, IR, UV, 1D and 2D NMR.     

紫乌头生物碱的化学研究

从紫乌头根中分出四种新二萜生物碱,分别命名为紫乌生、紫乌生宁、紫乌亭和紫乌定。根据红外光谱、紫外光谱、质谱、氢谱和碳谱以及制备衍生物,证明了前三个生物碱的结构(3,4,5),对紫乌定的结构曾初步推定为(8)⁽¹⁾;后来,经单晶X射线衍射结构分析修正为(9)。此外,作者认为,根据化学结构特点应从C₁₉二萜生物碱中划分出C-4失甲基的一类生物碱,称C₁₈二萜生物碱。     

Two new C19-diterpenoid alkaloids from Aconitum tsaii

Two new C₁₉-diterpenoid alkaloids, 14-benzoylliljestrandisine (1) and 14-anisoylliljestrandisine (2), were isolated from the roots of Aconitum tsaii. Their structures were elucidated by different spectroscopic (IR, UV, 1D and 2D NMR) and mass-spectrometric techniques.     

Two new C19-diterpenoid alkaloids from Aconitum straminiflorum

Two new C₁₉-diterpenoid alkaloids, straconitines A (1) and B (2), were isolated from the roots of Aconitum straminiflorum. Their structures were elucidated as 14-benzoylducloudine D (1) and 6-hydroxy-14-benzoylducloudine D (2) based on spectroscopic analysis, including IR, ESI-MS, HR-ESI-MS, 1D, and 2D NMR.     

Alkaloids with antioxidant activities from Aconitum handelianum

A new C₂₀-diterpenoid alkaloid handelidine (1) and twenty-seven known alkaloids (2–28) were isolated from the roots of Aconitum handelianum. Their structures were established on the basis of extensive spectroscopic analyses. The study indicated that denudatine-type C₂₀-diterpenoid alkaloids with vicinal-triol system and benzyltetrahydroisoquinoline alkaloids exhibited significant antioxidant activities measured by three antioxidant test systems. The aconitine-type C₁₉-diterpenoid alkaloids could serve as potential secondary antioxidants for their strong binding effects to metal ions.     

Conversional studies towards taxoids from C19-diterpenoid alkaloids by the BAC sequence

The conversional synthesis of taxoids by the BAC sequence from the C₁₉-diterpenoid alkaloids, 14-acetyltalatisamine (1), yunaconitine (12), and 14-acetylchasmanine (19), was designed and explored. Two aconane-type diterpenes 17 and 28, the advanced intermediates for our conversional synthesis, were synthesized. The key steps include the rupture of the C(7)–C(17) bond, the formation of imine, and the denitrogenation.     

Four new C20-diterpenoid alkaloids from Aconitum rotundifolium

Four new C₂₀-diterpenoid alkaloids, rotundifosines D-G (1–4), along with eight known ones (5–12) were isolated from the whole plant of Aconitum rotundifolium Kar. & Kir. The structures of the compounds were elucidated on the basis of spectroscopic analyses, including HR-ESI-MS and 1D, 2D NMR. Rotundifosine F (3) is a rare C₂₀-diterpenoid alkaloid with quaternary ammonium salt. Alkaloids 1–4, 5, 6, 9, and 12 were evaluated for cytotoxicity against MCF-7, HCT-116 and HepG2 human cancer cell lines.     

Four new C19-diterpenoid alkaloids from Aconitum hemsleyanum var. circinatum

Four new C19-diterpenoid alkaloids, hemaconitines A–D (1–4), were isolated from the roots of Aconitum hemsleyanum var. circinatum. Their structures were elucidated as 19R-hydroxyl-secoyunnaconitine (1), (3R)-hydroxyl-liwaconitine (2), 14-anisoyl-leucanthumsine E (3), and 19R -acetonyl-8-O-methyltalatisamine (4) by extensive spectroscopic analysis (IR, UV, HR-ESI-MS, 1D, and 2D NMR).     

