Spirotetrahydro beta-carbolines (spiroindolones): a new class of potent and orally efficacious compounds for the treatment of malaria

Cu(II)-Catalyzed Enantioselective Aza-Friedel-Crafts Reaction of 1-Naphthols and Electron-Rich Phenols with Isatin-Derived Ketimines

New chiral ligands could be obtained by introducing proline moieties and imidazoline moieties to binaphthyl skeletons. The chiral ligands exhibited balanced rigidity and flexibility which could allow the change of the conformations during the reactions on one hand, and could provide sufficient asymmetric induction on the other. The proline moiety could act as a linker connecting the binaphthyl skeletons and the imidazoline moieties as well as a coordinating group for the central metal, and the electronic and steric properties of the imidazoline groups could be carefully fine-tuned by the use of different substituents. In the presence of Cu(II) catalyst bearing such chiral ligands, aza-Friedel-Crafts reaction of 1-naphthols and electron-rich phenols with isatin-derived ketimines provided the desired products with good to excellent yields and up to 99 % ee. The reactions showed good scalability, and excellent ee could still be obtained when the reaction was carried out in gram-scale.

Diastereoselective Three-Component 1,3-Dipolar Cycloaddition to Access Functionalized β-Tetrahydrocarboline- and Tetrahydroisoquinoline-Fused Spirooxindoles

A chemselective catalyst-free three-component 1,3-dipolar cycloaddition has been described. The unique polycyclic THPI and THIQs were creatively employed as dipolarophiles, which led to the formation of functionalized β-tetrahydrocarboline- and tetrahydroisoquinoline-fused spirooxindoles in 60-94% of yields with excellent diastereoselectivities (10: 1->99: 1 dr). This reaction not only realizes a concise THPI- or THIQs-based 1,3-dipolar cycloaddition, but also provides a practical strategy for the construction of two distinctive spirooxindole skeletons.

Synthesis of benzimidazole-fused 1,4-benzoxazepines and benzosultams spiro-connected to a 2-oxindole core via a tandem epoxide-opening/SNAr approach

While hundreds of literature reports describe the preparation of spirooxindole-based five- and six-membered heterocycles, the construction of seven-membered heterocyclic rings spiro-connected to a 2-oxindole core has so far been less developed. Herein, we disclose a base-mediated (4 + 3) annulation of spiro-epoxyoxindoles and 2-(2-fluoroaryl)-1H-benzoimidazoles or 2-fluoro-N-arylbenzenesulfonamides toward the synthesis of two new classes of spirooxindole-based polycyclic systems. Mechanistically, this conceptually simple and high atom-economical reaction proceeds via an SN2-like intermolecular epoxide ring-opening, accompanied by a concomitant intramolecular SNAr reaction. From a synthetic aspect, the notable features of the process are its full regioselectivity, operational simplicity using readily available substrates under transition-metal-free conditions, high yields, and broad substrate scope.

Copper(II)-Catalyzed Enantioselective Aza-Friedel-Crafts Reaction of Indoles with Isatin-Derived N-Boc-Ketimines

The copper(II)-catalyzed enantioselective aza-Friedel-Crafts reaction of indoles with isatin-derived N-Boc-ketimines was developed by using tunable chiral O-N-N tridentate ligands derived from BINOL and proline. In general, the reaction afforded chiral 3-indolyl-3-aminooxindoles under mild conditions in high yields (83-97%) with excellent ee (69-99%).

1,3-Dipolar cycloaddition reactions of isatin-derived azomethine ylides for the synthesis of spirooxindole and indole-derived scaffolds: recent developments

The unique therapeutic and biological characteristics of spirooxindole have led to the presentation of numerous reactions for the synthesis of spirooxindoles through 1,3-Dipolar cycloaddition of highly reactive isatin-derived azomethine ylides with activated olefins as the main tool for the formation of spirocyclic oxindoles during the last 4 years. Therefore, there is a need to highlight the recent developments in this area, along with the representative synthetic methods and relevant reaction mechanisms from 2018 to 2021. The representative synthetic methodologies were listed in four sections based on the procedure to form the azomethine ylide species including isatins and amino acids, isatin-derived α-(trifluoromethyl)imine, isatins and benzylamines, and from isatin-derived cyclic imine 1,3-dipoles.

