Cholic acid derivatives as 1,2,4,5-tetraoxane carriers: structure and antimalarial and antiproliferative activity

1,2,4,5-Tetraoxane derivatives/hybrids as potent antimalarial endoperoxides: Chronological advancements, structure-activity relationship (SAR) studies and future perspectives

Malaria is a life-threatening disease that affects tropical and subtropical regions worldwide. Various drugs were used to treat malaria, including artemisinin and derivatives, antibiotics (tetracycline, doxycycline), quinolines (chloroquine, amodiaquine), and folate antagonists (sulfadoxine and pyrimethamine). Since the malarial parasites developed drug resistance, there is a need to develop new chemical entities with high efficacy and low toxicity. In this context, 1,2,4,5-tetraoxanes emerged as an essential scaffold and have shown promising antimalarial activity. To improve activity and overcome resistance to various antimalarial drugs; 1,2,4,5-tetraoxanes were fused with various aryl/heteroaryl/alicyclic/spiro moieties (steroid-based 1,2,4,5-tetraoxanes, triazine-based 1,2,4,5-tetraoxanes, aminoquinoline-based 1,2,4,5-tetraoxanes, dispiro-based 1,2,4,5-tetraoxanes, piperidine-based 1,2,4,5-tetraoxanes and diaryl-based 1,2,4,5-tetraoxanes). The present review aims to focus on covering the relevant literature published during the past 30 years (1992-2022). We summarize the most significant in vitro, in vivo results and structure-activity relationship studies of 1,2,4,5-tetraoxane-based hybrids as antimalarial agents. The structural evolution of different hybrids can provide the framework for the future development of 1,2,4,5-tetraoxane-based hybrids to treat malaria.

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).

Montmorillonite Catalyzed Synthesis of Novel Steroid Dimers

The reactions of sterols (androst-5-en-3β-ol-17-one, diosgenin, and cholesterol) and their tosylates with hydroquinone aimed at the synthesis of O,O-1,4-phenylene-linked steroid dimers were studied. The reaction course strongly depended on the conditions used. The study has shown that the major reaction products are the elimination products and unusual steroid dimers resulting from the nucleophilic attack of the hydroquinone C2 carbon atom on the steroid C3 position, followed by an intramolecular addition to the C5-C6 double bond. A different reaction course was observed when montmorillonite K10 was used as a catalyst. The reaction of androst-5-en-3β-ol-17-one under the promotion of this catalyst afforded the O,O-1,4-phenylene-linked steroid dimer in addition to the disteroidal ether. The formation of the latter compound was suppressed by using 3-tosylate as a substrate instead of the free sterol. The reactions of androst-5-en-3β-ol-17-one tosylate and cholesteryl tosylate with hydroquinone catalyzed by montmorillonite K10 carried out under optimized conditions afforded the desired dimers in 31% and 67% yield, respectively.

Feasibility study of separation and purification of bile acid derivatives by HPLC on C18 and F5 columns

Organic synthesis could be very demanding, usually due to difficulties related to the separation of main reaction products from by-products. Steroidal compounds could have similar lipophilicity, which is mostly based on the lipophilicity of the steroidal core. This causes many problems during purification, i.e. in obtaining a pure single steroidal compound. In this research, a group of bile acid derivatives were subjected to HPLC analysis using four experimental systems, which presented combinations of C18 and F5 columns with methanol-water and acetonitrile-water as mobile phases. Retention parameters and retention order of the compounds were established and indicated that all experimental systems could be applicable in order to separate and/or purify some individual compounds or a mixture of a few compounds. However, the only experimental system that could separate a mixture of all investigated derivatives proved to be a C18 column with acetonitrile-water as a mobile phase. Since complex interactions between F5 column and the analytes exist, molecular surface polarity (MSP) was tested as a lipophilicity parameter, and also compared with logP using multivariate statistics. Retention parameters obtained on F5 column were used as descriptors, both with MSP and with logP, concluding that logP has shown to be a better lipophilicity descriptor.

