New zwitterionic monoterpene indole alkaloids from Uncaria rhynchophylla

Isolation of new indole alkaloid triglucoside from the aqueous extract of Uncaria rhynchophylla

Uncaria rhynchophylla (Miq.) Miq. (Rubiaceae) is widely used as a botanical raw material for traditional Japanese and Chinese medicines. However, not all of its potentially bioactive constituents have been isolated and characterized. Herein, one new indole alkaloid triglucoside (1), nine known alkaloids (2-10) and thirteen known non-alkaloids (11-23) were isolated from the aqueous extract of Uncaria rhynchophylla hook and structurally characterized 1H and 13C NMR and high-resolution electrospray ionization mass spectrometry. The absolute configurations of isolated compounds (1, 2 and 3) were determined by the X-ray diffraction analysis of their single crystals obtained using a micro-drop crystallization technique. This technique allows single crystals to be obtained from samples as small as 50 µg, thus providing detailed structural information even on minor constituents and enabling the accurate quality monitoring of botanical raw materials more accurately.

Triterpenoids from the hook-bearing stems of Uncaria rhynchophylla

An unprescribed nortriterpenoid with an aromatic E ring, uncanortriterpenoid A (1), together with fourteen known triterpenoids (2-15), were isolated from the hook-bearing stems of Uncaria rhynchophylla Miq. Based on extensive spectroscopic analyses, the NMR data of 2, 5, and 10 in CD3OD were assigned for the first time, and the wrongly assigned δC of C-27 and C-29 of 2 were revised. Among the known compounds, 7, 13, and 15 were isolated from this species for the first time, and 15 represents the first lanostane triterpenoid bearing an extra methylidene at C-24 for the Rubiaceae family. Additionally, compounds 6 and 14 exhibited moderate ferroptosis inhibitory activity, with an EC50 value of 14.74 ± 0.20 μM for 6 and 23.11 ± 1.31 μM for 14.

The basic chemical substances of total alkaloids of Uncaria rhynchophylla and their anti-neuroinflammatory activities

To clarify the chemical basis of the total alkaloids of Uncaria rhynchophylla, HPLC-VWD chromatogram of total alkaloids was established. Under its guidance, modern chromatographic and spectroscopic techniques were used to track, isolate and identify the representative principal components. As a result, one new monoterpenoid indole alkaloid, 3S,15S-N4-methoxymethyl-geissoschizine methyl ether (1), together with 20 known alkaloids (2-21), and 5 other known compounds (22-26) were obtained. Meanwhile, sixteen characteristic peaks were identified from the total alkaloids using HPLC analysis. Then, the anti-neuroinflammatory effect of compounds 1-21 was assessed through inhibiting nitric ---oxide (NO) production in lipopolysaccharide (LPS)-induced BV-2 microglial cells. Among them, compounds 1, 3, 7, 8, 11, 12, 19 and 21 showed potent inhibitory activities with IC50 values of 5.87-76.78 μM.

Advanced researches of traditional uses, phytochemistry, pharmacology, and toxicology of medical Uncariae Ramulus Cum Uncis

ETHNOPHARMACOLOGICAL RELEVANCE

Medical Uncariae Ramulus Cum Uncis consists of Uncaria rhynchophylla (Miq.) Miq. ex Havil, Uncaria macrophylla Wall, Uncaria sinensis (Oliv.) Havil, Uncaria hirsuta Havil, and Uncaria sessilifructus Roxb, which belongs to the species widely used in the genus Uncaria. These species resource widely distributed in China and abroad, and the hook-bearing stem is the primary constituent enrichment site. There are many different forms and architectures of chemicals, depending on the extraction site. Traditional remedies employing URCU had been used widely in antiquity and were first compiled in renowned ancient masterpiece 'Mingyi Bielu ()' written by Hongjing Tao. In modern pharmacological studies, both the total extracts and the phytoconstituents isolated from URCU have been shown to have neuroprotective, antioxidant, anti-inflammatory, anticancer, antibacterial, and autophagy-enhancer properties.

AIM OF THE STUDY

This review concentrates on the traditional uses, phytochemistry, pharmacology, toxicology, and nanomaterials studies of URCU, with a perspective to assist with further research and advance.

MATERIAL AND METHODS

The Chinese and English literature studies of this review are based on these database searches including Science Direct, CNKI, Wiley online library, Spring Link, Web of Science, PubMed, Medalink, Google scholar, Elsevier, ACS Publications, iPlant, Missouri Botanical Garden, Plant of the World Online. The pertinent data on URCU was gathered.

