The chemistry, pharmacology, and clinical applications of qinghaosu (artemisinin) and its derivatives

Germline transformation of Artemisia annuaL. plant via in planta transformation technology “Floral dip”

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We for the first time proposed the in planta transformation technique in the Asteraceae plant family member Artemisia annua L.

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Numerous numbered, partially open, immature bud stage inflorescence is suitable for A. annua L. transformation.

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The infiltration media containing 1/2MS, Tween-20 (0.075%), and Acetosyringone (50mM) is found to be best for high efficiency transformation.

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Acetosyringone was more prevalent than Benzyl amino purine (BAP) for high efficiency transformation in A. annua L.

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Without including any labour intensive and time-consuming processes, we discovered a transformation efficiency of 26.9%, which is higher than previously reported studies.

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Transgene integration was further validated by quantitative Real time PCR using a low copy number hmgr as an endogenous reference gene.

The therapeutic efficacy of Artemisia annua L. is governed by artemisinin (ART), prevalently produced by A. annua extraction. Due to the modest amount of ART (0.01-1 %dw) in this plant, commercialization of ACTs is difficult. In this study, the floral-dip based transformation protocol for A. annua was developed to enhance expression of artemisinin biosynthesis genes and ART content. For dipping, the effective infiltration media components were optimized, and to obtain high transformation (26.9%) partially open bud stage capitulum of floral development was used. Hygromycin phospho-transferase (hptII) selection marker was used to validate the transformed T₁ progenies. The copy numbers of the transgene (hptII) in T₁ progenies were determined using a sensitive, high-throughput SYBR Green based quantitative RT-PCR. The results of the hptII transgene were compared with those of the low copy number, internal standard (hmgr). Using optimised PCR conditions, one, two and three transgene copies in T₁ transformants were achieved.

Exogenous hydrogen sulphide alleviates copper stress impacts in Artemisia annua L.: Growth, antioxidant metabolism, glandular trichome development and artemisinin biosynthesis

A supply of plant micronutrients (some of which are metals) is necessary to regulate many plant processes; their excess, however, can have detrimental consequences and can hamper plant growth, physiology and metabolism. Artemisia annua is an important crop plant used in the treatment of malaria. In this investigation, the physio-biochemical mechanisms involved in exogenous hydrogen sulphide-mediated (H₂ S) alleviation of copper (Cu) stress in A. annua were assessed.. Two different levels of Cu (20, 40 mg·kg^-1 ), one H₂ S treatment (200 µm) and their combinations were introduced while one set of plants was retained as control. Results showed that the presence of excess Cu in the soil reduced growth and biomass, photosynthetic parameters, chlorophyll content and fluorescence, gas exchange parameters and induced antioxidant enzyme activity. Copper stress enhanced the production of thiobarbituric acid reactive substances (TBARS) and increased Cu content in both roots and shoots of affected plants. Exogenous application of H₂ S restored the physio-biochemical characteristics of Cu-treated A. annua plants by reducing lipid peroxidation and enhancing the activity of antioxidant enzymes in Cu-stressed plants as compared with the controls. Hydrogen sulphide also reduced the Cu content in different plant parts, increased photosynthetic efficiency, trichome density, average area of trichomes and artemisinin content. Therefore, our results provide a comprehensive assessment of the defensive role of H₂ S in Cu-stressed A. annua.

Mechanistic Evaluation of the Stability of Arylvinyl-1,2,4-trioxanes under Acidic Conditions for Their Oral Administration as an Antimalarial Drug

A mechanistic approach to understand the course of metabolism for synthetic 1,2,4-trioxanes, potent antimalarial compounds, to evaluate their bioavailability for antimalarial action has been studied in the present work. It is an important parameter to study the course of metabolism of a drug candidate molecule when administered via oral route during its journey from oral intake to its target site. From the pharmacokinetics point of view, it determines the bioavailability of an active drug or a prodrug at the target point. In this work, synthetic arylvinyl-1,2,4-trioxanes 1a-u have been evaluated under various acidic conditions to mimic the milieu of the stomach (pH between 1.5 and 3.5) through which they have to pass when administered orally. The effect of acid on trioxanes led to their degradation into corresponding ketones and glyoxal. Under such acidic conditions glyoxal polymerized to form a nonisolable condensate product. The study indicates that the actual bioavailability of the drug is far less than the administered dose.

