Boron in drug design: Recent advances in the development of new therapeutic agents

Synthesis of Chiral δ-Aminoboronic Esters by Enantioselective Hydrogenation of 1,2-Azaborines

We describe herein an iridium-catalyzed highly diastereo- and enantioselective hydrogenation of 1,2-azaborines to access δ-aminoboronic esters of potential biological importance. This method represents the first enantioselective hydrogenation of a boron-containing heteroarene and features diverse substitution patterns and wide scope. The synthetic utility of our method was demonstrated by the synthesis of (-)-phenibut and the formal synthesis of (+)-3-PPP and fluvirucinine A1.

Cobalt-Catalyzed anti-Markovnikov-Selective Hydroborylation of Perfluoroalkylethylenes

A facile protocol for anti-Markovnikov-selective hydroborylation of perfluoroalkylethylenes with pinacolborane has been developed in the presence of Co(acac)2 and dppf in DMAC to furnish diverse perfluoroalkylethylboronate esters. Subsequently, perfluoroalkylethylboronate ester derivatives were further transformed into 2-perfluoroalkyl ethanol, amide, and cross-coupling products.

Expedient access to bora-butenolide bioisosteres by counteranion-mediated trans-hydroboration of alkynes

The hydroboration of alkynes is a textbook example of a syn-selective concerted addition reaction, while trans-selective additions of borane to alkynes remain to be developed. We herein report a transition metal-free anti-addition of pinacolborane to alkynes, facilitated by the counteranion effect. This work further develops Chan alkyne reduction by utilizing the borane instead of aluminohydride reagents, enabling the facile synthesis of valuable five-membered boracycles that constitute isosteric alternatives to bioactive butenolides and a versatile platform for abundant downstream transformations. The practical method is distinguished by excellent regioselectivity, a broad substrate scope, and high compatibility with a variety of functional groups. The exploration of trans-selective patterns affords not only a stereo-complementary approach to traditional organic synthesis, but also mandates a new perspective on the noncanonical trans-hydroboration mechanism. A combination of control experiments and computational studies at the DFT level of theory reveal the previously unrecognized role of the HMDS counteranion in a stepwise intermolecular hydrogen transfer process.

Self-assembled PROTACs enable glycoproteins degradation in the living cells

We report here a two-component proteolysis targeting chimeras (PROTACs) strategy selectively targeting O-GalNAcylated and O-GlcNAcylated proteins for proteasomal degradation, which leads to severe toxicity in human cancer cell lines through perturbation of critical metabolic and signaling pathways governed by glycoproteins. Our approach termed as GlyTAC leverages from metabolic incorporation of easily accessible and cell-permeable peracetylated N-acetylglucosamine (GlcNAc) or N-acetylgalactosamine (GalNAc) analogues bearing an azido group into glycoproteins. In the living cells, the azido-modified glycoproteins serve as covalent anchors for the introduction of thalidomide moiety by strain-promoted azide-alkyne cycloaddition (SPAAC) to recruit E3 ligase cereblon (CRBN), resulting in stepwise ubiquitination of 'sensitized' proteins and their degradation by proteasome. We show the efficiency of the system in a series of human cancer cell lines and verify the mechanistic pathway by performing control experiments at each stage of the process. Given the characteristic features of cancer cells including fast nutrient turnover, and overall increase of protein glycosylation, as well as the low cytotoxicity of the individual components, our approach may open a feasible strategy in cancer therapy.

Superficial Mycoses: A Mapping Through Bibliometric Research

Superficial mycosis is a common and recurrent infectious skin disease. It poses significant challenges, with high recurrence rates and drug resistance, which notably diminishes the quality of life for patients and presents substantial public health issues. Numerous publications on superficial mycosis have posed significant challenges for researchers to manage the overwhelming amount of information effectively. This study aims to comprehensively explore the current state and latest advancements in global research through bibliometric techniques, providing a holistic appraisal of the field. Publications from the Web of Science Core Collection database were analyzed, including publications and citations, author groups and their countries and regions, journal categories, publishing institutions, and keywords using Excel 2019, VOSviewer, and CiteSpace. A total of 2206 papers were reviewed, showing a stable increase in research output from 2020 to 2022 and a predicted growth trend. The United States and India published the most significant number of research papers. Key research areas identified were "Outbreak", "Desorption ionization time", "Formulations", "Impact", "Dermatophyte", and "Dermoscopy". This bibliometric analysis provides a comprehensive visualized map to describe current and development trends. Advanced diagnostic technologies and innovative delivery systems are key current research priorities and will remain focal areas in this field.

Modulating the JAK/STAT pathway with natural products: potential and challenges in cancer therapy

The Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) pathway is a critical signaling network governing cellular functions such as immune responses, proliferation, and apoptosis. Dysregulation of this pathway is strongly implicated in cancer progression. This review explores the therapeutic potential of natural products, including Curcumin, Resveratrol, Apigenin, and Epigallocatechin Gallate (EGCG), as modulators of the JAK/STAT pathway. These phytochemicals exhibit anticancer activity by inhibiting JAK/STAT phosphorylation, blocking STAT dimerization, and interfering with STAT-DNA binding. A systematic evaluation of included peer-reviewed studies highlights their promise as complementary agents to conventional cancer therapies. However, challenges such as poor bioavailability and the need for robust clinical validation remain significant hurdles. Addressing these limitations through advanced drug delivery systems and rigorous trials could unlock their full potential in cancer treatment.

Borax pentahydrate as a promising boron-based angiogenesis inhibitor

BACKGROUND

Boron, a trace element, is involved in various physiological and metabolic processes, and recent studies suggest that boron compounds may have potential in cancer prevention and treatment. In this study, the antiangiogenic effects of a boron compound, borax pentahydrate (BPH), were investigated. Angiogenesis is a tightly regulated biological process responsible for the formation of new blood vessels from existing vasculatures. This process plays a critical role in cancer progression, making it an important target for cancer therapy. Pancreatic and kidney cancers are difficult to treat because they are aggressive and resistant to chemotherapy.

METHODS

The antiproliferative activity was evaluated using the MTT assay, while antiangiogenic effects were tested through in vitro tube formation assays and in ovo chick chorioallantoic membrane (CAM) assay. The effect of BPH on VEGF levels was determined using Western blot analysis in HUVEC, ACHN, PANC-1 cells. The effect of BPH on tumor angiogenesis was investigated with an in vivo Ehrlich ascites carcinoma model (EAC).

RESULTS

BPH exhibited potent antiproliferative and antiangiogenic activities, inhibiting the proliferation of ACHN, PANC-1, and HUVECs, disrupting endothelial tube formation, and inhibiting vascular formation on the CAM surface in a dose-dependent manner. VEGF levels were significantly decreased in ACHN, PANC-1 and HUVECs. There was also a decrease in VEGF and TGF-β1 levels in BPH-treated tumor groups. In addition, BPH caused a decrease in tumor size.

