A Vibrational Study of Some 1,2,4-Trioxanes

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.

Ex Situ Generation of 18O2 and 17O2 from Endoperoxides for *O-Labeling and Mechanistic Studies of Oxidations by Dioxygen

Near-stoichiometric amounts of ¹⁸O₂ and ¹⁷O₂ were generated ex situ from endoperoxides in a two-chamber glassware to oxidize various substrates. This strategy gave [*O₂]endoperoxides, [*O₁]quinones, [*O₁]phenols, and [*O_x]artemisin in moderate to good yields and high isotopic enrichments (up to 84%) at affordable costs. Moreover, mass spectrometry and ¹⁷O NMR of the [*O]products provided valuable information about the chemical mechanisms involved.

Synthesis and Characterization of Atmospherically Relevant Hydroxy Hydroperoxides

Hydroxy hydroperoxides are formed upon OH oxidation of volatile organic compounds in the atmosphere and may contribute to secondary organic aerosol growth and aqueous phase chemistry after phase transfer to particles. Although the detection methods for oxidized volatile organic compounds improved much over the past decades, the limited availability of synthetic standards for atmospherically relevant hydroxy hydroperoxides prevented comprehensive investigations for the most part. Here, we present a straightforward improved synthetic access to isoprene-derived hydroxy hydroperoxides, i.e., 1,2-ISOPOOH and 4,3-ISOPOOH. Furthermore, we present the first successful synthesis of an α-pinene derived hydroxy hydroperoxide. All products were identified by 1H, 13C NMR spectroscopy for structure elucidation, additional 2D NMR experiments were performed. Furthermore, gas-phase FTIR- and UV/VIS spectra are presented for the first time. Using the measured absorption cross section, the atmospheric photolysis rate of up to 2.1 × 10−3 s−1 was calculated for 1,2-ISOPOOH. Moreover, we present the investigation of synthesized hydroxy hydroperoxides in an aerosol chamber study by online MS techniques, namely PTR-ToFMS and (NO3−)-CI-APi-ToFMS. Fragmentation patterns recorded during these investigations are presented as well. For the (NO3−)-CI-APi-ToFMS, a calibration factor for 1,2-ISOPOOH was calculated as 4.44 × 10−5 ncps·ppbv−1 and a LOD (3σ, 1 min average) = 0.70 ppbv.

Study on ozonolysis of asymmetric alkenes with matrix isolation and FT-IR spectroscopy

O₃ and alkenes are important reactants in the formation of SOA in the atmosphere. The intermediates and reaction mechanism of ozonation of alkene is an important topic in atmospheric chemistry. In this study, the low-temperature matrix isolation was used to capture the intermediates such as Primary ozonides (POZs), Criegee Intermediates (CIs), and Secondary ozonides (SOZs) generated from ozonation of 2-methyl-1-butene (2M1B) and 2-methyl-2-butene (2M2B). The results have been identified by the vacuum infrared spectroscopy and theoretical calculation. Our results show that during the ozonation of asymmetric alkenes, two kinds of CIs and more than two kinds of SOZs were generated due to the different decomposition modes of POZs. The infrared absorption peaks of (CH₃)₂COO and CH₃CH₂C(CH₃)OO for O-O telescopic vibration was determined to be 889 cm^-1 and 913 cm^-1, respectively. Using the merged jet method, it was found that a large amount of HCHO was produced during the ozonation of 2M1B, and glyoxal and methylglyoxal were produced in the ozonation of 2M2B. Our findings highlight the importance of asymmetric alkene ozonolysis reactions in producing CIs, further improving the understanding of the generation of CIs from ozonation of alkenes.

Heme-artemisinin adducts are crucial mediators of the ability of artemisinin to inhibit heme polymerization

A lack of molecular understanding of the targets and mechanisms of artemisinin action has impeded the improvisation of more efficient antimalarials based on this class of endoperoxide drugs. We have synthesized a heme-artemisinin adduct designated as "hemart" to discover if it mediates the ability of artemisinin to inhibit heme polymerization. Hemart mimics heme in binding to Plasmodium falciparum histidine-rich protein II (PfHRP II) but cannot self-polymerize. Instead, it inhibits all heme polymerizations, including basal and those triggered by PfHRP II, Monooleoyl glycerol (MOG), or P. yoelii extract. Hemart has an edge over heme in displacing heme from PfHRP II, and either low pH or chloroquine dissociates heme but not hemart from PfHRP II. Our results suggest that hemart, by mimicking heme, stalls all mechanisms of heme polymerization, resulting in the death of the malaria parasite.

Steroidal geminal dihydroperoxides and 1,2,4,5-tetraoxanes: structure determination and their antimalarial activity

Cholestane-derived gem-dihydroperoxides and tetraoxanes were synthesized starting from 5 alpha- and 5 beta-cholestan-3-ones by acid-catalyzed addition of hydrogen peroxide to the ketone. They were characterized by IR, NMR, and mass spectroscopy analysis aided by molecular mechanics calculations, and, in the instance of 5 beta-cholestane-3 alpha,3 beta-dihydroperoxide (6), by x-ray analysis. The synthesized compounds were tested in vitro against Plasmodium falciparum Sierra Leone (D6) and Indochina (W2) malaria clones. All compounds were inactive to both clones, with the exception of tetraoxane 7a, which exhibited modest activity toward D6 clone with IC50 = 155 nM.