Exogenous Strigolactone (GR24) Positively Regulates Growth, Photosynthesis, and Improves Glandular Trichome Attributes for Enhanced Artemisinin Production in Artemisia annua

Artemisia annua is a medicinal plant particularly known for the production of a sesquiterpene lactone artemisinin; a specialty metabolite known for its efficacy in the treatment of malaria by killing different strains of Plasmodium falciparum due to radicals released upon the cleavage of its endoperoxide motif. Considering these facts and the immense medicinal value of artemisinin, the enhancement of in planta production of artemisinin is highly desirable. As strigolactones are known to regulate various aspects of plant growth and development, the effects of foliar spray of different concentrations of synthetic strigolactone analog GR24 (0, 0.5, 1, 2, 4, and 8 µM) on A. annua were studied. As compared to the control group, the foliar application of GR24 had a positive impact on general growth, photosynthesis, and other physiological indices with 4 µM GR24 showing the best results. The results indicate that GR24 application increased the plant biomass and various attributes related to photosynthesis, like total chlorophyll content, chlorophyll fluorescence, stomatal conductance, internal CO2, and net photosynthetic rate. Moreover, the activity of various enzymes related to photosynthesis like carbonic anhydrase, nitrate reductase, and RuBisCO was escalated. The GR24 also improved certain attributes related to glandular trichomes, with a significant enhancement in content and yield of artemisinin as compared to untreated plants.

Antimalarial Natural Products

Natural products have made a crucial and unique contribution to human health, and this is especially true in the case of malaria, where the natural products quinine and artemisinin and their derivatives and analogues, have saved millions of lives. The need for new drugs to treat malaria is still urgent, since the most dangerous malaria parasite, Plasmodium falciparum, has become resistant to quinine and most of its derivatives and is becoming resistant to artemisinin and its derivatives. This volume begins with a short history of malaria and follows this with a summary of its biology. It then traces the fascinating history of the discovery of quinine for malaria treatment and then describes quinine's biosynthesis, its mechanism of action, and its clinical use, concluding with a discussion of synthetic antimalarial agents based on quinine's structure. The volume then covers the discovery of artemisinin and its development as the source of the most effective current antimalarial drug, including summaries of its synthesis and biosynthesis, its mechanism of action, and its clinical use and resistance. A short discussion of other clinically used antimalarial natural products leads to a detailed treatment of other natural products with significant antiplasmodial activity, classified by compound type. Although the search for new antimalarial natural products from Nature's combinatorial library is challenging, it is very likely to yield new antimalarial drugs. The chapter thus ends by identifying over ten natural products with development potential as clinical antimalarial agents.

Novel hydrazone derivatives of N-amino-11-azaartemisinin with high order of antimalarial activity against multidrug-resistant Plasmodium yoelii nigeriensis in Swiss mice via intramuscular route

Novel hydrazone derivatives 10a-m were prepared from N-Amino-11-azaartemisinin (9) and screened for their antimalarial activity by oral and intramuscular (i.m.) routes against multidrug-resistant Plasmodium yoelii in Swiss mice model. Several of the hydrazone derivatives showed higher order of antimalarial activity. Compounds 10b, 10g, 10m provided 100% protection to the infected mice at the dose of 24 mg/kg × 4 days via oral route. Fluorenone based hydrazone 10m the most active compound of the series, provided 100% protection at the dose of 6 mg/kg × 4 days via intramuscular route and also provided 100% protection at the dose of 12 mg/kg × 4 days via oral route. While artemisinin gave 100% protection at 48 mg/kg × 4 days and only 60% protection at 24 mg/kg × 4 days via intramuscular (i.m.) route. Compound 10m found to be four-fold more active than artemisinin via intramuscular route.

