A Study about Regioisomeric Hydroquinones with Multiple Intramolecular Hydrogen Bonding

Assessing mitochondria-targeted acyl hydroquinones on the mitochondrial platelet function and cytotoxic activity: Role of the linker length

INTRODUCTION

The use of triphenylphosphonium cation (TPP+) linked to phenolic compounds by alkyl chains has a significant relevance as a mitochondrial delivery strategy in biomedicine because it affects mitochondrial bioenergetics in models of noncommunicable diseases such as cancer and cardiovascular-related conditions. Studies indicate that a long alkyl chain (10-12 carbon) increases the mitochondrial accumulation of TPP+-linked drugs. In contrast, other studies show that these compounds are consistently toxic to micromolar concentrations (as observed in platelets). In the present study, we evaluated the in vitro effect of three series of triphenylphosphonium-linked acyl hydroquinones derivates on the metabolism and function of human platelets using 3-9 carbons for the alkyl linker. Those were assessed to determine the role of the length of the alkyl chain linker on platelet toxicity.

METHODS

Human platelets were exposed in vitro to different concentrations (2-40 μM) of every compound; cellular viability, phosphatidylserine exposition, mitochondrial membrane potential (ΔΨm), intracellular calcium release, and intracellular ROS generation were assessed by flow cytometry. An in silico energetic profile was generated with Umbrella sampling molecular dynamics (MD).

RESULTS AND CONCLUSIONS

There was an increase in cytotoxic activity directly related to the length of the acyl chain and lipophilicity, as seen by three techniques, and this was consistent with a decrease in ΔΨm. The in silico energetic profiles point out that the permeability of the mitochondrial membrane may be involved in the cytotoxicity of phosphonium salts. This information may be relevant for the design of new TPP+ -based drugs with a safe cardiovascular profile.

Regulation of mitochondrial function by hydroquinone derivatives as prevention of platelet activation

Platelet activation plays an essential role in the pathogenesis of thrombotic events in different diseases (e.g., cancer, type 2 diabetes, Alzheimer's, and cardiovascular diseases, and even in patients diagnosed with coronavirus disease 2019). Therefore, antiplatelet therapy is essential to reduce thrombus formation. However, the utility of current antiplatelet drugs is limited. Therefore, identifying novel antiplatelet compounds is very important in developing new drugs. In this context, the involvement of mitochondrial function as an efficient energy source required for platelet activation is currently accepted; however, its contribution as an antiplatelet target still has little been exploited. Regarding this, the intramolecular hydrogen bonding of hydroquinone derivatives has been described as a structural motif that allows the reach of small molecules at mitochondria, which can exert antiplatelet activity, among others. In this review, we describe the role of mitochondrial function in platelet activation and how hydroquinone derivatives exert antiplatelet activity through mitochondrial regulation.

Facile synthesis of 5-Isopropyl-2,3-dimethylbenzene-1,4-diol by Friedel-Crafts and Determination of Partition Coefficient in n- Octanol/Water

The wide therapeutic effect of quinone-based drugs has received considerable interest for a long time. In this research, Friedel-Crafts performed a facile synthesis of quinone derivatives using the mixture of Brønsted acid. Reflux of 2,3-dimethylhydroquinone (1), isopropanol, glacial acetic acid, and H2SO4 for 15 minutes gave yellow oil product of 5-isopropyl-2,3-dimethylbenzene-1,4-diol (2) as a major product. Characterization using Nuclear Magnetic Resonance (NMR) revealed the methine proton splitting for isopropyl at δ 3.13 ppm, which has a cross-coupling with aromatic carbon at δ 119.6 ppm suggested the substitution of a proton on quinone ring with isopropyl group. Analysis Fourier Transform Infra-Red (FT-IR) showed the broad spectrum of –OH, the vibration of CH sp3, and isopropyl groups. The minor products identified as 5-isopropyl-2,3-dimethylcyclohexa-2,5-diene-1,4-dione (3), 5-isopropyl-2,3-dimethyl-1,4 phenylene diacetate (4), and 2,3-dimethylbenzene-5,6-isopropyl-1,4-diol (5) confirmed from 2D HETCOR and MS analysis. The partition coefficient (log P) of compound 2 showed a higher solubility by 1.9-fold compared to hydroquinone 1. It is suggested that an additional methyl group increased the partition into the organic phase.

