Enantioselective Total Syntheses of (+)-Kobusine, (+)-Spirasine IX and the Purported Structure of (+)-Orgetine: Strategic Use of C-H Bonds

Enantioselective total syntheses of (+)-kobusine, (+)-spirasine IX and the proposed structure of (+)-orgetine were achieved. A unique approach was developed to construct a cage-like hexacyclic ring system that underwent an HAT-initiated radical rearrangement to forge the hetisine-type scaffold. Subsequent late-stage redox manipulations, including an intramolecular hydride shift, were deployed to provide different C20-diterpenoid alkaloids.

Chinese herbal medicine for the treatment of cardiovascular diseases ─ targeting cardiac ion channels

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality, imposing an increasing global health burden. Cardiac ion channels (voltage-gated Na_V, Ca_V, K_Vs, and others) synergistically shape the cardiac action potential (AP) and control the heartbeat. Dysfunction of these channels, due to genetic mutations, transcriptional or post-translational modifications, may disturb the AP and lead to arrhythmia, a major risk for CVD patients. Although there are five classes of anti-arrhythmic drugs available, they can have varying levels of efficacies and side effects on patients, possibly due to the complex pathogenesis of arrhythmias. As an alternative treatment option, Chinese herbal remedies have shown promise in regulating cardiac ion channels and providing anti-arrhythmic effects. In this review, we first discuss the role of cardiac ion channels in maintaining normal heart function and the pathogenesis of CVD, then summarize the classification of Chinese herbal compounds, and elaborate detailed mechanisms of their efficacy in regulating cardiac ion channels and in alleviating arrhythmia and CVD. We also address current limitations and opportunities for developing new anti-CVD drugs based on Chinese herbal medicines.

Dearomative logic in natural product total synthesis

Covering: 2011 to 2022The natural world is a prolific source of some of the most interesting, rare, and complex molecules known, harnessing sophisticated biosynthetic machinery evolved over billions of years for their production. Many of these natural products represent high-value targets of total synthesis, either for their desirable biological activities or for their beautiful structures outright; yet, the high sp3-character often present in nature's molecules imparts significant topological complexity that pushes the limits of contemporary synthetic technology. Dearomatization is a foundational strategy for generating such intricacy from simple materials that has undergone considerable maturation in recent years. This review highlights the recent achievements in the field of dearomative methodology, with a focus on natural product total synthesis and retrosynthetic analysis. Disconnection guidelines and a three-phase dearomative logic are described, and a spotlight is given to nature's use of dearomatization in the biosynthesis of various classes of natural products. Synthetic studies from 2011 to 2021 are reviewed, and 425 references are cited.

Electrophysiological Response to Acehytisine Was Modulated by Aldosterone in Rats with Aorto-Venocaval Shunts

Aldosterone induces cardiac electrical and structural remodeling, which leads to the development of heart failure and/or atrial fibrillation (AF). However, it remains unknown whether aldosterone-induced remodeling may modulate the efficacy of anti-AF drugs. In this study, we aimed to jeopardize the structural and functional remodeling by aldosterone in rats with aorto-venocaval shunts (AVS rats) and evaluate the effect of acehytisine in this model. An AVS operation was performed on rats (n = 6, male) and it was accompanied by the intraperitoneal infusion of aldosterone (AVS + Ald) at 2.0 µg/h for 28 d. The cardiopathy was characterized by echocardiography, electrophysiologic and hemodynamic testing, and morphometric examination in comparison with sham-operated rats (n = 3), sham + Ald (n = 6), and AVS (n = 5). Aldosterone accelerated the progression from asymptomatic heart failure to overt heart failure and induced sustained AF resistant to electrical fibrillation in one out of six rats. In addition, it prolonged PR, QT interval and Wenckebach cycle length. Acehytisine failed to suppress AF in the AVS + Ald rats. In conclusion, aldosterone jeopardized electrical remodeling and blunted the electrophysiological response to acehytisine on AF.