Reduction of the Double Bond of 6-Arylvinyl-1,2,4-trioxanes Leads to a Remarkable Increase in Their Antimalarial Activity against Multidrug-Resistant Plasmodium yoelii nigeriensis in a Swiss Mice Model

Novel 6-arylethyl-1,2,4-trioxanes6a-i and 7a-i are easily accessible in one step from the diimide reduction of 6-arylvinyl-1,2,4-trioxanes 5a-i. All of these new trioxanes were assessed for their oral antimalarial activity against multidrug-resistant Plasmodium yoelii nigeriensis in a Swiss mice model. Most of the saturated trioxanes 6c, 6f, 6g, 6h, and 6i, the active compounds of the series, provided 100% protection to the malaria-infected mice at a dose of 24 mg/kg × 4 days. Further, trioxane 6i, the most active compound of the series, also showed 100% protection even at a dose of 12 mg/kg × 4 days and 20% protection at a dose of 6 mg/kg × 4 days. In this model, β-arteether provided 100% protection at a dose of 48 mg/kg × 4 days and only 20% protection at a dose of 24 mg/kg × 4 days via the oral route, which was found to exhibit 4-fold antimalarial activity compared with the currently used drug β-arteether.

Enhancing artemisinin content in and delivery from Artemisia annua: a review of alternative, classical, and transgenic approaches

This review analyses the most recent scientific research conducted for the purpose of enhancing artemisinin production. It may help to devise better artemisinin enhancement strategies, so that its production becomes cost effective and becomes available to masses. Malaria is a major threat to world population, particularly in South-East Asia and Africa, due to dearth of effective anti-malarial compounds, emergence of quinine resistant malarial strains, and lack of advanced healthcare facilities. Artemisinin, a sesquiterpene lactone obtained from Artemisia annua L., is the most potent drug against malaria and used in the formulation of artemisinin combination therapies (ACTs). Artemisinin is also effective against various types of cancers, many other microbes including viruses, parasites and bacteria. However, this specialty metabolite and its derivatives generally occur in low amounts in the source plant leading to its production scarcity. Considering the importance of this drug, researchers have been working worldwide to develop novel strategies to augment its production both in vivo and in vitro. Due to complex chemical structure, its chemical synthesis is quite expensive, so researchers need to devise synthetic protocols that are economically viable and also work on increasing the in-planta production of artemisinin by using various strategies like use of phytohormones, stress signals, bioinoculants, breeding and transgenic approaches. The focus of this review is to discuss these artemisinin enhancement strategies, understand mechanisms modulating its biosynthesis, and evaluate if roots play any role in artemisinin production. Furthermore, we also have a critical analysis of various assays used for artemisinin measurement. This may help to develop better artemisinin enhancement strategies which lead to decreased price of ACTs and increased profit to farmers.

4-chloro eugenol interacts synergistically with artesunate against drug resistant P. falciparum inducing oxidative stress

4-chloro eugenol (4CE), a semisynthetic analog of phytomolecule eugenol exhibited potent antiplasmodial activity with IC₅₀ in the range of 1.5-5 μM against sensitive as well as drug resistant strain of P. falciparum. This analog also showed synergy with a clinically used antimalarial drug artesunate and was able to curtail the IC₅₀ of artesunate up to 4-5 folds. Although, 4CE did not show any effect on heme polymerization, the most common drug target in the malaria parasite, it could increase the level of reactive oxygen species (ROS) and reactive nitrogen species (RNS) alone as well as in combination with artesunate. Further, 4CE induced oxidative stress was observed to affect the macromolecules in terms of DNA damage, protein carbonylation and lipid peroxidation. At the physiological level, cellular organelles like mitochondria and endoplasmic reticulum were observed to be get affected by 4CE in terms of membrane depolarization and calcium ion leakage respectively. These observations could be validated by expression analysis of oxidative stress responsive genes and proteins. Further, in in vivo assay, 4CE showed significant chemo-suppression of parasitemia as well as an increase in mean survival time in the murine malaria model. Interestingly, in combination with artesunate, 4CE showed higher chemo-suppression as well as enhanced mean survival time at a much lower concentrations of both the partners as compared to an individual dose of artesunate and 4CE. A combination of 4CE and artesunate was also observed to attenuate cerebral malaria pathogenesis.