RESULTS

Based on the examination of the genus Uncaria, 107 newly marked chemical compositions have been identified from URCU from 2015 to present, including alkaloids, terpenoids, flavonoids, steroids, and others. Pharmacological studies have demonstrated that URCU has a variety of benefits in diseases such as neurodegenerative diseases, cancer, cardiovascular diseases, diabetes, and migraine, due to its neuroprotective, anti-inflammatory, antioxidant, anti-tumor, anti-bacterial and anti-viral properties. According to metabolic and toxicological studies, the dosage, frequency, and interactions of the drugs that occur in vivo are of great significance for determining whether the organic bodies can perform efficacy or produce toxicity. The research on URCU-mediated nanomaterials is expanding and increasing in order to address the inadequacies of conventional Chinese medicine. The alkaloids in URCU have the capability to self-assemble with other classes of components in addition to being biologically active.

CONCLUSION

URCU plants are widely distributed, abundant in chemical constituents, and widely used in both traditional and modern medicine for a variety of pharmacological effects. The utilization of herbal medicines can be raised by assessing the pharmacological distinctions among several species within the same genus and may accelerate the modernization of traditional Chinese medicine. Controlling the concentration of drug administration, monitoring metabolic markers, and inventing novel nanotechnologies are effective strategies for synergistic influence and detoxification to alleviate the main obstacles that toxicity, low bioavailability, and poor permeability. This review can assist further research and advances.

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.

Uncarialines A-E, new alkaloids from Uncaria rhynchophylla and their anticoagulant activity

Uncarialines A-E (1-5), five undescribed monoterpene indole alkaloids, together with five known analogues were obtained from the stems of Uncaria rhynchophylla. Alkaloids 1-3 were unique 3,4-seco-tricyclic alkaloids with a 6/5/10 ring system, while 4 and 5 possessed a rare rearranged scaffold originated from corynantheine-type alkaloids with C-2/C-7 oxidation. Their structures were characterized by a comprehensive analysis of MS, NMR, and ECD. Their effects on blood clotting times of human plasma were evaluated and alkaloid 5 had a slight prolongation effect on both thrombin time and activated partial thromboplastin time (p < 0.001).

The current scenario of naturally occurring indole alkaloids with anticancer potential

Naturally occurring indole alkaloids are ubiquitously present in nature and possess extensive biological properties and structural diversity. Mechanistically, naturally occurring indole alkaloids have the potential to inhibit cancer cell proliferation, arrest cell cycle and induce apoptosis. Accordingly, naturally occurring indole alkaloids exhibit promising activity against both drug-sensitive and drug-resistant cancers including multidrug-resistant forms. Therefore, naturally occurring indole alkaloids constitute an important source of anticancer drug leads and candidates. The goal of this review is to highlight the current scenario of naturally occurring indole alkaloids with anticancer potential, covering articles published from 2018 to present. The names, sources, and antiproliferative activity are discussed to continuously open up a map for the remarkable exploration of more effective candidates.

Comparative transcriptome analysis revealed the molecular mechanism of the effect of light intensity on the accumulation of rhynchophylline and isorhynchophylline in Uncaria rhynchophylla

Rhynchophylline (RIN) and isorhynchophylline (IRN), the main medicinal components in plant Uncaria rhynchophylla, have potential effects on Alzheimer's disease. Understanding the influence of environmental factors, especially light intensity, on the production of these active ingredients will help to improve cultivation techniques. Compared with the 100% light intensity (CK), the contents of RIN and IRN in U. rhynchophylla leaves significantly increased at 20% light intensity (HS) after 7 and 21 days. Short-term shading (21d) changed some morphological indicators of U. rhynchophylla, but did not affect its biomass. Transcriptome profile analysis was performed on data from two groups (7 and 21 days) of CK and HS samples and yielded 79,817 unigenes with an average length of 1023 bp. Concurrently, 2391 and 2136 differentially expressed genes were identified in the transcriptome data for, respectively, 7 and 21 days of shade treatment. Notably, unigenes known to be involved upstream in the biosynthesis of RIN and IRN, such as G8O, IO, 7-DLGT, LAMT, TDC, and STR, were mostly upregulated. In addition, 1065 putative transcription factors (TFs) were identified and grouped into 55 TF families; 26 TFs showed differential expression in the shade treatment after 7 and 21 days. HY5 and PIFs, two important TFs of the light signaling pathway, also showed differential expression. This study provides insight into how gene expression was affected by light intensity during RIN and IRN accumulation in U. rhynchophylla.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-022-01142-2.