Asymmetric Total Syntheses of (+)-Davisinol and (+)-18-Benzoyldavisinol: A HAT-Initiated Transannular Redox Radical Approach

The first and asymmetric total syntheses of two C11-oxygenated hetisine-type diterpenoid alkaloids, namely, (+)-davisinol and (+)-18-benzoyldavisinol, is described. The concise synthetic approach features a HAT-initiated transannular redox radical cyclization, an ODI-Diels-Alder cycloaddition, and an acylative kinetic resolution. By incorporating an efficient late-stage assembly of the azabicycle, our strategy would streamline the synthetic design of C₂₀-diterpenoid alkaloids and pave the way for their modular syntheses.

Acehytisine suppresses atrial fibrillation in rats with dilated atria caused by chronic volume overload

Atrial dilation is an independent risk factor for the development of atrial fibrillation (AF) and modulates the efficacy of anti-AF drugs, leading to the unsatisfactory control of AF. Pre-clinical studies showed anti-AF effects of acehytisine, a multi-ion channel inhibitor, in atria without structural and/or electrophysiological abnormalities, but information is limited regarding its anti-AF efficacy in dilated atria. We evaluated anti-AF effects of acehytisine at 4 and 10 mg/kg intravenously infused over 10 min using 8-week-old Wistar rats (n = 5; male) with atrial dilation caused by aorto-venocaval shunt (AVS). Echocardiography showed that atria were enlarged by +26.9% after one month of operation in AVS rats compared with sham-operated rats (n = 4; male). Electrophysiological examinations indicated burst pacing-induced AF reached 206 s. Acehytisine at doses of 4 and 10 mg/kg decreased the duration of burst pacing-induced AF with prolongation of Wenckebach cycle length and P wave duration in a dose-dependent manner. Importantly, the drug effectively terminated the persistent AF that was resistant to multiple programmed electrical stimulations in one rat. Therefore, these results provide in vivo evidence that acehytisine may be beneficial for preventing and terminating persistent AF in dilated atria.

Electropharmacological profile of an atrial-selective sodium channel blocker acehytisine assessed in the isoflurane-anesthetized guinea-pig model

Experimental evidence regarding the risk of proarrhythmic potential of acehytisine is limited. We assessed its electropharmacological effect together with proarrhythmic potential at intravenous doses of 4 and 10 mg/kg (n = 6) using isoflurane-anesthetized guinea pigs in comparison with that of bepridil at 1 and 3 mg/kg, intravenously (n = 6). Acehytisine at therapeutic dose (4 mg/kg) decreased the heart rate, prolonged P wave duration, QRS width, QT interval, QTc, MAP_90(sinus), MAP_90(CL300) and MAP_90(CL250). At supratherapeutic dose (10 mg/kg), it prolonged the PR interval besides enhancing the changes induced by the therapeutic dose. Quantitative assessment showed that peak changes in P wave duration by acehytisine at 10 mg/kg were 1.7 times longer than bepridil, and in MAP_90(sinus), MAP_90(CL300) and MAP_90(CL250) by acehytisine were 1.9, 1.5 and 1.5 times shorter than bepridil, respectively. Importantly, qualitative assessment indicated that bepridil increased beat-to-beat variability and J-T_peakc in a dose-related manner, confirming a higher proarrhythmic risk, whereas such dose-related responses were not observed in acehytisine, suggesting a lower proarrhythmic risk. These results suggest that acehytisine exhibits favorable pharmacological characters, i.e. potent atrial inhibition and lower proarrhythmic toxicity compared with bepridil, being a promising candidate for the treatment of paroxysmal supraventricular tachycardia.