Dihydroartemisinin, an active metabolite of artemisinin, interferes with Leishmania braziliensis mitochondrial bioenergetics and survival

Leishmaniasis is one of the most neglected parasitic infections of the world and current therapeutic options show several limitations. In the search for more effective drugs, plant compounds represent a powerful natural source. Artemisinin is a sesquiterpene lactone extracted from Artemisia annua L. leaves, from which dihydroartemisinin (DQHS) and artesunic acid (AA)/artesunate are examples of active derivatives. These lactones have been applied successfully on malaria therapy for decades. Herein, we investigated the sensitivity of Leishmania braziliensis, one of the most prevalent Leishmania species that cause cutaneous manifestations in the New World, to artemisinin, DQHS, and AA. L. braziliensis promastigotes and the stage that is targeted for therapy, intracelular amastigotes, were more sensitive to DQHS, showing EC₅₀ of 62.3 ± 1.8 and 8.9 ± 0.9 μM, respectively. Cytotoxicity assays showed that 50% of bone marrow-derived macrophages cultures were inhibited with 292.8 ± 3.8 μM of artemisinin, 236.2 ± 4.0 μM of DQHS, and 396.8 ± 6.7 μM of AA. The control of intracellular infection may not be essentially attributed to the production of nitric oxide. However, direct effects on mitochondrial bioenergetics and H₂O₂ production appear to be associated with the leishmanicidal effect of DQHS. Our data provide support for further studies of artemisinin and derivatives repositioning for experimental leishmaniasis.

Total Synthesis of (±)-Phaeocaulisin D

The tropone sesquiterpene phaeocaulisin D, isolated from the rhizomes of Curcuma phaeocaulis, has previously been shown to inhibit nitric oxide production in macrophages. A total synthesis of phaeocaulisin D was accomplished by using an intramolecular cyclization-dearomatization as a key step. The highlights of the synthesis are effective formation of the 5-7 fused tropone system, and selective methylation of a late-stage intermediate.

A diverse global fungal library for drug discovery

Background

Secondary fungal metabolites are important sources for new drugs against infectious diseases and cancers.

Methods

To obtain a library with enough diversity, we collected about 2,395 soil samples and 2,324 plant samples from 36 regions in Africa, Asia, and North America. The collection areas covered various climate zones in the world. We examined the usability of the global fungal extract library (GFEL) against parasitic malaria transmission, Gram-positive and negative bacterial pathogens, and leukemia cells.

Results

Nearly ten thousand fungal strains were isolated. Sequences of nuclear ribosomal internal transcribed spacer (ITS) from 40 randomly selected strains showed that over 80% were unique. Screening GFEL, we found that the fungal extract from Penicillium thomii was able to block Plasmodium falciparum transmission to Anopheles gambiae, and the fungal extract from Tolypocladium album was able to kill myelogenous leukemia cell line K562. We also identified a set of candidate fungal extracts against bacterial pathogens.

Artemisinin-derived antimalarial endoperoxides from bench-side to bed-side: Chronological advancements and future challenges

According to WHO World Malaria Report (2018), nearly 219 million new cases of malaria occurred and a total no. of 435 000 people died in 2017 due to this infectious disease. This is due to the rapid spread of parasite-resistant strains. Artemisinin (ART), a sesquiterpene lactone endoperoxide isolated from traditional Chinese herb Artemisia annua, has been recognized as a novel class of antimalarial drugs. The 2015 "Nobel Prize in Physiology or Medicine" was given to Prof Dr Tu Youyou for the discovery of ART. Hence, ART is termed as "Nobel medicine." The present review article accommodates insights from the chronological advancements and direct statistics witnessed during the past 48 years (1971-2019) in the medicinal chemistry of ART-derived antimalarial endoperoxides, and their clinical utility in malaria chemotherapy and drug discovery.