Lewis Acids and Heteropoly Acids in the Synthesis of Organic Peroxides

Organic peroxides are an important class of compounds for organic synthesis, pharmacological chemistry, materials science, and the polymer industry. Here, for the first time, we summarize the main achievements in the synthesis of organic peroxides by the action of Lewis acids and heteropoly acids. This review consists of three parts: (1) metal-based Lewis acids in the synthesis of organic peroxides; (2) the synthesis of organic peroxides promoted by non-metal-based Lewis acids; and (3) the application of heteropoly acids in the synthesis of organic peroxides. The information covered in this review will be useful for specialists in the field of organic synthesis, reactions and processes of oxygen-containing compounds, catalysis, pharmaceuticals, and materials engineering.

Reductive desymmetrization of steroid dimers

NaBH₃CN reduction of symmetric dimers in which two steroid units are linked by a 1,4-dimethylidenebenzene moiety followed two different courses: (a) hydrogenation of the benzylic double bond and (b) reductive F ring opening of the side chain. While courses a and b led to symmetrical dimers, the combination of both pathways produced an unsymmetrical dimer that bears different side chains in each half. The exhaustive NMR characterization of all obtained compounds is presented.

Dimeric Drugs

This review intends to summarize the structures of an extensive number of symmetrical-dimeric drugs, having two monomers linked via a bridging entity while emphasizing the large versatility of biologically active substances reported to possess dimeric structures. The largest number of classes of these compounds consist of anticancer agents, antibiotics/antimicrobials, and anti-AIDS drugs. Other symmetrical-dimeric drugs include antidiabetics, antidepressants, analgesics, anti-inflammatories, drugs for the treatment of Alzheimer's disease, anticholesterolemics, estrogenics, antioxidants, enzyme inhibitors, anti-Parkisonians, laxatives, antiallergy compounds, cannabinoids, etc. Most of the articles reviewed do not compare the activity/potency of the dimers to that of their corresponding monomers. Only in limited cases, various suggestions have been made to justify unexpected higher activity of the dimers vs. the corresponding monomers. These suggestions include statistical effects, the presence of dimeric receptors, binding of a dimer to two receptors simultaneously, and others. It is virtually impossible to predict which dimers will be preferable to their respective monomers, or which linking bridges will lead to the most active compounds. It is expected that the extensive number of articles summarized, and the large variety of substances mentioned, which display various biological activities, should be of interest to many academic and industrial medicinal chemists.

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.

Modified bile acids and androstanes-Novel promising inhibitors of human cytochrome P450 17A1

Cytochromes P450 are key enzymes for steroid hormone biosynthesis in human body. They are considered as targets for the screening of novel high efficient drugs. The results of screening of bile acids and androstane derivatives toward human recombinant steroid 17α-hydroxylase/17,20-lyase (CYP17A1) are presented in this paper. A group of steroids, binding with micromolar or submicromolar affinity (in a range from 9 μM - less than 0.1 μM), was identified. Results presented here showed that these steroidal compounds are able to decrease rate of hydroxylation of essential CYP17A1 substrate - progesterone, while some compounds completely inhibited enzyme activity. Structure-activity relationship (SAR) analysis based on in vitro and in silico studies showed that high affinity of the enzyme to bile acids derivatives is correlated with side chain hydrophobicity and presence of hydroxyl or keto group at C₃ position. From the other side, bile acid-derived compounds with more polar side chain or substituents at C₇ and C₁₂ positions possess higher K_d values. Among androstane-derived steroids couple of Δ⁵-steroids with hydroxyl group at C₃ position, as well as 16,17-secosteroids, were found to be high affinity ligands of this enzyme. The data obtained could be useful for the design of novel highly efficient inhibitors of CYP17A1, since the bile acids-derived compounds are for first time recognized as effective CYP17A1 inhibitors.

How the oxazole fragment influences the conformation of the tetraoxazocane ring in a cyclohexanespiro-3'-(1,2,4,5,7-tetraoxazocane): single-crystal X-ray and theoretical study