A Benzyne Insertion Approach to Hetisine-Type Diterpenoid Alkaloids: Synthesis of Cossonidine (Davisine)

The hetisine-type natural products exhibit one of the most complex carbon skeletons within the diterpenoid alkaloid family. The use of network analysis has enabled a synthesis strategy to access alkaloids in this class with hydroxylation on the A-ring. Key transformations include a benzyne acyl-alkylation to construct a key fused 6-7-6 tricycle, a chemoselective nitrile reduction, and sequential C-N bond formations using a reductive cyclization and a photochemical hydroamination to construct an embedded azabicycle. Our strategy should enable access to myriad natural and unnatural products within the hetisine-type.

The Role of Biologically Active Ingredients from Natural Drug Treatments for Arrhythmias in Different Mechanisms

Arrhythmia is a disease that is caused by abnormal electrical activity in the heart rate or rhythm. It is the major cause of cardiovascular morbidity and mortality. Although several antiarrhythmic drugs have been used in clinic for decades, their application is often limited by their adverse effects. As a result, natural drugs, which have fewer side effects, are now being used to treat arrhythmias. We searched for all articles on the role of biologically active ingredients from natural drug treatments for arrhythmias in different mechanisms in PubMed. This study reviews 19 natural drug therapies, with 18 active ingredient therapies, such as alkaloids, flavonoids, saponins, quinones, and terpenes, and two kinds of traditional Chinese medicine compound (Wenxin-Keli and Shensongyangxin), all of which have been studied and reported as having antiarrhythmic effects. The primary focus is the proposed antiarrhythmic mechanism of each natural drug agent. Conclusion. We stress persistent vigilance on the part of the provider in discussing the use of natural drug agents to provide a solid theoretical foundation for further research on antiarrhythmia drugs.

Atrial-selective block of sodium channels by acehytisine in rabbit myocardium

Acehytisine, a multi-ion channel blocker, can markedly inhibit I_Na, I_Ca, I_Kur, I_f at various concentrations and effectively terminate and prevent atrial fibrillation (AF) in patients and animal models, but the molecular mechanism underlying its blockage remains elusive. In this study, we investigated the effects of acehytisine on action potentials and sodium channels of atrial and ventricular myocytes isolated from rabbit, using whole-cell recording system. We found that acehytisine exerted stronger blocking effects on sodium channels in atria than in ventricles, especially at depolarization (IC₅₀: 48.48 ± 7.75 μmol/L in atria vs. 560.17 ± 63.98 μmol/L in ventricles). It also significantly shifted steady state inactivation curves toward negative potentials in atrial myocytes, without affecting the recovery kinetics from inactivation of sodium channels in the same cells. In addition, acehytisine inhibited I_Na in a use-dependent manner and regulated slow inactivation kinetics by different gating configurations. These findings indicate that acehytisine selectively blocks atrial sodium channels and possesses affinity to sodium channel in certain states, which provides additional evidence for the anti-AF of acehytisine.

Studies on C20-diterpenoid alkaloids: synthesis of the hetidine framework and its application to the synthesis of dihydronavirine and the atisine skeleton

The full details of a synthesis of the hetidine framework of the C20-diterpenoid alkaloids and its conversion to the atisine core structure are reported. The application of the hetidine framework to the synthesis of dihydronavirine, which is the formal reduction product of the natural product navirine, is also described. Key to the success of these studies is the use of a Ga(III)-catalyzed cycloisomerization reaction of alkynylindenes to prepare a [6-7-6] framework that was advanced to the hetidine skeleton. Furthermore, a Michael/aldol sequence was developed for the construction of the bicyclo[2.2.2] framework that is characteristic of the hetidines and atisines.