Traceless Protection for More Broadly Applicable Olefin Metathesis

An operationally simple in situ protection/deprotection strategy that significantly expands the scope of kinetically controlled catalytic Z- and E-selective olefin metathesis is introduced. Prior to the addition of a sensitive Mo- or Ru-based complex, treatment of a hydroxy- or a carboxylic-acid-containing olefin with commercially available HB(pin) or readily accessible HB(trip)₂ (pin=pinacolato, trip=2,4,6-tri(isopropyl)phenyl) for 15 min is sufficient for efficient generation of a desired product. Routine workup leads to quantitative deprotection. A range of stereochemically defined Z- and E-alkenyl chlorides, bromides, fluorides, and boronates or Z-trifluoromethyl-substituted alkenes with a hydroxy or carboxylic acid group were thus prepared in 51-97 % yield with 93 to >98 % stereoselectivity. We also show that, regardless of whether a polar functional unit is present or not, a small amount of HB(pin) may be used to remove residual water, significantly enhancing efficiency.

A Structural View on Medicinal Chemistry Strategies against Drug Resistance

The natural phenomenon of drug resistance is a widespread issue that hampers the performance of drugs in many major clinical indications. Antibacterial and antifungal drugs are affected, as well as compounds for the treatment of cancer, viral infections, or parasitic diseases. Despite the very diverse set of biological targets and organisms involved in the development of drug resistance, the underlying molecular mechanisms have been identified to understand the emergence of resistance and to overcome this detrimental process. Detailed structural information on the root causes for drug resistance is nowadays frequently available, so next-generation drugs can be designed that are anticipated to suffer less from resistance. This knowledge-based approach is essential for fighting the inevitable occurrence of drug resistance.

Antimalarial Activity of C-10 Substituted Triazolyl Artemisinin

We synthesized C-10 substituted triazolyl artemisinins by the Huisgen cycloaddition reaction between dihydroartemisinins (2) and variously substituted 1, 2, 3-triazoles (8a-8h). The antimalarial activities of 32 novel artemisinin derivatives were screened against a chloroquine-resistant parasite. Among them, triazolyl artemisinins with electron-withdrawing groups showed stronger antimalarial activities than those shown by the derivatives having electron-donating groups. In particularly, m-chlorotriazolyl artemisinin (9d-12d) showed antimalarial activity equivalent to that of artemisinin and could be a strong drug candidate.

A Review of Biotechnological Artemisinin Production in Plants

Malaria is still an eminent threat to major parts of the world population mainly in sub-Saharan Africa. Researchers around the world continuously seek novel solutions to either eliminate or treat the disease. Artemisinin, isolated from the Chinese medicinal herb Artemisia annua, is the active ingredient in artemisinin-based combination therapies used to treat the disease. However, naturally artemisinin is produced in small quantities, which leads to a shortage of global supply. Due to its complex structure, it is difficult chemically synthesize. Thus to date, A. annua remains as the main commercial source of artemisinin. Current advances in genetic and metabolic engineering drives to more diverse approaches and developments on improving in planta production of artemisinin, both in A. annua and in other plants. In this review, we describe efforts in bioengineering to obtain a higher production of artemisinin in A. annua and stable heterologous in planta systems. The current progress and advancements provides hope for significantly improved production in plants.

Population Pharmacokinetic and Pharmacodynamic Modeling of Artemisinin Resistance in Southeast Asia

Orally administered artemisinin-based combination therapy is the first-line treatment against uncomplicated P. falciparum malaria worldwide. However, the increasing prevalence of artemisinin resistance is threatening efforts to treat and eliminate malaria in Southeast Asia. This study aimed to characterize the exposure-response relationship of artesunate in patients with artemisinin sensitive and resistant malaria infections. Patients were recruited in Pailin, Cambodia (n = 39), and Wang Pha, Thailand (n = 40), and received either 2 mg/kg/day of artesunate mono-therapy for 7 consecutive days or 4 mg/kg/day of artesunate monotherapy for 3 consecutive days followed by mefloquine 15 and 10 mg/kg for 2 consecutive days. Plasma concentrations of artesunate and its active metabolite, dihydroartemisinin, and microscopy-based parasite densities were measured and evaluated using nonlinear mixed-effects modeling. All treatments were well tolerated with minor and transient adverse reactions. Patients in Cambodia had substantially slower parasite clearance compared to patients in Thailand. The pharmacokinetic properties of artesunate and dihydroartemisinin were well described by transit-compartment absorption followed by one-compartment disposition models. Parasite density was a significant covariate, and higher parasite densities were associated with increased absorption. Dihydroartemisinin-dependent parasite killing was described by a delayed sigmoidal Emax model, and a mixture function was implemented to differentiate between sensitive and resistant infections. This predicted that 84% and 16% of infections in Cambodia and Thailand, respectively, were artemisinin resistant. The final model was used to develop a simple diagnostic nomogram to identify patients with artemisinin-resistant infections. The nomogram showed > 80% specificity and sensitivity, and outperformed the current practice of day 3 positivity testing.

