Phenolic glycosides with antimalarial activity from Grevillea "Poorinda Queen"

One-pot chemo- and photo-enzymatic linear cascade processes

The combination of chemo- and photocatalyses with biocatalysis, which couples the flexible reactivity of the photo- and chemocatalysts with the highly selective and environmentally friendly nature of enzymes in one-pot linear cascades, represents a powerful tool in organic synthesis. However, the combination of photo-, chemo- and biocatalysts in one-pot is challenging because the optimal operating conditions of the involved catalyst types may be rather different, and the different stabilities of catalysts and their mutual deactivation are additional problems often encountered in one-pot cascade processes. This review explores a large number of transformations and approaches adopted for combining enzymes and chemo- and photocatalytic processes in a successful way to achieve valuable chemicals and valorisation of biomass. Moreover, the strategies for solving incompatibility issues in chemo-enzymatic reactions are analysed, introducing recent examples of the application of non-conventional solvents, enzyme-metal hybrid catalysts, and spatial compartmentalization strategies to implement chemo-enzymatic cascade processes.

Anion-Bridged Dual Hydrogen Bond Enabled Concerted Addition of Phenol to Glycal

A noncovalent organocatalytic concerted addition of phenol to glycal is developed for the stereoselective and regioselective construction of biologically important phenolic 2-deoxyglycosides, featuring wide substrate tolerance. The method relies on an anion-bridged dual hydrogen bond interaction which is experimentally proved by Nuclear Magnetic Resonance (NMR), Ultraviolet and visible (UV-vis), and fluorescence analysis. Experimental evidence including kinetic analysis, Kinetic Isotope Effect (KIE) studies, linear free energy relationship, Hammett plot, and density functional theory (DFT) calculations is provided for a concerted mechanism where a high-energy oxocarbenium ion is not formed. In addition, the potential utility of this method is further demonstrated by the synthesis of biologically active glycosylated flavones. The benchmarking studies demonstrate significant advances in this newly developed method compared to previous approaches.

Distinctive Arbutin-Containing Markers: Chemotaxonomic Significance and Insights into the Evolution of Proteaceae Phytochemistry

Natural products isolation studies of eight endemic Tasmanian Proteaceae species - Agastachys odorata, Persoonia juniperina, Hakea megadenia, Hakea epiglottis, Orites diversifolius, Orites acicularis, Orites revolutus, and Telopea truncata - and three endemic Australian Proteaceae species Banksia serrata, Banksia praemorsa, and Banksia marginata were undertaken. Two previously unreported glycoside-derived natural products were identified, in addition to four other tremendously rare arbutin esters. The results of this study provide further evidence consistent with the proposal that these distinctive arbutin esters represent markers that can provide valuable insights into the chemical evolution of plant species within the family Proteaceae.

In Silico Analysis of Plant Flavonoids as Potential Inhibitors of Newcastle Disease Virus V Protein

Newcastle disease is a viral infection causing serious economic losses to the global poultry industry. The V protein of Newcastle disease virus (NDV) is a pathogenicity determinant having various functions such as the suppression of apoptosis and replication of the NDV. This study was designed to assess the resistance potential of plant flavonoids against the V protein of Newcastle disease virus. Sequence analysis was performed using EXPASY and ProtParam tools. To build the three-dimensional structure of V protein, a homology-modeling method was used. Plant flavonoids with formerly reported therapeutic benefits were collected from different databases to build a library for virtual screening. Docking analysis was performed using the modeled structure of V protein on MOE software. Interaction analysis was also performed by MOE to explain the results of docking. Sequence analysis and physicochemical properties showed that V protein is negatively charged, acidic in nature, and relatively unstable. The 3D structure of the V protein showed eight β-pleated sheets, three helices, and ten coiled regions. Based on docking score, ten flavonoids were selected as potential inhibitors of V protein. Furthermore, a common configuration was obtained among these ten flavonoids. The interaction analysis also identified the atoms involved in every interaction of flavonoid and V protein. Molecular dynamics (MD) simulation confirmed the stability of two compounds, quercetin-7-O-[α-L-rhamnopyranosyl(1→6)-β-D-galactopyranoside] and luteolin 7-O-neohesperidoside, at 100 ns with V protein. The identified compounds through molecular docking and MD simulation could have potential as NDV-V protein inhibitor after further validation. This study could be useful for the designing of anti-NDV drugs.

