Three Pairs of Enantiomeric Sesquiterpenoids from Syringa pinnatifolia

Novel lignans from Syringa pinnatifolia and protective effect against H2O2-induced oxidative injury through regulating the expression of Nrf2/HO-1 in H9c2 cells

Phytochemical analysis of the peeled stems of Syringa pinnatifolia Hemsl. led to the discovery of 13 undescribed lignans, namely helanols A and B (1 and 2) and alashanenols W-G1 (3-13), as well as four known analogues, of which helanols A and B were lignans with novel skeleton of α-β' linkage. The structures were unambiguously established by extensive spectroscopic analyses, NMR calculations, ECD calculations, and single crystal X-ray crystallography. Five lignans (1, 2, 5, 11 and 13) exhibited a moderate protective effect against H2O2-induced oxidative injuries in H9c2 cells with the protective rates of 11.3-20.6 % at the concentration of 0.3-20 μM, while the positive control quercetin showed protective rates of 58.7 % at 10 μM. Further mechanism investigation suggested that 1 and 2 exerted the protective effect by regulating the expression of Nrf2/HO-1.

Dimeric eremophilane-type sesquiterpenoids from the peeled stems of Syringa pinnatifolia

A continued phytochemical investigation guided by 1H NMR and LC-MS data on the ethanol extract from the peeled stems of Syringa pinnatifolia Hemsl. led to the isolation of 16 undescribed dimeric eremophilane sesquiterpenoids, namely syringenes R-Z (1-9) and A1-G1 (10-16). These structures were elucidated by extensive analysis of spectroscopic data, including HRESIMS, NMR, quantum-mechanics-based computational analysis of NMR chemical shifts, and single-crystal X-ray diffraction analyses, and a concise rule for determination of relative configuration of angular methyl was proposed. The results of the cardioprotective assay demonstrated that 3 exhibits a protective effect against hypoxia-induced injuries in H9c2 cells. This effect was observed at a concentration of 10 μM, with a protective rate of 28.43 ± 11.80%.

Equivalent evaluation and biological ingredients of Syringa pinnatifolia against acute myocardial ischemia in mice

ETHNOPHARMACOLOGICAL RELEVANCE

The peeled roots, stems, and twigs of Syringa pinnatifolia Hemsl., known as Shan-Chen-Xiang (SCX) in Chinese, has the traditional effects such as anti-Khii, clearing heat and relieving pain. It has been clinically applied for the treatment of heart failure and mental abnormalities, and gradually replaced agarwood in Mongolian medicine.

AIM OF STUDY

The present study aims to evaluate whether the key subfraction C (C), a half composition in mass of total ethanol extract (T) of SCX, exerts an equivalent effect against acute myocardial ischemia (AMI) compared to fraction I (I), and what was the potential pharmacologically active constituents of SCX.

MATERIALS AND METHODS

Cardiac function, serum marker enzymes, and myocardial tissue pathology of infarcted mice with ligation of the anterior descending (LAD) branch of the left coronary artery were used to evaluate the anti-AMI effect of C and its equivalent potency to that of I. LCMS-IT-TOF was used to identify the main constituents in C and C-. The new and known compounds were isolated from C by a combination of mass spectrometry and bioactivity-guided fractionation methods, and structures were elucidated by extensive spectroscopic and chemical methods, including calculated 13C NMR data, calculated electronic circular dichroism, and single-crystal X-ray crystallography. The protective effect of isolates against oxidative injury induced by H2O2 in H9c2 cells was evaluated according to a previously reported protocol.

RESULTS

The results of cardiac function, serum marker enzymes and myocardial tissue pathology observations (fosinopril as a positive drug) suggested that C (40 mg/kg, orally administered once a day for 7 days) possessed the anti-AMI effect and was equivalent to that of I, while C- did not show the positive effect. Then, 32 lignans were isolated from C, including the majors (8R,8'R,9S)-4,4'-dihydroxy-3,3',9-trimethoxy-9,9'-epoxylignan (24) and (8R,8'R,9R)-4,4'-dihydroxy-3,3',9-trimethoxy-9,9'-epoxylignan (25), which were confirmed by HPLC and LC-MS characterization. Among them, 15 ones were previously undescribed, including a pair of enantiomers (6a/6b), and 11 ones (1, 2, 6a/6b, 8, 10, 12, 16, 17, 24, and 25) exhibited protective effect against oxidative injury to H9c2 cells at different concentrations (ranged from 0.156 to 80 μM).

