Synthetic Advances for Mechanistic Insights: Metal-Oxygen Intermediates with a Macrocyclic Pyridinophane System.

ConspectusMetalloenzymes, which are proteins containing earth-abundant transition-metal ions as cofactors in the active site, generate various metal-oxygen intermediates via activating a dioxygen molecule (O2) to mediate vital metabolic functions, such as the oxidative metabolism of xenobiotics and the biotransformation of naturally occurring molecules. By replicating the active sites of metalloenzymes, many bioinorganic chemists have studied the geometric and electronic properties and reactivities of model complexes to understand the nature of enzymatic intermediates and develop bioinspired metal catalysts. Among the reported model complexes, nonporphyrinic macrocyclic ligands are the predominant coordination system widely used in stabilizing and isolating diverse metal-oxygen intermediates, which allows us to extensively investigate the physicochemical characteristics of the analogs of reactive intermediates of metalloenzymes. In particular, it has been reported that the ring size of the macrocyclic ligands, defined by the number of atoms in the macrocyclic ring, drastically affects the identity of the metal-oxygen intermediate. Thus, systematic modification of the macrocyclic ligands has been a great subject being examined in various inorganic fields.In this Account, we describe synthetic advances of a macrocyclic ligand system by introducing pyridine donors into a 12-membered tetraazamacrocyclic ligand (12-TMC) that initially has 4 amine donors. Interestingly, the backbone of the pyridinophane ligand with 2 pyridine and 2 amine donors in a 12-membered ring is shown to be much more folded than in other macrocyclic ligands, thereby allowing the axial and equatorial donors to separately control the electronic structure of metal complexes. Then, we looked over independent electronic and steric effects on metal-oxygen species with thorough physicochemical analysis. The NiIII-peroxo complexes exhibit nucleophilic reactivity dependent on the steric hindrance of the second coordination sphere. Furthermore, the C-H bond strength of the second coordination sphere has also been an important factor in determining the stability of MnIV-bis(hydroxo) intermediates. Electronic tuning on CoIII-hydroperoxo intermediates results in a trend between the electron-donating abilities of para-substituents on pyridine in the pyridinophane ligand and electrophilic reactivities, from which mechanistic insights into the metal-hydroperoxo species have been gained. Importantly, the metal-oxygen intermediates supported by the pyridinophane ligand system have revealed quite challenging chemical reactions, including dioxygenase-like nitrile activation by CoIII-peroxo intermediates and the oxidation of aldehyde and aromatic compounds by manganese-oxygen intermediates. Based on the fine substitution of donors, we have addressed that those novel reactions originated from the unique framework of the pyridinophane system incorporating spin-crossover behavior and high redox potentials of the metal-oxygen intermediates. These results will be valuable for the structure-activity relationship of metal-oxygen intermediates, giving a better understanding on the enzymatic coordination system where amino acid ligands vary for specific chemical reactions.

Controlling Redox Potential of a Manganese(III)-Bis(hydroxo) Complex through Protonation and the Hydrogen-Atom Transfer Reactivity.

A series of mononuclear manganese(III)-hydroxo and -aqua complexes, [MnIII(TBDAP)(OH)2]+ (1), [MnIII(TBDAP)(OH)(OH2)]2+ (2) and [MnIII(TBDAP)(OH2)2]3+ (3), were prepared from a manganese(II) precursor and confirmed using various methods including X-ray crystallography. Thermodynamic analysis showed that protonation from hydroxo to aqua species resulted in increased redox potentials (E1/2) in the order of 1 (-0.15 V) < 2 (0.56 V) < 3 (1.11 V), while pKa values exhibited a reverse trend in the order of 3 (3.87) < 2 (11.84). Employing the Bordwell Equation, the O-H bond dissociation free energies (BDFE) of [MnII(TBDAP)(OH)(OH2)]+ and [MnII(TBDAP)(OH2)2]2+, related to the driving force of 1 and 2 in hydrogen atom transfer (HAT), were determined as 75.3 and 77.3 kcal mol-1, respectively. It was found that the thermodynamic driving force of 2 in HAT becomes greater than that of 1 as the redox potential of 2 increases through protonation from 1 to 2. Kinetic studies on electrophilic reactions using a variety of substrates revealed that 1 is only weakly reactive with O-H bonds, whereas 2 can activate aliphatic C-H bonds in addition to O-H bonds. The reaction rates increased by 1.4 × 104-fold for the O-H bonds by 2 over 1, which was explained by the difference in BDFE and the tunneling effect. Furthermore, 3, possessing the highest redox potential value, was found to undergo an aromatic C-H bond activation reaction under mild conditions. These results provide valuable insights into enhancing electrophilic reactivity by modulating the redox potential of manganese(III)-hydroxo and -aqua complexes through protonation.