Single crystals of (2S,5R)-2-isopropyl-5-methyl-7-(5-methylisoxazol-3-yl)cyclohexanespiro-3'-(1,2,4,5,7-tetraoxazocane), C₁₆H₂₆N₂O₅, have been studied via X-ray diffraction. The tetraoxazocane ring adopts a boat-chair conformation in the crystalline state, which is due to intramolecular interactions. Conformational analysis of the tetraoxazocane fragment performed at the B3LYP/6-31G(d,2p) level of theory showed that there are three minima on the potential energy surface, one of which corresponds to the conformation realized in the solid state, but not to a global minimum. Analysis of the geometry and the topological parameters of the electron density at the (3,-1) bond critical points (BCPs), and the charge transfer in the tetraoxazocane ring indicated that there are stereoelectronic effects in the O-C-O and N-C-O fragments. There is a two-cross hyperconjugation in the N-C-O fragment between the lone electron pair of the N atom (lpN) and the antibonding orbital of a C-O bond (σ*_C-O) and vice versa between lpO and σ*_C-N. The oxazole substituent has a considerable effect on the geometry and the topological parameters of the electron density at the (3,-1) BCPs of the tetraoxazocane ring. The crystal structure is stabilized via intermolecular C-H...N and C-H...O hydrogen bonds, which is unambiguously confirmed with PIXEL calculations, a quantum theory of atoms in molecules (QTAIM) topological analysis of the electron density at the (3,-1) BCPs and a Hirshfeld analysis of the electrostatic potential. The molecules form zigzag chains in the crystal due to intermolecular C-H...N interactions being electrostatic in origin. The molecules are further stacked due to C-H...O hydrogen bonds. The dispersion component in the total stabilization energy of the crystal lattice is 68.09%.

New cholic acid analogs: synthesis and 17β-hydroxydehydrogenase (17β-HSD) inhibition activity

The 17β-hydroxysteroid dehydrogenase (17β-HSD) enzyme family is involved in the biosynthesis of active steroids and its inhibition constitutes an interesting approach for treating estrogen-, androgen-dependent cancers and osteoporosis. In this study, a new series of cholic acid analogs was designed with the goal of improving the biological activity as 17β-HSD1 and 17β-HSD2 inhibitors. To this end, 23-cholyl amides 4–7, 3-O-p-toluenesulfonyl-23-cholyl amides 10–12, 23-cholyl-carbohydrazide 14, carbothioamide analog 15, and 23-cholyl-acylhydrazone derivatives 18–22 were synthesized from cholic acid (3) via coupling, sulfonation and substitution reactions. Basic treatment of keto group of 5 with p-bromoaniline afforded 8, meanwhile acidic treatment of 3 with thiosemicarbazide furnished the 23-cholyl-thiadiazole derivative 16. The synthesized compounds were evaluated for their inhibition activity against 17β-HSD1 and 17β-HSD2, and were found inactive at 1.0 μm concentration (inhibition <10%). However, the steroids 12, 21 and 22 showed inhibition of 21.1, 23.9 and 21.3%, respectively, against 17β-HSD2 at the same concentration. Therefore, these steroidal analogs can be further structurally modified to optimize their inhibition activity against 17β-HSD2 for the development of potential therapeutics.

Synthesis and antimalarial activity of 3'-trifluoromethylated 1,2,4-trioxolanes and 1,2,4,5-tetraoxane based on deoxycholic acid

A series of new steroidal peroxides - 3'-trifluoromethylated 1,2,4-trioxolanes and 1,2,4,5-tetraoxanes based on deoxycholic acid were prepared via the reactions of the Griesbaum coozonolysis and peroxycondensation, respectively. 1,2,4-Trioxolanes were synthesized by the interaction of methyl O-methyl-3-oximino-12α-acetoxy-deoxycholate with CF₃C(O)CH₃ or CF₃C(O)Ph and O₃ as the mixtures of four possible stereoisomers at ratios of 1:2:2:1 and in yields of 50% and 38%, respectively. The major diastereomer of methyl 12α-acetoxy-5β-cholan-24-oate-3-spiro-5'-(3'-methyl-3'-trifluoromethyl-1',2',4'-trioxolane) was isolated via crystallization of a mixture of stereoisomers from hexane and its (3S,3'R)-configuration was determined using X-ray crystallographic analysis. Peroxycondensation of methyl 3-bishydroperoxy-12α-acetoxy-deoxycholate with CF₃C(O)CH₃ or acetone led to 1,2,4,5-tetraoxanes in yields of 44% and 37%, respectively. Antimalarial activity of these new steroidal peroxides was evaluated in vitro against the chloroquine-sensitive (CQS) T96 and chloroquine-resistant (CQR) K1 strains of Plasmodium falciparum. Deoxycholic acid 3'-trifluoromethylated 1,2,4,5-tetraoxane demonstrated a good IC₅₀ value against CQR-strain (IC₅₀ (K1) = 7.6 nM) of P. falciparum. Tetraoxane with the acetone subunit demonstrated the best results among all tested peroxides with an IC₅₀ value of 3 nM against the CQ-resistant K1 strain. In general, 1,2,4-trioxolanes of deoxycholic acid are less active than 1,2,4,5-tetraoxanes.