CONCLUSION

C (40 mg/kg) exerts cardioprotective effect in mice, which was equivalent to that of I and T. Lignans, including both representative compounds (24, 25) and other undescribed molecules with low content, significantly contribute to the anti-AMI effect of SCX. However, the anti-AMI property assessment of SCX should not exclude the contribution from the representative sesquiterpenoid ZER. Hence, the exploration of the final potential substances in SCX requires further investigation.

Benzylisoquinoline alkaloids with their antitumor activity from the aerial parts of Corydalis impatiens (pall.) Fisch

Phytochemical investigation on the aerial parts of Corydalis impatiens (pall.) Fisch (Papaveraceae) resulted in the identification of four previous undescribed benzylisoquinoline alkaloids, impatienines A-D (1-4), together with 14 known analogues (5-18). The structures of these compounds were elucidated by extensive spectroscopic analysis (IR, HR-ESIMS, 1D- and 2D-NMR) as well as ECD calculations. All the compounds obtained were investigated for their inhibitory effect on the growth of A549, H1299 and HepG2 cancer cells. Compounds 7 and 15 exhibited pronounced inhibition against the A549 cancer cells with IC50 values of 6.81 μM and 3.17 μM, while the positive control cisplatin was 1.83 μM. Compounds 1-3 showed moderate inhibitory on the H1299 cancer cells. Compounds 4, 10-12, and 16 showed signiffcant activity against HepG2 cancer cells with IC50 values range of 4.41-8.75 μM.

Alashanines A-C, Three Quinone-Terpenoid Alkaloids from Syringa pinnatifolia with Cytotoxic Potential by Activation of ERK

Three quinone-terpenoid alkaloids, alashanines A-C (1-3), possessing an unprecedented 6/6/6 tricyclic conjugated backbone and quinone-quinoline-fused characteristic, were isolated from the peeled stems of Syringa pinnatifolia. Their structures were elucidated by analysis of extensive spectroscopic data and quantum chemical calculations. A hypothesis of biosynthesis pathways for 1-3 was proposed on the basis of the potential precursor iridoid and benzoquinone. Compound 1 exhibited antibacterial activities against Bacillus subtilis and cytotoxicity against HepG2 and MCF-7 human cancer cell lines. The results of the cytotoxic mechanism revealed that compound 1 induced apoptosis of HepG2 cells through activation of ERK.

Diverse lignans with protective effect against hypoxia/oxidative injuries to H9c2 cells from Syringa pinnatifolia Hemsl

A bioactivity-guided fractionation on the phenolic fractions from the peeled stems of Syringa pinnatifolia Hemsl., one of representative Mongolian folk medicine in China, led to the isolation and structural determination of 11 undescribed lignans and 12 known ones. These lignans cover diverse types, among them syringanones A and B represent an unprecedented carbon skeleton (proposed syringanane) and alashanenol A possesses a rare bicyclo [3.3.1]nonadienemethanol core. Their structures were established by extensive spectroscopic data analysis, X-ray diffraction, and quantum chemical calculations. All isolates were evaluated for their cardioprotective activities on H9c2 cardiomyocytes in vitro. The results showed that five lignans exhibited the protective effects against hypoxia-induced injury at the concentrations of 1.2-40 μM and six lignans exhibited anti-oxidative stress injury at 10-40 μM. These findings account to some extend for the traditional therapeutic effects of S. pinnatifolia for the treatment of ischemic heart diseases in clinic.

Zerumbone, a major sesquiterpene from Syringa pinnatifolia Hemsl., exerts the sedative effect by regulating GABAergic nervous system

ETHNOPHARMACOLOGICAL RELEVANCE

Zerumbone (ZER) is a humulane sesquiterpenoid isolated from Syringa pinnatifolia Hemsl. (SP), its content accounts for 64.7% of volatile oil and 0.86% of total ethanol extract (TEE), representing one of characteristic ingredient of SP. As a representative Mongolian medicine with anti-"Khii", anti-asthma, and clearing-heat effects, SP has been used for the treatment of cardiovascular diseases, upset, insomnia, and other symptoms.

