Novel Bis- and Tris-1,2,4-trioxanes: Synthesis and Antimalarial Activity against Multidrug-Resistant Plasmodium yoelii in Swiss Mice

Recent advances in the synthesis and antimalarial activity of 1,2,4-trioxanes

The increasing resistance of various malarial parasite strains to drugs has made the production of a new, rapid-acting, and efficient antimalarial drug more necessary, as the demand for such drugs is growing rapidly. As a major global health concern, various methods have been implemented to address the problem of drug resistance, including the hybrid drug concept, combination therapy, the development of analogues of existing medicines, and the use of drug resistance reversal agents. Artemisinin and its derivatives are currently used against multidrug- resistant P. falciparum species. However, due to its natural origin, its use has been limited by its scarcity in natural resources. As a result, finding a substitute becomes more crucial, and the peroxide group in artemisinin, responsible for the drugs biological action in the form of 1,2,4-trioxane, may hold the key to resolving this issue. The literature suggests that 1,2,4-trioxanes have the potential to become an alternative to current malaria drugs, as highlighted in this review. This is why 1,2,4-trioxanes and their derivatives have been synthesized on a large scale worldwide, as they have shown promising antimalarial activity in vivo and in vitro against Plasmodium species. Consequently, the search for a more convenient, environment friendly, sustainable, efficient, and effective synthetic pathway for the synthesis of 1,2,4-trioxanes continues. The aim of this work is to provide a comprehensive analysis of the synthesis and mechanism of action of 1,2,4-trioxanes. This systematic review highlights the most recent summaries of derivatives of 1,2,4-trioxane compounds and dimers with potential antimalarial activity from January 1988 to 2023.

An overview on the antimalarial activity of 1,2,4-trioxanes, 1,2,4-trioxolanes and 1,2,4,5-tetraoxanes

The demand for novel, fast-acting, and effective antimalarial medications is increasing exponentially. Multidrug resistant forms of malarial parasites, which are rapidly spreading, pose a serious threat to global health. Drug resistance has been addressed using a variety of strategies, such as targeted therapies, the hybrid drug idea, the development of advanced analogues of pre-existing drugs, and the hybrid model of resistant strains control mechanisms. Additionally, the demand for discovering new potent drugs grows due to the prolonged life cycle of conventional therapy brought on by the emergence of resistant strains and ongoing changes in existing therapies. The 1,2,4-trioxane ring system in artemisinin (ART) is the most significant endoperoxide structural scaffold and is thought to be the key pharmacophoric moiety required for the pharmacodynamic potential of endoperoxide-based antimalarials. Several derivatives of artemisinin have also been found as potential treatments for multidrug-resistant strain in this area. Many 1,2,4-trioxanes, 1,2,4-trioxolanes, and 1,2,4,5-tetraoxanes derivatives have been synthesised as a result, and many of these have shown promise antimalarial activity both in vivo and in vitro against Plasmodium parasites. As a consequence, efforts to develop a functionally straight-forward, less expensive, and vastly more effective synthetic pathway to trioxanes continue. This study aims to give a thorough examination of the biological properties and mode of action of endoperoxide compounds derived from 1,2,4-trioxane-based functional scaffolds. The present system of 1,2,4-trioxane, 1,2,4-trioxolane, and 1,2,4,5-tetraoxane compounds and dimers with potentially antimalarial activity will be highlighted in this systematic review (January 1963-December 2022).

Photocatalytic Transformation of Biomass and Biomass Derived Compounds-Application to Organic Synthesis

Biomass and biomass-derived compounds have become an important alternative feedstock for chemical industry. They may replace fossil feedstocks such as mineral oil and related platform chemicals. These compounds may also be transformed conveniently into new innovative products for the medicinal or the agrochemical domain. The production of cosmetics or surfactants as well as materials for different applications are examples for other domains where new platform chemicals obtained from biomass can be used. Photochemical and especially photocatalytic reactions have recently been recognized as being important tools of organic chemistry as they make compounds or compound families available that cannot be or are difficultly synthesized with conventional methods of organic synthesis. The present review gives a short overview with selected examples on photocatalytic reactions of biopolymers, carbohydrates, fatty acids and some biomass-derived platform chemicals such as furans or levoglucosenone. In this article, the focus is on application to organic synthesis.

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.

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.

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.