Validated Quantitative 1H NMR Method for Simultaneous Quantification of Indole Alkaloids in Uncaria rhynchophylla

Uncariae Ramulus Cum Uncis, known as "Gou-Teng" in Chinese, is derived mainly from the dried hook-bearing stems of Uncaria rhynchophylla. Quantitative determination of monoterpenoid indole alkaloids is critical for controlling its quality. In the present study, a rapid, accurate, and precise method was developed for the simultaneous quantitation of four characteristic components, namely, rhynchophylline (1), isorhynchophylline (2), corynoxeine (3), and isocorynoxeine (4), through 1H NMR spectrometry techniques. This method was performed on a 600 MHz NMR spectrometer with optimized acquisition parameters for performing quantitative experiments within 14 min. The highly deshielded signal of NH was at δH 10-11 in the aprotic solvent DMSO-d 6, which enables satisfactory separation of the signals to be integrated. Validation of the quantitative method was also performed in terms of specificity, linearity, sensitivity, accuracy, and precision. The method is linear in the concentration range of 25-400 μg/mL. The lower limit of quantification is 25 μg/mL. The intra- and interday relative standard deviation across three validation runs over the entire concentration range is less than 2.51%. The accuracy determined at three concentrations was within ±4.4% in terms of relative error. The proposed qNMR method was demonstrated to be a powerful tool for quantifying the alkaloids in traditional Chinese medicines (TCMs) due to its unique advantages of high precision, rapid analysis, and nonrequirement of standard compounds for calibration curve preparation. Moreover, qNMR represents a feasible alternative to high-performance liquid chromatography-based methods for the quality control of TCMs.

Minor alkaloids from an aqueous extract of the hook-bearing stem of Uncaria rhynchophylla

Seven new monoterpene alkaloids (1-7), along with 18 known analogues, were isolated from an aqueous decoction of the hook-bearing stems of Uncaria rhynchophylla (Gou-teng). Their structures were determined by spectroscopic data analysis and electronic circular dichroism (ECD) calculations. Compound 1 is the first monoterpene 22-norindoloquinolizidine alkaloid with a ketene unit, while 2 and 3 are unusual indoloquinolizidine alkaloids having an oxazinane ring.[Formula: see text].

Antiplasmodial activities of indole alkaloids from Tabernaemontana penduliflora K. Schum (Apocynaceae)

Five undescribed carboxy-indole alkaloids with corynanthe skeleton, penduflorines A-E (1-3) as well as a voacangine-N-oxide alkaloid, tabernaemontine (4), were isolated along with eight other known compounds (5-12) from the trunk bark of Tabernaemontana penduliflora K. Schum (Apocynaceae). Their structures were determined by means of spectroscopic and spectrometric methods such as UV, IR, NMR and HR-ESI-MS. Antiplasmodial activities of new isolates were evaluated against two strains of Plasmodium falciparum 3D7 and Dd2 by the Sybr green I-based fluorescence assay setup. Those compounds showed good in vitro activities. Among them, penduflorines A and B (1a and 1b) as well as tabernaemontine (4) showed significant inhibitory activities against the two strains with IC₅₀ values ranged between 1.85 and 7.88 μg/mL. This is the first report of quaternary-N-indole alkaloids (1a, 1b, 2, 3a, 3b and 4) occurring in the form of zwitterion from Tabernaemontana genus.

Uncaria rhynchophylla and its Major Constituents on Central Nervous System: A Review on Their Pharmacological Actions

BACKGROUND

Uncaria rhynchophylla (Miq.) Jacks (Rubinaceae), a common herbal medicine known as Gou-teng in Chinese, is commonly used in Chinese medicine practice for the treatment of convulsions, hypertension, epilepsy, eclampsia and other cerebral diseases. The major active components of U. rhynchophylla are alkaloids, terpenoids and flavonoids. The protective effects of U. rhynchophylla and its major components on central nervous system (CNS) have become a focus of research in recent decades.

OBJECTIVE

The study aimed to systematically summarize the pharmacological activities of U. rhynchophylla and its major components on the CNS.

METHODS

This review summarized the experimental findings from our laboratories, together with other literature data obtained through a comprehensive search of databases including the Pubmed and the Web of Science.

RESULTS

U. rhynchophylla and its major components such as rhynchophylline and isorhynchophylline have been shown to have neuroprotective effects on Alzheimer's disease, Parkinson's disease, depression, cerebral ischaemia through a number of mechanisms including anti-oxidant, anti-inflammatory actions and regulation on neurotransmitters.