An effective O-demethylation of some C19-diterpenoid alkaloids with HBr–glacial acetic acid

The aconitine-type alkaloids talatisamine (1), 8,14-diacetyltalatisamine (11), and compound 3, the lycoctonine-type alkaloid deltaline (5), and the 7,17-seco C₁₉-diterpenoid alkaloids 7 and 9 were treated with HBr–glacial acetic acid to give useful O-demethylated derivatives 2, 2, 4, 6, 8, and 10 respectively in good to high yields (49–90%).     

Regioselective O-demethylation of two C19-diterpenoid alkaloids

The regioselective demethylations of two C₁₉-diterpenoid alkaloids, 2 and 3, have been achieved with HBr–HOAc, trimethylsilyl iodide, or BBr₃. It was observed that HBr–HOAc is an optimal demethylating agent for these two C₁₉-diterpenoid alkaloids because it could provide different O-demethylation products by using different reaction temperature and reaction time. Especially, 1-O-methyl group in 2 and 3, one of the most difficult ones to be demethylated, could be removed by the treatment with HBr–HOAc at an elevated temperature and a prolonged reaction time.     

A new cassane diterpenoid from the seeds of Caesalpinia decapetala

Phytochemical investigation on the seeds of Caesalpinia decapetala led to the isolation of a new cassane diterpenoid with an unusual O bridge between C-19 and C-20, named phanginin Q (1), together with three known cassane diterpenoids, caesaljapin (2), caesaldekarin A (3), and caesaldekarin B (4). The structure of the new compound was elucidated by spectroscopic methods, including ¹H NMR, ¹³C NMR, HSQC, ¹H ? ¹H COSY, HMBC, NOESY, and HR-ESI-MS.     

Structure of lasiansine from Aconitum nagarum var. lasiandrum

A new C₁₉-diterpenoid alkaloid, lasiansine (1), was isolated from the roots of Aconitu nagarum var. lasiandrum (Ranunculaceae) together with six known diterpenoid alkaloids. The structure of 1 was elucidated by spectral methods (¹H-NMR, ¹³C-NMR, 2D-NMR, HRMS, IR), and the ¹³C-NMR spectrum of 16-epipyroaconine (3) and the single-crystal X-ray analysis of its derivative (5) are reported for the first time.     

Two new bis-C20-diterpenoid alkaloids with anti-inflammation activity from Aconitum bulleyanum

Two new bis-C₂₀-diterpenoid alkaloids, bulleyanines A and B (1 and 2), were isolated from Aconitum bulleyanum. Their structures were elucidated by comprehensive spectroscopic analyses including UV, IR, MS, 1D and 2D NMR. Biological activity tests indicated that compound 1 exhibited significant inhibitory activity against nitric oxide (NO) production in lipopolysaccharide (LPS)-activated RAW264.7 macrophages with the inhibition rate of 74.60% (40 μmol/L), while positive control dexamethasone gave 78.70% inhibition at 100 μg/ml.     

Two new sesquiterpenoids from cultures of the basidiomycete Tremella foliacea

Two new sesquiterpenoids, trefoliol B (1) and trefoliol C (2), together with known echinocidin A (3), were isolated from cultures of the basidiomycetes Tremella foliacea. The new structures were elucidated on the basis of extensive spectroscopic methods. At the same time, trefoliol B (1) and echinocidin A (3) were tested for their cytotoxicities against five human cancer cell lines and for their inhibitory activities against isozymes of 11β-hydroxysteroid dehydrogenases (11β-HSD). No compound showed significant activity (IC₅₀ > 40 μM). Compound 1 showed moderate inhibitory activities against 11β-HSD1 (human IC₅₀ = 13.1 μM; mouse IC₅₀ = 91.8 μM).     