Molybdenum chloride catalysts for Z-selective olefin metathesis reactions

The development of catalyst-controlled stereoselective olefin metathesis processes has been a pivotal recent advance in chemistry. The incorporation of appropriate ligands within complexes based on molybdenum, tungsten and ruthenium has led to reactivity and selectivity levels that were previously inaccessible. Here we show that molybdenum monoaryloxide chloride complexes furnish higher-energy (Z) isomers of trifluoromethyl-substituted alkenes through cross-metathesis reactions with the commercially available, inexpensive and typically inert Z-1,1,1,4,4,4-hexafluoro-2-butene. Furthermore, otherwise inefficient and non-stereoselective transformations with Z-1,2-dichloroethene and 1,2-dibromoethene can be effected with substantially improved efficiency and Z selectivity. The use of such molybdenum monoaryloxide chloride complexes enables the synthesis of representative biologically active molecules and trifluoromethyl analogues of medicinally relevant compounds. The origins of the activity and selectivity levels observed, which contradict previously proposed principles, are elucidated with the aid of density functional theory calculations.

A Perspective on the Phytopharmaceuticals Responsible for the Therapeutic Applications

The word phytopharmaceutical deals with a complex mixture of compounds derived from the plant source that is used as a medicine or drug. Primitive human societies have been depending on plants and plant products for various remedies. Several plants in the different forms have been reported in traditional medicine and to find a rational for the treatment of various diseases than to isolated single compounds. Many of the single compounds isolated from the plant origin are effectively used in the medicine. The search of natural products in drug discovery has been greatly enhanced in the last few years. The impetus to use phytopharmaceutical agents for the treatment of disease, most of the plant based drugs are quite safe and have lesser adverse effects and are claimed that it works as synergistic effects.

Endoperoxide antimalarials: development, structural diversity and pharmacodynamic aspects with reference to 1,2,4-trioxane-based structural scaffold

Malaria disease continues to be a major health problem worldwide due to the emergence of multidrug-resistant strains of Plasmodium falciparum. In recent days, artemisinin (ART)-based drugs and combination therapies remain the drugs of choice for resistant P. falciparum malaria. However, resistance to ART-based drugs has begun to appear in some parts of the world. Endoperoxide compounds (natural/semisynthetic/synthetic) representing a huge number of antimalarial agents possess a wide structural diversity with a desired antimalarial effectiveness against resistant P. falciparum malaria. The 1,2,4-trioxane ring system lacking the lactone ring that constitutes the most important endoperoxide structural scaffold is believed to be the key pharmacophoric moiety and is primarily responsible for the pharmacodynamic potential of endoperoxide-based antimalarials. Due to this reason, research into endoperoxide, particularly 1,2,4-trioxane-, 1,2,4-trioxolane- and 1,2,4,5-teraoxane-based scaffolds, has gained significant interest in recent years for developing antimalarial drugs against resistant malaria. In this paper, a comprehensive effort has been made to review the development of endoperoxide antimalarials from traditional antimalarial leads (natural/semisynthetic) and structural diversity of endoperoxide molecules derived from 1,2,4-trioxane-, 1,2,4-trioxolane- and 1,2,4,5-teraoxane-based structural scaffolds, including their chimeric (hybrid) molecules, which are newer and potent antimalarial agents.

