Boron-containing compounds: chemico-biological properties and expanding medicinal potential in prevention, diagnosis and therapy

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.

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.

Mechanism and Origins of Regio- and Stereoselective Alkylboration of Endocyclic Olefins Enabled by Nickel Catalysis

The Ni-catalyzed alkylboration of endocyclic olefins is a stereo- and regioselective approach for the synthesis of boron-containing compounds. We report a detailed density functional theory (DFT) study to elucidate the mechanism and origins of the stereo-, chemo-, and regioselectivity of alkylboration of endocyclic olefins enabled by nickel catalysis. The alkylboration proceeds via the migratory insertion of alkenes, β-H elimination of the Ni(II) complex, subsequent migratory insertion leading to a new Ni(II) complex, combined with an alkyl radical, and reductive eliminations. The electronic effects of the endocyclic olefins synergistically control the regioselectivity toward the C1- and C2-position boration. In C1-position boration, a more electron-deficient carbon atom tends to combine with an electron-rich -Bpin group and leads to C1-position boration products. The stereoselectivity is influenced by the solvent effect, and the interaction between the substrate and Ni-catalyzed groups, the low-polarity solvent 1,4-dioxane, and a favorable steric hindrance effect result in the cis-alkylboration product. Chemoselectivity toward 1,3-alkylboration results from the steric hindrance effects of the -Bpin group.

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.

Effects of Boron-Containing Compounds on Liposoluble Hormone Functions

Boron-containing compounds (BCC), particularly boronic acids and derivatives, are being increasingly tested as diagnostic and therapeutic agents. Some effects of BCC involve phenomena linked to the action of steroid or thyroid hormones; among these, are the effects on muscle mass or basal metabolism. Additionally, some toxicology reports on mammals, including humans, sound an alert concerning damage to several systems, among which are the negative effects on the induction of male infertility. Systemic and local mechanisms to explain changes in metabolism and impaired fertility were collected and presented. Then, we presented the putative pharmacodynamic and pharmacokinetic mechanisms involved and demonstrated in these events. In addition, it is proposed that there are adducts of some oxygenated BCC with cis-diols in fructose, an essential source of energy for sperm–cell motility, an uncoupling of sex hormone-binding globulin (SHBG) and its ligands, and the modulation of the DNA synthetic rate. These effects share the reactivity of boron-containing compounds on the cis-diols of key molecules. Moreover, data reporting no DNA damage after BCC administration are included. Further studies are required to support the clear role of BCC through these events to disrupt metabolism or fertility in mammals. If such phenomena are confirmed and elucidated, an advance could be useful to design strategies for avoiding BCC toxicity after BCC administration, and possibly for designing metabolism regulators and contraceptive drugs, among other purposes. Boronic derivatives and carboranes have been proposed and studied in this field.

Synthesis of Novel Multifunctional bora-Ibuprofen Derivatives

A unique class of β-boron-functionalized non-steroidal anti-inflammatory compound (pinB-NSAID) was previously synthesized via copper-catalyzed 1,2-difunctionalization of the respective vinyl arene with CO2 and B2pin2 reagents. Here, pinacolylboron-functionalized ibuprofen (pinB-ibuprofen) was used as a model substrate to develop the conditions for pinacol deprotection and subsequent boron functionalization. Initial pinacol-boronic ester deprotection was achieved by transesterification with diethanolamine (DEA) from the boralactonate organic salt. The resulting DEA boronate adopts a spirocyclic boralactonate structure rather than a diazaborocane–DABO boronate structure. The subsequent acid-mediated hydrolysis of DEA and transesterification/transamination provided a diverse scope of new boron-containing ibuprofen derivatives.

The effects of boron-supplemented diets on adipogenesis-related gene expressions, anti-inflammatory, and antioxidative response in high-fat fed rats

The fatty liver syndrome caused by nutritional factors is a common cause of hepatic dysfunction globally. This research was designed to study the shielding effect of boron in rats fed a diet having high fat. Overall, 40 Wistar albino male rats were placed into one control and four treatment groups, that is, each having eight rats. Group I was provided with a standard rat diet while group II was only provided a high-fat diet for 60 days. Groups III, IV, and V were provided with 5, 10, and 20 mg/kg/day boron, respectively, by gastric gavage besides a high-fat diet for 60 days. Malondialdehyde was increased significantly in rats' blood and tissue because of high-fat diets. Glutathione was decreased significantly in blood and tissues because of a high-fat diet. Moreover, the activities of superoxide dismutase (SOD) and catalase (CAT) were decreased in the blood and tissues of the high-fat-fed rats. The genes expression for C-reactive protein, interleukin-1β, leptin, and tumor necrosis factor-α were increased while gene expression for peroxisome proliferator-activated receptors was decreased in the liver of rats fed with a high-fat diet. Contrariwise, boron supplementation improves antioxidative response in terms of increased SOD and CAT activities, gene expression regulation, and improved anti-inflammatory activities. In a nutshell, boron has dose-dependent shielding antioxidative and tissue regenerative effects in rats.

Computer simulation of molecular recognition in biomolecular system: from in silico screening to generalized ensembles

Prediction of ligand-receptor complex structure is important in both the basic science and the industry such as drug discovery. We report various computation molecular docking methods: fundamental in silico (virtual) screening, ensemble docking, enhanced sampling (generalized ensemble) methods, and other methods to improve the accuracy of the complex structure. We explain not only the merits of these methods but also their limits of application and discuss some interaction terms which are not considered in the in silico methods. In silico screening and ensemble docking are useful when one focuses on obtaining the native complex structure (the most thermodynamically stable complex). Generalized ensemble method provides a free-energy landscape, which shows the distribution of the most stable complex structure and semi-stable ones in a conformational space. Also, barriers separating those stable structures are identified. A researcher should select one of the methods according to the research aim and depending on complexity of the molecular system to be studied.