CONCLUSION

These findings suggest that BPH may be a new antiangiogenic and antitumoral agent. BPH may contribute to drug development studies targeting angiogenesis-related diseases as a promising new therapeutic agent.

Synthesis and Evaluation of Boron-Containing Heterocyclic Compounds with Antimicrobial and Anticancer Activities

Organoboron compounds, especially those containing boronic acid and benzoxaborole in their structure, have been gaining prominence in medicinal chemistry, following the FDA approval of tavaborole for the treatment of onychomycosis and bortezomib for multiple myeloma. The antimicrobial and anticancer effects of organoboron compounds motivate the investigation of the effects of the novel derivatives described here. A total of fourteen new boronic derivatives were synthesized and characterized using analytical methods. The antimicrobial activities were evaluated against M. tuberculosis (Mtb) H37Rv strains and fungal dermatophytes (C. albicans, ATCC 90028; T. rubrum, ATCC 28189; and T. mentagrophytes, ATCC 11481), while the anticancer effect was evaluated against oral squamous cell carcinoma (SCC) cell lines. Several promising boron-containing prototypes were identified, providing a foundation for further molecular optimization in the development of new antimicrobial and anticancer compounds.

Dual-Target Inhibitors─Discovery of Novel Diphenyl-(Thio)ether-Containing Benzoxaborole Derivatives as Potential Antifungal and Herbicidal Agents

LeuRS and PPO are important targets in the development of green pesticides; novel diphenyl-(thio)ether-containing benzoxaborole derivatives were designed and synthesized as novel dual-target enzyme inhibitors; their antifungal activities against six kinds of common plant pathogens in vitro and their herbicidal activities against purslane and barnyard grass were studied. Most of the target compounds showed excellent antifungal activity against six kinds of plant pathogenic fungi in vitro, and this is highlighted by compounds 6c and 6h, both displayed 100.0% inhibition effects against three kinds of the tested plant pathogenic fungi under the concentrations of 50.0 μg/mL, and the EC50 value of compound 6r against Rhizoctonia solani was 0.763 μg/mL, significantly lower than that of boscalid (1.20 μg/mL). In addition, compound 6c was also used in negative control experiments, and the results revealed that compound 6c had no significant effect on the growth of noninfected plants. Meanwhile, most of the compounds also demonstrated promising herbicidal activity, as compounds 6b, 6h, 6m, and 7e showed effective control on purslane and barnyard grass. Beyond that, compound 6s demonstrated certain safety against rape. Enzymatic inhibition experiments further confirmed that compound 7e exhibited remarkable inhibitory activity against NtPPO. Moreover, the molecular docking results between 6c and 7g and tLeuRS and NtPPO further revealed the mechanisms of action for their biological activities. In summary, compounds 6b, 6c, 6h, 7e, and 7g showed excellent antifungal and herbicidal activities and can be further studied as new antifungal and herbicidal agents in the next step.

Synthesis and mechanistic investigation of BPA fluorescent probes targeting BPA for potential application in Boron Neutron Capture Therapy (BNCT)

Boronic acid analogs are crucial in modern organic chemistry and drug development, serving as versatile reagents and intermediates with significant therapeutic applications. This area has gained increased interest with the recent development of the drug 4-boron-L-phenylalanine (L-BPA) for boron neutron capture therapy (BNCT). Fluorescent probe technology offers an essential pathway for imaging drugs in vitro and in vivo, providing high sensitivity with great spatial and temporal resolution for both disease diagnosis and drug development. In this paper, we designed and investigated three fluorescent probes-W-1-NN, W-2-NS and W-3-NO-for sensing 4-boron-L-phenylalanine (L-BPA). Among these, only W-1-NN reacts with L-BPA, resulting in a spectral blue-shift change. This probe can "ratiometrically" and specifically detect L-BPA among various metals, with a limit of detection (LOD) of 7.11 μM. Mechanistic studies revealed that the addition of L-BPA disrupts the inherent ESIPT mechanism of W-1-NN in protonic solutions, resulting in the appearance of a new peak at 372 nm. Additionally, theoretical computational studies have also demonstrated that the complexation of W-1-NN with L-BPA triggers a change in the resonance structure, resulting in a larger energy gap and causing a blue shift in the spectrum. Furthermore, W-1-NN has been successfully applied to the detection of L-BPA in human urine. Therefore, the template probe with N/O as the target and the introduction of N atoms can specifically detect L-BPA. This template probe lays the foundation for the detection of L-BPA, and provides great possibilities for the future realization of the template probe to be connected with different fluorophores to make it emit at long wavelengths to reach the target of the near-infrared.

Photocatalytic [3 + 2]-annulation via sodium tetraarylborate: a fundamental approach for synthesizing 1,4,2-diazaborole analogs

Substantial advancements have been achieved in the field of photocatalytic borylation utilizing 4c-7e Lewis base-boryl radicals. However, the utilization of 3c-5e neutral boryl radicals for C-B bond formation remains relatively underexplored due to their inherent instability. In this study, we successfully demonstrated the direct construction of C-B bonds using sodium tetraarylborate as a key reagent. This was accomplished by effectively stabilizing diaryl boryl radicals with nitrile compounds, thereby facilitating the synthesis of valuable boron-containing compounds. Overall, our research elucidates the significant role played by sodium tetraarylborate in enabling an efficient and versatile approach for synthesizing of 1,4,2-diazaborole analogs through a photocatalyzed [3 + 2]-annulation reaction. This mild and adaptable methodology expands synthetic strategies for obtaining diverse derivatives of 1,4,2-diazaboroles, with the RCN-BAr2 complex serving as an effective boron-nitrogen synthon that opens up pathways to multiple boron-nitrogen heterocycles. Furthermore, this breakthrough significantly enhances the applicability of sodium tetraarylborate in photoredox catalysis.

Exploring the role of boron-containing compounds in biological systems: Potential applications and key challenges

BACKGROUND

Boron, a naturally abundant trace element, plays a crucial role in various biological processes and influences important physiological functions such as bone health, immune response, and cellular metabolism. Its applications span diverse scientific fields including anatomy, pharmacology, reproduction, medicine, and agriculture.

OBJECTIVES

This review examines the diverse functions of boron-compounds in biological systems and highlights their therapeutic potential, challenges associated with toxicity, and mechanisms underlying their biological interactions.

METHODS

In this paper, the literature on boron action was reviewed, paying special attention to studies that examined the effects of boron on health and its therapeutic applications in multiple areas.

RESULTS

Boron exhibits broad therapeutic potential by affecting several pathways. However, excessive consumption can cause toxicity and negatively impact health. Current research only partially elucidates the mechanisms of boron's biological effects, so further studies are needed.