A H2O2/HBr system – several directions but one choice: oxidation–bromination of secondary alcohols into mono- or dibromo ketones

Convenience of application, multifaceted reactivity, and compliance with green chemistry principles: H₂O₂–HBr(aq) system for preparation of bromo ketones with yields up to 91%.

Synthesis of some novel steroidal 1,2,4,5-tetraoxanes

A facile synthesis of A-ring manipulated C-20 methyl carboxylate steroid derivative with unsymmetrical dispiro 1,2,4,5-tetraoxanes has been focused herein via acid catalyzed cyclocondensation of bis-epidioxy ketone.

Synthesis and Spectroscopic Characterisation of O-Chlorocarbonyl Derivatives of Bile Acid Methyl Esters

The synthesis of O-chlorocarbonyl derivatives of a series of bile acid methyl esters is described. The steroidal chloroformate esters were prepared by the reaction of the respective hydroxy derivatives with triphosgene–pyridine in benzene at 25 °C. The O-chlorocarbonyl derivatives were characterised by spectroscopic methods.

Steroid dimers-in vitro cytotoxic and antimicrobial activities

The in vitro cytotoxic activity of previously synthesized steroid dimers with different spacer group (sulfide, trithiolane ring or phosphorotrithioate) and the substituent at C-17 position was tested for their possible effects against following human tumor cell lines: cervical adenocarcinoma (HeLa), chronic myelogenous leukemia (K562) and two human breast cancer cell lines (MDA-MB-361 and MDA-MB-453). These compounds, applied at micromolar concentrations, exhibited cytotoxic activity of different intensity (compared with cisplatin as a control), modality and selectivity in these malignant cell lines. The best activity against all four cell cancer lines was exhibited by dimer-sulfides. All screened compounds exerted concentration-dependent cytotoxic activity against leukemia K562 cells. The compounds which exerted the most pronounced cytotoxic action exhibited notably higher cytotoxic activities against K562, HeLa and MDA-MB-453 cells in comparison to resting and PHA-stimulated PBMC, pointing to a significant selectivity in their antitumor actions. Examination of the mechanisms of cytotoxicity on leukemia K562 cells revealed pro-apoptotic action of each of the investigated compounds applied at concentrations 2IC50. The most prominent pro-apoptotic action was exhibited by dimer-sulfide of cholest-4-en-3-one. Furthermore, almost all of the tested compounds at IC50 concentrations induced G1 phase cell cycle arrest in K562 cells. Antimicrobial activity against Gram-positive, Gram-negative bacteria and fungal cells, and toxicity to brine shrimp Artemia salina, were evaluated. There was no antibacterial activity. The best antifungal activity was exhibited against Saccharomyces cerevisiae by dimers linked with trithiolane ring, indicating a selective activity of investigated compounds.

Design, synthesis and biological evaluation of novel steroidal spiro-oxindoles as potent antiproliferative agents

Two series of novel steroidal spiro-pyrrolidinyl oxindoles 3a-t and 6a-c were designed and synthesized from dehydroepiandrosterone using the 1,3-dipolar cycloaddition as the key step and further evaluated for their antiproliferative activities for four human cancer cell lines (MGC-803, EC109, SMMC-7721 and MCF-7). This protocol achieved the formation of two CC bonds, one CN bond and the creation of one new five-membered pyrrolidine ring and three contiguous stereocenters in a single operation. Biological evaluation showed that these synthesized steroidal spiro-pyrrolidinyl oxindoles possessed moderate to good antiproliferative activities against the tested cell lines and some of them were more potent than 5-Fu. Particularly, compound 3g showed good antiproliferative activity against SMMC-7721 (IC50=0.71μM). Steroid dimer 6b showed improved antiproliferative activities against SMMC-7721 and MCF-7 with the IC50 values of 4.30 and 2.06μM, respectively. Flow cytometry analysis demonstrated that compound 3n caused the cellular early apoptosis and cell cycle arrest at G2/M phase in a concentration- and time-dependent manner. [Corrected]

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.