Chemo-/Regio-Selective Synthesis of Novel Functionalized Spiro[pyrrolidine-2,3'-oxindoles] under Microwave Irradiation and Their Anticancer Activity

A novel series of nitrostyrene-based spirooxindoles were synthesized via the reaction of substituted isatins 1a-b, a number of α-amino acids 2a-e and (E)-2-aryl-1-nitroethenes 3a-e in a chemo/regio-selective manner using [3+2] cycloaddition (Huisgen) reaction under microwave irradiation conditions. The structure elucidation of all the synthesized spirooxindoles were done using 1H and 13C NMR and HRMS spectral analysis. The single crystal X-ray crystallographic study of compound 4l was used to assign the stereochemical arrangements of the groups around the pyrrolidine ring in spiro[pyrrolidine-2,3'-oxindoles] skeleton. The in vitro anticancer activity of spiro[pyrrolidine-2,3'-oxindoles] analogs 4a-w against human lung (A549) and liver (HepG2) cancer cell lines along with immortalized normal lung (BEAS-2B) and liver (LO2) cell lines shows promising results. Out of the 23 synthesized spiro[pyrrolidine-2,3'-oxindoles], while five compounds (4c, 4f, 4m, 4q, 4t) (IC50 = 34.99-47.92 µM; SI = 0.96-2.43) displayed significant in vitro anticancer activity against human lung (A549) cancer cell lines, six compounds (4c, 4f, 4k, 4m, 4q, 4t) (IC50 = 41.56-86.53 µM; SI = 0.49-0.99) displayed promising in vitro anticancer activity against human liver (HepG2) cancer cell lines. In the case of lung (A549) cancer cell lines, these compounds were recognized to be more efficient and selective than standard reference artemisinin (IC50 = 100 µM) and chloroquine (IC50 = 100 µM; SI: 0.03). However, none of them were found to be active as compared to artesunic acid [IC50 = 9.85 µM; SI = 0.76 against lung (A549) cancer cell line and IC50 = 4.09 µM; SI = 2.01 against liver (HepG2) cancer cell line].

Recent developments in antimalarial drug discovery

Although malaria remains a big burden to many countries that it threatens their socio-economic stability, particularly in the countries where malaria is endemic, there have been great efforts to eradicate this disease with both successes and failures. For example, there has been a great improvement in malaria prevention and treatment methods with a net reduction in infection and mortality rates. However, the disease remains a global threat in terms of the number of people affected because it is one of the infectious diseases that has the highest prevalence rate, especially in Africa where the deadly Plasmodium falciparum is still widely spread. Methods to fight malaria are being diversified, including the use of mosquito nets, the target candidate profiles (TCPs) and target product profiles (TPPs) of medicine for malarial venture (MMV) strategy, the search for newer and potent drugs that could reverse chloroquine resistance, and the use of adjuvants such as rosiglitazone and sevuparin. Although these adjuvants have no antiplasmodial activity, they can help to alleviate the effects which result from plasmodium invasion such as cytoadherence. The list of new antimalarial drugs under development is long, including the out of ordinary new drugs MMV048, CDRI-97/78 and INE963 from South Africa, India and Novartis, respectively.

Harnessing Protonated 2,2'-Bipyridinium Salts as Powerful Brønsted Acid Catalysts in Organic Reactions

It is the first time that the readily available protonated 2,2'-bipyridinium salts are used as Brønsted acid catalysts to accelerate a series of organic transformations that included the hydration of aromatic alkynes, etherification of alcohols, cyclotrimerization of aliphatic aldehydes, Ritter reaction, Mannich reaction, Biginelli reaction, preparation of substituted alkenes from alcohols, synthesis of spirooxindole, bisindolylmethane, and noncyclized tetraketone with good to excellent yields. These results strongly suggest that there exists enormous potentiality in the development of the protonated 2,2'-bipyridinium catalytic system.