CONCLUSION

Understanding boron's interactions in biological systems is critical to optimizing its application in healthcare and ensuring safety. Future research will improve our knowledge of boron's biological effects and promote innovative therapeutic applications.

Boric acid impedes glioblastoma growth in a rat model: insights from multi-approach analysis

Limited advancements in managing malignant brain tumors have resulted in poor prognoses for glioblastoma (GBM) patients. Standard treatment involves surgery, radiotherapy, and chemotherapy, which lack specificity and damage healthy brain tissue. Boron-containing compounds, such as boric acid (BA), exhibit diverse biological effects, including anticancer properties. This study aimed to examine whether boron supplementation, as BA, can inhibit glioblastoma growth in a xenograft animal model. Using MRI-based tumor size measurement, survival rates, hematological, clinical biochemistry analyses, and genotoxicity parameters, we assessed the impact of BA. Histopathological, immunohistochemical, and immunofluorescence examinations were also conducted. All BA doses (3.25, 6.5, and 13 mg kg-1 b.w.) extended survival compared to GBM controls after 14 days, with a dose-dependent anti-GBM effect observed in MRI analyses. BA treatment improved hematological (WBC and PLT counts) and biochemical parameters (LDL-C, CREA, and ALP). Histopathological examination revealed a significant reduction in tumor diameter with 6.5 and 13 mg kg-1 BA. Immunohistochemical and immunofluorescence staining showed modulation of intracytoplasmic Ki67, cytoplasmic CMPK2, and GFAP expressions in tumor cells post-BA treatment. Additionally, BA did not increase micronuclei formations, indicating its non-genotoxic nature. In conclusion, targeting tumor suppressor networks with boron demonstrates significant therapeutic potential for GBM treatment.

Photoinduced B-H Arylation of N-Heterocyclic Carbene Boranes with Sulfonyl(hetero)arenes

Arylborane complexes ligated by N-heterocyclic carbenes (NHCs) can be synthesized by photoirradiation of a mixture of NHC-boranes and sulfonyl(hetero)arenes. The reaction occurs under mild and convenient conditions without any photocatalyst, which are realized by a radical chain mechanism involving NHC-boryl radicals and sulfonyl radicals. This reaction offered the opportunity to reveal the photophysical property of a 2-borylnaphtho[1,2-d]thiazole derivative.

Boronic Acid-Containing 3H- pyrazolo[4,3-f]quinoline Compounds as Dual CLK/ROCK Inhibitors with Anticancer Properties

Background: The protein kinases CLK and ROCK play key roles in cell growth and migration, respectively, and are potential anticancer targets. ROCK inhibitors have been approved by the FDA for various diseases and CLK inhibitors are currently being trialed in the clinic as anticancer agents. Compounds with polypharmacology are desired, especially in oncology, due to the potential for high efficacy as well as addressing resistance issues. In this report, we have identified and characterized novel, boron-containing dual CLK/ROCK inhibitors with promising anticancer properties. Methods: A library of boronic acid-based CLK/ROCKi was synthesized via Povarov/Doebner-type multicomponent reactions. Kinase inhibition screening and cancer cell viability assays were performed to identify the hit compounds. To gain insights into the probable binding modes of the compounds to the kinases, docking studies were performed. Cell cycle analysis, qPCR and immunoblotting were carried out to further characterize the mode(s) of action of the lead candidates. Results: At 25 nM, the top compounds HSD1400 and HSD1791 inhibited CLK1 and 2 and ROCK2 at greater than 70%. While HSD1400 also inhibited CLK4, the C1 methylated analog HSD1791 did not inhibit CLK4. Antitumor effects of the top compounds were evaluated and dose-response analysis indicated potent inhibition of renal cancer and leukemia cell growth. Immunoblotting results indicated that the top compounds induce DNA damage via upregulation of p-H2AX. Moreover, flow cytometry results demonstrated that the top compounds promote cell cycle arrest in the renal cancer cell line, Caki-1. qPCR and immunoblotting analysis upon HSD1791 dosing indicated suppression of cyclin D/Rb oncogenic pathway upon compound treatment. Conclusions: Novel boronic acid-containing pyrazolo[4,3-f]quinoline-based dual CLK/ROCK inhibitors were identified. The so-called "magic methylation" design approach was used to tune CLK selectivity. Additionally, the findings demonstrate potent in vitro anticancer activity of the lead candidates against renal cancer and leukemia. This adds to the growing list of boron-containing compounds that display biological activities.

Exploring the pharmaceutical potential of ammonium organotrifluoroborate functional group: Comprehensive chemical, metabolic, and plasma stability evaluation

Boronated carbohydrate derivatives have good potential for targeting malignant cells in Boron Neutron Capture Therapy (BNCT) due to their preferential glucose uptake. In particular, with the introduction of the ammonium trifluoroborate moiety, boronated sugars can function as both BNCT agents and Positron Emission Tomography (PET) tracers. Their 18F radiolabeling allows real-time tracking of biodistribution. This study evaluates the chemical, metabolic, and plasma stability of ammonium trifluoroborates for pharmaceutical purposes using LC-HRMS, presenting stability data under various conditions -acidic, basic, pseudophysiological, and oxidative- and highlighting degradation products and mechanisms. The data are supported by 1H NMR and 19F NMR. Metabolic and plasma stabilities, along with preliminary toxicological data (MTT assays), are also provided to better predict the clinical applicability of these compounds.

Combining crystallographic and binding affinity data towards a novel dataset of small molecule overlays

Although small molecule superposition is a standard technique in drug discovery, a rigorous performance assessment of the corresponding methods is currently challenging. Datasets in this field are sparse, small, tailored to specific applications, unavailable, or outdated. The newly developed LOBSTER set described herein offers a publicly available and method-independent dataset for benchmarking and method optimization. LOBSTER stands for "Ligand Overlays from Binding SiTe Ensemble Representatives". All ligands were derived from the PDB in a fully automated workflow, including a ligand efficiency filter. So-called ligand ensembles were assembled by aligning identical binding sites. Thus, the ligands within the ensembles are superimposed according to their experimentally determined binding orientation and conformation. Overall, 671 representative ligand ensembles comprise 3583 ligands from 3521 proteins. Altogether, 72,734 ligand pairs based on the ensembles were grouped into ten distinct subsets based on their volume overlap, for the benefit of introducing different degrees of difficulty for evaluating superposition methods. Statistics on the physicochemical properties of the compounds indicate that the dataset represents drug-like compounds. Consensus Diversity Plots show predominantly high Bemis-Murcko scaffold diversity and low median MACCS fingerprint similarity for each ensemble. An analysis of the underlying protein classes further demonstrates the heterogeneity within our dataset. The LOBSTER set offers a variety of applications like benchmarking multiple as well as pairwise alignments, generating training and test sets, for example based on time splits, or empirical software performance evaluation studies. The LOBSTER set is publicly available at https://doi.org/10.5281/zenodo.12658320 , representing a stable and versioned data resource. The Python scripts are available at https://github.com/rareylab/LOBSTER , open-source, and allow for updating or recreating superposition sets with different data sources.