Hydrogen bond activated glycosylation under mild conditions

Herein, we report a new glycosylation system for the highly efficient and stereoselective formation of glycosidic bonds using glycosyl N-phenyl trifluoroacetimidate (PTFAI) donors and a charged thiourea hydrogen-bond-donor catalyst. The glycosylation protocol features broad substrate scope, controllable stereoselectivity, good to excellent yields and exceptionally mild catalysis conditions. Benefitting from the mild reaction conditions, this new hydrogen bond-mediated glycosylation system in combination with a hydrogen bond-mediated aglycon delivery system provides a reliable method for the synthesis of challenging phenolic glycosides. In addition, a chemoselective glycosylation procedure was developed using different imidate donors (trichloroacetimidates, N-phenyl trifluoroacetimidates, N-4-nitrophenyl trifluoroacetimidates, benzoxazolyl imidates and 6-nitro-benzothiazolyl imidates) and it was applied for a trisaccharide synthesis through a novel one-pot single catalyst strategy.

A mild glycosylation system was developed using glycosyl imidate donors and a charge-enhanced thiourea H-bond donor catalyst. The method can be used for the effective synthesis of O-, C-, S- and N-glycosides and chemoselective one-pot glycosylation.

Kolaviron: A Biflavonoid with Numerous Health Benefits

BACKGROUND

The increasing interests on the healing properties of medicinal plants have led to a paradigm shift from the use of synthetic drug to the search of natural medicines for the treatment and management of several diseases. Like other phenolics flavonoids have been continuously explored for their medicinal benefits, with their potent antioxidant activity being a major interest. Kolaviron (KVN) is a biflavonoid isolated from Garcinia kola Heckel, which has been reported for its potent antioxidant and anti-inflammatory properties. These properties have been explored in several disease models including reproductive toxicity, cardiotoxicity, diabetes mellitus, gastrotoxicity and hepatotoxicity.

OBJECTIVES

The present study was aimed to review the reported medicinal properties of KVN in order to provide some guidelines and direction to researchers on KVN research.

METHODS

A literature search was conducted with the aim of identifying peer-reviewed published data on KVN and their biological activities. Different academic and/or scientific search engines were utilized including but not limited to Google Scholar, PubMed, ScienceDirect and so on.

RESULTS

Among all the studied disease models obtained from the literatures, the effect of KVN on reproductive toxicity was the most studied as it represented 25% of all the studies, followed by neuroprotective, cardioprotective and hepatoprotective activities of Kolaviron. From our identified studies, KVN has been shown to have antidiabetic, cardioprotective, neuroprotective, hematoprotective, nephroprotective, gastroprotective, hepatoprotective activities. KVN also has effects on malaria and reproductive health, which can be explored for novel drug and nutraceutical developments for related ailments. Unfortunately, while toxicity data are lacking, most studies are limited to in vitro and/or in vivo models, which may impede translation in this area of research.

CONCLUSION

Based on data gathered from the literature search, it is evident that KVN possesses numerous health benefits, which can be attributed to its potent antioxidant and anti-inflammatory activities. However, more studies are required in this area of research to validate the medicinal value of kolaviron, which may positively influence the economic value of plant, Garcinia kola.

Flavonoids from the peels of Citrus unshiu Markov. and their inhibitory effects on RANKL-induced osteoclastogenesis through the downregulation of c-Fos signaling in vitro

Phytochemical investigation of Citrus unshiu peels led to the isolation of eight new flavonols (7-9, 11-15) and sixteen known compounds (1-6, 10, 16-24). Their structures were elucidated using spectroscopic analysis (1D, 2D NMR, and HR-MS). Besides, all isolated compounds (1-24) were evaluated for their inhibitory effects on receptor activator of RANKL-induced osteoclastogenesis in BMMs. Among them, dimethylmikanin (1), quercetogetin (2), 3,3',4',5,7,8-hexamethoxyflavone (3), 3-methoxynobiletin (4) showed a significant inhibitory effect on RANKL-induced osteoclast differentiation at a concentration of 10 μM. Moreover, 3-methoxynobiletin (4) suppressed RANKL-induced osteoclastogenesis by decreasing the number of osteoclasts and osteoclast actin-ring formation in a dose-dependent manner without causing any cytotoxic effects on BMMs. At the molecular level, 3-methoxynobiletin (4) inhibited RANKL-induced c-Fos expression and subsequently NFATc1 activation, as well as the expression of osteoclastogenesis-related marker genes c-Src and CtsK. These findings suggested that 3-methoxynobiletin (4) attenuated osteoclast differentiation by inhibiting RANKL-mediated c-Fos signaling and that it may have therapeutic potential for treating or preventing bone resorption-related diseases, such as osteoporosis.

