A facile bromination of hydroxyheteroarenes

Bioorthogonal catalytic microvesicle-mediated prodrug activation against liver cancer

OBJECTIVE

Exploring the role and mechanism of a novel bioorthogonal system using transition metals as catalysts in the treatment of hepatocellular carcinoma (HCC).

METHODS

Initially, a catalytic ruthenium (Ru) complex and the substrate alloc-RH 110 were synthesized, followed by the identification of their structures utilizing mass spectrometry and nuclear magnetic resonance (NMR) techniques. The catalytic efficacy of the Ru complex was then assessed using a fluorescence spectrophotometer. Subsequently, employing HepG2 cells as the cellular source, cell-derived vesicles encapsulating the Ru complexes, designated as EVs@Ru, were prepared. The EVs@Ru were characterized by measuring their particle size and Zeta potential, observing morphological features under transmission electron microscopy (TEM), and detecting specific protein expressions via Western blot analysis. Drug loading within the EVs@Ru was quantified using inductively coupled plasma mass spectrometry (ICP-MS), and their catalytic efficiency was evaluated. In vitro, the low-activity prodrug alloc-DOX was synthesized and its toxicity, along with the drug concentration in EVs@Ru, was determined. Further, the catalytic cytotoxicity of alloc-DOX against HepG2 cells encapsulated in EVs@Ru was analyzed through microscopic observation, CCK-8 assays, and apoptosis experiments. For in vivo studies, a tumor-bearing mouse model was established using human liver cancer HepG2 cells to observe the antitumor effects. Finally, the primary organs of each group of tumor-bearing mice were assessed for in vivo safety.

RESULTS

ESI-MS and 1H NMR confirmed the accurate structure of Ru complexes and alloc-RH 110. The Ru complexes achieved full catalytic conversion of alloc-RH 110 within 24 hours. EVs and EVs@Ru exhibited particle sizes of ∼116.85 nm and ∼281.88 nm, respectively, with Zeta potentials of ∼-20.86 mV and ∼-25.89 mV, both appearing quasi-circular under TEM. WB analysis verified the presence of vesicle-specific marker proteins in both, confirming their cell-derived nature. ICP-MS determined a drug loading of 21.90 μg/mL for EVs@Ru, with an encapsulation efficiency of ∼24.86%. Fluorescence spectrophotometry demonstrated 100% catalytic efficiency for EVs@Ru. Synthetic alloc-DOX validated by 1H NMR and ESI-MS matched literature data. MTT and CCK-8 assays confirmed low toxicity for alloc-DOX and Ru complexes, setting the experimental drug concentration at 4μM. In vitro, the EVs@Ru+alloc-DOX group exhibited potent HepG2 cell killing and apoptosis. In vivo, this group significantly inhibited tumor growth in tumor-bearing mice, with no observed toxicity to vital organs, indicating good biosafety.

CONCLUSION

The integration of bio-derived microvesicles (MVs) with transition metal catalysts has resulted in a biologically orthogonal system for efficient Ru complex delivery to tumor sites. This system facilitates controlled release of the Ru complexes, enabling tumor cell elimination. This innovative strategy holds great promise for enhancing tumor immunity and targeted therapeutic approaches.

Identification of 5-(Aryl/Heteroaryl)amino-4-quinolones as Potent Membrane-Disrupting Agents to Combat Antibiotic-Resistant Gram-Positive Bacteria

Nosocomial infections caused by resistant Gram-positive organisms are on the rise, presumably due to a combination of factors including prolonged hospital exposure, increased use of invasive procedures, and pervasive antibiotic therapy. Although antibiotic stewardship and infection control measures are helpful, newer agents against multidrug-resistant (MDR) Gram-positive bacteria are urgently needed. Here, we describe our efforts that led to the identification of 5-amino-4-quinolone 111 with exceptionally potent Gram-positive activity with minimum inhibitory concentrations (MICs) ≤0.06 μg/mL against numerous clinical isolates. Preliminary mechanism of action and resistance studies demonstrate that the 5-amino-4-quinolones are bacteriostatic, do not select for resistance, and selectively disrupt bacterial membranes. While the precise molecular mechanism has not been elucidated, the lead compound is nontoxic displaying a therapeutic index greater than 500, is devoid of hemolytic activity, and has attractive physicochemical properties (clog P = 3.8, molecular weight (MW) = 441) that warrant further investigation of this promising antibacterial scaffold for the treatment of Gram-positive infections.