Novel pleuromutilin derivatives conjugated with phenyl-sulfide and boron-containing moieties as potent antibacterial agents against antibiotic-resistant bacteria

In response to the escalating threat of microbial resistance, a series of novel pleuromutilin derivatives, conjugated with phenyl-sulfide and boron-containing moieties, were designed and synthesized. Most derivatives, especially 14b and 16b, demonstrated significant efficacy against Gram-positive bacteria, including multidrug-resistant strains, as well as pleuromutilin-resistant strains. Compound 16b showed high stability in the liver microsomes of rats and humans, along with acceptable tolerance in vitro and in vivo. Additionally, compound 16b exhibited promising efficacy in MRSA-infected mouse models. Our data highlight the potential of conjugated pleuromutilin derivatives as valuable agents against drug-resistant bacteria.

Synthesis and Optoelectronic Properties of Threaded BODIPYs

We report on the synthesis of two new threaded BODIPYs 5 and 6 in good yields using boron as a gathering atom and a macrocycle with a 2,2'-biphenol unit. In addition to usual techniques, they were characterized by X-ray crystallography. Their electrochemical and optical properties were investigated. In particular, both compounds are highly emissive with photoluminescence quantum yields of 54 and 81 % respectively. In addition, they both show a high photostability.

Stereodivergency in Copper-Catalyzed Borylative Difunctionalizations: The Impact of Boron Coordination

A reagent-controlled diastereodivergent copper-catalyzed borylative difunctionalization is reported. The formation of Lewis adducts that guide selectivity is commonly invoked in organic reaction mechanisms. Using density functional theory calculations, we identified BpinBdan as a sterically similar and less Lewis acidic alternative to B2pin2. Using a newly developed borylative aldol domino reaction as the proof-of-concept, we demonstrate a change in stereochemical outcome by a simple change of borylating reagent-B2pin2 affords the diastereomer associated with coordination control while BpinBdan overturns this mode of binding. We show that this strategy can be generalized to other scaffolds and, more importantly, that BpinBdan does not alter the diastereomeric outcome of the reaction when coordination is not involved. BpinBdan can be viewed as a mechanistic probe for coordination in future copper-catalyzed borylation reactions.

Benzoxaborinine, New Chemotype for Carbonic Anhydrase Inhibition: Ex Novo Synthesis, Crystallography, In Silico Studies, and Anti-Melanoma Cell Line Activity

The benzoxaborinine scaffold, a homologue of benzoxaborole with an additional carbon atom in the boracycle, shows significant potential in developing new therapeutic agents. This study reports the synthesis, inhibition assays against four human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, and anti-melanoma evaluation of 7-aryl(thio)ureido-substituted benzoxaborinines. Some derivatives, particularly compound 11, exhibited potent inhibitory activity (below 65 nM) against hCA IX and XII and stronger antiproliferative effects than SLC-0111 on human melanoma cells under hypoxia. Crystallographic studies of benzoxaborinine 3 adducts with hCA I and II demonstrated the binding mode of this chemotype, revealing that although both benzoxaborinine 3 and benzoxaborole 10 share a similar zinc-binding mode, the expanded ring in benzoxaborinine led to a different orientation within the active site. These findings suggest that benzoxaborinines hold promise for designing novel carbonic anhydrase inhibitors.

The Potential Role of Boron in the Modulation of Gut Microbiota Composition: An In Vivo Pilot Study

Background/Objectives: The role of the gut microbiome in the development and progression of many diseases has received increased attention in recent years. Boron, a trace mineral found in dietary sources, has attracted interest due to its unique electron depletion and coordination characteristics in chemistry, as well as its potential role in modulating the gut microbiota. This study investigates the effects of inorganic boron derivatives on the gut microbiota of mice. Methods: For three weeks, boric acid (BA), sodium pentaborate pentahydrate (NaB), and sodium perborate tetrahydrate (SPT) were dissolved (200 mg/kg each) in drinking water and administered to wild-type BALB/c mice. The composition of the gut microbiota was analyzed to determine the impact of these treatments. Results: The administration of BA significantly altered the composition of the gut microbiota, resulting in a rise in advantageous species such as Barnesiella and Alistipes. Additionally, there was a decrease in some taxa associated with inflammation and illness, such as Clostridium XIVb and Bilophila. Notable increases in genera like Treponema and Catellicoccus were observed, suggesting the potential of boron compounds to enrich microbial communities with unique metabolic functions. Conclusions: These findings indicate that boron compounds may have the potential to influence gut microbiota composition positively, offering potential prebiotic effects. Further research with additional analyses is necessary to fully understand the interaction between boron and microbiota and to explore the possibility of their use as prebiotic agents in clinical settings.

The current utility and future potential of multiborylated alkanes

Organoboron chemistry has become a cornerstone of modern synthetic methodology. Most of these reactions use an organoboron starting material that contains just one C(sp2)-B or C(sp3)-B bond; however, there has been a recent and accelerating trend to prepare multiborylated alkanes that possess two or more C(sp3)-B bonds. This is despite a lack of general reactivity, meaning many of these compounds currently offer limited downstream synthetic value. This Review summarizes recent advances in the exploration of multiborylated alkanes, including a discussion on how these products may be elaborated in further synthetic manipulations.

Replacement of nitro function by free boronic acid in non-steroidal anti-androgens

A new series of potential flutamide-like antiandrogens has been designed and synthesized to treat prostate cancer. This new series results from our research, which has been aimed at discovering new compounds that can be used for androgen deprivation treatment. The antiandrogens were designed and synthesized by varying the acyl part, linker, and substitution of the benzene ring in the 4-nitro-3-trifluoromethylanilide scaffold of non-steroidal androgens. In addition, the characteristic feature of the nitro group was replaced by a boronic acid functionality. Compound 9a was found to be more effective against LAPC-4 than the standard antiandrogens flutamide, hydroxyflutamide, and bicalutamide. Moreover, it exhibited lower toxicity against the non-cancerous cell line HK-2. The initial in silico study did not show evidence of covalent bonding to the androgen receptor, which was confirmed by an NMR binding experiment with arginine methyl ester. The structure-activity relationships discovered in this study could provide directions for further research on non-steroidal antiandrogens.