New diterpenoid alkaloids from Aconitum coreanum and their anti-arrhythmic effects on cardiac sodium current

Two new diterpenoid alkaloids, Guan-Fu base J (GFJ, 1) and Guan-Fu base N (GFN, 2) along with nineteen known alkaloids (3-21) were isolated from the roots of Aconitum coreanum (Lèvl.) Rapaics, which is the raw material of a new approval anti-arrhythmia drug "Acehytisine Hydrochloride". The structures of isolated compounds were established by means of 1D, 2D NMR spectroscopic and chemical methods. All isolates obtained in the present study were evaluated for their inhibitory effects on blocking the ventricular specific sodium current using a whole-cell patch voltage-clamp technique. Among these 21 compounds, Guan-Fu base S (GFS, 3) showed the strongest inhibitory effect with an IC50 value of 3.48 μM, and only hetisine-type C20 diterpenoid alkaloids showed promising IC50 values for further development.

Current pharmacogenomic studies on hERG potassium channels

Genetic polymorphisms in human ether-a-go-go-related gene (hERG) potassium channels are associated with many complex diseases and sensitivity to channel-related drugs. Genotypes may underlie different sensitivities to the same drug, and different drugs selectively repair the functional deficits caused by individual mutations. In fact, not all drugs that block hERG function have adverse effects as previously thought. This suggests that the severe adverse reactions observed clinically may only occur in subjects with a particular genotype, but to others may be safe. Similarly, a drug that is ineffective in one population may be both safe and effective in another. Therefore, detecting polymorphisms in KCNH2 encoding hERG1 is of great significance in guiding the prevention and treatment of related diseases, re-evaluating drug safety, and individualizing treatment. This article reviews current pharmacogenomic studies on hERG potassium channels to provide a reference for developing individualized treatments and evaluating their safety.

Comparative effects of Guanfu base A and Guanfu base G on HERG K+ channel

BACKGROUND

Guanfu base A (GFA) and Guanfu base G (GFG) are chemicals isolated from Aconitum coreanum. The potassium channel encoded by the human ether-a-go-go related gene (HERG) plays an important role in repolarization of the cardiac action potential. The purpose of the present study was to investigate the effects of GFA and GFG on the HERG channel and its structure-function relationship.

METHODS

The effects of GFA and GFG were investigated in human embryonic kidney 293 (HEK293) cells transiently transfected with HERG complementary DNA using a whole-cell patch clamp technique.

RESULTS

GFA and GFG inhibited HERG channel current in concentration-, voltage-, and time-dependent manners. The IC50 for GFA and GFG was 1.64 mM and 17.9 μM, respectively. Both GFA and GFG shifted the activation curve in a negative direction and accelerated channel inactivation but showed no effect on the inactivation curve. Moreover, GFG also accelerated channel recovery from inactivation.

CONCLUSIONS

Both GFA and GFG blocked HERG channel current. This effect was stronger after GFG treatment rather than GFA treatment. This blockade was dependent on open and inactivated channel states. These results indicate that GFA could be a rather promising antiarrhythmic drug without severe side effects, whereas GFG could cause QT prolongation and requires further research.

Inhibitory effects of a bisbenzylisoquinline alkaloid dauricine on HERG potassium channels

ETHNOPHARMACOLOGICAL RELEVANCE

The roots of Menispermum dauricum have been widely used for the treatment of inflammation, allergy and arrhythmia in China for a long time. Dauricine (Dau), a bisbenzylisoquinline alkaloid from Menispermum dauricum, mainly contributes to the anti-arrhythmic effect and has received pharmacological attention. Dau can prolong the action potential duration (APD), which has been attributed to its ability to modulate Ca(2+) and several K(+) channels. However, its effects on human-ether-a-go-go-related gene (HERG) channels are unknown.

AIM OF THE STUDY

The effects of Dau on HERG channels were investigated.

MATERIALS AND METHODS

Whole-cell patch-clamp technique was used to record HERG current (I(HERG)) carried by recombinant HERG channels expressed in HEK293 cells.

RESULTS

Dau inhibited I(HERG) in a concentration-dependent manner with an IC(50) of 3.5 μM. Development of block and washout were fast. The inhibitory action of Dau was contingent on channel gating, showing significant voltage and time dependence. Dau inhibited I(HERG) in the open and inactivated states, but not in the closed states. The activation curve was shifted in a negative direction.