Novel naphthyl based 1,2,4-trioxanes: Synthesis and in vivo efficacy in the Plasmodium yoelii nigeriensis in Swiss mice

A new series of 1,2,4-trioxanes 9a1-a4, 9b1-b4, 10-13 and 9c1-c4 were synthesized and evaluated against multidrug-resistant Plasmodium yoelii nigeriensis in Swiss mice via oral and intramuscular (i.m.) routes. Adamantane-based trioxane 9b4, the most active compound of the series, provided 100% protection to the infected mice at the dose 48 mg/kg × 4 days and 100% clearance of parasitemia at the dose 24 mg/kg × 4 days via oral route. Adamantane-based trioxane 9b4, is twice active than artemisinin. We have also studied the photooxygenation behaviour of allylic alcohols 6a-b (3-(4-alkoxynaphthyl)-but-2-ene-1-ols) and 6c (3-[4-(tert-butyl-dimethyl-silanyloxy)-naphthalen-1-yl]-but-2-en-1-ol). Being behaving as dienes, they furnished corresponding endoperoxides, while behaving as allylic alcohols, they yielded β-hydroxyhydroperoxides. All the endoperoxides (7a-c) and β-hydroxyhydroperoxides (8a-c) have been separately elaborated to the corresponding 1,2,4-trioxanes, except from endoperoxide 7c. It is worthy to note that TBDMS protected naphthoyl endoperoxide 7c unable to deliver 1,2,4-trioxane, which demonstrated the strength of the O-Si bond is not easy to cleave under acidic condition.

Synthesis of novel 1,2,4-trioxanes and antimalarial evaluation against multidrug-resistant Plasmodium yoelii nigeriensis

Malaria epidemics represent one of the life-threatening diseases to low-income lying countries which subsequently affect the economic and social condition of mankind. In continuation in the development of a novel series of 1,2,4-trioxanes 13a1-c1, 13a2-c2, and 13a3-c3 have been prepared and further converted into their hemisuccinate derivatives 14a1-c1, 14a2-c2, and 14a3-c3 respectively. All these new compounds were evaluated for their antimalarial activity against multidrug-resistant Plasmodium yoelii nigeriensis in mice by both oral and intramuscular (im) routes. Hydroxy-functionalized trioxane 13a1 showed 80% protection and its hemisuccinate derivative 14a1 showed 100% protection at a dose of 48 mg/kg × 4 days by both routes, which is twice active than artemisinin by oral route.

Exploration of artemisinin derivatives and synthetic peroxides in antimalarial drug discovery research

Malaria is a life-threatening infectious disease caused by protozoal parasites belonging to the genus Plasmodium. It caused an estimated 405,000 deaths and 228 million malaria cases globally in 2018 as per the World Malaria Report released by World Health Organization (WHO) in 2019. Artemisinin (ART), a "Nobel medicine" and its derivatives have proven potential application in antimalarial drug discovery programs. In this review, antimalarial activity of the most active artemisinin derivatives modified at C-10/C-11/C-16/C-6 positions and synthetic peroxides (endoperoxides, 1,2,4-trioxolanes, 1,2,4-trioxanes, and 1,2,4,5-tetraoxanes) are systematically summarized. The developmental trend of ART derivatives, and cyclic peroxides along with their antimalarial activity and how the activity is affected by structural variations on different sites of the compounds are discussed. This compilation would be very useful towards scaffold hopping aimed at avoiding the unnecessary complexity in cyclic peroxides, and ultimately act as a handy resource for the development of potential chemotherapeutics against Plasmodium species.

Recent updates in the discovery and development of novel antimalarial drug candidates

Though morbidity and mortality due to malaria have declined in the last 15 years, emerging resistance to first-line artemisinin-based antimalarials, absence of efficacious vaccines and limited chemotherapeutic alternatives imperil the consolidation of these gains. As a blueprint to steer future designs of new medicines, malaria drug discovery recently adopted a descriptive proposal for the ideal candidate molecules and drugs likely to successfully progress into the final stages of clinical development. As an audit of recent developments in the chemotherapy of malaria in the last five years, this review captures a landscape of diverse molecules at various stages of drug development and discusses their progress. In brief, we also discuss how omics data on Plasmodium has been extensively leveraged to identify potential vaccine candidates and putative targets of molecules in development and clinical use as well as map loci implicit in their modes of resistance. Future perspective on malaria drug development should involve a reconciliation of some of the challenges of the target candidate profiles (TCPs), specifically TCP3, with the promise of effective anti-hypnozoite medicines. Similarly, with the recent development of a humanized mouse model that can evaluate the prophylactic potential of candidate drugs, we argue for increased effort at identifying more liver-stage molecules, which are often only secondarily prioritized in conventional screening programs.