Synthesis of Highly Substituted Oxaboroles from Oxaboranes via a Selective Petasis Borono-Mannich Reaction

We present a novel and efficient method for the synthesis of highly substituted non-benzofused oxaboroles. Reactions of oxaboranes, morpholine, and salicylaldehyde in toluene heated to 85 °C for 4 h produce the corresponding oxaborole products in yields up to 93%. The process is effective across a diverse substrate scope and can be scaled to produce gram quantities of densely functionalized oxaboroles in excellent yield. Exclusive aryl transfer over vinyl transfer is observed. Computational insights further elucidate the inherent selectivity of this process.

ROS-responsive hydrogels: from design and additive manufacturing to biomedical applications

Hydrogels with intricate 3D networks and high hydrophilicity have qualities resembling those of biological tissues, making them ideal candidates for use as smart biomedical materials. Reactive oxygen species (ROS) responsive hydrogels are an innovative class of smart hydrogels, and are cross-linked by ROS-responsive modules through covalent interactions, coordination interactions, or supramolecular interactions. Due to the introduction of ROS response modules, this class of hydrogels exhibits a sensitive response to the oxidative stress microenvironment existing in organisms. Simultaneously, due to the modularity of the ROS-responsive structure, ROS-responsive hydrogels can be manufactured on a large scale through additive manufacturing. This review will delve into the design, fabrication, and applications of ROS-responsive hydrogels. The main goal is to clarify the chemical principles that govern the response mechanism of these hydrogels, further providing new perspectives and methods for designing responsive hydrogel materials.

Novel biaryloxazolidinone derivatives with broad-spectrum antibacterial activity, favorable drug-like profiles and in vivo efficacy against linezolid-resistant Staphylococcusaureus

The emergence of multidrug-resistant bacteria along with a declining pipeline of clinically useful antibiotics has led to the urgent need for the development of more effective antibacterial agents to treat drug-resistant bacteria. We previously discovered compound OB-158 with potent antibacterial activity but exhibited poor oral bioavailability. Herein, a systematic structural optimization of OB-158 to improve pharmacokinetic profiles yielded 26 novel biaryloxazolidinone analogues, and their activities against Gram-positive S. aureus, multidrug resistant S. aureus and Enterococcus faecalis were evaluated. Remarkably, compound 8b was identified with potent antibacterial activity against S. aureus (MIC = 0.06 μg/mL), MSSA (MIC = 0.125 μg/mL), MRSA (MIC = 0.06 μg/mL), LRSA (MIC = 0.125 μg/mL) and LREFa (MIC = 0.5 μg/mL). Compound 8b was demonstrated as a promising candidate through druglikeness evaluation including metabolism in microsomes and plasma, Caco-2 cell permeability, plasma protein binding, cytotoxicity, and inhibition of CYP450 and human monoamine oxidase. Notably, compound 8b displayed excellent PK profile with appropriate T1/2 of 1.49 h, high peak plasma concentration (Cmax = 2320 ng/mL), high plasma exposure (AUC0-t = 8310 h ng/mL), and superior oral bioavailability (F = 68.1 %) in Sprague-Dawley rats. Ultimately, in vivo efficacy of compound 8b in a mouse model of LRSA systemic infection was also demonstrated. Taken together, compound 8b represents a promising drug candidate for the treatment of linezolid-resistant Gram-positive bacterial strains infection.

Enantioselective Synthesis of β-Aminoboronic Acids via Borylalkylation of Enamides

Aminoboronic acids represent a class of significant compounds that have attracted significant attention in the fields of drug discovery and organic synthesis. Despite notable progress in their synthesis, the efficient construction of chiral β-aminoboronic acids with alkyl side chains remains a challenging endeavor. Here, we introduce an unprecedented nickel-catalyzed asymmetric borylalkylation of enamides, employing a simple chiral diamine ligand, readily available B2pin2, and alkyl halides as coupling partners. This reaction serves as an efficient platform for assembling a diverse range of β-aminoboronic acid derivatives with flexible alkyl side chains, displaying exceptional regio-, stereo-, and enantioselectivities. Moreover, this transformation exhibits a broad substrate scope and remarkable tolerance toward various functional groups. Theoretical calculations demonstrate that the benzyl group on the ligand is the key to the high enantiocontrol in this transformation. Additionally, we exemplify the practical application of this strategy through the concise synthesis of complex bioactive molecules.

Emerging and Re-emerging Warheads for Targeted Covalent Inhibitors: An Update

Covalent inhibitors and other types of covalent modalities have seen a revival in the past two decades, with a variety of new targeted covalent drugs having been approved in recent years. A key feature of such molecules is an intrinsically reactive group, typically a weak electrophile, which enables the irreversible or reversible formation of a covalent bond with a specific amino acid of the target protein. This reactive group, often called the "warhead", is a critical determinant of the ligand's activity, selectivity, and general biological properties. In 2019, we summarized emerging and re-emerging warhead chemistries to target cysteine and other amino acids (Gehringer, M.; Laufer, S. A. J. Med. Chem. 2019, 62, 5673-5724; DOI: 10.1021/acs.jmedchem.8b01153). Since then, the field has rapidly evolved. Here we discuss the progress on covalent warheads made since our last Perspective and their application in medicinal chemistry and chemical biology.

Identification, crystallization, and first X-ray structure analyses of phenyl boronic acid-based inhibitors of human carbonic anhydrase-II

Human carbonic anhydrases (hCAs) play a central role in various physiological processes in the human body. HCAs catalyze the reversible hydration of CO2 into HCO3-, and hence maintains the fluid and pH balance. Overexpression of CA II is associated with diseases, such as glaucoma, and epilepsy. Therefore, CAs are important clinical targets and inhibition of different isoforms, especially hCA II is used in treatment of glaucoma, altitude sickness, and epilepsy. Therapeutically used CA inhibitors (CAI) are sulfonamide-based, such as acetazolamide, dichlorphenamide, methazolamide, ethoxzolamide, etc. However, they exhibit several undesirable effects such as numbness, tingling of extremities, malaise, metallic taste, fatigue, renal calculi, and metabolic acidosis. Therefore, there is an urgent need to identify safe and effective inhibitors of the hCAs. In this study, different phenyl boronic acids 1-5 were evaluated against bovine (bCA II) and hCA II. Among all, compound 1 (4-acetylphenyl boronic acid) was found to be active against bCAII and hCA II with IC50 values of 246 ± 0.48 and 281.40 ± 2.8 μM, respectively, while the remaining compounds were found in-active. Compound 1 was identified as competitive inhibitor of hCA II enzyme (Ki = 283.7 ± 0.002 μM). Additionally, compound 1 was found to be non-toxic against BJ Human fibroblast cell line. The X-ray crystal structure for hCA II in-complex with compound 1 was evaluated to a resolution of 2.6 Å. In fact, this the first structural analysis of a phenyl boron-based inhibitor bound to hCA II, allowing an additional structure-activity analysis of the compounds. Compound 1 was found to be directly bound in the active site of hCA II by interacting with His94, His119, and Thr199 residues. In addition, a bond of 3.11 Å between the zinc ion and coordinated boron atom of the boronic acid moiety of compound 1 was also observed, contributing to binding affinity of compound 1 for hCA II. PDB ID: 8IGF.

