[(NHC)Pd(OAc)2]: Highly Active Carboxylate Pd(II)-NHC (NHC = N-Heterocyclic Carbene) Precatalysts for Suzuki-Miyaura and Buchwald-Hartwig Cross-Coupling of Amides by N-C(O) Activation.

In the past eight years, the selective cross-coupling of amides by N-C(O) bond activation has emerged as a highly attractive manifold for the manipulation of traditionally unreactive amide bonds. In this Special Issue on Next-Generation Cross-Coupling Chemistry, we report the Suzuki-Miyaura and Buchwald-Hartwig cross-coupling of amides by selective N-C(O) cleavage catalyzed by bench-stable, well-defined carboxylate Pd(II)-NHC (NHC = N-heterocyclic carbene) catalysts {[(NHC)Pd(O2CR)2]}. This class of Pd(II)-NHCs promotes cross-coupling under exceedingly mild room-temperature conditions owing to the facile dissociation of the carboxylate ligands to form the active complex. These readily accessible Pd(II)-NHC precatalysts show excellent functional group tolerance and are compatible with a broad range of amide activating groups. Considering the mild conditions for the cross-coupling and the facile access to carboxylate Pd(II)-NHC complexes, we anticipate that this class of bench-stable complexes will find wide application in the activation of amide N-C(O) and related acyl X-C(O) bonds.

Wingtip-Flexible N-Heterocyclic Carbenes: Unsymmetrical Connection between IMes and IPr.

IMes (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and IPr (IPr=1,3- bis(2,6-diisopropylphenyl)imidazol-2-ylidene) represent by far the most frequently used N-heterocyclic carbene ligands in homogeneous catalysis, however, despite numerous advantages, these ligands are limited by the lack of steric flexibility of catalytic pockets. We report a new class of unique unsymmetrical N-heterocyclic carbene ligands that are characterized by freely-rotatable N-aromatic wingtips in the imidazol-2-ylidene architecture. The combination of rotatable N-CH2 Ar bond with conformationally-fixed N-Ar linkage results in a highly modular ligand topology, entering the range of geometries inaccessible to IMes and IPr. These ligands are highly reactive in Cu(I)-catalyzed ß-hydroboration, an archetypal borylcupration process that has had a transformative impact on the synthesis of boron-containing compounds. The most reactive Cu(I)-NHC in this class has been commercialized in collaboration with MilliporeSigma to enable broad access of the synthetic chemistry community. The ligands gradually cover %Vbur geometries ranging from 37.3 % to 52.7 %, with the latter representing the largest %Vbur described for an IPr analogue, while retaining full flexibility of N-wingtip. Considering the modular access to novel geometrical space in N-heterocyclic carbene catalysis, we anticipate that this concept will enable new opportunities in organic synthesis, drug discovery and stabilization of reactive metal centers.

Ag-NHC Complexes in the π-Activation of Alkynes.

Silver-NHC (NHC = N-heterocyclic carbene) complexes play a special role in the field of transition-metal complexes due to (1) their prominent biological activity, and (2) their critical role as transfer reagents for the synthesis of metal-NHC complexes by transmetalation. However, the application of silver-NHCs in catalysis is underdeveloped, particularly when compared to their group 11 counterparts, gold-NHCs (Au-NHC) and copper-NHCs (Cu-NHC). In this Special Issue on Featured Reviews in Organometallic Chemistry, we present a comprehensive overview of the application of silver-NHC complexes in the p-activation of alkynes. The functionalization of alkynes is one of the most important processes in chemistry, and it is at the bedrock of organic synthesis. Recent studies show the significant promise of silver-NHC complexes as unique and highly selective catalysts in this class of reactions. The review covers p-activation reactions catalyzed by Ag-NHCs since 2005 (the first example of p-activation in catalysis by Ag-NHCs) through December 2022. The review focuses on the structure of NHC ligands and p-functionalization methods, covering the following broadly defined topics: (1) intramolecular cyclizations; (2) CO2 fixation; and (3) hydrofunctionalization reactions. By discussing the role of Ag-NHC complexes in the p-functionalization of alkynes, the reader is provided with an overview of this important area of research and the role of Ag-NHCs to promote reactions that are beyond other group 11 metal-NHC complexes.