Synthesis of aryl ethers of carbohydrates via reaction with arynes: selective O-arylation of trans-vicinal dihydroxyl groups in carbohydrates

A new method for the O-arylation of carbohydrates under metal-free conditions using arynes as an aryl source has been developed. This approach works well with mono, di and trihydroxy compounds. Preferential O-arylation takes place at primary over secondary and equatorial over axial. Site-selective O-arylation was achieved with the substrate having trans vicinal diequatorial hydroxyls.

Antiplasmodial natural products: an update

Background

Malaria remains a significant public health challenge in regions of the world where it is endemic. An unprecedented decline in malaria incidences was recorded during the last decade due to the availability of effective control interventions, such as the deployment of artemisinin-based combination therapy and insecticide-treated nets. However, according to the World Health Organization, malaria is staging a comeback, in part due to the development of drug resistance. Therefore, there is an urgent need to discover new anti-malarial drugs. This article reviews the literature on natural products with antiplasmodial activity that was reported between 2010 and 2017.

Methods

Relevant literature was sourced by searching the major scientific databases, including Web of Science, ScienceDirect, Scopus, SciFinder, Pubmed, and Google Scholar, using appropriate keyword combinations.

Results and Discussion

A total of 1524 compounds from 397 relevant references, assayed against at least one strain of Plasmodium, were reported in the period under review. Out of these, 39% were described as new natural products, and 29% of the compounds had IC₅₀ ≤ 3.0 µM against at least one strain of Plasmodium. Several of these compounds have the potential to be developed into viable anti-malarial drugs. Also, some of these compounds could play a role in malaria eradication by targeting gametocytes. However, the research into natural products with potential for blocking the transmission of malaria is still in its infancy stage and needs to be vigorously pursued.

A systematic review on anti-malarial drug discovery and antiplasmodial potential of green synthesis mediated metal nanoparticles: overview, challenges and future perspectives

BACKGROUND

The recent emergence in Southeast Asia of artemisinin resistance poses major threats to malaria control and elimination globally. Green nanotechnologies can constitute interesting tools for discovering anti-malarial medicines. This systematic review focused on the green synthesis of metal nanoparticles as potential source of new antiplasmodial drugs.

METHODS

Seven electronic database were used following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

A total of 17 papers were included in the systematic review. 82.4% of the studies used plant leaves to produce nanoparticles (NPs) while three studies used microorganisms, including bacteria and fungi. Silver was the main metal precursor for the synthesis of NPs. The majority of studies obtained nanoparticles spherical in shape, with sizes ranging between 4 and 65 nm, and reported no or little cytotoxic effect of the NPs. Results based on 50% inhibitory concentration (IC50) varied between studies but, in general, could be divided into three NP categories; (i) those more effective than positive controls, (ii) those more effective than corresponding plant extracts and, (iii) those less effective than the positive controls or plant extracts.

CONCLUSIONS

This study highlights the high antiplasmodial potential of green-synthesized metal nanoparticles thereby underscoring the possibility to find and develop new anti-malarial drugs based on green synthesis approaches. However, the review also highlights the need for extensive in vitro and in vivo studies to confirm their safety in humans and the elucidation of the mechanism of action.

Copper-Catalyzed Anomeric O-Arylation of Carbohydrate Derivatives at Room Temperature

Direct and practical anomeric O-arylation of sugar lactols with substituted arylboronic acids has been established. Using copper catalysis at room temperature under an air atmosphere, the protocol proved to be general, and a variety of aryl O-glycosides have been prepared in good to excellent yields. Furthermore, this approach was extended successfully to unprotected carbohydrates, including α-mannose, and it was demonstrated here how the interaction between carbohydrates and boronic acids can be combined with copper catalysis to achieve selective anomeric O-arylation.