Synthesis, Characterization, and Reactivity of a Highly Oxidative Mononuclear Manganese(IV)-Bis(Fluoro) Complex.

Recently, transition-metal terminal nonoxo complexes have shown a remarkable ability to activate and functionalize C-H bonds via proton-coupled electron transfer (PCET). Here we report the first example of a mononuclear manganese(IV) bis(fluoro) complex bearing a tetradentate pyridinophane ligand, [MnIV(TBDAP)(F)2]2+ (3), with an X-ray single crystal structure and physicochemical characterization. The manganese(IV) bis(fluoro) complex has a very high reduction potential of 1.61 V vs SCE, thereby enabling the four-electron oxidation of mesitylene to 3,5-dimethylbenzaldehyde. Kinetic studies, including the kinetic isotope effect and employment of other toluene derivatives, reveal the electron transfer (ET)-driven PCET in the C-H bond activation of mesitylene by 3. This novel metal halide intermediate would be prominently valuable for expanding transition-metal halide chemistry.

Controlling Reactivity through Spin Manipulation: Steric Bulkiness of Peroxocobalt(III) Complexes.

The intrinsic relationship between spin states and reactivity in peroxocobalt(III) complexes was investigated, specifically focusing on the influence of steric modulation on supporting ligands. Together with the previously reported [CoIII(TBDAP)(O2)]+ (2Tb), which exhibits spin crossover characteristics, two peroxocobalt(III) complexes, [CoIII(MDAP)(O2)]+ (2Me) and [CoIII(ADDAP)(O2)]+ (2Ad), bearing pyridinophane ligands with distinct N-substituents such as methyl and adamantyl groups, were synthesized and characterized. By manipulating the steric bulkiness of the N-substituents, control of spin states in peroxocobalt(III) complexes was demonstrated through various physicochemical analyses. Notably, 2Ad oxidized the nitriles to generate hydroximatocobalt(III) complexes, while 2Me displayed an inability for such oxidation reactions. Furthermore, both 2Ad and 2Tb exhibited similarities in spectroscopic and geometric features, demonstrating spin crossover behavior between S = 0 and S = 1. The steric bulkiness of the adamantyl and tert-butyl group on the axial amines was attributed to inducing a weak ligand field on the cobalt(III) center. Thus, 2Ad and 2Tb are an S = 1 state under the reaction conditions. In contrast, the less bulky methyl group on the amines of 2Me resulted in an S = 0 state. The redox potential of the peroxocobalt(III) complexes was also influenced by the ligand field arising from the steric bulkiness of the N-substituents in the order of 2Me (-0.01 V) < 2Tb (0.29 V) = 2Ad (0.29 V). Theoretical calculations using DFT supported the experimental observations, providing insights into the electronic structure and emphasizing the importance of the spin state of peroxocobalt(III) complexes in nitrile activation.

Timosaponin A3 Induces Anti-Obesity and Anti-Diabetic Effects In Vitro and In Vivo.

Obesity is a serious global health challenge, closely associated with numerous chronic conditions including type 2 diabetes. Anemarrhena asphodeloides Bunge (AA) known as Jimo has been used to address conditions associated with pathogenic heat such as wasting-thirst in Korean Medicine. Timosaponin A3 (TA3), a natural compound extracted from AA, has demonstrated potential therapeutic effects in various disease models. However, its effects on diabetes and obesity remain largely unexplored. We investigated the anti-obesity and anti-diabetic properties of TA3 using in vitro and in vivo models. TA3 treatment in NCI-H716 cells stimulated the secretion of glucagon-like peptide 1 (GLP-1) through the activation of phosphorylation of protein kinase A catalytic subunit (PKAc) and 5'-AMP-activated protein kinase (AMPK). In 3T3-L1 adipocytes, TA3 effectively inhibited lipid accumulation by regulating adipogenesis and lipogenesis. In a high-fat diet (HFD)-induced mice model, TA3 administration significantly reduced body weight gain and food intake. Furthermore, TA3 improved glucose tolerance, lipid profiles, and mitigated hepatic steatosis in HFD-fed mice. Histological analysis revealed that TA3 reduced the size of white adipocytes and inhibited adipose tissue generation. Notably, TA3 downregulated the expression of lipogenic factor, including fatty-acid synthase (FAS) and sterol regulatory element-binding protein 1c (SREBP1c), emphasizing its potential as an anti-obesity agent. These findings revealed that TA3 may be efficiently used as a natural compound for tackling obesity, diabetes, and associated metabolic disorders, providing a novel approach for therapeutic intervention.