Synthesis and pharmacological evaluation of acylhydroquinone derivatives as potent antiplatelet agents

Platelets are the smallest blood cells, and their activation (platelet cohesion or aggregation) at sites of vascular injury is essential for thrombus formation. Since the use of antiplatelet therapy is an unsolved problem, there are now focused and innovative efforts to develop novel antiplatelet compounds. In this context, we assessed the antiplatelet effect of an acylhydroquinone series, synthesized by Fries rearrangement under microwave irradiation, evaluating the effect of diverse acyl chain lengths, their chlorinated derivatives, and their dimethylated derivatives both in the aromatic ring and also the effect of the introduction of a bromine atom at the terminus of the acyl chain. Findings from a primary screening of cytotoxic activity on platelets by lactate dehydrogenase assay identified 19 non-toxic compounds from the 27 acylhydroquinones evaluated. A large number of them showed IC₅₀ values less than 10 µM acting against specific pathways of platelet aggregation. The highest activity was obtained with compound 38, it exhibited sub-micromolar IC₅₀ of 0.98 ± 0.40, 1.10 ± 0.26, 3.98 ± 0.46, 6.79 ± 3.02 and 42.01 ± 3.48 µM against convulxin-, collagen-, TRAP-6-, PMA- and arachidonic acid-induced platelet aggregation, respectively. It also inhibited P-selectin and granulophysin expression. We demonstrated that the antiplatelet mechanism of compound 38 was through a decrease in a central target in human platelet activation as in mitochondrial function, and this could modulate a lower response of platelets to activating agonists. The results of this study show that the chemical space around ortho-carbonyl hydroquinone moiety is a rich source of biologically active compounds, signaling that the acylhydroquinone scaffold has a promising role in antiplatelet drug research.

Glycerol as Alternative Co-Solvent for Water Extraction of Polyphenols from Carménère Pomace: Hot Pressurized Liquid Extraction and Computational Chemistry Calculations

Glycerol is a co-solvent for water extraction that has been shown to be highly effective for obtaining polyphenol extracts under atmospheric conditions. However, its efficacy under subcritical conditions has not yet been studied. We assessed different water-glycerol mixtures (15%, 32.5%, and 50%) in a hot pressurized liquid extraction system (HPLE: 10 MPa) at 90 °C, 120 °C, and 150 °C to obtain extracts of low molecular weight polyphenols from Carménère grape pomace. Under the same extraction conditions, glycerol as a co-solvent achieved significantly higher yields in polyphenols than ethanol. Optimal extraction conditions were 150 °C, with 32.5% glycerol for flavonols and 50% for flavanols, stilbenes, and phenolic acids. Considering gallic acid as a model molecule, computational chemistry calculations were applied to explain some unusual extraction outcomes. Furthermore, glycerol, methanol, ethanol, and ethylene glycol were studied to establish an incipient structure-property relationship. The high extraction yields of gallic acid obtained with water and glycerol solvent mixtures can be explained not only by the additional hydrogen bonds between glycerol and gallic acid as compared with the other alcohols, but also because the third hydroxyl group allows the formation of a three-centered hydrogen bond, which intensifies the strongest glycerol and gallic acid hydrogen bond. The above occurs both in neutral and deprotonated gallic acid. Consequently, glycerol confers to the extraction solvent a higher solvation energy of polyphenols than ethanol.

Synthesis of antiplatelet ortho-carbonyl hydroquinones with differential action on platelet aggregation stimulated by collagen or TRAP-6

Cardiovascular diseases are the leading cause of death in the world. Platelets have a major role in cardiovascular events as they bind to the damaged endothelium activating and forming thrombi. Although some hydroquinone scaffold-containing compounds have known antiplatelet activities, currently there is a lack of evidence on the antiplatelet activity of hydroquinones carrying electron attractor groups. In this work, we evaluate the antiplatelet effect of a series of ortho-carbonyl hydroquinone derivatives on cytotoxicity and function of human platelets, using collagen and thrombin receptor activator peptide 6 (TRAP-6) as agonists. Our structure-activity relationship study shows that gem-diethyl/methyl substitutions and the addition/modifications of the third ring of ortho-carbonyl hydroquinone scaffold influence on the selective index (IC₅₀ TRAP-6/IC₅₀ Collagen) and the inhibitory capacity of platelet aggregation. Compounds 3 and 8 inhibit agonist-induced platelet aggregation in a non-competitive manner with IC₅₀ values of 1.77 ± 2.09 μM (collagen) and 11.88 ± 4.59 μM (TRAP-6), respectively and show no cytotoxicity. Both compounds do not affect intracellular calcium levels and mitochondrial bioenergetics. Consistently, they reduce the expression of P-selectin, activation of glycoprotein IIb/IIIa, and release of adenosine triphosphate and CD63 from platelet. Our findings may be used for further development of new drugs in platelet-related thrombosis diseases.