Practical Synthesis of 6-Amino-1-hydroxy-2,1-benzoxaborolane: A Key Intermediate of DNDI-6148

Visceral leishmaniasis (VL), a parasitic, poverty-linked, neglected disease, is endemic across multiple regions of the world and fatal if untreated. There is an urgent need for a better and more affordable treatment for VL. DNDI-6148 is a promising drug candidate being evaluated for the treatment of VL; however, the current process for producing the key intermediate of DNDI-6148, 6-amino-1-hydroxy-2,1-benzoxaborolane, is expensive and difficult to scale up. Herein, we describe two practical approaches to synthesizing 6-amino-1-hydroxy-2,1-benzoxaborolane from inexpensive and readily available raw materials. Starting with 4-tolunitrile, the first approach is a five-step sequence involving a Hofmann rearrangement, resulting in an overall yield of 40%. The second approach utilizes 2-methyl-5-nitroaniline as the starting material and features borylation of aniline and continuous flow hydrogenation as the key steps, with an overall yield of 46%. Both routes bypass the nitration of 1-hydroxy-2,1-benzoxaborolane, which is challenging and expensive to scale. In particular, the second approach is more practical and scalable because of the mild operating conditions and facile isolation process.

Solid-State Synthesis of B←N Adducts by the Amine-Facilitated Trimerization of the Phenylboronic Acid

Stable boroxine-amine adducts comprising dative B←N bond(s) were prepared by mechanochemically-induced reactions of phenylboronic acid (PBA) and amines (pyridine, DMAP, 1H-pyrazole, piperidine, DABCO, hexamethylenetetramine, or 4,4'-bipyridine). In-situ Raman monitoring, ex-situ PXRD and DFT calculations were used for product identification. Stoichiometry of the product (3 : 1, 3 : 2 or 6 : 1 adduct) was controlled by the amine structure and the molar ratio of the reactants. The 1 : 2 H-bonded assembly of PBA and 4,4'-bipyridine (bpy) was confirmed as an intermediate in the adduct formation for bpy. Competitive binding experiments indicated that the exchange of the amines in the 3 : 1 adducts follows the computed adduct stabilities that increase with the amine basicity. Following the DFT prediction, the first adduct with two different amines, DMAP and pip, bound to one boroxine moiety was isolated and structurally characterized. Results show that calculations can be used to predict possible and preferred product(s) and their spectral characteristics.

Development of Hsp90 C-terminal inhibitors with noviomimetics that manifest anti-proliferative activities

Inhibition of the Hsp90 C-terminal domain offers a promising opportunity to treat numerous diseases/indications. Furthermore, the development of Hsp90 C-terminal inhibitors (CTIs) is advantageous over N-terminal inhibitors because it avoids the detriments associated with induction of the heat shock response (HSR). However, the lack of co-crystal structures of small molecules bound to the C-terminus have hindered their development. Therefore, structure-activity relationship (SAR) studies have been pursued to optimize such inhibitors. Noviose sugar surrogates, also known as noviomimetics have been prepared to investigate the size and nature of the C-terminal domain binding pocket. Herein, we report the synthesis and anti-proliferative activity manifested by this new series of Hsp90 C-terminal inhibitors.

The Rise of Boron-Containing Compounds: Advancements in Synthesis, Medicinal Chemistry, and Emerging Pharmacology

Boron-containing compounds (BCC) have emerged as important pharmacophores. To date, five BCC drugs (including boronic acids and boroles) have been approved by the FDA for the treatment of cancer, infections, and atopic dermatitis, while some natural BCC are included in dietary supplements. Boron's Lewis acidity facilitates a mechanism of action via formation of reversible covalent bonds within the active site of target proteins. Boron has also been employed in the development of fluorophores, such as BODIPY for imaging, and in carboranes that are potential neutron capture therapy agents as well as novel agents in diagnostics and therapy. The utility of natural and synthetic BCC has become multifaceted, and the breadth of their applications continues to expand. This review covers the many uses and targets of boron in medicinal chemistry.

Synthesis of Boron-Containing Nucleoside Analogs

Over the last century, nucleoside-based therapeutics have demonstrated remarkable effectiveness in the treatment of a wide variety of diseases from cancer to HIV. In addition, boron-containing drugs have recently emerged as an exciting and fruitful avenue for medicinal therapies. However, borononucleosides have largely been unexplored in the context of medicinal applications. Herein, we report the synthesis, isolation, and characterization of two novel boron-containing nucleoside compound libraries which may find utility as therapeutic agents. Our synthetic strategy employs efficient one-step substitution reactions between a diverse variety of nucleoside scaffolds and an assortment of n-alkyl potassium trifluoroborate-containing electrophiles. We demonstrated that these alkylation reactions are compatible with cyclic and acyclic nucleoside substrates, as well as increasing alkyl chain lengths. Furthermore, regioselective control of product formation can be readily achieved through manipulation of base identity and reaction temperature conditions.

Boron-containing carbonic anhydrases inhibitors

Over the last decades, the medicinal chemistry of boron-based compounds has been extensively explored, designing valuable small molecule drugs to tackle diseases and conditions, such as cancer, infections, inflammatory and neurological disorders. Notably, boron has proven to also be a valuable element for the development of inhibitors of the metalloenzymes carbonic anhydrases (CAs), a class of drug targets with significant potential in medicinal chemistry. Incorporating boron into carbonic anhydrase inhibitors (CAIs) can modulate the ligand ability to recognize the target and/or influence selectivity towards different CA isoforms, using the tail approach and boron-based tails. The electron-deficient nature of boron and its associated properties have also led to the discovery of novel zinc-binding CAIs, such as boronic acids and the benzoxaboroles, capable of inhibiting the CAs upon a Lewis acid-base mechanism of action. The present manuscript reviews the state-of-the-art of boron-based CAIs. As research in the applications of boron compounds in medicinal chemistry continues, it is anticipated that new boron-based CAIs will soon expand the current array of such compounds. However, further research is imperative to fully unlock the potential of boron-based CAIs and to advance them towards clinical applications.

