Stereoselective Epoxidation of Alkenes with Hydrogen Peroxide using a Bipyrrolidine‐Based Family of Manganese Complexes

Transition Metal-Catalyzed Transformations of Chalcones

Chalcones are a class of naturally occurring flavonoid compounds associated to a variety of biological and pharmacological properties. Several reviews have been published describing the synthesis and biological properties of a vast array of analogues. However, overviews on the reactivity of chalcones has only been explored in a few accounts. To fill this gap, a systematic survey on the most recent developments in the transition metal-catalyzed transformation of chalcones was performed. The chemistry of copper, palladium, zinc, iron, manganese, nickel, ruthenium, cobalt, rhodium, iridium, silver, indium, gold, titanium, platinum, among others, as versatile catalysts will be highlighted, covering the literature from year 2000 to 2023, in more than 380 publications.

Asymmetric Epoxidation of Olefins with Sodium Percarbonate Catalyzed by Bis-amino-bis-pyridine Manganese Complexes

Asymmetric epoxidation of a series of olefinic substrates with sodium percarbonate oxidant in the presence of homogeneous catalysts based on Mn complexes with bis-amino-bis-pyridine ligands is reported. Sodium percarbonate is a readily available and environmentally benign oxidant that is studied in these reactions for the first time. The epoxidation proceeded with good to high yields (up to 100%) and high enantioselectivities (up to 99% ee) using as low as 0.2 mol. % catalyst loadings. The epoxidation protocol is suitable for various types of substrates, including unfunctionalized alkenes, α,β-unsaturated ketones, esters (cis- and trans-), and amides (cis- and trans-). The reaction mechanism is discussed.

Exploration of highly electron-rich manganese complexes in enantioselective oxidation catalysis; a focus on enantioselective benzylic oxidation

The development of highly electron-rich manganese complexes for enantioselective benzylic oxidation (and asymmetric epoxidation) is described, to provide chiral benzylic alcohols and epoxides in good yields and enantioselectivites.

Relevance of Trypanothione Reductase Inhibitors on Trypanosoma cruzi Infection: A Systematic Review, Meta-Analysis, and In Silico Integrated Approach

Due to the rudimentary antioxidant defenses in Trypanosoma cruzi, disruptors of redox balance are promising candidates for new antitrypanosomal drugs. We developed an integrated model based on systematic review, meta-analyses, and molecular modeling to evaluate the effect of trypanothione reductase (TR) inhibitors in T. cruzi infections. Our findings indicated that the TR inhibitors analyzed were effective in reducing parasitemia and mortality due to Trypanosoma cruzi infection in animal models. The most investigated drugs (clomipramine and thioridazine) showed no beneficial effects on the occurrence of infection-related electrocardiographic abnormalities or the affinity and density of cardiac β-adrenergic receptors. The affinity between the tested ligands and the active site of TR was confirmed by molecular docking. However, the molecular affinity score was unable to explain TR inhibition and T. cruzi death in vitro or the antiparasitic potential of these drugs when tested in preclinical models of T. cruzi infection. The divergence of in silico, in vitro, and in vivo findings indicated that the anti-T. cruzi effects of the analyzed drugs were not restricted to TR inhibition. As in vivo studies on TR inhibitors are still scarce and exhibit methodological limitations, mechanistic and highly controlled studies are required to improve the quality of evidence.