Current development of β-carboline derived potential antimalarial scaffolds

β-Carboline alkaloids are an eminent class of nitrogen-based natural alkaloids and therapeutic molecules which exert various pharmacological activities through diverse mechanisms. A lot of attention has recently been directed towards this moiety in order to develop effective antimalarial drugs. "Malaria", an acute febrile illness caused by diverse Plasmodium parasites, is a continuing and escalating problem that devastates economically less developed countries by significantly increased morbidity and mortality rates. The mounting parasite resistance towards the antimalarial drugs and augmenting the 'habitat of the insect vector' are creating a catastrophe, indicating an urgent need for new efficacious therapeutics to combat this tropical disease. This article comprehensively encapsulates the clinical and preclinical antimalarial scaffolds comprising β-carboline moiety in their structure. Herein, various classes of natural and semi-synthetic analogues of β-carbolines reported in the last decade (2011-2021) have been extensively studied and illustrated. This review will help the readers to develop an insight into the β-carboline based antimalarials and molecular mechanisms lying behind their mode of action, which is anticipated to be beneficial for the future development of new β-carboline based therapeutics.

Regioselective synthesis of enantiopure 1,2- and 1,3-dispirooxindoles along with a DFT study

In the present study, a library of important enantiopure dispirooxindole [indolizidine, pyrrolizidine, and pyrrolidine] derivatives with three or four contiguous and two quaternary stereogenic centers using different amino acids (pipecolic acid, sarcosine, proline and hydroxyproline) were synthesized in high yields (up to 96%) through a regio- and diastereoselective (up to 99 : 1) multicomponent 1,3-dipolar cycloaddition strategy. Based on the results, the alteration of amino acids led to a change in the regioselectivity and unusual regioisomers (pyrrolizidine versus indolizidine/pyrrolidine) were obtained to construct a novel enantiopure 1,3-dispirooxindole skeleton. The stereochemical outcome of the cycloaddition was determined by single crystal X-ray diffraction analysis and the self-disproportionation of enantiomers (SDE) test confirmed the enantiomeric purity of the desired products. The mechanism and differences in the regioselectivity of the 1,3-dipolar cycloaddition reactions between the stable azomethane ylides obtained from ninhydrin, pipecolinic acid, and proline with (E)-2-oxoindolin-3-ylideneacetyl sultam were theoretically studied through DFT calculations at the M06-2X/6-31G(d,p) level in methanol.

Spirofused Tetrahydroisoquinoline-Oxindole Hybrids (Spiroquindolones) as Potential Multitarget Antimalarial Agents: Preliminary Hit Optimization and Efficacy Evaluation in Mice

Previous studies suggest that 3',5'-dihydro-2'H-spiro[indoline-3,1'-isoquinolin]-2-ones (DSIIQs [spiroquindolones]) are multitarget antiplasmodial agents that combine the actions of spiroindolone and naphthylisoquinoline antimalarial agents. In this study, 12 analogues of compound (±)-5 (moxiquindole), the prototypical spiroquindolone, were synthesized and tested for antiplasmodial activity. Compound (±)-11 (a mixture of compounds 11a and 11b), the most potent analogue, displayed low-nanomolar activity against P. falciparum chloroquine-sensitive 3D7 strain (50% inhibitory concentration [IC₅₀] for 3D7 = 21 ± 02 nM) and was active against all major erythrocytic stages of the parasite life cycle (ring, trophozoite, and schizont); it also inhibited hemoglobin metabolism and caused extensive vacuolation in parasites. In drug-resistant parasites, compound (±)-11 exhibited potent activity (IC₅₀ for Dd2 = 58.34 ± 2.04 nM) against the P. falciparum multidrug-resistant Dd2 strain, and both compounds (±)-5 and (±)-11 displayed significant cross-resistance against the P. falciparum ATP4 mutant parasite Dd2 SJ733 but not against the Dd2 KAE609 strain. In mice, both compounds (±)-5 and (±)-11 displayed dose-dependent reduction of parasitemia with suppressive 50% effective dose (ED₅₀) values of 0.44 and 0.11 mg/kg of body weight, respectively. The compounds were also found to be curative in vivo and are thus worthy of further investigation.

Multicomponent Synthesis of Spiro-dihydropyridine Oxindoles via Cascade Spiro-cyclization of Knoevenagel/Aza-Michael Adducts

An efficient, straightforward, and one-pot synthesis of biologically relevant spiro-dihydropyridine oxindoles was described via readily available isatin, malononitrile, allenoate, and amines. The metal/organocatalyst-free, Et₃N-mediated reaction proceeds via cascade spiro-cyclization of in situ generated Knoevenagel/aza-Michael adducts. The reaction has great flexibility over electron-rich and electron-poor substituents affording desired products in good to excellent yields. We have also demonstrated the selected spiro-dihydropyridines for late-stage diversification into new spiro-dihydropyridine hybrids of pharmaceutical relevance.