11B NMR of the Morphological Evolution of Traditional Chinese Medicine Borax

This article applies nuclear magnetic resonance technology to the study of boron-containing traditional Chinese medicine, in order to explore the morphological evolution of boron elements in traditional Chinese medicine. Borax is a traditional Chinese medicine with anti-corrosion, anti-inflammatory, antibacterial, and anticonvulsant effects. It is made by boiling, removing stones, and drying borax minerals like borate salts. This article introduces an 11B nuclear magnetic resonance method for identifying and characterizing boron-containing compounds in TCM. We applied this technology to borax aqueous solutions in different chemical environments and found that with boron mixed in the form of SP2 hybridization in equilateral triangles and SP3 hybridization in equilateral tetrahedra, the pH changes in alkaline environments significantly affected the ratio of the two. At the same time, it was found that in addition to the raw material peak, boron signals of other boron-containing compounds were also detected in 20 commercially available boron-containing TCM preparations. These new boron-containing compounds may be true pharmaceutical active ingredients, and adding them directly to the formula can improve quality and safety. This article describes the detection of 11B NMR in boron-containing traditional Chinese medicine preparations. It is simple, non-destructive, and can provide chemical fingerprint studies for boron-containing traditional Chinese medicine.

Visible-Light-Driven Decarboxylative Borylation: Rapid Access to α- and β-Amino-boronamides

In this study, we described a two-step process involving an efficient visible-light-induced decarboxylative borylation of α- and β-amino redox-active esters with bis(catecholato)diboron, followed by transamination with 1,8-diaminonapthalene (DANH2). A series of boronamides were obtained in moderate to excellent yields in this one-pot procedure. The photochemical process proved to be very efficient even when conducted under flow conditions with shorter reaction durations and scalable synthesis of DAN boronates.

Elemental exchange: Bioisosteric replacement of phosphorus by boron in drug design

Continuous efforts are being directed toward the employment of boron in drug design due to its advantages and unique characteristics including a plethora of target engagement modes, lower metabolism, and synthetic accessibility, among others. Phosphates are components of multiple drug molecules as well as clinical candidates, since they play a vital role in various biochemical functions, being components of nucleotides, energy currency- ATP as well as several enzyme cofactors. This review discusses the unique chemistry of boron functionalities as phosphate bioisosteres - "the boron-phosphorus elemental exchange strategy" as well as the superiority of boron groups over other commonly employed phosphate bioisosteres. Boron phosphate-mimetics have been utilized for the development of enzyme inhibitors as well as novel borononucleotides. Both the boron functionalities described in this review-boronic acids and benzoxaboroles-contain a boron connected to two oxygens and one carbon atom. The boron atom of these functional groups coordinates with a water molecule in the enzyme site forming a tetrahedral molecule which mimics the phosphate structure. Although boron phosphate-mimetic molecules - FDA-approved Crisaborole and phase II/III clinical candidate Acoziborole are products of the boron-phosphorus bioisosteric elemental exchange strategy, this technique is still in its infancy. The review aims to promote the use of this strategy in future medicinal chemistry projects.

Microbiota-Accessible Boron-Containing Compounds in Complex Regional Pain Syndrome

The microbiota-gut-brain axis has garnered increasing attention in recent years for its role in various health conditions, including neuroinflammatory disorders like complex regional pain syndrome (CRPS). CRPS is a debilitating condition characterized by chronic neuropathic pain, and its etiology and pathophysiology remain elusive. Emerging research suggests that alterations in the gut microbiota composition and function could play a significant role in CRPS development and progression. Our paper explores the implications of microbiota in CRPS and the potential therapeutic role of boron (B). Studies have demonstrated that individuals with CRPS often exhibit dysbiosis, with imbalances in beneficial and pathogenic gut bacteria. Dysbiosis can lead to increased gut permeability and systemic inflammation, contributing to the chronic pain experienced in CRPS. B, an essential trace element, has shown promise in modulating the gut microbiome positively and exerting anti-inflammatory effects. Recent preclinical and clinical studies suggest that B supplementation may alleviate neuropathic pain and improve CRPS symptoms by restoring microbiota balance and reducing inflammation. Our review highlights the complex interplay between microbiota, inflammation, and neuropathic pain in CRPS and underscores the potential of B as a novel therapeutic approach to target the microbiota-gut-brain axis, offering hope for improved management of this challenging condition.

Desulfurative Borylation of Small Molecules, Peptides, and Proteins

We introduce a direct conversion of alkyl thiols into boronic acids, facilitated by a water-soluble phosphine, 1,3,5-triaza-7-phosphaadamantane (PTA), in conjunction with tetrahydroxydiboron (B2(OH)4), acting as both a radical initiator and a boron source. This desulfurative borylation reaction has been successfully applied to various substrates, including cysteine residues in oligopeptides and small proteins, primary alkyl thiols found in pharmaceutical compounds, disulfides, and selenocysteine. Optimization of reaction conditions was undertaken to reduce the formation of unwanted reactions, such as the reduction of alanyl or other primary radicals, and to prevent deleterious reactions between the phosphine and N-terminal amine that lead to methylene adducts by utilizing a buffer containing glycine-glycine (GG) dipeptide. The developed method is characterized by its operational simplicity and robustness. Moreover, its compatibility with various functional groups present in peptides and proteins makes it a promising tool for late-stage functionalization, extending its potential application across a broad spectrum of chemical and biological targets.

Recent Expedition in Pd- and Rh-Catalyzed C(Ar) -B Bond Formations and Their Applications in Modern Organic Syntheses

Transition metal-catalyzed borylation has emerged as a powerful and versatile strategy for synthesizing organoboron compounds. These compounds have found widespread applications in various aspects, including organic synthesis, materials science, and medicinal chemistry. This review provides a concise summary of the recent advances in palladium- and rhodium-catalyzed borylation from 2013 to 2023. The review covers the representative examples of catalysts, substrates scope and reaction conditions, with particular emphasis on the development of catalyst systems, such as phosphine ligands, NHC-carbene, and more. The diverse array of borylative products obtained for further applications in Suzuki-Miyaura coupling, and other transformations, are also discussed. Future directions in this rapidly evolving field, with the goal of designing more efficient, selective borylation methodologies are highlighted, too.

Crisaborole loaded nanoemulgel for the mitigation of atopic dermatitis in mice model

OBJECTIVE

The present work aims to formulate nanoemulgel of crisaborole (CB) and evaluate its effectiveness against 2,4-Di-nitrochlorobenzene induced (DNCB) atopic dermatitis (AD) in mice.

SIGNIFICANCE

AD is a chronic inflammation of the skin affecting the quality of life. CB is a topical PDE4 inhibitor marketed as a 2% ointment. It, however, possesses poor aqueous solubility. An o/w nanoemulsion shall exhibit an enhanced therapeutic effect owing to the increased solubility of CB and an augmented skin penetration. The addition of a gelling agent to form a nanoemulgel further provides ease of application to the patients.