L-Shaped Heterobidentate Imidazo[1,5-a]pyridin-3-ylidene (N,C)-Ligands for Oxidant-Free AuI /AuIII Catalysis.

In the last decade, major advances have been made in homogeneous gold catalysis. However, AuI /AuIII catalytic cycle remains much less explored due to the reluctance of AuI to undergo oxidative addition and the stability of the AuIII intermediate. Herein, we report activation of aryl halides at gold(I) enabled by NHC (NHC=N-heterocyclic carbene) ligands through the development of a new class of L-shaped heterobidentate ImPy (ImPy=imidazo[1,5-a]pyridin-3-ylidene) N,C ligands that feature hemilabile character of the amino group in combination with strong σ-donation of the carbene center in a rigid conformation, imposed by the ligand architecture. Detailed characterization and control studies reveal key ligand features for AuI /AuIII redox cycle, wherein the hemilabile nitrogen is placed at the coordinating position of a rigid framework. Given the tremendous significance of homogeneous gold catalysis, we anticipate that this ligand platform will find widespread application.

Bimetallic Cooperative Catalysis for Decarbonylative Heteroarylation of Carboxylic Acids via C-O/C-H Coupling.

Cooperative bimetallic catalysis is a fundamental approach in modern synthetic chemistry. We report bimetallic cooperative catalysis for the direct decarbonylative heteroarylation of ubiquitous carboxylic acids via acyl C-O/C-H coupling. This novel catalytic system exploits the cooperative action of a copper catalyst and a palladium catalyst in decarbonylation, which enables highly chemoselective synthesis of important heterobiaryl motifs through the coupling of carboxylic acids with heteroarenes in the absence of prefunctionalization or directing groups. This cooperative decarbonylative method uses common carboxylic acids and shows a remarkably broad substrate scope (>70 examples), including late-stage modification of pharmaceuticals and streamlined synthesis of bioactive agents. Extensive mechanistic and computational studies were conducted to gain insight into the mechanism of the reaction. The key step involves intersection of the two catalytic cycles via transmetallation of the copper-aryl species with the palladium(II) intermediate generated by oxidative addition/decarbonylation.

A Smart Fluorescent Probe for NO Detection and Application in Myocardial Fibrosis Imaging.

On the basis of the pyridazinone scaffold and photoinduced electron transfer (PET) mechanism, we designed a smart nitric oxide (NO) probe, PYSNO, with high sensitivity and selectivity. PYSNO exhibited a rapid response to both exogenous and endogenous NO. This probe can also be used in tracking and investigating NO generation in animal tissue. In the myocardial fibrosis model for mice, PYSNO exhibited a powerful imaging property in vivo as a result of unravelling the progressive relationship between the generation of myocardial NO and the occurrence of myocardial fibrosis.

Revelation of the dynamic progression of hypoxia-reoxygenation injury by visualization of the lysosomal hydrogen peroxide.