Crystallization-Enabled Henry Reactions: Stereoconvergent Construction of Fully Substituted [N]-Asymmetric Centers

Tetrasubstituted stereogenic carbon centers bearing a nitrogen substituent represent important motifs in medicinal chemistry and natural products; therefore, the development of efficient methods for the stereoselective synthesis of this class of compounds continues to be an important problem. This article describes stereoconvergent Henry reactions of γ,γ-disubstituted nitroalkanes to deliver highly functionalized building blocks containing up to five contiguous stereogenic centers including a fully substituted [N]-asymmetric center. Henry reactions of higher order nitroalkanes are often characterized by their reversibility and minimal accompanying thermodynamic stereocontrol. In contrast, mechanistic studies for the present case suggest a scenario in which reversibility is productively leveraged through crystallization-based stereocontrol, thereby enabling the efficient sequential π-additions of readily accessible starting materials to assemble complex acyclic stereoarrays.

Highly Selective Synthesis of Seven-Membered Azaspiro Compounds by a Rh(I)-Catalyzed Cycloisomerization/Diels-Alder Cascade of 1,5-Bisallenes

The synthesis of spiro compounds featuring seven- and six-membered rings in the spirobicyclic motif is successfully achieved through a cascade process encompassing a rhodium(I)-catalyzed cycloisomerization followed by a highly selective Diels–Alder homodimerization. The scope of the reaction is analyzed based on a series of synthetic substrates, and control experiments and DFT calculations led us to justify the exquisite degree of selectivity observed.

Recent Progress in the Development of Indole-Based Compounds Active against Malaria, Trypanosomiasis and Leishmaniasis

Human protozoan diseases represent a serious health problem worldwide, affecting mainly people in social and economic vulnerability. These diseases have attracted little investment in drug discovery, which is reflected in the limited available therapeutic arsenal. Authorized drugs present problems such as low efficacy in some stages of the disease or toxicity, which result in undesirable side effects and treatment abandonment. Moreover, the emergence of drug-resistant parasite strains makes necessary an even greater effort to develop safe and effective antiparasitic agents. Among the chemotypes investigated for parasitic diseases, the indole nucleus has emerged as a privileged molecular scaffold for the generation of new drug candidates. In this review, the authors provide an overview of the indole-based compounds developed against important parasitic diseases, namely malaria, trypanosomiasis and leishmaniasis, by focusing on the design, optimization and synthesis of the most relevant synthetic indole scaffolds recently reported.

Benzodioxole grafted spirooxindole pyrrolidinyl derivatives: synthesis, characterization, molecular docking and anti-diabetic activity

A highly stereoselective, three-component method has been developed to synthesize pyrrolidine and pyrrolizidine containing spirooxindole derivatives. The interaction between the dipolarophile α,β-unsaturated carbonyl compounds and the dipole azomethine ylide formed in situ by the reaction of 1,2-dicarbonyl compounds and secondary amino acids is referred to as the 1,3-dipolar cycloaddition reaction. The reaction conditions were optimized to achieve excellent stereo- and regioselectivity. Shorter reaction time, simple work-up and excellent yields are the salient features of the present approach. Various spectroscopic methods and single crystal X-ray diffraction examinations of one example of compound 6i validated the stereochemistry of the expected products. The anti-diabetic activity of the newly synthesized spirooxindole derivatives was tested against the α-glucosidase and α-amylase enzymes. Compound 6i was found to exhibit potent inhibition activity against α-glucosidase and α-amylase enzymes which is further evidenced by molecular docking studies.

A highly stereoselective, three-component method has been developed for the synthesis of pyrrolidine and pyrrolizidine containing spirooxindole derivatives that exhibits excellent anti-diabetic activity.

Lewis acid-catalyzed [4 + 2] cycloaddition of donor–acceptor cyclobutanes with iminooxindoles: access to spiro[piperidine-3,2′-oxindoles]

A Lewis acid-catalyzed [4 + 2] cycloaddition reaction from D–A cyclobutanes and iminooxindoles, providing the corresponding spiro[piperidine-3,2′-oxindoles] under mild conditions.

