Tetraoxanes: Synthetic and Medicinal Chemistry Perspective

A Mini Review on Isatin, an Anticancer Scaffold with Potential Activities against Neglected Tropical Diseases (NTDs)

Isatin, chemically an indole-1H-2,3-dione, is recognised as one of the most attractive therapeutic fragments in drug design and development. The template has turned out to be exceptionally useful for developing new anticancer scaffolds, as evidenced by the increasing number of isatin-based molecules which are either in clinical use or in trials. Apart from its promising antiproliferative properties, isatin has shown potential in treating Neglected Tropical Diseases (NTDs) not only as a parent core, but also by attenuating the activities of various pharmacophores. The objective of this mini-review is to keep readers up to date on the latest developments in the biological potential of isatin-based scaffolds, targeting cancer and NTDs such as tuberculosis, malaria, and microbial infections.

Synthesis of Non-symmetrical Dispiro-1,2,4,5-Tetraoxanes and Dispiro-1,2,4-Trioxanes Catalyzed by Silica Sulfuric Acid

A novel protocol for the preparation of non-symmetrical 1,2,4,5-tetraoxanes and 1,2,4-trioxanes, promoted by the heterogeneous silica sulfuric acid (SSA) catalyst, is reported. Different ketones react under mild conditions with gem-dihydroperoxides or peroxysilyl alcohols/β-hydroperoxy alcohols to generate the corresponding endoperoxides in good yields. Our mechanistic proposal, assisted by molecular orbital calculations, at the ωB97XD/def2-TZVPP/PCM(DCM)//B3LYP/6-31G(d) level of theory, enhances the role of SSA in the cyclocondensation step. This novel procedure differs from previously reported methods by using readily available and inexpensive reagents, with recyclable properties, thereby establishing a valid alternative approach for the synthesis of new biologically active endoperoxides.

Sterically Tuned N-Heterocyclic Carbene Ligands for the Efficient Formation of Hindered Products in Ru-Catalyzed Olefin Metathesis

Formation of tetrasubstituted C-C double bonds via olefin metathesis is considered very challenging for classical Ru-based complexes. In the hope to improve this condition, three ruthenium olefin metathesis catalysts bearing sterically reduced N-heterocyclic carbene (NHC) ligands with xylyl "arms" were synthesized, characterized using both computational and experimental techniques, and tested in a number of challenging reactions. The catalysts are predicted to initiate much faster than the analogue with mesityl N-substituents. We also foreboded the rotation of xylyl side groups at ambient temperature and the existence of all four atropoisomers in the solution, which was in agreement with experimental data. These catalysts exhibited high activity at relatively low temperatures (45-60 °C) and at reduced catalyst loadings in various reactions of sterically hindered alkenes, including complex polyfunctional substrates of pharmaceutical interest, such as yangonin precursors, chrysantemic acid derivatives, analogues of cannabinoid agonists, α-terpineol, and finally a thermally unstable peroxide.

Design, synthesis, heme binding and density functional theory studies of isoindoline-dione-4-aminoquinolines as potential antiplasmodials

Aim: WHO Malaria report 2017 estimated 216 million cases of malaria and 445,000 deaths worldwide, with 91% of deaths affecting the African region. Results/methodology: Microwave promoted the synthesis of cycloalkyl amine substituted isoindoline-1,3-dione-4-aminoquinolines was urbanized for evaluating their antiplasmodial activities. Compound with the optimum combination of propyl chain length and hydroxyethyl piperazine proved to be the most potent among the synthesized scaffolds against chloroquine-resistant W2 strain of Plasmodium falciparum with an IC50 value of 0.006 μM. Heme-binding along with density functional theory studies were further carried out in order to delineate the mechanism of action of the most active compound. Conclusion: The synthesized scaffold can act as a therapeutic template for further synthetic modifications toward the search for a new antimalarial agent.

Synthesis and Antileishmanial Activity of 1,2,4,5-Tetraoxanes against Leishmania donovani

A chemically diverse range of novel tetraoxanes was synthesized and evaluated in vitro against intramacrophage amastigote forms of Leishmania donovani. All 15 tested tetraoxanes displayed activity, with IC₅₀ values ranging from 2 to 45 µm. The most active tetraoxane, compound LC140, exhibited an IC₅₀ value of 2.52 ± 0.65 µm on L. donovani intramacrophage amastigotes, with a selectivity index of 13.5. This compound reduced the liver parasite burden of L. donovani-infected mice by 37% after an intraperitoneal treatment at 10 mg/kg/day for five consecutive days, whereas miltefosine, an antileishmanial drug in use, reduced it by 66%. These results provide a relevant basis for the development of further tetraoxanes as effective, safe, and cheap drugs against leishmaniasis.

