Structural influences on the oxidation of a series of 2-benzothiazoline analogs

A Reactivity-Based 18F-Labeled Probe for PET Imaging of Oxidative Stress in Chemotherapy-Induced Cardiotoxicity

Oxidative stress underlies the pathology of many human diseases, including the doxorubicin-induced off-target cardiotoxicity in cancer chemotherapies. Since current diagnostic procedures are only capable of monitoring cardiac function, a noninvasive means of detecting biochemical changes in redox status prior to irreversible functional changes is highly desirable for both early diagnosis and prognosis. We designed a novel ¹⁸F-labeled molecular probe, ¹⁸F-FPBT, for the direct detection of superoxide in vivo using positron emission tomography (PET). ¹⁸F-FPBT was radiosynthesized in one step by nucleophilic radiofluorination. In vitro, ¹⁸F-FPBT showed rapid and selective oxidation by superoxide (around 60% in 5 min) compared to other physiological ROS. In healthy mice and rats, ¹⁸F-FBPT is distributed to all major organs in the first few minutes post injection and is rapidly cleared via both renal and hepatobiliary routes with minimal background retention in the heart. In a rat model of doxorubicin-induced cardiotoxicity, ¹⁸F-FBPT showed significantly higher (P < 0.05) uptake in the hearts of treated animals compared to healthy controls. These results warrant further optimization of ¹⁸F-FBPT for clinical translation.

Lewis acid-promoted formation of benzoselenazole derivatives using SeO2 as a selenium source

A new one-pot method of using both ortho-inactivated anilines and acetophenones (or methylquinolines) which possess an active H in the α-position of ketones (or benzyl positions) as starting materials to make benzoselenazole derivatives has been developed, which uses SeO2 as a selenium agent. This method first establishes SeO2 as a source of selenium to form benzoselenazole derivatives, which enriches the synthesis method of benzoselenazole. This method has several advantages, including good yields, simple operation, and availability of raw materials. Furthermore, the reaction could be easily scaled and its practical value in organic synthesis is displayed.

1,2-Disubstituted Benzimidazoles by the Iron Catalyzed Cross-Dehydrogenative Coupling of Isomeric o-Phenylenediamine Substrates

Benzimidazoles are common in nature, medicines, and materials. Numerous strategies for preparing 2-arylbenzimidazoles exist. In this work, 1,2-disubstituted benzimidazoles were prepared from various mono- and disubstituted ortho-phenylenediamines (OPD) by iron-catalyzed oxidative coupling. Specifically, O₂ and FeCl₃·6H₂O catalyzed the cross-dehydrogenative coupling and aromatization of diarylmethyl and dialkyl benzimidazole precursors. N,N'-Disubstituted-OPD substrates were significantly more reactive than their N,N-disubstituted isomers, which appears to be relative to their propensity for complexation and charge transfer with Fe³⁺. The reaction also converted N-monosubstituted OPD substrates to 2-substituted benzimidazoles; however, electron-poor substrates produce 1,2-disubstituted benzimidazoles by intermolecular imino-transfer. Kinetic, reagent, and spectroscopic (UV-vis and EPR) studies suggest a mechanism involving metal-substrate complexation, charge transfer, and aerobic turnover, involving high-valent Fe(IV) intermediates. Overall, comparative strategies for the relatively sustainable and efficient synthesis of 1,2-disubstituted benzimidazoles are demonstrated.

Effects of Thiolate Ligation in Monoiron Hydrogenase (Hmd): Stability of the {Fe(CO)2}2+ Core with NNS Ligands