2-Aminopyridine - an unsung hero in drug discovery

2-Aminopyridine is a simple, low molecular weight and perfectly functionalised moiety known for the synthesis of diverse biological molecules. Many pharmaceutical companies across the globe aim to synthesise low-molecular weight molecules for use as pharmacophores against various biological targets. 2-Aminopyridine can serve as a perfect locomotive in the synthesis and pulling of such molecules towards respective pharmacological goals. The major advantage of this moiety is its simple design, which can be used to produce single products with minimum side reactions. Moreover, the exact weight of synthesised compounds is low, which enables facile identification of toxicity-causing metabolites in drug discovery programmes. This manuscript is a quick review of such pharmacophores derived from 2-aminopyridine.

Fe₃O4@MCM@ZrCI₂: A Practical Magnetic Mesoporous Zirconium-Based Nanocomposite as a Reusable Catalyst for the Synthesis of Spirooxindoles

In the present study, we aimed to investigate the catalytic role of the newly reported MCM-41 -based nanocomposite in which the low acidity of this mesoporous moiety was favourably improved via the stabilization of zirconium nanoparticles and was magnetized to make a facile work-up procedure as an applicable and efficient method. The prepared Fe₃O₄@MCM-41 @ZrCI₂ nanocomposite was successfully characterized using different analyses and then it was favourably exploited for the synthesis of spirooxindoles as the most prominent spiro compounds. As predicted, Fe₃O₄@MCM- 41 @ZrCI₂ showed considerable efficiency in the promotion of the studied reaction.

Multicomponent reactions in the synthesis of antiviral compounds

BACKGROUND

Multicomponent reactions are one-pot processes for the synthesis of highly functionalized hetero-cyclic and hetero-acyclic compounds, often endowed with biological activity.

OBJECTIVE

Multicomponent reactions are considered green processes with high atom economy. In addition, they present advantages compared to the classic synthetic methods such as high efficiency and low wastes production.

METHOD

In these reactions two or more reagents are combined together in the same flask to yield a product containing almost all the atoms of the starting materials.

RESULTS

The scope of this review is to present an overview of the application of multicomponent reactions in the synthesis of compounds endowed with antiviral activity. The syntheses are classified depending on the viral target.

CONCLUSION

Multicomponent reactions can be applied to all the stages of the drug discovery and development process making them very useful in the search for new agents active against emerging (viral) pathogens.

Protecting future antimalarials from the trap of resistance: Lessons from artemisinin-based combination therapy (ACT) failures

Having faced increased clinical treatment failures with dihydroartemisinin-piperaquine (DHA-PPQ), Cambodia swapped the first line artemisinin-based combination therapy (ACT) from DHA-PPQ to artesunate-mefloquine given that parasites resistant to piperaquine are susceptible to mefloquine. However, triple mutants have now emerged, suggesting that drug rotations may not be adequate to keep resistance at bay. There is, therefore, an urgent need for alternative treatment strategies to tackle resistance and prevent its spread. A proper understanding of all contributors to artemisinin resistance may help us identify novel strategies to keep artemisinins effective until new drugs become available for their replacement. This review highlights the role of the key players in artemisinin resistance, the current strategies to deal with it and suggests ways of protecting future antimalarial drugs from bowing to resistance as their predecessors did.

Site-specific role of bifunctional graphitic carbon nitride catalyst for the sustainable synthesis of 3,3-spirocyclic oxindoles in aqueous media

Functionalized graphitic carbon nitride (Sg-C₃N₄) has been manufactured and used as a reusable catalyst for the one-pot production of various spiro-pyrano chromenes and spiro indole-3,1′-naphthalene tetracyclic systems in aqueous media. An ultrasound-assisted method has been used for the functionalization of g-C₃N₄. The catalytic functionalities and the structural integrity of the catalyst were characterized via different analytical tools. The catalytic site-specific role of Sg-C₃N₄ was confirmed via various control experiments in one-pot reaction sequences. We recognized that Sg-C₃N₄ acts as a bifunctional acid–base catalyst for the first reaction sequence whereas it is an acidic catalyst for the second reaction sequence during the one-pot production of various spiro-pyrano chromenes. In addition, the bifunctional acid–base catalytic role of Sg-C₃N₄ has been confirmed for the first reaction sequence whereas it has a basic catalytic role for the second reaction sequence during the one-pot production of spiro indole-3,1′-naphthalene tetracyclic systems. Diverse C–C, C–O, and C–N bonds, six-membered cycles, stereogenic centers, and spiro frameworks were formed in a single reaction, enhancing the biocidal profile and possibly resulting in the discovery of new medicinal properties. The mild reaction environment, simple workup, easy separation, low cost, heterogeneity, and recyclability of Sg-C₃N₄ are some rewards of this approach.