Chemiluminescence in the reaction of 1,2,4,5-tetraoxanes with ferrous ions in the presence of xanthene dyes: fundamentals and perspectives of analytical applications

The reaction of biologically active bridged 1,2,4,5-tetraoxanes and diperoxide of trifluoroacetone with Fe²⁺ ions in the presence of xanthenes, methylene blue and methylene green is accompanied by bright chemiluminescence.

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.

D-Glucose-Derived 1,2,4-Trioxepanes: Synthesis, Conformational Study, and Antimalarial Activity

New enantiomerically pure 1,2,4-trioxepanes 10a,b/11a,b were synthesized from D-glucose. Their conformational behavior was studied by low-temperature NMR and substantiated by DFT calculations. On evaluation of in vitro antimalarial activity, the adamantyl derivative 11b showed IC50 values in the low micromolar range, particularly against the W2 chloroquine-resistant Plasmodium falciparum strain (IC50 = 0.15 ± 0.12 μM).

Glycosyl hydroperoxides: a new class of potential antimalarial agents

Motivated by the antimalarial properties observed in organic peroxides, an extensive series of glycosyl hydroperoxides was prepared with the aim of identifying new bioactive molecules. Selected compounds were tested against a Plasmodium falciparum culture (chloroquine-susceptible strain D10 and chloroquine-resistant strain W2). Screening results indicated that the factors critical for antimalarial activity were the presence of a hydroperoxide moiety and solubility in water at pH 5.0. Moreover, the ability to inhibit β-hematin formation in vitro has been evaluated (BHIA Assay).

Activation of aqueous hydrogen peroxide for non-catalyzed dihydroperoxidation of ketones by azeotropic removal of water

Cyclic and acyclic ketones were selectively converted to gem-dihydroperoxides in 72–99% yield with 30% aq. hydrogen peroxide by azeotropic distillation of water from the reaction mixture without any catalyst.

Mutual action of anticancer and antiparasitic drugs: are there any shared targets?

ABSTRACT 

Parasites and cancers have some common features. It has been shown that some parasites interfere with tumor growth. In addition, they both have common antigens such as the Tn antigen. A communal action of anticancer and antiparasitic drugs has been reported. This shared action may be related to common targets for these drugs in cancers and parasites. In this paper, mutual action of anticancer and antiparasitic drugs, with the aim of discussing shared targets of these drugs, has been reviewed.

β-amino-alcohol tethered 4-aminoquinoline-isatin conjugates: synthesis and antimalarial evaluation

A series of β-amino alcohol tethered 4-aminoquinoline-isatin conjugates were synthesized with the aim of probing their antimalarial structure activity relationship. Two of the most active conjugates (11b and 11f) exhibited antimalarial efficacy comparable to that of chloroquine, with IC₅₀ values of 11.8 and 13.5 nM, respectively against chloroquine resistant W2 strain of Plasmodium falciparum and are devoid of any cytotoxicity.

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Synthesis of β-amino alcohol tethered isatin 4-aminoquinoline conjugates.

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Antimalarial evaluation against W2 strains of Plasmodium falciparum.

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Most active and non-cytotoxic conjugate exhibited an IC₅₀ 11.7 nM.

Theoretical study of the gas-phase thermolysis of 3-methyl-1,2,4,5-tetroxane

Cyclic organic peroxides are a broad and highly sought-after class of peroxide compounds that present high reactivity and even explosive character. The unusually high reactivity of these peroxides can generally be attributed to the rupture of O-O bonds. Cyclic diperoxides are a very interesting series of substituted compounds in which tetroxane is the most prominent member. Gas-phase thermolysis of the simplest substituted member of the series [3-methyl-1,2,4,5-tetroxane or methylformaldehyde diperoxide (MFDP)] has been observed to yield one acetaldehyde, one formaldehyde, and one oxygen molecule as reaction products. DFT at the 6-311 + G** level of theory using the BHANDHLYP correlation-exchange functional was applied via the Gaussian09 program to calculate the critical points of the potential energy surface (PES) of this reaction. Equatorial and axial isomers were studied. The singlet state PES of MFDP was calculated, and an open diradical structure was found to be the first intermediate in a stepwise reaction. Two PESs were subsequently obtained: singlet state (S) and triplet state (T) PESs. After that, two alternative stepwise reactions were found to be possible: 1) one in which either an acetaldehyde, or 2) formaldehyde molecule is initially formed. For second one, exothermic reactions were observed for both the S and T PESs. The reaction products include a oxygen molecule in either S or T state, with the T reaction being the most exothermic. When calculations were performed at the CASSCF(10,10)/6-311 + G** level, spin-orbit coupling permitted S to T crossing at the open diradical intermediate stage, a non-adiabatic reaction was observed, and lower activation energies and higher exothermicity were generally seen for the T PES than for the S PES. These results were compared with the corresponding results for tetroxane. The spin-orbit coupling of MFDP and tetroxane yielded identical values, so it appears that the methyl substituent does not have any effect on this coupling.