Trypanocidal activity of tetradentated pyridine-based manganese complexes is not linked to inactivation of superoxide dismutase

Two tetradentated pyridine-based manganese complexes (Cpd2 and Cpd3) were previously reported to inhibit efficiently the growth of Trypanosoma cruzi in vitro and in vivo. Cpd3 was also shown to be a potent inhibitor of trypanosomal iron superoxide dismutase (Fe-SOD) and its trypanocidal activity linked to the inhibition of this enzyme. Here we investigated the anti-trypanosomal activity of the two compounds against bloodstream forms of Trypanosoma brucei. Both compounds displayed potent trypanocidal activity against T. brucei bloodstream forms with minimum inhibitory concentrations (MICs) and 50% growth inhibition (GI₅₀) values of 1 μM and 0.2-0.3 μM, respectively. Cpd2 and Cpd3 also showed cytotoxicity against HL-60 cells but based on GI₅₀ values the human cells were 14 and 87 times less sensitive indicating moderate selectivity. In contrast to previous observation, Cpd3 did not inhibit Fe-SOD within trypanosomes and Cpd2 inhibited the enzyme only by 34%. As Fe-SOD together with ornithine decarboxylase play vital roles in the antioxidant defence in bloodstream forms of T. brucei, inhibition of both enzymes should be synergistically. Therefore, the interaction of Cpd2 and Cpd3 with the ornithine decarboxylase inhibitor eflornithine was determined. Both compounds were found in combination with eflornithine to produce only an additive effect. Thus, the observed lack of synergy between Cpd2/Cpd3 and eflornithine can be regarded as further indication that both compounds are not very strong inhibitors of trypanosomal Fe-SOD. Nevertheless, tetradentated pyridine-based manganese complexes are interesting compounds with promising anti-trypanosomal activity.

Delivering aminopyridine ligands into cancer cells through conjugation to the cell-penetrating peptide BP16

Peptide conjugates incorporating the N-based ligands (Me2)PyTACN or (S,S')-BPBP at the N- or the C-terminus of the cell-penetrating peptide were synthesized (PyTACN-BP16 (), BP16-PyTACN (), BPBP-BP16 (), and BP16-BPBP ()). Metal binding peptides bearing at the N-terminus the ligand, an additional Lys and a β-Ala were also prepared (PyTACN-βAK-BP16 () and BPBP-βAK-BP16 ()). Moreover, taking into account the clathrin-dependent endocytic mechanism of , the enzymatic cleavable tetrapeptide Gly-Phe-Leu-Gly was incorporated between the ligand and the N- or C-terminus of (BPBP-GFLG-BP16 () and BP16-GLFG-BPBP ()). Analysis of the cytotoxicity of all the peptide conjugates showed that: (i) the position of the ligand influenced the IC50 values, (ii) the incorporation of the βAla-Lys dipeptide rendered non active sequences, (iii) peptide conjugates derived from the (S,S')-BPBP ligand were more active than those bearing (Me2)PyTACN, and (iv) the introduction of the cleavable tetrapeptide significantly enhanced the activity of the BPBP conjugates (IC50 of 4.3 to 11.7 μM ( and ) compared to 26.0 to >50 μM (, and )). The most active peptide was BPBP-GFLG-BP16 () (IC50 of 4.3 to 5.0 μM). This high activity was attributed to its high internalization in MCF-7 cells, as shown by flow cytometry, and to the subsequent release of the ligand by the intracellular cleavage of the enzyme-labile spacer, as observed in cathepsin B enzymatic assays. Therefore, these results pave the way for the design of novel peptide conjugates to be used in pro-oxidant anticancer therapies.

Design, Preparation, and Characterization of Zn and Cu Metallopeptides Based On Tetradentate Aminopyridine Ligands Showing Enhanced DNA Cleavage Activity