AIM OF STUDY

Previous results showed that TEE has sedative effect, but the pharmacological substances and its sedative mechanism remains unclear. This study aims to determine whether ZER, as one of major and characteristic sesquiterpenoids of SP, contributes to the sedative effect of SP and its underlying mechanism.

MATERIALS AND METHODS

Locomotor activity and threshold dose of pentobarbital sodium sleep experiments were used to evaluate the sedative effects in mice. ELISA assay was used to examine the level of GABA/Glu ratio in rats hippocampus, cortex and hypothalamus tissue. The binding ability of ZER with glutamic acid decarboxylase 67 (GAD67) and Gephyrin protein were predicted by molecular docking. Western blot and Immunohistochemistry assay were used to determine the expression of GABAergic nerve system related proteins (GAD67, Gephyrin) in rat's hypothalamus. ZER was co-administrated with flumazenil and bicuculline (GABA_A antagonist) to determine whether it acts on GABA_A receptor. Furthermore, MQAE assay was used to test the effect of ZER on the chloride ion concentration in cerebellar granule cells.

RESULTS

Current data demonstrated that ZER dose-dependently (5-20 mg/kg) reduces the locomotor activity and sleep latency of mice, and extend sleeping time of mice. The results of ELISA showed that ZER increases the level of GABA/Glu in rats brain tissue, in particular in hypothalamus. Molecular docking results revealed that ZER has a strong affinity to GAD67 and Gephyrin protein. The Western blot and Immunohistochemistry data indicated that ZER up-regulates the expression of GAD67 and Gephyrin protein in rat's hypothalamus. Antagonism test results demonstrated that flumazenil and bicuculline reverse the effect of ZER on threshold dose of pentobarbital sodium sleep experiments. In addition, ZER also could dose-dependently (5-20 μM) increase the chloride ion concentration in cerebellar granule cell, suggesting that ZER induces the opening of chloride channel, exerts central inhibitory effect.

CONCLUSION

ZER has a significant sedative effect in mice and rat, and the effect is associated with GABAergic nervous system. The present results suggest that ZER, as one of the major bioactive ingredients of SP, contributes to the sedative effect and provide substantial evidence for its traditional use of anti-"Khii" in clinic of Syringa pinnatifolia.

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.

Syringenes M - Q, Eremophilane Sesquiterpenoid Dimers from the Peeled Stems of Syringa pinnatifolia

As a part of systematic studies on Syringa pinnatifolia, a continued phytochemical investigation guided by ¹ H-NMR and LC/MS data on the ethanol extract afforded five new dimeric eremophilane sesquiterpenoids, namely syringenes M-Q (1-5). These structures were elucidated by extensive analysis of spectroscopic data, including infrared (IR), high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), nuclear magnetic resonance (NMR), quantum-mechanics-based computational analysis of NMR chemical shifts, and single-crystal X-ray diffraction. Compounds 4 and 5 showed inhibitory activities against NO production induced by lipopolysaccharide in RAW264.7 macrophage cells, with IC₅₀ values of 5.1 and 9.3 μM, compared to positive control indomethacin (IC₅₀ 33.6 μM). These dimeric eremophilane sesquiterpenoids may be potential markers for discriminating this species from the genus Syringa and the Oleaceae family.

Zerumbone, a humulane sesquiterpene from Syringa pinnatifolia, attenuates cardiac fibrosis by inhibiting of the TGF-β1/Smad signaling pathway after myocardial infarction in mice

BACKGROUND

Zerumbone (ZER) is a humulane sesquiterpene isolated from Syringa pinnatifolia Hemsl., a representative Mongolian herbal medicine that is used to treat cardiovascular diseases. Cardiac fibrosis is a common pathological process in cardiovascular disease that results from the excessive accumulation of extracellular matrix (ECM), and the transforming growth factor (TGF)-β/Smad pathway is a canonical signaling pathway that directly induces expressions of ECM-related genes. Currently, the cardioprotective effect and underlying mechanisms of ZER on the inhibition of cardiac fibrosis are not well known.