Hydrogen peroxide (H2O2) plays an important role in pathological conditions, such as cerebral ischemia-reperfusion (I-R) injury. Fluorescent probes may serve as valuable tools to detect the amount, temporal and spatial distribution of H2O2 in living cells. To investigate the role of lysosomal H2O2 involved in cerebral I-R injury, we designed and synthesized a lysosome-targetable two-photon fluorescent probe ztl-4, through expansion and substitution of the original pyridazinone scaffold, conjugation of electronic-donating aromatic ring and precise terminal modification of the alkyl linker. The probe ztl-4 exhibited fast, sensitive and highly selective response toward H2O2. ztl-4 could image exogenous H2O2 in SH-SY5Y cells and brain slices. In addition, ztl-4 was located in lysosomes with high colocalization coefficient compared with LysoTracker. ztl-4 was further applied for detecting the endogenous generation of H2O2 in SH-SY5Y cells subjected to oxygen and glucose deprivation (OGD) or OGD/reoxygenation (OGD/R) injury. Both OGD- and OGD/R-induced cell injury caused a time-dependent increase of H2O2 production within lysosomes. Moreover, OGD/R-treated cells showed much more amount of H2O2 than OGD-treated cells, indicating that reoxygenation will promote H2O2 accumulation in lysosomes of post-hypoxia cells. Therefore, the probe is suitable for monitoring the dynamic changes of lysosomal H2O2 in cells.

Discovery of a cobalt complex with high MEK1 binding affinity.

A series of Schiff base ligands (L1-L5) and their cobalt(II) complexes (1-5) were designed and synthesized for MEK1 binding experiment. The biological evaluation results showed that Bis(N,N'-disalicylidene)-3,4-phenylenediamine-cobalt(II) 1 and Bis(N,N'-disalicylidene)-1,2-cyclohexanediamine-cobalt(II) 2 are much more effective than the parent Schiff bases (L1 and L2). Importantly, 2 exhibited MEK1 binding affinity with IC5071nM, which is so far the best result for metal complexes and more potent than U0126 (7.02µM) and AZD6244 (2.20µM). Docking study was used to elucidate the binding modes of complex 2 with MEK1. Thus cobalt(II) complex 2 may be further developed as a novel MEK1 inhibitor.

[Effect of Bushen Qiangdu Recipe on Histomorphology and Wnt Pathway of DBA/1 Mice].

Objective To observe the effect of Bushen Qiangdu Recipe (BQR) on the entheses ossification histomorphology of articular ligament of DBA/1 mice with spontaneous ankylosing spondylitis (AS) , and to study its mechanism for prevention and treatment of AS. Methods Thirty 12-week old male DBA/1 mice were randomly divided into the model group, the positive drug group, low, medium, high dose BQR groups, 6 in each group. Another 6 C57BLE mice of the same age were recruited as a blank control group. BQR containing 11. 25, 22. 50, 45.00 g/kg crude drugs was respectively adminis- tered to mice in low, medium, high dose BQR groups by gastrogavage, 0. 2 mL for each mouse, once per day. Celecoxib Capsule (0. 2 mL/0. 8 mg for each mouse, once per day) was administered to mice in the positive drug group by gastrogavage. Equal volume of normal saline was administered to mice in the model group and the blank control group by gastrogavage. All mice were fed and intragastically adminis- tered for 12 successive weeks. Body weight, diet, stools, and hair were routinely observed. Signs of ar- thritis were evaluated once per two weeks. Mice were sacrifice, and then general observation of achilles tendon was performed. The achilles tendon tissue was HE stained. Protein expressions of alkaline phos- phatase (ALP) , bone gamma-carboxyglutamic-acid-containing proteins (BGP) , Dickkopfl (DKK1) , and Wnt5a in the achilles tendon were detected using immunohistochemical method. Results Compared with the blank control group, the scoring of arthritis obviously increased in the model group (P <0. 05). But the scoring of arthritis was obviously lower in the 3 BQR groups and the positive drug group than in the model group (P <0. 05). Histopathological results of achilles tendon tissue showed that no infiltration of inflammatory cells or fibroblasts occurred in the normal group. Their histomorphological structures were normal. Cartilage formation and bone formation at various degrees occurred in the model group. Filtration of fibroblast-like cells occurred in inflammatory cells and attachment points. Scattered lymphocyte infiltra- tion was often seen in the achilles tendon tissue of each medicated group. Cartilage formation and bone formation were rarely seen. Compared with the blank control group, the scoring of arthritis increased in the model group (P <0. 05). Compared with the model group, the scoring of arthritis was decreased in the 3 BQR groups and the positive drug group (P <0. 05). Compared with the blank control group, protein expression of DKK1 decreased and protein expression of Wnt5a increased in the model group (P <0. 05). Compared with the model group, protein expression of DKK1 increased and protein expression of Wnt5a decreased in middle and high dose BQR groups (P <0. 05). Conclusion BQR could delay the occur- rence and development of arthritis and ossification in DBA/1 mice of spontaneous AS model possibly by inhibiting classical Wnt pathway.