CONCLUSIONS

Dau inhibits HERG encoded potassium channels and this action might be a molecular mechanism for the previously reported APD prolongation with this drug.

Hirsutenone directly blocks human ether-a-go-go related gene K+ channels

The aim of the present study was to investigate whether hirsutenone affects the human ether-a-go-go related gene (hERG) K(+) channels. Many drugs promote formation of the acquired form of long QT syndrome (LQTS) by blocking the hERG K(+) channels. Hirsutenone, a new candidate for the treatment inflammatory skin lesions, induced a concentration-dependent decrease in hERG K(+) current amplitudes. Hirsutenone significantly decreased the time constants at the onset of inactivation. However, the reductions in the time constants of steady-state inactivation and the recovery from inactivation after hirsutenone treatment were not significant. In addition, the drug had no effect on the voltage-dependent activation curve or the steady-state inactivation curve. In summary, hirsutenone potentially acts as a blocker of hERG K(+) channels functioning by modifying the channel inactivation kinetics.

Blocking effects of acehytisine on pacemaker currents (I(f)) in sinoatrial node cells and human HCN4 channels expressed in Xenopus laevis oocytes

ETHNOPHARMACOLOGICAL RELEVANCE

The root of Aconitum coreanum (Levl.) Raipaics has been extensively used to treat various kinds of disorders including cardiovascular disease in China for a long time. According to recent studies, its antiarrhythmic actions are attributable to the active component, acehytisine. However, the underlying mechanism remains poorly understood.

AIM OF THE STUDY

The effects of acehytisine on the spontaneous activity in sinoatrial nodes and the electropharmacological action of this drug on I(f) in pacemaker cells and hHCN4 channels in oocytes were to be investigated.

MATERIALS AND METHODS

Sinoatrial nodes were cut from rabbit heart, and transmembrane potentials were recorded by standard microelectrode technique. A whole-cell patch clamp technique was employed to record I(f) isolated enzymatically from rabbit sinoatrial node pacemaker cells. Human HCN4 channels were heterologously expressed in Xenopus oocytes and studied using the two-electrode voltage clamp technique.

RESULTS

Acehytisine decreased the pacemaker rate of firing and slope of diastolic depolarization, modified the action potential configurations and blocked I(f) in rabbit sinoatrial node cells and hHCN4 channels expressed in Xenopus oocytes in a concentration-dependent, voltage-independent and non-use-dependent manner. Its electropharmacological properties were consistent with those of a close-state blocker.

CONCLUSION

Our findings are likely to shed light on the clinical application of acehytisine in the treatment of cardiovascular disorders.

Cyclovirobuxine D inhibits the currents of HERG potassium channels stably expressed in HEK293 cells

Cyclovirobuxine D (CVB-D) has been widely used for treatment of cardiac insufficiency and arrhythmias in China. The antiarrhythmic and proarrhythmic potential of this drug might be concerned with prolongation of action potential duration and QT interval. Human-ether-a-go-go-related gene (HERG) has an important role in the repolarization of the cardiac action potential. This study investigated for the first time the effect of CVB-D on HERG channels stably expressed in HEK293 cells using the whole-cell patch-clamp technique. CVB-D inhibited HERG current (IHERG) in a concentration-dependent manner with an IC50 of 19.7 μM. IHERG blockade required channel activation and was time-dependent, suggesting an open channel block. Moreover, IHERG inhibition by CVB-D was relieved by depolarization to a highly positive membrane potential (+80 mV) that favored HERG channel inactivation. These findings suggested that CVB-D inhibit HERG channels in the open states. CVB-D had no effect on HERG current kinetics. Thus, we conclude that CVB-D inhibits HERG encoded potassium channels and this action might be a molecular mechanism for the previously reported APD prolongation and QT interval prolongation with this drug.