METHODS

Nanoemulsion was prepared by aqueous titration method using caproyl PGMC, cremophore EL and propylene glycol as the oil, surfactant, and cosurfactant respectively. The formulations were characterized by their size, zeta potential and polydispersity index (PDI). 1% Carbopol 934 was used as the gelling agent to formulate nanoemulgel comprising of optimized nanoemulsion (NE 9). Ex vivo skin permeation of the CB nanoemulgel was compared with the CB ointment. Its therapeutic effect was evaluated in Balb/c mice.

RESULTS

NE 9 comprised of 7.49% oil, 37.45% Smix (1:3) and water 55.06%. Its particle size, PDI and zeta potential were 15.45 ± 5.265 nm, 0.098 and -17.9 ± 8.00 mV respectively. The nanoemulgel exhibited a 3-fold higher permeation flux as compared to the ointment. In vivo studies demonstrated that the nanoemulgel provided better therapeutic effect than the ointment.

CONCLUSION

We can thereby conclude that nanoemulgel formulation can be a successful drug delivery strategy for enhancing the therapeutic effect of CB.

Redox Mechanisms Underlying the Cytostatic Effects of Boric Acid on Cancer Cells-An Issue Still Open

Boric acid (BA) is the dominant form of boron in plasma, playing a role in different physiological mechanisms such as cell replication. Toxic effects have been reported, both for high doses of boron and its deficiency. Contrasting results were, however, reported about the cytotoxicity of pharmacological BA concentrations on cancer cells. The aim of this review is to briefly summarize the main findings in the field ranging from the proposed mechanisms of BA uptake and actions to its effects on cancer cells.

Stereoselective formation of boron-stereogenic organoboron derivatives

Four-coordinate organoboron derivatives present interesting chemical, physical, biological, electronical, and optical properties. Given the increasing demand for the synthesis of smart functional materials based on chiral organoboron compounds, the exploration of stereoselective synthesis of boron-stereogenic organo-derivatives is highly desirable. However, the stereoselective construction of organoboron compounds stereogenic at boron has been far less studied than other elements of the main group due to configurational stability concerns. Nowadays, these species are no longer elusive and configurationally stable compounds have been highlighted. The idea is to show the potential of the stereoselective building of the four-coordinate boron centre and encourage future endeavors and developments in the field.

Enolates ambushed - asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

Metal enolates are useful intermediates and building blocks indispensable in many organic synthetic transformations. Chiral metal enolates obtained by asymmetric conjugate additions of organometallic reagents are structurally complex intermediates that can be employed in many transformations. In this review, we describe this burgeoning field that is reaching maturity after more than 25 years of development. The effort of our group to broaden possibilities to engage metal enolates in reactions with new electrophiles is described. The material is divided according to the organometallic reagent employed in the conjugate addition step, and thus to the particular metal enolate formed. Short information on applications in total synthesis is also given.

Boron-Containing Compounds for Prevention, Diagnosis, and Treatment of Human Metabolic Disorders

The application of natural and synthetic boron-containing compounds (BCC) in biomedical field is expanding. BCC have effects in the metabolism of living organisms. Some boron-enriched supplements are marketed as they exert effects in the bone and skeletal muscle; but also, BCC are being reported as acting on the enzymes and transporters of membrane suggesting they could modify the carbohydrate metabolism linked to some pathologies of high global burden, as an example is diabetes mellitus. Also, some recent findings are showing effects of BCC on lipid metabolism. In this review, information regarding the effects and interaction of these compounds was compiled, as well as the potential application for treating human metabolic disorders is suggested.

Alkynone β-trifluoroborates: A new class of amine-specific biocompatible click reagents

Amine-targeting reactions that work under biocompatible conditions or in water are green processes that are extremely useful for the synthesis of functional materials and biotherapeutics. Unfortunately, despite the usefulness of this reaction, there are very few good amine-specific click methods reported thus far. Here, we report an amine-specific click reagent using alkynone β-trifluoroborates as the electrophiles. These boron-containing alkynyl reagents exhibit extremely high chemoselectivity toward amines even in the presence of thiols. The resulting oxaboracycle products are bench-stable, displaying the reactivities of both organoborates and enaminones. Intrinsic advantages of this methodology include benign reaction conditions, operational simplicity, remarkable product stability, and excellent chemoselectivity, which satisfy the criteria of click chemistry and demonstrate the high potential in bioconjugation. Hence, this water-based chemical approach is also applicable to the modification of native amino acids, peptides, and proteins. Ultimately, the essential role of water during the reaction was elucidated.

Discovery of Novel Benzoxaborole-Containing Streptochlorin Derivatives as Potential Antifungal Agents

Streptochlorin is a kind of indole alkaloid derived from marine microorganisms. It is a promising lead compound due to its potent bioactivity in preventing many phytopathogens, as shown in our previous study. To explore the potential applications of this natural product, a series of novel benzoxaborole-containing streptochlorin derivatives were designed and synthesized through a one-step and catalyst-free reaction in water at room temperature. All target compounds were first screened for their antifungal profiles in vitro against six common phytopathogenic fungi. The results of bioassay revealed that most of the designed compounds exhibited more significant antifungal activities against Botrytis cinrea, Gibberella zeae, Rhizoctorzia solani, Colletotrichum lagenarium, and alternaria leaf spot under the concentration of 50 μg/mL, and this is highlighted by compounds 4i and 5f, which demonstrated impressive antifungal effects against G. zeae and R. solani, with their corresponding EC₅₀ values 0.2983 and 0.2657 μg/mL, which are obviously better than positive control flutriafol and boscalid (5.2606 and 1.2048 μg/mL, respectively). Scanning electron microscopy on the hyphae morphology showed that compound 5b might cause mycelial abnormalities of G. zeae. 3D-QSAR studies of CoMFA and CoMSIA were carried out on 29 target compounds with antifungal activity against B. cinrea. The analysis results indicated that introducing appropriate electronegative groups at the 5-position of benzoxaborole and the 4,5-positions of the indole ring could effectively improve the anti-B. cinrea activity. Moreover, compound 5b showed good antifungal activities in vivo against Phytophthora capsici. Molecular docking was further explored to ascertain the practical value of the active compound as a potential inhibitor of LeuRS. The abovementioned results indicate that the designed benzoxaborole-containing streptochlorin derivatives could be further studied as template molecules of novel antifungal agents.

Cope-Type Hydroamination of Vinylboronates

Aminoboronic acid derivatives can serve as versatile synthetic intermediates and pharmacophores but remain difficult to synthesize. Herein we report a synthesis of the β-aminoboronic acid motif via anti-Markovnikov hydroamination of vinylboronates. This reaction benefits from the activating effect of the boronate substituent and forms novel BON-containing heterocycles, oxazaborolidine zwitterions. A computational study is included to help determine the effects of alkene boron substitution. Derivatization reactions also support the synthetic utility of the oxazaborolidine adducts.