CONCLUSION

U. rhynchophylla and its major components have multiple beneficial pharmacological effects on CNS. Further studies on U. rhynchophylla and its major components are warranted to fully illustrate the underlying molecular mechanisms, pharmacokinetics, and toxicological profiles of these naturally occurring compounds and their potential for clinical application.

Pharmacokinetics of isocorynoxeine in rat plasma after intraperitoneal administration by UPLC–MS/MS

Isocorynoxeine is one of the main alkaloids in Chinese medicinal herbs, and has pharmacological activities such as antihypertensive, sedative, anticonvulsant, and neuronal protection. It is an effective component of Uncaria for the treatment of hypertension. In this study, we used a fast and sensitive ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) to detect isocorynoxeine in rat plasma and investigated its pharmacokinetics in rats. Six rats were given isocorynoxeine (15 mg/kg) by intraperitoneal (i.p.) administration. Blood (100 μL) was withdrawn from the caudal vein at 5 and 30 min and 1, 2, 4, 6, 8, 12, and 24 h after administration. Chromatographic separation was achieved using a UPLC BEH C18 column using a mobile phase of acetonitrile–0.1% formic acid with gradient elution. Electrospray ionization (ESI) tandem mass spectrometry in the multiple reaction monitoring (MRM) mode with positive ionization was applied. Intra-day and inter-day precisions (relative standard deviation, %RSD) of isocorynoxeine in rat plasma were lower than 12%. The method was successfully applied in the pharmacokinetics of isocorynoxeine in rats after intraperitoneal administration. The t1/2 of isocorynoxeine is 4.9 ± 2.1 h, which indicates quick elimination.

The genus Uncaria: A review on phytochemical metabolites and biological aspects

The genus Uncaira (Rubiaceae) comprises of 34 species, many of which are usually used as traditional Chinese medicines (TCMs) to treat hypertension, fever, headache, gastrointestinal illness, and fungal infection. Over the past twenty years, Uncaira species have been paid the considerable attentions in phytochemical and biological aspects, and about 100 new secondary metabolites, including alkaloids, triterpenes, and flavonoids, have been elucidated. This review aims to present a comprehensive and up-to date overview of the biological source, structures and their biosynthetic pathways, as well as the pharmacological of the compounds reported in the genus Uncaria for the past two decades. It would provide an insight into the emerging pharmacological applications of the genus Uncaria.

Recent research progress of Uncaria spp. based on alkaloids: phytochemistry, pharmacology and structural chemistry

Medicinal plants are well-known in affording clinically useful agents, with rich medicinal values by combining with disease targets through various mechanisms. Plant secondary metabolites as lead compounds lay the foundation for the discovery and development of new drugs in disease treatment. Genus Uncaria from Rubiaceae family is a significant plant source of active alkaloids, with anti-hypertensive, sedative, anti-Alzheimer's disease, anti-drug addiction and anti-inflammatory effects. This review summarizes and discuss the research progress of Uncaria based on alkaloids in the past 15 years, mainly in the past 5 years, including biosynthesis, phytochemistry, pharmacology and structural chemistry. Among, focusing on representative compounds rhynchophylline and isorhynchophylline, the pharmacological activities surrounding the central nervous system and cardiovascular system are described in detail. On the basis of case studies, this article provides a brief overview of the synthesis and analogues of representative compounds types. In summary, this review provides an early basis for further searching for new targets and activities, discussing the mechanisms of pharmacological activity and studying the structure-activity relationships of active molecules.

Review of the Syntheses and Activities of Some Sulfur-Containing Drugs

Background:

Sulfur-containing compounds represent an important class of chemical compounds due to their wide range of biological and pharmaceutical properties. Moreover, sulfur-containing compounds may be applied in other fields, such as biological, organic, and materials chemistry. Several studies on the activities of sulfur compounds have already proven their anti-inflammatory properties and use to treat diseases, such as Alzheimer’s, Parkinson’s, and HIV. Moreover, examples of sulfur-containing compounds include dapsone, quetiapine, penicillin, probucol, and nelfinavir, which are important drugs with known activities.

Objective:

This review will focus on the synthesis and application of some sulfur-containing compounds used to treat several diseases, as well as promising new drug candidates.

Results:

Due to the variety of compounds containing C-S bonds, we have reviewed the different synthetic routes used toward the synthesis of sulfur-containing drugs and other compounds.

