A Chemical Proteomics Approach to Defining the Mechanism of Artemisinin Action and Resistance in PfK13 Resistant parasites

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

Publication . Amado, Patrícia; Frija, Luís M. T.; Coelho, Jaime A. S.; O’Neill, Paul M.; Cristiano, Maria De Lurdes

A novel protocol for the preparation of nonsymmetrical 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 gemdihydroperoxides or peroxysilyl alcohols/beta-hydroperoxy alcohols to generate the corresponding endoperoxides in good yields. Our mechanistic proposal, assisted by molecular orbital calculations, at the.B97XD/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.

2021Journal article

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Unravelling the structure of peroxides with antiparasitic activity: the relative impact of a trioxolane or a tetraoxane pharmacophore on the overall molecular structure

Publication . Amado, Patrícia; Jesus, A. J. Lopes; Paixão, José A.; Fausto, Rui; Cristiano, Maria De Lurdes

Plasmodium falciparum artemisinin-resistance boosted the quest for novel plasmodial "fast killers," uncovering antimalarial candidates OZ439 and E209, whose peroxide precursors are 1,2,4-trioxolane (1) and 1,2,4,5-tetraoxane (2), differing solely in the pharmacophore (trioxolane or tetraoxane). Combining X-ray crystallography and vibrational spectroscopy, along with Hirsh-feld surface analysis and calculations (CE-B3LYP/6-31G(d,p)) of pairwise interaction energies of intermolecular contacts existing in the crystal structure, may deepen the understanding of relative reactivity and properties of these endoperoxides classes. In the crystal, the tetraoxane ring in 2 and the trioxolane-adamantyl fragment in 1 are disordered, with molecules 1 and 2 existing as two distinct, stable conformations. Whereas the dominant C-H center dot center dot center dot O H-bonds in 1 connect an adamantyl C-H and O1 or O2 of the trioxolane ring, in 2 they involve the carbonyl oxygen, acting as a double acceptor from phenyl ring C-H groups. C-H center dot center dot center dot O and C-H center dot center dot center dot pi H-bonds define the molecular packing of 2, while C-H center dot center dot center dot H-C van der Waals interactions determine the packing of 1. The dispersive component dominates the interaction energies calculated for the most representative molecular pairs.

2022Journal article

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Molecular and crystal structure, spectroscopy, and photochemistry of a dispiro compound bearing the tetraoxane pharmacophore

Publication . Amado, Patrícia; Lopes, Susy; Brás, Elisa M.; Paixão, José A.; Takano, Ma‐aya; Abe, Manabu; Fausto, Rui; Cristiano, Maria De Lurdes

The molecular structure and photochemistry of dispiro[cyclohexane-1,3′-[1,2,4,5]tetraoxane-6′,2′′-tricyclo[3.3.1.13,7]decan]-4-one (TX), an antiparasitic 1,2,4,5-tetraoxane was investigated using matrix isolation IR and EPR spectroscopies, together with quantum chemical calculations undertaken at the DFT(B3LYP)/6-311++G(3df,3pd) level of theory, with and without Grimme's dispersion correction. Photolysis of the matrix-isolated TX, induced by in situ broadband (λ>235 nm) or narrowband (λ in the range 220–263 nm) irradiation, led to new bands in the infrared spectrum that could be ascribed to two distinct photoproducts, oxepane-2,5-dione, and 4-oxohomoadamantan-5-one. Our studies show that these photoproducts result from initial photoinduced cleavage of an O−O bond, with the formation of an oxygen-centered diradical that regioselectivity rearranges to a more stable (secondary carbon-centered)/(oxygen-centered) diradical, yielding the final products. Formation of the diradical species was confirmed by EPR measurements, upon photolysis of the compound at λ=266 nm, in acetonitrile ice (T=10–80 K). Single-crystal X-ray diffraction (XRD) studies demonstrated that the TX molecule adopts nearly the same conformation in the crystal and matrix-isolation conditions, revealing that the intermolecular interactions in the TX crystal are weak. This result is in keeping with observed similarities between the infrared spectrum of the crystalline material and that of matrix-isolated TX. The detailed structural, vibrational, and photochemical data reported here appear relevant to the practical uses of TX in medicinal chemistry, considering its efficient and broad parasiticidal properties.

2023Journal article

Open Access

Recent advances of DprE1 inhibitors against mycobacterium tuberculosis: computational analysis of physicochemical and ADMET properties

Publication . Amado, Patrícia; Woodley, Christopher; Lurdes S. Cristiano, M.; O’Neill, Paul M.

D e cap renylp ho sp ho ryl-beta-D-rib os e 2 '-epimerase (DprE1) is a critical flavoenzyme in Mycobacterium tuberculosis, catalyzing a vital step in the production of lipoarabinomannan and arabinogalactan, both of which are essential for cell wall biosynthesis. Due to its periplasmic localization, DprE1 is a susceptible target, and several compounds with diverse scaffolds have been discovered that inhibit this enzyme, covalently or noncovalently. We evaluated a total of similar to 1519 DprE1 inhibitors disclosed in the literature from 2009 to April 2022 by performing an in-depth analysis of physicochemical descriptors and absorption, distribution, metabolism, excretion, and toxicity (ADMET), to gain new insights into these properties in DprE1 inhibitors. Several molecular properties that should facilitate the design and optimization of future DprE1 inhibitors are described, allowing for the development of improved analogues targeting M. tuberculosis.

2022-11Journal article

Open Access

1,2,4-Trioxolane and 1,2,4,5-Tetraoxane endoperoxides against old-world Leishmania parasites: in vitro activity and mode of action

Publication . Mendes, Andreia; Armada, Ana; Cabral, Lília; Amado, Patrícia; Campino, Lenea; Cristiano, Maria de Lurdes; Cortes, Sofia

Leishmaniasis remains one of the ten Neglected Tropical Diseases with significant morbidity and mortality in humans. Current treatment of visceral leishmaniasis is difficult due to a lack of effective, non-toxic, and non-extensive medications. This study aimed to evaluate the selectivity of 12 synthetic endoperoxides (1,2,4-trioxolanes; 1,2,4,5-tetraoxanes) and uncover their biochemical effects on Leishmania parasites responsible for visceral leishmaniasis. The compounds were screened for in vitro activity against L. infantum and L. donovani and for cytotoxicity in two monocytic cell lines (J774A.1 and THP-1) using the methyl thiazol tetrazolium assay. Reactive oxygen species formation, apoptosis, and mitochondrial impairment were measured by flow cytometry. The compounds exhibited fair to moderate anti-proliferative activity against promastigotes of the 2 Leishmania species, with IC₅₀ values ranging from 13.0 ± 1.7 µM to 793.0 ± 37.2 µM. Tetraoxanes LC132 and LC138 demonstrated good leishmanicidal activity on L. infantum amastigotes (IC₅₀ 13.2 ± 5.2 and 23.9 ± 2.7 µM) with low cytotoxicity in mammalian cells (SIs 22.1 and 118.6), indicating selectivity towards the parasite. Furthermore, LC138 was able to induce late apoptosis and dose-dependent oxidative stress without affecting mithocondria. Compounds LC132 and LC138 can be further explored as potential antileishmanial chemotypes.

2022-04-03Journal article

Open Access