Homology modeling and docking analysis of ßC1 protein encoded by Cotton leaf curl Multan betasatellite with different plant flavonoids

Cotton leaf curl Multan virus (CLCuMuV) belonging to begomoviruses (Family Geminiviridae) can infect cotton and many other agricultural crops. Betasatellite associated with CLCuMuV i.e., cotton leaf curl Multan betasatellite (CLCuMuB) is a small circular single-stranded deoxyribose nucleic acid (ssDNA) molecule that is essential for CLCuMuV to induce disease symptoms. Betasatellite molecule contains a ßC1 gene encoding for a pathogenicity determinant multifunctional protein, which extensively interacts with host plant machinery to cause virus infection. In this study the interaction of ßC1 with selected plant flavonoids has been studied. The study was focused on sequence analysis, three-dimensional structural modeling and docking analysis of ßC1 protein of CLCuMuB. Sequence analysis and physicochemical properties showed that ßC1 is negatively charged protein having more hydrophilic regions and is not very stable. Three-dimensional model of this protein revealed three helical, four beta pleated sheets and four coiled regions. The score of docking experiments using flavonoids as ligand indicated that plant flavonoids robinetinidol-(4alpha,8)-gallocatechin, quercetin 7-O-beta-D-glucoside, swertianolin, 3',4',5-trihydroxy-3-methoxyflavon-7-olate, agathisflavone, catiguanin B, 3',4',5,6-tetrahydroxy-3,7-dimethoxyflavone, quercetin-7-O-[alpha-L-rhamnopyranosyl(1->6)-beta-D-galactopyranoside], prunin 6″-O-gallate and luteolin 7-O-beta-D-glucosiduronic acid have strong binding with active site of ßC1 protein. The results obtained from this study clearly indicate that flavonoids are involved in defense against the virus infection, as these molecules binds to the active site of ßC1 protein. This information might be interesting to study plant defense mechanism based on the special compounds produced by the plants.

Synthesis of Phenolic Glycosides: Glycosylation of Sugar Lactols with Aryl Bromides via Dual Photoredox/Ni Catalysis

Multifarious sugar lactols were efficiently transformed into the corresponding phenolic glycosides by treating with aryl bromides in acetonitrile with Ir[dF(CF₃)ppy]₂(dtbbpy)(PF₆) as a photocatalyst under visible light irradiation. Both pyranoses and furanoses or even disaccharide could all suffer this glycosylation protocol under mild reaction conditions. A variety of phenyl glycosides can be produced in moderate to good yields (up to 93% yield), and a gram scale process of this protocol was also well-established.

Comparison of the Pharmacokinetics and Ex Vivo Antimalarial Activities of Artesunate-Amodiaquine and Artemisinin-Piperaquine in Healthy Volunteers for Preselection Malaria Therapy

The pharmacokinetics (PK) and ex vivo activity (pharmacodynamics [PD]) of two artemisinin combination therapies (ACTs) (artemisinin-piperaquine [ARN-PPQ] [Artequick®] and artesunate-amodiaquine [ARS-AQ] [Coarsucam™]) in healthy Vietnamese volunteers were compared following 3-day courses of the ACTs for the preselection of the drugs for falciparum malaria therapy. For PK analysis, serial plasma samples were collected from two separate groups of 22 volunteers after ACT administration. Of these volunteers, ex vivo activity was assessed in plasma samples from seven volunteers who received both ACTs. The area under the concentration-time curve (AUC0-∞) was 3.6-fold higher for dihydroartemisinin (active metabolite of ARS) than that for ARN, whereas the AUC0-∞ of desethylamodiaquine (active metabolite of AQ) was 2.0-fold lower than that of PPQ. Based on the 50% inhibitory dilution values of the volunteers' plasma samples collected from 0.25 to 3 hours after the last dose, the ex vivo activity of ARS-AQ was 2.9- to 16.2-fold more potent than that of ARN-PPQ against the drug-sensitive D6 Plasmodium falciparum line. In addition, at 1.5, 4.0, and 24 hours after the last dose, the ex vivo activity of ARS-AQ was 20.8-, 3.5-, and 8.5-fold more potent than that of ARN-PPQ against the ARN-sensitive MRA1239 line. By contrast, at 1.5 hours, the ex vivo activity of ARS-AQ was 5.4-fold more active than that of ARN-PPQ but had similar activities at 4 and 24 hours against the ARN-resistant MRA1240 line. The PK-PD data suggest that ARS-AQ possesses superior antimalarial activity than that of ARN-PPQ and would be the preferred ACT for further in vivo efficacy testing in multidrug-resistant falciparum malaria areas.