Functionalized graphitic carbon nitride (Sg-C₃N₄) has been manufactured and used as a reusable catalyst for the one-pot production of various spiro-pyrano chromenes and spiro indole-3,1′-naphthalene tetracyclic systems in aqueous media.

Synthesis of Spirotetrahydrofuran Oxindoles via Palladium-Catalyzed [4 + 1] Cycloaddition of Diphenyl 2-Oxoindolin-3-yl Phosphates and 2-Methylidenetrimethylene Carbonate

A novel palladium-catalyzed [4 + 1] cycloaddition to give spirotetrahydrofuran oxindoles has been developed, in which diphenyl 2-oxoindolin-3-yl phosphates were used as the both electrophilic and nucleophilic C₁ synthons at C-3 of the oxindole unit and 2-methylidenetrimethylene carbonate was used as the 1,4-dipole. The cycloannulation was performed at room temperature and provided the corresponding spirotetrahydrofuran oxindoles in good to excellent yields. The present method affords a new strategy for the construction of spirooxindole derivatives with unique three-dimensional structures.

Antimalarial drug discovery: from quinine to the most recent promising clinical drug candidates

Malaria is a tropical threatening disease caused by Plasmodium parasites, resulting in 409,000 deaths in 2019. The delay of mortality and morbidity has been compounded by the widespread of drug resistant parasites from Southeast Asia since two decades. The emergence of artemisinin-resistant Plasmodium in Africa, where most cases are accounted, highlights the urgent need for new medicines. In this effort, the World Health Organization and Medicines for Malaria Venture joined to define clear goals for novel therapies and characterized the target candidate profile. This ongoing search for new treatments is based on imperative labor in medicinal chemistry which is summarized here with particular attention to hit-to-lead optimizations, key properties, and modes of action of these novel antimalarial drugs. This review, after presenting the current antimalarial chemotherapy, from quinine to the latest marketed drugs, focuses in particular on recent advances of the most promising antimalarial candidates in clinical and preclinical phases.

Identification of Spiro-Fused [3-azabicyclo[3.1.0]hexane]oxindoles as Potential Antitumor Agents: Initial In Vitro Evaluation of Anti-Proliferative Effect and Actin Cytoskeleton Transformation in 3T3 and 3T3-SV40 Fibroblast

Novel heterocyclic compounds containing 3-spiro[3-azabicyclo[3.1.0]hexane]oxindole framework (4a, 4b and 4c) have been studied as potential antitumor agents. The in silico ADMET (adsorption, distribution, metabolism, excretion and toxicity) analysis was performed on 4a-c compounds with promising antiproliferative activity, previously synthetized and screened against human erythroleukemic cell line K562 tumor cell line. Cytotoxicity of 4a-c against murine fibroblast 3T3 and SV-40 transformed murine fibroblast 3T3-SV40 cell lines were evaluated. The 4a and 4c compounds were cytotoxic against 3T3-SV40 cells in comparison with those of 3T3. In agreement with the DNA cytometry studies, the tested compounds have achieved significant cell-cycle perturbation with higher accumulation of cells in G0/G1 phase. Using confocal microscopy, we found that with 4a and 4c treatment of 3T3 cells, actin filaments disappeared, and granular actin was distributed diffusely in the cytoplasm in 82-97% of cells. The number of 3T3-SV40 cells with stress fibers increased to 7-30% against 2% in control. We discovered that transformed 3T3-SV40 cells after treatment with compounds 4a and 4c significantly reduced the number of cells with filopodium-like membrane protrusions (from 86 % in control cells to 6-18% after treatment), which indirectly suggests a decrease in cell motility. We can conclude that the studied compounds 4a and 4c have a cytostatic effect, which can lead to a decrease in the number of filopodium-like membrane protrusions.