Synthesis and antimalarial activity of novel bicyclic and tricyclic aza-peroxides

Bicyclic and tricyclic aza-peroxides were synthesized and assessed for theirin vitroandin vivoantimalarial activities againstPlasmodium falciparum(3D7 strain) andPlasmodium yoelii nigeriensisin Swiss mice by an oral route, respectively.

In vitro antimalarial activity and molecular modeling studies of novel artemisinin derivatives

Cerebral malaria is a serious and sometimes fatal disease caused by aPlasmodium falciparumparasite that infects a female anopheles mosquito which feeds on humans.

Design, synthesis, and biological evaluation of artemisinin-indoloquinoline hybrids as potent antiproliferative agents

A series of artemisinin-indoloquinoline hybrids were designed and synthesized in an attempt to develop potent and selective anti-tumor agents. Compounds 7a–7f, 8 and 9 were prepared and characterized. Their antiproliferative activities against MV4-11, HCT-116, A549, and BALB/3T3 cell lines in vitro were tested. Nearly all of the tested compounds (7–9, except for compounds 7d and 7e against HCT-116) showed an increased antitumor activity against HCT-116 and A549 cell lines when compared to the dihydroartemisinin control. Especially for the artemisinin-indoloquinoline hybrid 8, with an 11-aminopropylamino-10H-indolo[3,2-b]quinoline substituent, the antiproliferative activity against the A549 cell line had improved more than ten times. The IC₅₀ value of hybrid 8 against A549 cell lines was decreased to 1.328 ± 0.586 μM, while dihydroartemisin showed IC₅₀ value of >20 µM in the same cell line. Thus, these results have proven that the strategy of introducing a planar basic fused aromatic moiety, such as the indoloquinoline skeleton, could improve the antiproliferative activity and selectivity towards cancer cell lines.

Natural products in medicine: transformational outcome of synthetic chemistry

This review brings to the forefront key synthetic modifications on natural products (NPs) that have yielded successful drugs. The emphasis is placed on the power of targeted chemical transformations in enhancing the therapeutic value of NPs through optimization of pharmacokinetics, stability, potency, and/or selectivity. Multiple classes of NPs such as macrolides, opioids, steroids, and β-lactams used to treat a variety of conditions such as cancers, infections, inflammation are exemplified. Molecular modeling or X-ray structures of NP/protein complexes supporting the observed boost in therapeutic value of the modified NPs are also discussed. Significant advancement in synthetic chemistry, in structure determination, and in the understanding of factors controlling pharmacokinetics can now better position drug discovery teams to undertake NPs as valuable leads. We hope that the beneficial NPs synthetic modifications outlined here will reignite medicinal chemists' interest in NPs and their derivatives.

Artesunate abolishes germinal center B cells and inhibits autoimmune arthritis

The antimalarial drug artemisinin and its derivatives exhibit potent immunosuppressive activity in several autoimmune disease models, however the mechanisms are not well-understood. This study was designed to investigate the therapeutic effects and the underlying mechanisms of the artemisinin analog artesunate using the K/BxN mouse model of rheumatoid arthritis. The well-studied disease mechanisms of K/BxN model allowed us to pinpoint the effect of artesunate on disease. Artesunate treatment prevented arthritis development in young K/BxN mice by inhibiting germinal center (GC) formation and production of autoantibodies. In adult K/BxN mice with established arthritis, artesunate diminished GC B cells in a few days. However, artesunate did not affect the follicular helper T cells (Tfh). In contrast to the spontaneous K/BxN model, artesunate treatment exerted minor influence on K/BxN serum transfer induced arthritis suggesting that artesunate has minimal effect on inflammatory responses downstream of antibody production. Finally, we showed that artesunate preferentially inhibits proliferating GC B cells. These results identify GC B cells as a target of artesunate and provide a new rationale for using artemisinin analogues to treat autoimmune diseases mediated by autoantibodies.