Second generation steroidal 4-aminoquinolines are potent, dual-target inhibitors of the botulinum neurotoxin serotype A metalloprotease and P. falciparum malaria

Significantly more potent second generation 4-amino-7-chloroquinoline (4,7-ACQ) based inhibitors of the botulinum neurotoxin serotype A (BoNT/A) light chain were synthesized. Introducing an amino group at the C(3) position of the cholate component markedly increased potency (IC50 values for such derivatives ranged from 0.81 to 2.27 μM). Two additional subclasses were prepared: bis(steroidal)-4,7-ACQ derivatives and bis(4,7-ACQ)cholate derivatives; both classes provided inhibitors with nanomolar-range potencies (e.g., the Ki of compound 67 is 0.10 μM). During BoNT/A challenge using primary neurons, select derivatives protected SNAP-25 by up to 89%. Docking simulations were performed to rationalize the compounds' in vitro potencies. In addition to specific residue contacts, coordination of the enzyme's catalytic zinc and expulsion of the enzyme's catalytic water were a consistent theme. With respect to antimalarial activity, the compounds provided better IC90 activities against chloroquine resistant (CQR) malaria than CQ, and seven compounds were more active than mefloquine against CQR strain W2.

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.

Synthesis, antimalarial activity, heme binding and docking studies of 4-aminoquinoline–pyrimidine based molecular hybrids

A series of novel 4-aminoquinoline–pyrimidine hybrids was synthesized and evaluated for their antimalarial activity.

Synthesis of piperazine tethered 4-aminoquinoline-pyrimidine hybrids as potent antimalarial agents

Piperazine linked 4-aminoquinoline-pyrimidine hybrids were synthesized and evaluated for in vitro antimalarial activity against W2 and D6 strains of plasmodium falciparum.

4-aminoquinoline-triazine-based hybrids with improved in vitro antimalarial activity against CQ-sensitive and CQ-resistant strains of Plasmodium falciparum

A systematic chemical modification in the triazine moiety covalently attached via suitable linkers to 4-amino-7-chloroquinolines yielded a series of new 7-chloro-4-aminoquinoline-triazine hybrids exhibiting high in vitro activity against W2 (chloroquine-resistant) and D6 (chloroquine-sensitive) strains of Plasmodium falciparum without any toxicity against mammalian cell lines (Vero, LLC-PK11, HepG2). Many of the compounds (6, 8, 10, 11, 13, 14, 16, 27, 29 and 33) showed excellent potency against chloroquine sensitive and resistant strains. In particular, compounds 6, 8, 14, 16 and 29 were found to be significantly more active than chloroquine against the chloroquine-resistant strains (W2 clone) of P. falciparum.

Novel 4-aminoquinoline-pyrimidine based hybrids with improved in vitro and in vivo antimalarial activity

A class of hybrid molecules consisting of 4-aminoquinoline and pyrimidine were synthesized and tested for antimalarial activity against both chloroquine (CQ)-sensitive (D6) and chloroquine (CQ)-resistant (W2) strains of Plasmodium falciparum through an in vitro assay. Eleven hybrids showed better antimalarial activity against both CQ-sensitive and CQ-resistant strains of P. falciparum in comparison to standard drug CQ. Four molecules were more potent (7-8-fold) than CQ in D6 strain, and eight molecules were found to be 5-25-fold more active against resistant strain (W2). Several compounds did not show any cytotoxicity up to a high concentration (60 μM), others exhibited mild toxicities, but the selective index for the antimalarial activity was very high for most of these hybrids. Two compounds selected for in vivo evaluation have shown excellent activity (po) in a mouse model of Plasmodium berghei without any apparent toxicity. The X-ray crystal structure of one of the compounds was also determined.