Single Ascending Dose Safety and Pharmacokinetics of CDRI-97/78: First-in-Human Study of a Novel Antimalarial Drug

Background. CDRI 97/78 has shown efficacy in animal models of falciparum malaria. The present study is the first in-human phase I trial in healthy volunteers. Methods. The study was conducted in 50 healthy volunteers in a single, ascending dose, randomized, placebo-controlled, double blind design. The dose ranges evaluated were from 80 mg to 700 mg. Volunteers were assessed for clinical, biochemical, haematological, radiographic, and electrocardiographic parameters for any adverse events in an in-house facility. After evaluation of safety study results, another cohort of 16 participants were administered a single oral dose of 200 mg of the drug and a detailed pharmacokinetic analysis was undertaken. Results. The compound was found to be well tolerated. MTD was not reached. The few adverse events noted were of grade 2 severity, not requiring intervention and not showing any dose response relationship. The laboratory and electrocardiographic parameters showed statistically significant differences, but all were within the predefined normal range. These parameters were not associated with symptoms/signs and hence regarded as clinically irrelevant. Mean values of T_1/2, MRT, and AUC_0−∞ of the active metabolite 97/63 were 11.85 ± 1.94 h, 13.77 ± 2.05 h, and 878.74 ± 133.15 ng·h/mL, respectively Conclusion. The novel 1,2,4 trioxane CDRI 97/78 is safe and will be an asset in malarial therapy if results are replicated in multiple dose studies and benefit is shown in confirmatory trials.

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

The present review describes the current status of synthetic five and six-membered cyclic peroxides such as 1,2-dioxolanes, 1,2,4-trioxolanes (ozonides), 1,2-dioxanes, 1,2-dioxenes, 1,2,4-trioxanes, and 1,2,4,5-tetraoxanes. The literature from 2000 onwards is surveyed to provide an update on synthesis of cyclic peroxides. The indicated period of time is, on the whole, characterized by the development of new efficient and scale-up methods for the preparation of these cyclic compounds. It was shown that cyclic peroxides remain unchanged throughout the course of a wide range of fundamental organic reactions. Due to these properties, the molecular structures can be greatly modified to give peroxide ring-retaining products. The chemistry of cyclic peroxides has attracted considerable attention, because these compounds are used in medicine for the design of antimalarial, antihelminthic, and antitumor agents.

Recent advances in malaria drug discovery

This digest covers some of the most relevant progress in malaria drug discovery published between 2010 and 2012. There is an urgent need to develop new antimalarial drugs. Such drugs can target the blood stage of the disease to alleviate the symptoms, the liver stage to prevent relapses, and the transmission stage to protect other humans. The pipeline for the blood stage is becoming robust, but this should not be a source of complacency, as the current therapies set a high standard. Drug discovery efforts directed towards the liver and transmission stages are in their infancy but are receiving increasing attention as targeting these stages could be instrumental in eradicating malaria.

Synthesis and antimalarial activity of 3,3-spiroanellated 5,6-disubstituted 1,2,4-trioxanes

Novel 3,3-spiroanellated 5-aryl, 6-arylvinyl-substituted 1,2,4-trioxanes 19-34 have been synthesized and appraised for their antimalarial activity against multidrug-resistant Plasmodium yoelii nigeriensis in Swiss mice by oral route at doses ranging from 96 mg/kg × 4 days to 24 mg/kg × 4 days. The most active compound of the series (compound 25) provided 100% protection at 24 mg/kg × 4 days, and other 1,2,4-trioxanes 22, 26, 27, and 30 also showed promising activity. In this model, β-arteether provided 100 and 20% protection at 48 mg/kg × 4 days and 24 mg/kg × 4 days, respectively, by oral route. Compound 25 displayed a similar in vitro pharmacokinetic profile to that of reference drug β-arteether. The activity results demonstrated the importance of an aryl moiety at the C-5 position on the 1,2,4-trioxane pharmacophore.

Simple analogues of qinghaosu (artemisinin)

A series of 1,2,4-trioxanes were synthesized in which the key peroxy bonds were installed through a molybdenum-catalyzed perhydrolysis of the epoxy rings. A core structure was identified that may serve as a promising lead structure for further investigations because of its high antimalarial activity (comparable to that of artesunate and chloroquine), apparent potential for scale-up and derivatization, and facile monitoring/tracing by using UV light.

Coumarin-trioxane hybrids: synthesis and evaluation as a new class of antimalarial scaffolds

First synthesis of novel coumarin-trioxane hybrids is reported. The synthesis was achieved via condensation of β-hydroxyhydroperoxides with coumarinic-aldehydes in presence of p-toluenesulfonic acid in good yields and the novel hybrids were evaluated for their antimalarial activity both in vitro and in vivo.

Optically pure bulky (hetero)arylalkyl carbinols via kinetic resolution

Planar chiral nucleophilic catalyst Fc-PIP was employed in the kinetic resolution of bulky (hetero)arylalkyl carbinols delivering unreacted alcohols with extremely high enantiomeric excess (>99.0% ees) in ideal conversions ranging from 50.4-56.7%.