A phenolic glycoside from Flacourtia indica induces heme mediated oxidative stress in Plasmodium falciparum and attenuates malaria pathogenesis in mice

BACKGROUND

Flacourtia indica is especially popular among the various communities of many African countries where it is being used traditionally for the treatment of malaria. In our previous report, we have identified some phenolic glycosides from the aerial parts of F. indica as promising antiplasmodial agents under in vitro conditions.

PURPOSE

Antimalarial bioprospection of F. indica derived phenolic glycoside in Swiss mice (in vivo) with special emphasis on its mode of action.

METHODS

Chloroquine sensitive strain of Plasmodium falciparum was routinely cultured and used for the in vitro studies. The in vivo antimalarial potential of phenolic glycoside was evaluated against P. berghei in Swiss mice through an array of parameters viz., hematological, biochemical, chemo-suppression and mean survival time.

RESULTS

2-(6-benzoyl-β-d-glucopyranosyloxy)-7-(1α, 2α, 6α-trihydroxy-3-oxocyclohex-4-enoyl)-5-hydroxybenzyl alcohol (CPG), a phenolic glycoside isolated from the aerial parts of F. indica was found to exhibit promising antiplasmodial activity by arresting the P. falciparum growth at the trophozoite stage. Spectroscopic investigations reveal that CPG possesses a strong binding affinity with free heme moieties. In addition, these interactions lead to the inhibition of heme polymerization in malaria parasite, augmenting oxidative stress, and delaying the rapid growth of parasite. Under in-vivo condition, CPG exhibited significant antimalarial activity against P. berghei at 50 and 75mg/kg body weight through chemo-suppression of parasitemia and ameliorating the parasite induced inflammatory and oxidative (hepatic) imbalance in the experimental mice.

CONCLUSION

CPG was found to be a potential antimalarial constituent of F. indica with an explored mechanism of action, which also offers the editing choices for developing CPG based antimalarial chemotypes.

A new phenylpropanoid glucoside and a chain compound from the roots of Allium tuberosum

A new phenylpropanoid glucoside tuberosinine D (1) and a chain compound (Z)-11R,12S,13S-trihydroxy-9-octadecenoate (2) were isolated from the roots of Allium tuberosum. The absolute configuration of 1 was established by comparing of experimental and calculated electronic circular dichroism. The absolute configuration of 2 was determined using the modified Mosher's method for the first time.

In vivo Antimalarial Activity of α-Mangostin and the New Xanthone δ-Mangostin

Based on the previously reported in vitro antiplasmodial activity of several xanthones from Garcinia mangostana, two xanthones, α-mangostin and a new compound, δ-mangostin, were isolated from mangosteen husk, and the in vitro antiplasmodial and cytotoxic effects were determined. α-Mangostin was more active against the resistant Plasmodium falciparum chloroquine-resistant (FCR3) strain (IC50  = 0.2 ± 0.01 μM) than δ-mangostin (IC50  = 121.2 ± 1.0 μM). Furthermore, the therapeutic response according to the administration route was evaluated in a Plasmodium berghei malarial murine model. The greatest therapeutic response was obtained with intraperitoneal administration; these xanthones reduced parasitemia by approximately 80% with a daily dose of 100 mg/kg administered twice a day for 7 days of treatment. Neither compound was effective by oral administration. Noticeable toxicological effects were not observed. In addition to the antimalarial effect of these xanthones isolated from G. mangostana husk, the availability of larger amounts of husk raw material to purify the bioactive xanthones is advantageous, permitting additional preclinical assays or chemical transformations to enhance the biological activity of these substances.