Preparation of Au and Ag nanoparticles using Artemisia annua and their in vitro antibacterial and tyrosinase inhibitory activities

This work describes a plant-mediated approach to the preparation of metal nanoparticles using leaf extract of Artemisia annua (A. annua), an ethno-medicinal plant widely found in Asia, which was used as reducing and stabilizing agent. A. annua is used in traditional Chinese medicine to alleviate fever. Au and Ag nanoparticles were prepared using a one-step aqueous method at room temperature without any toxic chemicals. The formation of Au and Ag nanoparticles was monitored by UV-vis spectroscopy. Synthesized nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). TEM analysis of Au nanoparticles showed that they had triangular and spherical shapes with sizes ranging from 15 to 40 nm. The silver nanoparticles were predominantly spherical and uniformly sized (30-50 nm). The Au and Ag nanoparticles produced showed significant tyrosinase inhibitory and antibacterial effects. These results suggest that the synthesized nanoparticles provide good alternatives in varied medical and industrial applications.

Artesunate inhibits the growth of gastric cancer cells through the mechanism of promoting oncosis both in vitro and in vivo

This study aims to investigate the significance and mechanism of artesunate involved in suppressing the proliferation of gastric cancer in vitro and in vivo. In the in-vitro experiments, artesunate inhibited the growth of gastric cancer cell lines (SGC-7901, BGC-823, and AGS) with concentration-dependent activity, with no significant effect on GES-1 cells. BGC-823 cells treated with artesunate showed the typical morphologic features of oncosis rather than apoptosis. Meanwhile, we observed calcium overload, downregulation of vascular endothelial growth factor expression, and upregulation of calpain-2 expression in the artesunate-treated BGC-823 cells. In addition, the in-vivo study showed that artesunate produced a dose-dependent tumor regression in nude mice. The antitumor activity of 240 mg/kg artesunate was similar to that of 10 mg/kg docetaxel. Furthermore, compared with the control group, no significant difference was observed in the body weight of artesunate-treated nude mice other than docetaxel-treated nude mice. These observations show that artesunate has concentration-dependent inhibitory activities against gastric cancer in vitro and in vivo by promoting cell oncosis through an impact of calcium, vascular endothelial growth factor, and calpain-2 expression.

One-pot green synthesis of β-artemether/arteether

We have developed an efficient one pot green synthesis of β-artemether/arteether from artemisinin, which involves combination of a sodium borohydride – cellulose sulfuric acid (CellSA) catalyst system. This green methodology is high yielding and the catalyst has good recyclability. The developed methodology is simple, cost-effective and the catalyst used is eco-friendly, reusable, and biodegradable.

Plant growth regulatory activities of artemisinin and its related compounds

Artemisinin, a sesquiterpene lactone produced in the leaves ofArtemisia annua, was evaluated for its phytotoxicity in mono- and dicotyledonous plants. Artemisinin inhibited seed germination, seedling growth, and root induction in all species tested. The concentration of artemisinin required for 50% inhibition ofLemna minor growth was 5 μM. Inhibitory plant responses appeared to require the endoperoxide moiety of this compound since similar chemicals without endoperoxide, deoxyartemisinin, arteannuic acid, and arteannuin B, were less phytotoxic. InL. minor, artemisinin and arteannuic acid caused the leakage of proteins into the growth medium, suggesting the site of activity was at the plant cell membrane.

Effects of two sesquiterpene lactones isolated fromArtemisia annua on physiology ofLemna minor

The effects of artemisinin and arteannuic acid extracted fromArtemisia annua on the physiology ofLemna minor were evaluated. Changes in frond production, growth, dry weight, and chlorophyll content ofL. minor were determined. Photosynthesis and respiration were evaluated with a differential respirometer. Artemisinin (5 µM) inhibitedL. minor frond production and dry weight 82 and 83%, relative to methanol controls. Chlorophyll content was reduced 44% by artemisinin (2.5 µM). Arteannuic acid (10 µM) was less active, inhibiting frond production 61% and reducing chlorophyll content 66% at 5 µM. Artemisinin (1 µM) reducedL. minor photosynthesis 30% and 2.5 µM reduced respiration 39%. Arteannuic acid had no significant effect on photosynthesis or respiration at the levels tested.