Rational Design of Fluorescent Phthalazinone Derivatives for One- and Two-Photon Imaging.

Phthalazinone derivatives were designed as optical probes for one- and two-photon fluorescence microscopy imaging. The design strategy involves stepwise extension and modification of pyridazinone by 1) expansion of pyridazinone to phthalazinone, a larger conjugated system, as the electron acceptor, 2) coupling of electron-donating aromatic groups such as N,N-diethylaminophenyl, thienyl, naphthyl, and quinolyl to the phthalazinone, and 3) anchoring of an alkyl chain to the phthalazinone with various terminal substituents such as triphenylphosphonio, morpholino, triethylammonio, N-methylimidazolio, pyrrolidino, and piperidino. Theoretical calculations were utilized to verify the initial design. The desired fluorescent probes were synthesized by two different routes in considerable yields. Twenty-two phthalazinone derivatives were synthesized and their photophysical properties were measured. Selected compounds were applied in cell imaging, and valuable information was obtained. Furthermore, the designed compounds showed excellent performance in two-photon microscopic imaging of mouse brain slices.

Discovery of a potent and highly specific ß2 proteasome inhibitor from a library of copper complexes.

We reported the synthesis, characterization and biological activity of several copper(II) Schiff base complexes, which exhibit high proteasome inhibitory activities with particular selectivity of ß2 subunit. Structure-activity relationships information obtained from complex Na2[Cu(a4s1)] demonstrated that distinct bonding modes in ß2 and ß5 subunits determines its selectivity and potent inhibition for ß2 subunit.

Carboxylic-Phosphoric Anhydrides as Direct Electrophiles for Decarbonylative Hirao Cross-Coupling of Carboxylic Acids: DFT Investigation of Mechanistic Pathway.

In this anniversary issue, we present a DFT study of the mechanism of decarbonylative Hirao cross-coupling of carboxylic-phosphoric anhydrides to afford aryl phosphonates. Traditionally, the direct activation of carboxylic acids to participate in decarbonylative couplings is performed in the presence of carboxylic acid anhydride activators. We discovered that direct dehydrogenative decarbonylative phosphorylation of benzoic acid can be performed in high yield via dehydrogenative and decarbonylative coupling in the presence of phosphite as dual activating and nucleophilic reagent, enabling direct decarbonylative phosphorylation. Control studies demonstrated that carboxylic-phosphoric anhydride (acyl phosphate) is an intermediate in this process. DFT studies were conducted to gain insight into this decarbonylative process and compare the selectivity of C-O and P-O bond activations. Considering the utility of ubiquitous carboxylic acids, this alternative activation pathway may find applications in decarbonylative coupling of carboxylic acids for the synthesis of valuable molecules in organic synthesis.

Shengjie Tongyu Granule Inhibits Vascular Remodeling in ApoE-Gene-Knockout Mice.