Effect of Moxibustion Combined with Other Interventions on Body Weight Reduction in the Treatment of Obesity: A Systematic Review and Meta-Analysis.

Background: Moxibustion has been used in the treatment and prevention of obesity. However, there has been no systematic review or meta-analysis conducted on the use of moxibustion on obesity treatment. This study aimed to evaluate the role of moxibustion in the treatment of obesity. Methods: The Cochrane Central Register of Controlled Trials, EMBASE, and MEDLINE/PubMed databases were searched to identify all randomized controlled trials (RCTs) that evaluated the effect of moxibustion on obesity. The primary outcome was body weight. The secondary outcomes were the body mass index (BMI), waist circumference (WC), hip circumference (HC), and waist-to-hip ratio (WHR). The risk of bias assessment and meta-analysis were conducted using the Cochrane Collaboration tool. Results: Eleven RCTs involving 761 participants were included in this systematic review and meta-analysis. Other interventions that were included in the analyses were manual acupuncture, electroacupuncture, embedding therapy, herbal medicine, and diet control. Moxibustion combined with other interventions resulted in a significant improvement in body weight reduction (mean difference [MD] -3.32, 95% confidence interval [CI: -4.25 to -2.38]; I2 = 17%), BMI (MD -1.51, 95% CI [-1.88 to -1.14]; I2 = 76%), and WC (MD -2.82, 95% CI [-3.50 to -2.13]; I2 = 75%), but did not improve HC (MD -2.05, 95% CI [-4.21 to 0.11]; I2 = 0%) or WHR (MD -0.01, 95% CI [-0.03 to 0.01]; I2 = 57%). Conclusions: Moxibustion can be used with other interventions to improve body weight, BMI, and WC in people with obesity. However, the conclusions of this review should be cautiously applied to clinical practice because most of the included studies had a high or unclear risk of bias.

Effectiveness and safety of hominis placental pharmacopuncture for chronic temporomandibular disorder: A multi-center randomized controlled trial.

Background: Hominis placental (HPP) extract has been approved by the Ministry of Food and Drug Safety in Korea for treating chronic liver diseases and postmenopausal syndrome. However, its efficacy and safety for treating chronic temporomandibular disorder (TMD) remains unclear. We aimed to assess the effectiveness and safety of HPP for treating chronic TMD compared with physical therapy (PT). Methods: This study is a 2-arm parallel, multi-center, randomized controlled trial. We enrolled 82 chronic TMD patients from 2 Korean medicine hospitals between December 2019 and January 2021. We included patients with chronic TMD and randomly assigned them to undergo HPP or PT. The primary outcome was the difference in the scores for temporomandibular joint (TMJ) pain at baseline and week 6. The secondary outcomes were the scores for TMJ pain and bothersomeness, TMJ range of motion, the Korean version of Beck's depression index-Ⅱ, jaw functional limitation scale (JFLS) score, patient global impression of change (PGIC) scores, EuroQoL 5-dimension 5-level score, and short form-12 health survey (SF-12) scores. Results: Compared with PT, HPP showed significantly superior effects on TMJ pain and bothersomeness, protrusive movement pain, JFLS (verbal, emotional, and global), SF-12, and PGIC scores at week 6 (P < 0.05). Compared with the PT group, the HPP group showed a significantly higher recovery rate (≥50 % reduction in the scores for TMJ pain at the 24-week follow-up). Conclusion: HPP was more effective than PT managing pain and improving function and quality of life. Our findings demonstrate the effectiveness and safety of HPP for TMD treatment. Trial registration: This study has been registered at clinicalTrials.gov (NCT04087005), Clinical Research Information Service (CRIS) (KCT0004437), and Ministry of Food and Drug Safety (No. 31886).

Effects of electroacupuncture on obesity: A systematic review and meta-analysis.