Ionic Reactivity of 2-Isocyanoaryl Thioethers: Access to 2-Halo and 2-Aminobenzothia/Selenazoles

An ionic cascade insertion/cyclization reaction of thia-/selena-functionalized arylisocyanides has been successfully developed for the efficient and practical synthesis of 2-halobenzothiazole/benzoselenazole derivatives. This synthetic protocol, incorporating a halogen atom when forming the five-membered ring of benzothia/selenazoles, is different from the existing ones, where halogenation of the preformed benzothia/selenazole precursors happens. Additionally, a facile access to 2-aminobenzothiazoles is also achieved by the one-pot cascade reaction of 2-isocyanoaryl thioethers, iodine, and amines.

Activated carbon/Brønsted acid-promoted aerobic benzylic oxidation under "on-water" condition: Green and efficient synthesis of 3-benzoylquinoxalinones as potent tubulin inhibitors

Green chemistry is becoming the favored approach to preparing drug molecules in pharmaceutical industry. Herein, we developed a clean and efficient method to synthesize 3-benzoylquinoxalines via activated carbon promoted aerobic benzylic oxidation under "on-water" condition. Moreover, biological studies with this class of compounds reveal an antiproliferative profile. Further structure modifications are performed and the investigations exhibited that the most active 12a could inhibit the microtubule polymerization by binding to tubulin and thus induce multipolar mitosis, G2/M phase arrest, and apoptosis of cancer cells. In addition, molecular docking studies allow the rationalization of the pharmacodynamic properties observed. Our systematic studies provide not only guidance for applications of O₂/AC/H₂O system, but also a new scaffold targeting tubulin for antitumor agent discovery.

Transition metal catalysis in the mitochondria of living cells

The development of transition metal catalysts capable of promoting non-natural transformations within living cells can open significant new avenues in chemical and cell biology. Unfortunately, the complexity of the cell makes it extremely difficult to translate standard organometallic chemistry to living environments. Therefore, progress in this field has been very slow, and many challenges, including the possibility of localizing active metal catalysts into specific subcellular sites or organelles, remain to be addressed. Herein, we report a designed ruthenium complex that accumulates preferentially inside the mitochondria of mammalian cells, while keeping its ability to react with exogenous substrates in a bioorthogonal way. Importantly, we show that the subcellular catalytic activity can be used for the confined release of fluorophores, and even allows selective functional alterations in the mitochondria by the localized transformation of inert precursors into uncouplers of the membrane potential.

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.

Recent advance in heterocyclic organozinc and organomanganese compounds; direct synthetic routes and application in organic synthesis

A practical synthetic route for the preparation of 2-pyridyl and 3-pyridyl derivatives has been accomplished by utilizing a simple coupling reaction of stable 2-pyridylzinc bromides and 3-pyridylzinc bromides. The organozincs used in this study were easily prepared via the direct insertion of active zinc into the corresponding bromopyridines. The subsequent coupling reactions with a variety of different electrophiles have afforded the corresponding coupling products. Using highly active manganese, a variety of Grignard-type organomanganese reagents have been obtained. The subsequent coupling reactions of the resulting organomanganese reagents with several electrophiles have also been accomplished under mild conditions.