The aim of the present paper was to investigate the effect of Shengjie Tongyu granule on vascular remodeling in atherosclerotic mice and the relevant underlying mechanism. Sixty male ApoE-gene-knockout mice, fed a high-fat diet from 6 weeks of age, were randomized into a Shengjie Tongyu granule group (4.00 g/kg/d), a simvastatin group (9.01 mg/kg/d), and a control group (normal saline: 0.2 mL/d). At the ages of 30 and 40 weeks, we sacrificed the mice for various measurements. The results show that treatment with Shengjie Tongyu granule and simvastatin significantly decreased lumen and plaque areas in the aortic root at 30 and 40 weeks of age, decreased grade II elastic fiber lesions in the ascending aorta at 30 weeks of age, and decreased both grade II and III lesions at 40 weeks of age, compared to controls. The content of superoxide anions, and expression of MOMA-2, plasma ICAM-1, and NFκB p50 in 30- and 40-week-old mice in the Shengjie Tongyu granule and simvastatin groups were also significantly reduced compared to the control group. In conclusion, Shengjie Tongyu granule has a clear inhibitory effect on vascular remodeling and on inflammatory pathways in ApoE-gene-knockout mice.

[Mechanism of p38 mitogen-activated protein kinase inhibitor SB203580 to glucocorticoid sensitivity].

OBJECTIVE: To establish a model of cigarette smoke exposure to asthmatic rats and glucocorticoid resistance induced by nicotine in alveolar epithelioid cells A549 and study the mechanism for the change of glucocorticoid sensitivity induced by p38 mitogen-activated protein kinase (p38 MAPK) inhibitor SB203580. METHODS: Sixty Wistar rats were randomly divided into 4 groups: normal group, asthmatic group, cigarette smoke exposure to asthmatic group and SB203580 group. The mRNA expressions of glucocorticoid receptor (GR), heat shock protein 90 (HSP90) and p38 MAPK were detected by real time-polymerase chain reaction (RT-PCR) while their protein expressions detected by Western blot in vivo. A549 cells were divided averagely into 4 groups: group A: normal; group B: 1 µmol/L dexamethasone (DEX); group C: 1 µmol/L DEX +1 µmol/L nicotine; group D: 1 µmol/L DEX +1 µmol/L nicotine+1 µmol/L SB203580. Immunofluorescence staining was used to study the in vitro colocalization of glucocorticoid receptor (GR) in A549 cells. RESULTS: The mRNA expression of GR was 0.671 ± 0.002 in cigarette smoke exposure to asthmatic group and 0.595 ± 0.061 in SB203580 group (P = 0.065). The protein expression of GR was 0.700 ± 0.033 in cigarette smoke exposure to asthmatic group and 0.628 ± 0.091 in SB203580 group (P = 0.148). The mRNA expression of HSP90 was 0.558 ± 0.009 in cigarette smoke exposure to asthmatic group and 0.377 ± 0.046 in SB203580 group (P = 0.000). The protein expression of HSP90 was 0.507 ± 0.030 in cigarette smoke exposure to asthmatic group and 0.402 ± 0.050 in SB203580 group (P = 0.005). The mRNA expression of p38 MAPK was 0.971 ± 0.012 in cigarette smoke exposure to asthmatic group and 0.278 ± 0.049 in SB203580 group (P = 0.000). The protein expression of p38 MAPK was 0.982 ± 0.038 in cigarette smoke exposure to asthmatic group and 0.338 ± 0.042 in SB203580 group (P = 0.000). The ratio of GR amount within A549 nucleus versus that in cytoplasm was 0.077 ± 0.047 in group C and 0.592 ± 0.249 in group D (P = 0.000). CONCLUSION: The mechanism of SB203580 enhancing the corticosteroid sensitivity may be improving nuclear translocation of GR to elevate corticosteroid sensitivity.

[Aortic artery elastic lamina degradation, collagen remodeling, oxides stress and inflammation in the apolipoprotein E deficient mice with or without aortic banding].