BACKGROUND: This systematic review and meta-analysis evaluated the efficacy of electroacupuncture for the treatment of obesity. METHODS: We searched 8 electronic databases for articles published between 2005 and 2021, including only randomized controlled trials (RCTs) in the review. The intervention groups received either electroacupuncture alone or electroacupuncture with standard care, whereas the control groups received sham electroacupuncture, standard care, or no treatment. The primary outcome was the body mass index (BMI), and the secondary outcomes were the body weight (BW), waist circumference (WC), hip circumference, waist-to-hip ratio (WHR), body fat mass, body fat percentage, and adverse effects. Continuous outcome data are presented as mean differences (MDs) with 95% confidence intervals (CIs). RESULTS: This systematic review and meta-analysis included 13 RCTs involving 779 participants. Results revealed that the BMI (MD: -0.98; 95% CI: -1.35 to -0.61), BW (MD: -1.89; 95% CI: -2.97 to -0.80), WC (MD: -2.67; 95% CI: -4.52 to -0.82), and WHR (MD: -0.03; 95% CI: -0.06 to -0.01) were significantly improved in the intervention groups compared with those in the control groups. Adverse effects were reported in 5 studies. The most commonly used acupoint in the abdomen was ST25, whereas the most commonly used acupoints in other regions were ST36 and SP6 for the treatment of obesity. ST25 was the most commonly used acupoint connected by electroacupuncture. CONCLUSION: This systematic review and meta-analysis suggested that electroacupuncture is an effective and safe therapy for simple obesity. To increase the reliability of this study, further detailed, long-term studies should be conducted on the effects of electroacupuncture on obesity.

Bibliometric analysis of auriculotherapy research trends over the past 20 years.

OBJECTIVES: Auriculotherapy has long been used to treat various diseases. We analyzed and visualized auriculotherapy's geographical distribution, key contributors, and thematic trends over the past 20 years to provide current trends in auriculotherapy field and to offer recommendations for future research directions. DESIGN/SETTING: We searched for relevant studies in the Web of Science between January 10, 2003, and December 31, 2022. A bibliometric analysis was performed using VOSviewer for annual publications, journals, countries, institutions, authors, and keywords. RESULTS: A total of 800 studies were included in the analysis, and the number of studies steadily increased over the 20 examined years. In 2018, there was a noteworthy rise in publications, nearly twice as many as the preceding year. Integrative & complementary medicine was the most researched area, with most articles published in Evidence-Based Complementary and Alternative Medicine. China was the country with the most published research, and the most active organization was Guangzhou University of Chinese Medicine in China, followed by Kyung Hee University in South Korea. The most prolific author was Yeh Mei-ling, who reported the effects of auriculotherapy on dysmenorrhea and smoking cessation. Keyword analysis revealed four clusters: pain, mental health, obesity, and smoking cessation. CONCLUSION: Auriculotherapy research primarily focused on clinical studies related to pain, obesity, smoking cessation, and depression. Future research should place greater emphasis on verifying the mechanisms of auriculotherapy for specific ailments and may require efforts to enhance the robustness of clinical trials. Through visual analysis, our study may serve as a foundational resource, offering valuable insights into the trajectory of auriculotherapy research.

Survey on the current usage of ultrasound-guided procedures in Korean Medicine Clinics and Hospitals.

Ultrasound-guidance is applied during the administration of Korean medicine (KM) interventions to improve the safety and effectiveness of the interventions. Although many case series and reports on the use of ultrasound-guided KM interventions have been reported, no study has investigated the current use of ultrasound-guidance in clinical practice by doctors of Korean medicine (KMDs). An online survey was conducted with questions examining the status of ultrasound-guidance usage among KMDs practicing in various KM clinical settings. Survey responses from 335 KMDs were collected. Ultrasound started to be widely used in the clinical practice of KM since 2022. The primary objective of using ultrasound-guidance was "To improve the accuracy and efficacy" by 54.6%. Ultrasound-guidance was most frequently applied for shoulder joint diseases, and pharmacopuncture was the most frequently used intervention (76.1% and 90.4%, respectively). The respondents reported that effectiveness could be enhanced the most in nerve entrapment syndromes and especially when used in shoulder joints. Over 90% of KMDs responded that the safety and efficacy of treatment, specialty, and patients' satisfaction were improved after adopting ultrasound-guidance. Moreover, 94.9% of KMDs agreed with the necessity for reimbursement of ultrasound-guidance in KM under national health insurance coverage. Most KMDs responded that they had positive perceptions regarding the clinical use of ultrasound-guidance in KM in terms of treatment effects, safety, and patient satisfaction, and the need for national health insurance coverage of the service. Our findings may provide practice-based evidence for conducting clinical studies.