Discovery of a long-acting, peripherally selective inhibitor of catechol-O-methyltransferase

Novel nitrocatechol-substituted heterocycles were designed and evaluated for their ability to inhibit catechol-O-methyltransferase (COMT). Replacement of the pyrazole core of the initial hit 4 with a 1,2,4-oxadiazole ring resulted in a series of compounds endowed with longer duration of COMT inhibition. Incorporation of a pyridine N-oxide residue at position 3 of the 1,2,4-oxadiazole ring led to analogue 37f, which was found to possess activity comparable to entacapone and lower toxicity in comparison to tolcapone. Lead structure 37f was systematically modified in order to improve selectivity and duration of COMT inhibition as well as to minimize toxicity. Oxadiazole 37d (2,5-dichloro-3-(5-(3,4-dihydroxy-5-nitrophenyl)-1,2,4-oxadiazol-3-yl)-4,6-dimethylpyridine 1-oxide (BIA 9-1067)) was identified as a long-acting, purely peripheral inhibitor, which is currently under clinical evaluation as an adjunct to L-Dopa therapy of Parkinson's disease.

Catalytic chain-breaking pyridinol antioxidants

The synthesis of 3-pyridinols carrying alkyltelluro, alkylseleno, and alkylthio groups is described together with a detailed kinetic, thermodynamic, and mechanistic study of their antioxidant activity. When assayed for their capacity to inhibit azo-initiated peroxidation of linoleic acid in a water/chlorobenzene two-phase system, tellurium-containing 3-pyridinols were readily regenerable by N-acetylcysteine contained in the aqueous phase. The best inhibitors quenched peroxyl radicals more efficiently than alpha-tocopherol, and the duration of inhibition was limited only by the availability of the thiol reducing agent. In homogeneous phase, inhibition of styrene autoxidation absolute rate constants k(inh) for quenching of peroxyl radical were as large as 1 x 10(7) M(-1) s(-1), thus outperforming the best phenolic antioxidants including alpha-tocopherol. Tellurium-containing 3-pyridinols could be quantitatively regenerated in homogeneous phase by N-tert-butoxycarbonyl cysteine methyl ester, a lipid-soluble analogue of N-acetylcysteine. In the presence of an excess of the thiol, a catalytic mode of action was observed, similar to the one in the two-phase system. Overall, compounds bearing the alkyltelluro moiety ortho to the OH group were much more effective antioxidants than the corresponding para isomers. The origin of the high reactivity of these compounds was explored using pulse-radiolysis thermodynamic measurements, and a mechanism for their unusual antioxidant activity was proposed. The tellurium-containing 3-pyridinols were also found to catalyze reduction of hydrogen peroxide in the presence of thiol reducing agents, thereby acting as multifunctional (preventive and chain-breaking) catalytic antioxidants.

Synthesis of gerfelin and related analogous compounds

Gerfelin, an inhibitor of human geranylgeranyl diphosphate (GGPP) synthase that has been isolated from a culture broth of Beauveria felina QN22047, was synthesized in 4 and 3 steps starting from 2,4-dihydroxy-6-methylbenzoic acid and 3,4,5-trihydroxytoluene, respectively. An effective ligand, 2-(di-tert-butylphosphino)biphenyl, was used in the palladium-catalyzed diaryl ether-forming reaction. Five analogous compounds of gerfelin were also synthesized for a study of the structure-activity relationship.

Ruthenium-Catalyzed Asymmetric Epoxidation of Olefins Using H2O2, Part I: Synthesis of New ChiralN,N,N-Tridentate Pybox and Pyboxazine Ligands and Their Ruthenium Complexes

The synthesis of chiral tridentate N,N,N-pyridine-2,6-bisoxazolines 3 (pybox ligands) and N,N,N-pyridine-2,6-bisoxazines 4 (pyboxazine ligands) is described in detail. These novel ligands constitute a useful toolbox for the application in asymmetric catalysis. Compounds 3 and 4 are conveniently prepared by cyclization of enantiomerically pure alpha- or beta-amino alcohols with dimethyl pyridine-2,6-dicarboximidate. The corresponding ruthenium complexes are efficient asymmetric epoxidation catalysts and have been prepared in good yield and fully characterized by spectroscopic means. Four of these ruthenium complexes have been characterized by X-ray crystallography. For the first time the molecular structure of a pyboxazine complex [2,6-bis-[(4S)-4-phenyl-5,6-dihydro-4H-[1,3]oxazinyl]pyridine](pyridine-2,6-dicarboxylate)ruthenium (S)-2 aa, is presented.