The conjugation of redox-active complexes that can function as chemical nucleases to cationic tetrapeptides is pursued in this work in order to explore the expected synergistic effect between these two elements in DNA oxidative cleavage. Coordination complexes of biologically relevant first row metal ions, such as Zn(II) or Cu(II), containing the tetradentate ligands 1,4-dimethyl-7-(2-pyridylmethyl)-1,4,7-triazacyclononane ((Me2)PyTACN) and (2S,2S')-1,1'-bis(pyrid-2-ylmethyl)-2,2'-bipyrrolidine ((S,S')-BPBP) have been linked to a cationic LKKL tetrapeptide sequence. Solid-phase synthesis of the peptide-tetradentate ligand conjugates has been developed, and the preparation and characterization of the corresponding metallotetrapeptides is described. The DNA cleavage activity of Cu and Zn metallopeptides has been evaluated and compared to their metal binding conjugates as well as to the parent complexes and ligands. Very interestingly, the oxidative Cu metallopeptides 1Cu and 2Cu show an enhanced activity compared to the parent complexes, [Cu(PyTACN)](2+) and [Cu(BPBP)](2+), respectively. Under optimized conditions, 1Cu displays an apparent pseudo first-order rate constant (kobs) of ∼0.16 min(-1) with a supercoiled DNA half-life time (t1/2) of ∼4.3 min. On the other hand, kobs for 2Cu has been found to be ∼0.11 min(-1) with t1/2 ≈ 6.4 min. Hence, these results point out that the DNA cleavage activities promoted by the metallopeptides 1Cu and 2Cu render ∼4-fold and ∼23 rate accelerations in comparison with their parent Cu complexes. Additional binding assays and mechanistic studies demonstrate that the enhanced cleavage activities are explained by the presence of the cationic LKKL tetrapeptide sequence, which induces an improved binding affinity to the DNA, thus bringing the metal ion, which is responsible for cleavage, in close proximity.

Asymmetric Epoxidation Using Hydrogen Peroxide as Oxidant

Asymmetric epoxidation is one of the most important transformations in organic synthesis. Although tremendous progress was achieved in this field in the 1980s and 1990s, it is still desirable from both economical and ecological views to develop environmentally friendly catalytic epoxidation with a broad substrate scope. Hydrogen peroxide is a safe and cheap oxidant, which is easy to handle and generates water as the sole byproduct. Therefore, asymmetric epoxidation of olefins using hydrogen peroxide as oxidant has been a very active research field and has been investigated by many research groups in recent years. In this review, the exciting very recent developments of this rapidly growing area are surveyed and organized according to the catalyst systems.

Asymmetric epoxidation of olefins with hydrogen peroxide by an in situ-formed manganese complex

Asymmetric epoxidation of a variety of cis, trans, terminal, and trisubstituted olefins in excellent yields (up to 94%) and enantioselectivities (>99% ee) by an in situ-formed manganese complex using H2O2 has been developed. A relationship between the hydrophobicity of the catalyst imposed by ligand and the catalytic activity has been observed. The influence of the amount and identity of the acid additive was examined, and improved enantioselectivities were achieved through the use of a catalytic amount of a carboxylic acid additive.

Manganese(ii) complexes of tetradentate 4N ligands with diazepane backbones for catalytic olefin epoxidation: effect of nucleophilicity of peroxo complexes on reactivity

Mononuclear Mn(ii) complexes of linear 4N ligands have been studied as catalysts for deformylation of aldehydes and epoxidation (H₂O₂) of unfunctionalised olefins to understand the role of ligand stereoelectronic factors.

Asymmetric epoxidation with H2O2 by manipulating the electronic properties of non-heme iron catalysts

A non-heme iron complex that catalyzes highly enantioselective epoxidation of olefins with H2O2 is described. Improvement of enantiomeric excesses is attained by the use of catalytic amounts of carboxylic acid additives. Electronic effects imposed by the ligand on the iron center are shown to synergistically cooperate with catalytic amounts of carboxylic acids in promoting efficient O-O cleavage and creating highly chemo- and enantioselective epoxidizing species which provide a broad range of epoxides in synthetically valuable yields and short reaction times.

Asymmetric epoxidation of alkenes catalyzed by a porphyrin-inspired manganese complex

A novel strategy for catalytic asymmetric epoxidation of a wide variety of olefins by a porphyrin-inspired chiral manganese complex using H2O2 as a terminal oxidant in excellent yield with up to greater than 99% ee has been successfully developed.