Spirocyclic derivatives as antioxidants: a review

In recent years, spiro compounds have attracted significant interest in medicinal chemistry due to their numerous biological activities attributed primarily to their versatility and structural similarity to important pharmacophore centers. Currently, the development of drugs with potential antioxidant activities is of great importance since numerous investigations have shown that oxidative stress is involved in the development and progression of numerous diseases such as cancer, senile cataracts, kidney failure, diabetes, high blood pressure, cirrhosis, and neurodegenerative diseases, among others. This article provides an overview of the synthesis and various antioxidant activities found in naturally occurring and synthetic spiro compounds. Among the antioxidant activities reviewed are DPPH, ABTS, FRAP, anti-LPO, superoxide, xanthine oxidase, peroxide, hydroxyl, and nitric oxide tests, among others. Molecules that presented best results for these tests were spiro compounds G14, C12, D41, C18, C15, D5, D11, E1, and C14. In general, most active compounds are characterized for having at least one oxygen atom; an important number of them (around 35%) are phenolic compounds, and in molecules where this functional group was absent, aryl ethers and nitrogen-containing functional groups such as amine and amides could be found. Recent advances in the antioxidant activity profiles of spiro compounds have shown that they have a significant position in discovering drugs with potential antioxidant activities.

This article provides an overview of the synthesis and various antioxidant activities found in naturally occurring and synthetic spiro compounds.

Structure activity relationship in β-carboline derived anti-malarial agents

Malaria, even though an avoidable and treatable disease, can be fatal if ignored. Artemisinin Combination Therapy (ACT) and RTS, S/AS01 vaccine (Mosquirix™) are the only modest means available with humans to overcome malaria, a lethal affliction wreaking havoc across the globe. Employment of ACT is associated with problems such as 'Artemisinin Resistance' and the 'Hypnozoite conundrum' that hinder the complete eradication of malaria. In this view, the natural products specifically comprising β-carboline scaffold have shown good antiplasmodial responses against different strains of malaria. Taking these observations forward, researchers have performed structure-activity relationship (SAR) studies around three different β-carboline skeletons (tetrahydro β-carbolines, dihydro β-carbolines, β-carbolines) to design new β-carboline derived heterocyclic structures or modified naturally occurring derivatives. In addition, different approaches such as dimerization and linkage to other moieties have also been adopted to enhance the antimalarial activity. The present review describes a comprehensive SAR study encapsulating various natural and synthetic β-carbolines to elaborate upon the utility of these skeletons in designing drugs to subdue this deadly disease.

Simple amino silyl ether organocatalyst for asymmetric hetero Diels-Alder reaction of isatins with enones

New two catalysts component system comprising of a primary β-amino silyl ethers as an organocatalyst and N-protected amino acids as a co-catalyst put together worked as an efficient organocatalyst system in the hetero Diels-Alder reaction of isatins with enones affording the chiral spirooxindole-tetrahydropyranones in good chemical yields and stereoselectivities (up to 94%, up to dr 78:22., up to 85% ee).

Discovery of Potent and Fast-Acting Antimalarial Bis-1,2,4-triazines

Novel 3,3'-disubstituted-5,5'-bi(1,2,4-triazine) compounds with potent in vitro activity against Plasmodium falciparum parasites were recently discovered. To improve the pharmacokinetic properties of the triazine derivatives, a new structure-activity relationship (SAR) investigation was initiated with a focus on enhancing the metabolic stability of lead compounds. These efforts led to the identification of second-generation highly potent antimalarial bis-triazines, exemplified by triazine 23, which exhibited significantly improved in vitro metabolic stability (8 and 42 μL/min/mg protein in human and mouse liver microsomes). The disubstituted triazine dimer 23 was also observed to suppress parasitemia in the Peters 4-day test with a mean ED50 value of 1.85 mg/kg/day and exhibited a fast-killing profile, revealing a new class of orally available antimalarial compounds of considerable interest.