Terpenoids from the tuber of Cremastra appendiculata

Two new terpenoids including a cadinane sesquiterpene (1), and an ent-kaurane diterpene diglycoside (2), together with a known triterpene containing 32 carbons (3), have been isolated from the ethanolic extract of Cremastra appendiculata. Their structures were established by the spectroscopic methods including the IR, MS, 1D-, and 2D-NMR experiments as ( ? )-cadin-4,10(15)-dien-11-oic acid (1), ( ? )-ent-12β-hydroxykaur-16-en-19-oic acid, 19-O-β-d-xylopyranosyl-(1 → 6)-O-β-d-glucopyranoside (2), and (+)-24,24-dimethyl-25,32-cyclo-5α-lanosta-9(11)-en-3β-ol (3). Compounds 1–3 were evaluated against several human cancer cell lines. Compound 3 showed in vitro-selective cytotoxicity against human breast cancer cell lines (MCF-7) with an IC₅₀ of 3.18 μM, but 1 and 2 were inactive (IC₅₀>10 μg/ml).     

C18-Diterpenoid alkaloids from Delphinium anthriscifolium var. majus

Five new C₁₈-diterpenoid alkaloids, anthriscifoltines C-G (1–5), along with four known diterpenoid alkaloids anthriscifolcines C-F (6–9), were isolated from the extract of Delphinium anthriscifolium var. majus. Their structures were elucidated by extensive spectroscopic analyses (including 1D-, 2D-NMR, and HR-ESI-MS). Compounds 1–5 were also evaluated for their cytotoxic activity against MCF-7, HepG2, and H460 human cancer cell lines.     

Triterpene saponins with α-glucosidase inhibition and cytotoxic activity from the leaves of Schefflera sessiliflora

From the leaves of Schefflera sessiliflora De P. V., two new triterpene saponins including one oleanane-type saponin, named scheffleraside C (1) and one lupane-type saponin scheffleraside D (2), together with six known triterpene saponins (3–8), were isolated by various chromatography methods. Among them, 3 was found for the first time from natural sources, while 6–8 were isolated for the first time from the genus Schefflera. Their structures were elucidated by IR, UV, HR-ESI-MS, NMR 1D and 2D experiments, and comparison of their NMR data with previously reported data. Their α-glucosidase inhibition and cytotoxic activity against MCF-7 human breast cancer cell lines were evaluated. The isolates (1, 3–5, 8) showed stronger α-glucosidase inhibitory activity (IC₅₀ = 5.99–76.58 μM) than the standard drug acarbose (IC₅₀ = 214.50 μM). At the concentration of 100 μg/ml, the isolates (1, 2) showed appreciable cytotoxic activity (67.92, 63.83%, respectively).     

Structure–activity relationships and the cytotoxic effects of novel diterpenoid alkaloid derivatives against A549 human lung carcinoma cells

The cytotoxicity of three alkaloids from the roots of Aconitum yesoense var. macroyesoense as well as 36 semi-synthetic C₂₀-diterpenoid atisine-type alkaloid derivatives against A549 human lung carcinoma cells was examined. Ten acylated alkaloid derivatives, pseudokobusine 11-veratroate (9), 11-anisoate (12), 6,11-dianisoate (14), 11-p-nitrobenzoate (18), 11,15-di-p-nitrobenzoate (22), 11-cinnamate (25) and 11-m-trifluoromethylbenzoate (27), and kobusine 11-p-trifluoromethylbenzoate (35), 11-m-trifluoromethylbenzoate (36) and 11,15-di-p-nitrobenzoate (39), exhibited cytotoxic activity, and 11,15-dianisoylpseudokobusine (16) was found to be the most potent cytotoxic agent. Their IC₅₀ values against A549 cells ranged from 1.72 to 5.44 μM. In the occurrence of cytotoxic effects of atisine-type alkaloids, replacement by an acyl group at both C-11 and C-15 resulted in the enhancement of activity of the parent alkaloids compared to that from having hydroxy groups at this position, and the presence of a hydroxy group at the C-6 position was required for the cytotoxic effects. These acylated alkaloid derivatives inhibit cell growth through G1 arrest.