PURPOSE

To explore the cardioprotective properties and pharmacological mechanism of ZER against cardiac fibrosis via the TGF-β1/Smad signaling pathway.

METHODS

Myocardial infarction (MI) model was induced by ligation of the left anterior descending coronary artery in ICR mice. The mice were randomly divided into six groups: sham, model, low-dose ZER (ZER-L), medium-dose ZER (ZER-M), high-dose ZER (ZER-H) and fosinopril. Mice in each group were intragastrically administered treatments for 21 days, and cardiac function was evaluated by 2D echocardiography. The pathological structure of the heart was examined by hematoxylin and eosin (HE) and Masson staining. Content of collagen I and collagen III were assessed by immunofluorescence methods. The inhibitory effect of ZER on TGF-β1 protein expression was predicted by molecular docking technology. Reverse transcriptase polymerase chain reaction (RT-PCR) and western blotting were used to measure the levels of genes and proteins expressed in the TGF-β1/Smad signaling pathway and MMPs. TGF-β1-treated cardiac fibroblasts (CFs) of neonatal SD rats were adopted for in vitro studies.

RESULTS

Cardiac ejection fraction (EF) and fractional shortening (FS) in the model group were markedly decreased compared with those in the sham group, indicating that the MI model was successfully established. ZER and fosinopril elevated EF and FS values, suggesting cardioprotective effects. Pathological staining and immunofluorescence analysis showed that the content of collagen I and collagen III increased in the cardiac tissue of mice in model group, while ZER treatment obviously reduced collagen levels. The molecular docking simulations predicted the hydrophobic interactions between ZER and TGF-β1. In addition, the expression of TGF-β1, p-Smad2/3 and MMPs in the ZER treatment group was significantly decreased compared with the model group. In vitro studies further confirmed that α-smooth muscle actin (α-SMA) and p-Smad2/3 increased markedly in cardiac fibroblasts after incubation with TGF-β1, and treatment with ZER suppressed the expression of α-SMA and TGF-β1 downstream proteins in cardiac fibroblasts.

CONCLUSION

ZER rescues cardiac function by attenuating cardiac fibrosis, and the antifibrotic effect may be mediated by blocking the TGF-β1/Smad pathway.

Eremophilane and Cadinene Sesquiterpenes from Syringa oblata and Their Protective Effects against Hypoxia-Induced Injury on H9c2 Cells

Seven sesquiterpenes including four eremophilanes (1-4) and three cadinenes (5-7), were isolated from the heartwood of Syringa oblata Lindl. Among them, three new eremophilane-type sesquiterpenes were identified and named oblatanoids A-C (1-3), respectively. Their structures were established by extensive analyses of spectroscopic methods, and their absolute configurations were determined by electronic circular dichroism (ECD) calculations. All these new compounds were evaluated for protective effects against hypoxia-induced injury on H9c2 cells, and 1-3 exhibited significantly protective activities toward H9c2 cells in vitro.

Alashanoids O-S, Seco-humulane and Eremophilane Sesquiterpenoids from Syringa pinnatifolia

Five new sesquiterpenoids, alashanoids O-S ( 1 - 5 ), along with three known analogues ( 6 - 8 ) were isolated from the peeled stems of Syringa pinnatifolia . Their structures were elucidated by analysis of extensive spectroscopic data including ESI-MS, 1D, 2D NMR. The absolute configurations were determined by comparing its experimental and calculated electronic circular dichroism, calculated OR, calculated NMR, and single crystal X-ray diffraction data analysis. Compounds 1 and 2 belong to the seco-humulane type and possess a rare 13-membered oxygen heterocycle framework, and 3 - 5 belong to eremophilane-type. Compounds 1 , 2 , and 5 showed inhibition effects against NO production in LPS-induced RAW264.7 macrophage cells with its IC 50 values of 11.86 ± 2.34, 72.08 ± 7.72, and 69.22 ± 15.29 μM, respectively, compared with the positive control indomethacin (IC 50 = 31.52 μM).

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