Artemisinin-derived dimer phosphate esters as potent anti-cytomegalovirus (anti-CMV) and anti-cancer agents: a structure-activity study

We recently reported the anti-cancer and anti-cytomegalovirus (CMV) activity of artemisinin-derived trioxane diphenylphosphate dimer 838. To probe the relationship between chemical structure and anti-CMV and anti-cancer activities, we now report synthesis and evaluation of a series of eight new dimer phosphate ester analogs of 838. This series of novel molecules was screened against human foreskin fibroblasts (HFFs) infected with CMV and against the human Jurkat T cell acute lymphoblastic leukemia cell line. This SAR study confirms the very high anti-CMV and anti-cancer potencies of dimer diphenyl phosphate ester 838 without its being toxic to normal cells.

TiCl4-catalyzed synthesis of peroxyacetals from aldehydes

Peroxyacetals 2a–2j were prepared by TiCl4-promoted nucleophilic addition of both tert-butyl hydroperoxide (TBHP) and an alcohol to the corresponding aldehyde. The reaction works well with a variety of aldehydes, but not with ketones. The magnitude of the equilibrium constant for hemiacetal formation plays an important role; a large constant enables high conversion to peroxyacetal.

Antitumor activity of artemisinin and its derivatives: from a well-known antimalarial agent to a potential anticancer drug

Improvement of quality of life and survival of cancer patients will be greatly enhanced by the development of highly effective drugs to selectively kill malignant cells. Artemisinin and its analogs are naturally occurring antimalarials which have shown potent anticancer activity. In primary cancer cultures and cell lines, their antitumor actions were by inhibiting cancer proliferation, metastasis, and angiogenesis. In xenograft models, exposure to artemisinins substantially reduces tumor volume and progression. However, the rationale for the use of artemisinins in anticancer therapy must be addressed by a greater understanding of the underlying mechanisms involved in their cytotoxic effects. The primary targets for artemisinin and the chemical base for its preferential effects on heterologous tumor cells need yet to be elucidated. The aim of this paper is to provide an overview of the recent advances and new development of this class of drugs as potential anticancer agents.

A chemotype that inhibits three unrelated pathogenic targets: the botulinum neurotoxin serotype A light chain, P. falciparum malaria, and the Ebola filovirus

A 1,7-bis(alkylamino)diazachrysene-based small molecule was previously identified as an inhibitor of the botulinum neurotoxin serotype A light chain metalloprotease. Subsequently, a variety of derivatives of this chemotype were synthesized to develop structure-activity relationships, and all are inhibitors of the BoNT/A LC. Three-dimensional analyses indicated that half of the originally discovered 1,7-DAAC structure superimposed well with 4-amino-7-chloroquinoline-based antimalarial agents. This observation led to the discovery that several of the 1,7-DAAC derivatives are potent in vitro inhibitors of Plasmodium falciparum and, in general, are more efficacious against CQ-resistant strains than against CQ-susceptible strains. In addition, by inhibiting β-hematin formation, the most efficacious 1,7-DAAC-based antimalarials employ a mechanism of action analogous to that of 4,7-ACQ-based antimalarials and are well tolerated by normal cells. One candidate was also effective when administered orally in a rodent-based malaria model. Finally, the 1,7-DAAC-based derivatives were examined for Ebola filovirus inhibition in an assay employing Vero76 cells, and three provided promising antiviral activities and acceptably low toxicities.

Mild and efficient strontium chloride hexahydrate-catalyzed conversion of ketones and aldehydes into corresponding gem-dihydroperoxides by aqueous H2O2

SrCl₂·6H₂O has been shown to act as an efficient catalyst for the conversion of aldehydes or ketones into the corresponding gem-dihydroperoxides (DHPs) by treatment with aqueous H₂O₂ (30%) in acetonitrile. The reactions proceed under mild and neutral conditions at room temperature to afford good to excellent yields of product.

A facile catalyst-free synthesis of gem-dihydroperoxides with aqueous hydrogen peroxide

gem-Dihydroperoxides were easily obtained from the corresponding carbonyl compounds in high yields through a catalyst-free method with aqueous H(2)O(2) (35%) in 1,2-dimethoxyethane at room temperature.