Indole alkaloids: 2012 until now, highlighting the new chemical structures and biological activities

Indole alkaloids have attracted attention because of their therapeutic properties, being anti-inflammatory, antinociceptive, antitumoural, antioxidant and antimicrobial. These compounds present a wide structural diversity, which is directly related to the genera of the producing plants, as well as the biological activities. Indole alkaloids have attracted attention over the last decade because of this combination of bioactivity and structural diversity. Therefore, this review presented recent (2012-2018) advances in alkaloids, focusing on new compounds, extraction methods and biological activities. As such, approximately 70 articles were identified, which showed 261 new compounds produced by plants of the families Apocynaceae, Rubiaceae, Annonaceae and Loganiaceae. In addition, different extraction methods were identified, and the structures of the new compounds were analysed. In addition to indole molecules, there were mono-indole-, di-indole-, vinblastine-, vimblastine-, gelsedine-, geissospermidine-, koumine-, geissospermidine-, iboga-, perakine-, corynanthe-, vincamine-, ajmaline-, aspidorpema-, strychnos-type, β-carboline alkaloids and indole alkaloid glucosides. The reported biological activities are mainly anticancer, antibacterial, antimalarial, antifungal, antiparasitic, and antiviral, as well as anti-acetylcholinesterase and anti-butyrylcolinesterase properties. This review serves as a guide for those wishing to find the most recently identified alkaloid structures and their associated activities.

Tissue Distribution of Hirsutine and Hirsuteine in Mice by Ultrahigh-Performance Liquid Chromatography-Mass Spectrometry

Hirsutine and hirsuteine were two alkaloid monomers extracted from the traditional Chinese medicine Uncaria rhynchophylla, which have pharmacological effects such as antihypertension, anti-infection, and heart protection. An ultrahigh-performance liquid chromatography-mass spectrometry was established for the determination of hirsutine and hirsuteine in tissues (liver, kidney, heart, spleen, brain, and lung), and their absorption, distribution, and metabolism were studied for providing information on its pharmacological mechanism. UPLC BEH C18 column (2.1  mm × 100  mm, 1.7 μm) was used for chromatographic separation. The mobile phase was acetonitrile-0.1% formic acid, with a gradient elution, and the total run time was 4 min. Electrospray was used in the positive ion mode, and the multiple reaction monitoring (MRM) mode was for quantification. The acetonitrile precipitation method was used to remove protein-treated mouse plasma and tissue homogenate samples. In the concentration range of 2-5000 ng/g, hirsutine and hirsuteine in tissues showed good linearity (r > 0.995), and the lower limit of quantification was 2 ng/g. In the plasma and liver tissues, the interday and intraday precision of hirsutine and hirsuteine was less than 15%, the accuracy was between 90.9% and 110.1%, and the average recovery was better than 73.0%. The matrix effect was between 86.2% and 104.7%. The results showed that the precision, accuracy, recovery, and matrix effects meet the requirements for the study on the distribution of hirsutine and hirsuteine. After intraperitoneal administration of 10 mg/kg hirsutine and hirsuteine in mice, the distribution levels were highest in liver and kidney tissues, followed by the spleen and lung. Hirsutine and hirsuteine were low in brain tissue, but had obvious distribution, suggesting that they may pass through the blood-brain barrier.

Glucoconjugated Monoterpene Indole Alkaloids from Uncaria rhynchophylla

Twenty-six glucoconjugated monoterpene indole alkaloids, including 12 new compounds, rhynchophyllosides A-L (1-12), and 14 known ones, 13-26, were obtained from the hook-bearing stems of Uncaria rhynchophylla (Miq.) Miq. ex Havil. Their structures were unambiguously elucidated by analyses of UV, MS, NMR, ECD, and single-crystal X-ray diffraction data. The ESI-MSⁿ behavior of the new glucoalkaloids was also elucidated. Although comprising the same glucosyl moiety, the aglycone skeletons and glucosidic numbers and linkage varied greatly, implying the diversity in biosynthetic pathways. This is the first report of such structurally diverse glucoconjugated monoterpene indole alkaloids from U. rhynchophylla. Compound 1 represents a new subtype of oxindole alkaloid with a seven-membered D-ring, 10 is a rare monoterpene indole alkaloid with the glucosyl moiety located at C-9, 4 and 5 are the first two oxindole alkaloid diglycosides, and 11 and 12 represent the first two examples of alkaloids with a quinolone nucleus from the genus Uncaria. Compound 10 exhibited moderate acetylcholinesterase (AChE) inhibitory activity with an IC₅₀ value of 10.5 μM. Molecular docking was performed to explore the binding mode of inhibitor 10 at the active site of AChE.