An insight in anti-malarial potential of indole scaffold: A review

Malaria is a major parasitic disease in tropical and sub-tropical regions. Pertaining to the sustaining resistance in malarial parasite against the available drugs, novel treatment options are the need of the hour. In this resolve recently, focus has shifted to finding the natural alternatives that possess anti-plasmodial activity for combatting malaria. Drawing on the text written in ancient scriptures and Ayurveda, natural compounds are now being screened for their therapeutic properties. Indole is one such natural compound, present in all living organisms, it displays a range of therapeutic activities including anticancer, anti-inflammatory, antimalarial etc. In this review, we have discussed various indole scaffold as well as the semi-synthetic drugs containing indole moiety that have been synthesized for malaria treatment.

Synthesis of aza-quaternary centers via Pictet-Spengler reactions of ketonitrones

Despite the array of advances that have been made in Pictet-Spengler chemistry, particularly as it relates to the synthesis of β-carboline derivatives of both natural and designed origin, the ability to use such reactions to generate aza-quaternary centers remains limited. Herein, we report a simple procedure that enables the synthesis of a variety of such products by harnessing the distinct reactivity profiles of ketonitrones as activated by commercially available acyl chlorides. Notably, the reaction process is mild, fast, and high-yielding (54-97%) for a diverse collection of substrates, including some typically challenging ones, such as indole cores with electron-deficient substituents. In addition, by deploying an acyl bromide in combination with a thiourea promoter, a catalytic, asymmetric version has been established, leading to good levels of enantioselectivity (up to 83% ee) for several ketonitrones. Finally, the resultant N-O bonds within the products can also be functionalized in several unique ways, affording valuable complementarity to existing Pictet-Spengler variants based on the use of imines.

Synthesis of Aminomethylene-gem-bisphosphonates Containing an Aziridine Motif: Studies of the Reaction Scope and Insight into the Mechanism

A broad range of N-carbamoylaziridines were obtained and then treated by the diethyl phosphonate anion to afford α-methylene-gem-bisphosphonate aziridines. Study of the reaction's scope and additional experiments indicates that the transformation proceeds via a new mechanism involving the chelation of lithium ion. This last step is crucial for the reaction to occur and disfavors the aziridine ring-opening. A phosphonate-phosphate rearrangement from a α-hydroxybisphosphonate aziridine intermediate is also proposed for the first time. This reaction provides a simple and convenient method for the synthesis of a highly functionalized phosphonylated aziridine motif.

Defining the Antimalarial Activity of Cipargamin in Healthy Volunteers Experimentally Infected with Blood-Stage Plasmodium falciparum

The spiroindolone cipargamin, a new antimalarial compound that inhibits Plasmodium ATP4, is currently in clinical development. This study aimed to characterize the antimalarial activity of cipargamin in healthy volunteers experimentally infected with blood-stage Plasmodium falciparum.

The spiroindolone cipargamin, a new antimalarial compound that inhibits Plasmodium ATP4, is currently in clinical development. This study aimed to characterize the antimalarial activity of cipargamin in healthy volunteers experimentally infected with blood-stage Plasmodium falciparum. Eight subjects were intravenously inoculated with parasite-infected erythrocytes and received a single oral dose of 10 mg cipargamin 7 days later. Blood samples were collected to monitor the development and clearance of parasitemia and plasma cipargamin concentrations. Parasite regrowth was treated with piperaquine monotherapy to clear asexual parasites, while allowing gametocyte transmissibility to mosquitoes to be investigated. An initial rapid decrease in parasitemia occurred in all participants following cipargamin dosing, with a parasite clearance half-life of 3.99 h. As anticipated from the dose selected, parasite regrowth occurred in all 8 subjects 3 to 8 days after dosing and allowed the pharmacokinetic/pharmacodynamic relationship to be determined. Based on the limited data from the single subtherapeutic dose cohort, a MIC of 11.6 ng/ml and minimum parasiticidal concentration that achieves 90% of maximum effect of 23.5 ng/ml were estimated, and a single 95-mg dose (95% confidence interval [CI], 50 to 270) was predicted to clear 10⁹ parasites/ml. Low gametocyte densities were detected in all subjects following piperaquine treatment, which did not transmit to mosquitoes. Serious adverse liver function changes were observed in three subjects, which led to premature study termination. The antimalarial activity characterized in this study supports the further clinical development of cipargamin as a new treatment for P. falciparum malaria, although the hepatic safety profile of the compound warrants further evaluation. (This study has been registered at ClinicalTrials.gov under identifier NCT02543086.)