In this work, we report the effects of NNS-thiolate ligands and nuclearity (monomer, dimer) on the stability of iron complexes related to the active site of monoiron hydrogenase (Hmd). A thermally stable iron(II) dicarbonyl motif is the core feature of the active site, but the coordination features that lead to this property have not been independently evaluated for their contributions to the {Fe(CO)₂}²⁺ stability. As such, non-bulky and bulky benzothiazoline ligands (thiolate precursors) were synthesized and their iron(II) complexes characterized. The use of non-bulky thiolate ligands and low-temperature crystallizations result in isolation of the dimeric species [(NNS)₂Fe₂(CO)₂(I)₂] (1), [(N^PhNS)₂Fe₂(CO)₂(I)₂] (2), and [(^MeNNS)₂Fe₂(CO)₂(I)₂] (3), which exhibit dimerization via thiolato (μ₂-S)₂ bridges. In one particular case (unsubstituted NNS ligand), the pathway of decarbonylation and oxidation from 1 was crystallographically elucidated, via isolation of the half-bis-ligated monocarbonyl dimer [(NNS)₃Fe₂(CO)]I (4) and the fully decarbonylated and oxidized mononuclear [(NNS)₂Fe]I (5). The transformations of dicarbonyl complexes (1, 2, and 3) to monocarbonyl complexes (4, 6, and 7) were monitored by UV/vis, demonstrating that 1 and 3 exhibit longer t_1/2 (80 and 75 min, respectively) than 2 (30 min), which is attributed to distortion of the ligand backbone. Density functional theory calculations of isolated complexes and putative intermediates were used to corroborate the experimentally observed IR spectra. Finally, dimerization was prevented using a bulky ligand featuring a 2,6-dimethylphenyl substituent, which affords mononuclear iron dicarbonyl complex, [(N^PhNS^DMPh)Fe(CO)₂Br] (8), identified by IR and NMR spectroscopies. The dicarbonyl complex decomposes to the decarbonylated [(N^PhNS^DMPh)₂Fe] (9) within minutes at room temperature. Overall, the work herein demonstrates that the thiolate moiety does not impart thermal stability to the {Fe(CO)₂}²⁺ unit formed in the active site, further indicating the importance of the organometallic Fe-C(acyl) bond in the enzyme.

4-(Benzo[d]thiazol-2-yl)-N,N-dimethylaniline

The whole molecule of the title compound, C15H14N2S, is approximately planar, with an r.m.s. deviation of 0.0382 Å from the best-fit mean plane through all 18 non-H atoms. In the crystal, dimers form through π–π stacking interactions between the benzene rings of adjacent benzothiazole ring systems, with a centroid–centroid separation of 3.6834 (16) Å.

Click with a boronic acid handle: a neighboring group-assisted click reaction that allows ready secondary functionalization

The feasibility of a neighboring boronic acid-facilitated facile condensation of an aldehyde is described. This reaction is bio-orthogonal, complete at room temperature within minutes, and suitable for bioconjugation chemistry. The boronic acid group serves the dual purpose of catalyzing the condensation reaction and being a handle for secondary functionalization.

Synthesis and properties of arsenic(III)-reactive coumarin-appended benzothiazolines: a new approach for inorganic arsenic detection

The EPA has established a maximum contaminant level (MCL) of 10 ppb for arsenic (As) in drinking water requiring sensitive and selective detection methodologies. To tackle this challenge, we have been active in constructing small molecules that react specifically with As(3+) to furnish a new fluorescent species (termed a chemodosimeter). We report in this contribution, the synthesis and spectroscopy of two small-molecule fluorescent probes that we term ArsenoFluors (or AFs) as As-specific chemodosimeters. The AFs (AF1 and AF2) incorporate a coumarin fluorescent reporter coupled with an As-reactive benzothiazoline functional group. AFs react with As(3+) to yield the highly fluorescent coumarin-6 dye (C6) resulting in a 20-25-fold fluorescence enhancement at λem ∼ 500 nm with detection limits of 0.14-0.23 ppb in tetrahydrofuran (THF) at 298 K. The AFs also react with common environmental As(3+) sources such as sodium arsenite in a THF/CHES (N-cyclohexyl-2-aminoethanesulfonic acid) (1:1, pH 9, 298 K) mixture resulting in a modest fluorescence turn-ON (1.5- to 3-fold) due to the quenched nature of coumarin-6 derivatives in high polarity solvents. Bulk analysis of the reaction of the AFs with As(3+) revealed that the C6 derivatives and the Schiff-base disulfide of the AFs (SB1 and SB2) are the ultimate end-products of this chemistry with the formation of C6 being the principle photoproduct responsible for the As(3+)-specific turn-ON. It appears that a likely species that is traversed in the reaction path is an As-hydride-ligand complex that is a putative intermediate in the proposed reaction path.