OBJECTIVE: To explore the elastic lamina degradation and the collagen remodeling of aortic artery as well as oxides stress and inflammation of the apolipoprotein (Apo E) deficient mice with or without experimental hypertension. METHODS: Eighty male Apo E deficient mice were fed with high-fat diet beginning at six weeks of age. At 8-week old, they were randomly divided into hypertension group and control group (n=40 each), the mice in hypertension group were subjected the suprarenal aortic constriction operation and then randomly divided into two subgroups: 15 weeks age and 30 weeks age groups. At the end of experiment, the vascular elastic lamina degradation and the content of collagen were determined by morphological method, plasma ICAM-1 level was measured by ELISA, and the rennin activity measured by radioimmunoassay, the superoxide anion detected by fluorescence, the MOMA-2 observed by immunofluorescence in all animals. mRNA expression of NF-κB P65 and MMP9 was detected by real-time PCR. RESULT: In 15-week old group, the elastic lamina degradation Grade II and the intima-media thickness in the hypertension group were significantly higher than in the control group [(5.4±3.3)% vs. (8.9±2.5)%, P<0.05; (98.66±18.90) µm vs. (70.08±11.71) µm, P<0.05]. In 30-week old group, the elastic lamina degradation Grade III, the III type of collagen and the intima-media thickness were also significantly higher than in the control group [(15.2±3.7)% vs. (8.1±3.3)%, P<0.01; (23.00±7.73)% vs. (11.00±3.82)%, P<0.05; (147.31±22.60) µm vs. (103.98±17.21) µm, P<0.01]. The level of ICAM-1 in hypertension group was significantly higher than that of control group in both 15-week old and in 30-week old mice [(46.3±3.7) µg/ml vs. (40.6±5.7) µg/ml, P<0.05; (56.0±3.1) µg/ml vs. (45.2±2.8) µg/ml, P<0.05]. The superoxide anion, the MOMA-2, mRNA expression of NF-κB P65 and MMP9 in the hypertension group were significantly higher than in the control group in both 15-week old and in the 30-week old mice. The increase in hypertension group was more pronounced in the 30-week old mice than in the 15-week old mice. CONCLUSION: The elastic lamina degradation and the collagen remodeling of aortic artery as well as oxides stress and inflammation are more significant in the Apo E deficient mice with hypertension than in control Apo E deficient mice.

CAAC-IPr*: easily accessible, highly sterically-hindered cyclic (alkyl)(amino)carbenes.

IPr* (IPr* = 1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) has emerged as a powerful highly hindered and sterically-flexible ligand platform for transition-metal catalysis. CAACs (CAAC = cyclic (al-kyl)(amino)carbenes) have gained major attention as strongly electron-rich carbon analogues of NHCs (NHC = N-heterocyclic carbene) with broad applications in both industry and academia. Herein, we report a merger of CAAC ligands with highly-hindered IPr*. The efficient synthesis, electronic characterization and application in model Cu-catalyzed hydroboration of alkynes is described. The ligands are strongly electron-rich, bulky and flexible around the N-Ar wingtip. The availability of various IPr* and CAAC templates offers a significant potential to expand the existing arsenal of NHC ligands to electron-rich bulky architectures with critical applications in metal stabilization and catalysis.

Well-Defined, Air- and Moisture-Stable Palladium-Imidazo[1,5-a]pyridin-3-ylidene Complexes: A Versatile Catalyst Platform for Cross-Coupling Reactions by L-Shaped NHC Ligands.

We describe the development of [(NHC)Pd(cinnamyl)Cl] complexes of ImPy (ImPy = imidazo[1,5-a]pyridin-3-ylidene) as a versatile class of precatalysts for cross-coupling reactions. These precatalysts feature fast activation to monoligated Pd(0) with 1:1 Pd to ligand ratio in a rigid imidazo[1,5-a]pyridin-3-ylidene template. Steric matching of the C5-substituent and N2-wingtip in the catalytic pocket of the catalyst framework led to the discovery of ImPyMesDipp as a highly reactive imidazo[1,5-a]pyridin-3-ylidene ligand for Pd-catalyzed cross-coupling of nitroarenes by challenging C-NO2 activation. Kinetic studies demonstrate fast activation and high reactivity of this class of well-defined ImPy-Pd catalysts. Structural studies provide full characteristics of this new class of imidazo[1,5-a]pyridin-3-ylidene ligands. Computational studies establish electronic properties of sterically-restricted imidazo[1,5-a]pyridin-3-ylidene ligands. Finally, a scalable synthesis of C5-substituted imidazo[1,5-a]pyridin-3-ylidene ligands through Ni-catalyzed Kumada cross-coupling is disclosed. The method obviates chromatographic purification at any of the steps, resulting in a facile and modular access to ImPy ligands. We anticipate that well-defined [Pd-ImPy] complexes will find broad utility in organic synthesis and catalysis for activation of unreactive bonds.