Twelve formyl phloroglucinol meroterpenoids from the leaves of Eucalyptus robusta

Twelve formyl phloroglucinol meroterpenoids (FPMs) were isolated from the leaves of Eucalyptus robusta Smith. Their structures were elucidated via spectroscopic data analysis, the circular dichroism (CD) exciton chirality method, Rh₂(OCOCF₃)₄-induced CD experiments, and application of the Snatzke chirality rules. Eucalrobusones Q, S, and X are the first FPMs that have been identified in which the C-7' of phloroglucinol is linked to the C-15 of cadinane, the C-4 of cubebane, and the C-8 of menthane, respectively. (+)-Eucalrobusone X exhibited the most potent antifungal ability against Candida albicans with a MIC₅₀ value of 10.78 μg/mL, and eucalrobusone U exhibited the greatest anti-C. glabrata activity with MIC₅₀ value of 1.53 μg/mL.

Regulation of mitochondrial function as a promising target in platelet activation-related diseases

Platelets are anucleated cell elements produced by fragmentation of the cytoplasm of megakaryocytes and have a unique metabolic phenotype compared with circulating leukocytes, exhibiting a high coupling efficiency to mitochondrial adenosine triphosphate production with reduced respiratory reserve capacity. Platelet mitochondria are well suited for ex vivo analysis of different diseases. Even some diseases induce mitochondrial changes in platelets without reflecting them in other organs. During platelet activation, an integrated participation of glycolysis and oxidative phosphorylation is mediated by oxidative stress production-dependent signaling. The platelet activation-dependent procoagulant activity mediated by collagen, thrombin and hyperglycemia induce mitochondrial dysfunction to promote thrombosis in oxidative stress-associated pathological conditions. Interestingly, some compounds exhibit a protective action on platelet mitochondrial dysfunction through control of mitochondrial oxidative stress production or inhibition of respiratory complexes. They can be grouped in a) Natural source-derived compounds (e.g. Xanthohumol, Salvianoloc acid A and Sila-amide derivatives of NAC), b) TPP⁺-linked small molecules (e.g. mitoTEMPO and mitoQuinone) and c) FDA-approved drugs (e.g. metformin and statins), illustrating the wide range of molecular structures capable of effectively interacting with platelet mitochondria. The present review article aims to discuss the mechanisms of mitochondrial dysfunction and their association with platelet activation-related diseases.

Assessing Parameter Suitability for the Strength Evaluation of Intramolecular Resonance Assisted Hydrogen Bonding in o-Carbonyl Hydroquinones

Intramolecular hydrogen bond (IMHB) interactions have attracted considerable attention due to their central role in molecular structure, chemical reactivity, and interactions of biologically active molecules. Precise correlations of the strength of IMHB's with experimental parameters are a key goal in order to model compounds for drug discovery. In this work, we carry out an experimental (NMR) and theoretical (DFT) study of the IMHB in a series of structurally similar o-carbonyl hydroquinones. Geometrical parameters, as well as Natural Bond Orbital (NBO) and Quantum Theory of Atoms in Molecules (QTAIM) parameters for IMHB were compared with experimental NMR data. Three DFT functionals were employed to calculated theoretical parameters: B3LYP, M06-2X, and ωB97XD. O…H distance is the most suitable geometrical parameter to distinguish among similar IMHBs. Second order stabilization energies ΔEij(2) from NBO analysis and hydrogen bond energy (EHB) obtained from QTAIM analysis also properly distinguishes the order in strength of the studied IMHB. ΔEij(2) from NBO give values for the IMHB below 30 kcal/mol, while EHB from QTAIM analysis give values above 30 kcal/mol. In all cases, the calculated parameters using ωB97XD give the best correlations with experimental ¹H-NMR chemical shifts for the IMHB, with R² values around 0.89. Although the results show that these parameters correctly reflect the strength of the IMHB, when the weakest one is removed from the analysis, arguing experimental considerations, correlations improve significantly to values around 0.95 for R².