Suzuki-Miyaura Cross-Coupling of Esters by Selective O-C(O) Cleavage Mediated by Air- and Moisture-Stable [Pd(NHC)(µ-Cl)Cl]2 Precatalysts: Catalyst Evaluation and Mechanism.

The cross-coupling of aryl esters has emerged as a powerful platform for the functionalization of otherwise inert acyl C-O bonds in chemical synthesis and catalysis. Herein, we report a combined experimental and computational study on the acyl Suzuki-Miyaura cross-coupling of aryl esters mediated by well-defined, air- and moisture-stable Pd(II)-NHC precatalysts [Pd(NHC)(µ-Cl)Cl]2. We present a comprehensive evaluation of [Pd(NHC)(µ-Cl)Cl]2 precatalysts and compare them with the present state-of-the-art [(Pd(NHC)allyl] precatalysts bearing allyl-type throw-away ligands. Most importantly, the study reveals [Pd(NHC)(µ-Cl)Cl]2 as the most reactive precatalysts discovered to date in this reactivity manifold. The unique synthetic utility of this unconventional O-C(O) cross-coupling is highlighted in the late-stage functionalization of pharmaceuticals and sequential chemoselective cross-coupling, providing access to valuable ketone products by a catalytic mechanism involving Pd insertion into the aryl ester bond. Furthermore, we present a comprehensive study of the catalytic cycle by DFT methods. Considering the clear advantages of [Pd(NHC)(µ-Cl)Cl]2 precatalysts on several levels, including facile one-pot synthesis, superior atom-economic profile to all other Pd(II)-NHC catalysts, and versatile reactivity, these should be considered as the 'first-choice' catalysts for all routine applications in ester O-C(O) bond activation.

Pd-Catalyzed Double-Decarbonylative Aryl Sulfide Synthesis through Aryl Exchange between Amides and Thioesters.

We report the palladium-catalyzed double-decarbonylative synthesis of aryl thioethers by an aryl exchange reaction between amides and thioesters. In this method, amides serve as aryl donors and thioesters are sulfide donors, enabling the synthesis of valuable aryl sulfides. The use of Pd/Xantphos without any additives has been identified as the catalytic system promoting the aryl exchange by C(O)-N/C(O)-S cleavages. The method is amenable to a wide variety of amides and sulfides.

Early Diagnosis of Cerebral Ischemia Reperfusion Injury and Revelation of Its Regional Development by a H3R Receptor-Directed Probe.

In vivo imaging of cerebral hydrogen peroxide (H2O2) may facilitate early diagnosis of cerebral ischemia reperfusion injury (CIRI) and a revelation of its pathological progression. In this study, we report our rational design of a brain-targeting fluorescent probe using the basis of a pyridazinone scaffold. A structure-activity relationship study reveals that PCAB is the best candidate (Ki = 15.8 nM) for a histamine H3 receptor (H3R), which is highly expressed in neurons of the central nervous system. As a two-photon fluorescent probe, PCAB exhibits a fast, selective reaction toward both extra- and intracellular H2O2 in SH-SY5Y cells under oxygen glucose deprivation and resupply. In vivo fluorescent imaging of a middle cerebral artery occlusion mouse confirms that PCAB is an ultrasensitive probe with potent blood-brain barrier penetration, precise brain targeting, and fast detection of CIRI.