Effects of boric acid and potassium metaborate on cytokine levels and redox stress parameters in a wound model infected with methicillin‑resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) infections are usually found in hospital settings and, frequently, in patients with open wounds. One of the most critical virulence factors affecting the severity and recurrence of infections is the biofilm; increasing antibiotic resistance due to biofilm formation has led to the search for alternative compounds to antibiotics. The present study aimed to use boric acid and potassium metaborate against MRSA infection in a fibroblast wound model. For this purpose, a two-part experiment was designed: First, MRSA strains were used for the test, and both boric acid and potassium metaborate were prepared in microdilution. In the second step, an MRSA wound model was prepared using a fibroblast culture, and treatments with boric acid and potassium metaborate were applied for 24 h. For the evaluation of the effects of treatment, cell viability assay (MTT assay), analysis of redox stress parameters, including total oxidant status and total antioxidant capacity analyses, lactate dehydrogenase analysis and immunohistochemical staining were performed. In addition, IL-1β and IL-10 gene expression levels were assayed. According to the results, potassium metaborate was more effective and exhibited a lower toxicity to fibroblast cells compared to boric acid; moreover, potassium metaborate decreased the level of prooxidant species and increased the antioxidant status more effectively than boric acid. The IL-1β level in the bacteria group was high; however, boric acid and potassium metaborate significantly decreased the expression levels of inflammatory markers, exhibiting the potential to improve the resolution of the lesion. On the whole, the findings of the present study suggest that boric acid and potassium metaborate may be effective on the tested microorganisms.

Boron Chemicals in Drug Discovery and Development: Synthesis and Medicinal Perspective

A standard goal of medicinal chemists has been to discover efficient and potent drug candidates with specific enzyme-inhibitor abilities. In this regard, boron-based bioactive compounds have provided amphiphilic properties to facilitate interaction with protein targets. Indeed, the spectrum of boron-based entities as drug candidates against many diseases has grown tremendously since the first clinically tested boron-based drug, Velcade. In this review, we collectively represent the current boron-containing drug candidates, boron-containing retinoids, benzoxaboroles, aminoboronic acid, carboranes, and BODIPY, for the treatment of different human diseases.In addition, we also describe the synthesis, key structure-activity relationship, and associated biological activities, such as antimicrobial, antituberculosis, antitumor, antiparasitic, antiprotozoal, anti-inflammatory, antifolate, antidepressant, antiallergic, anesthetic, and anti-Alzheimer's agents, as well as proteasome and lipogenic inhibitors. This compilation could be very useful in the exploration of novel boron-derived compounds against different diseases, with promising efficacy and lesser side effects.

Novel boron-containing compound, halogenated boroxine, induces selective cytotoxicity through apoptosis triggering in UT-7 leukemia

Apoptosis induction is a promising approach in targeting tumor cells. As halogenated boroxine (HB) shows antitumor activity, but its mechanism of action in hematological tumors remains unclear, in this study, we aimed to analyze apoptosis triggering in normal and UT-7 leukemia cells by HB. Methods for assessing cell viability and cytotoxicity, apoptosis detection, relative expression of 84 apoptosis-associated genes and BCL-2, and functional analysis were applied. Pronounced HB activities in inhibition of cell viability, cytotoxicity, and apoptosis induction with measurable differences between tumor and normal cells were found. HB modulated the expression of 21 genes, predominantly downregulated the antiapoptotic genes in leukemia. The functional association revealed HB's impact on inhibition of NF-κB signaling pathway. BCL-2 expression decreasing was found only in UT-7 leukemia. This study identified HB as an apoptosis inducer affecting leukemia but not normal cells considering mechanisms of selective activity that may be a great advantage of HB applications.

Interactions of a boron-containing levodopa derivative on D2 dopamine receptor and its effects in a Parkinson disease model

Levodopa is a cornerstone in Parkinson's disease treatment. Beneficial effects are mainly by binding on D₂ receptors. Docking simulations of a set of compounds including well-known D₂-ligands and a pool of Boron-Containing Compounds (BCC), particularly boroxazolidones with a tri/tetra-coordinated boron atom, were performed on the D₂ Dopamine receptor (D2DR). Theoretical results yielded higher affinity of the compound DPBX, a Dopaboroxazolidone, than levodopa on D2DR. Essential interactions with residues in the third and sixth transmembrane domains of the D2DR appear to be crucial to induce and stabilize interactions in the active receptor state. Results from a motor performance evaluation of a murine model of Parkinson's disease agree with theoretical results, as DPBX showed similar efficacy to that of levodopa for diminishing MPTP-induced parkinsonism. This beneficial effect was disrupted with prior Risperidone (D2DR antagonist) administration, supporting the role of D2DR in the biological effect of DPBX. In addition, DPBX limited neuronal loss in substantia nigra in a similar manner to that of levodopa administration.

Triphenylboroxine stability under low energy electron interactions

Triphenylboroxine (TFB) has chemical properties of great interest in organic synthesis allowing the development of promising molecular architectures. Based on the possibility of geometric arrangement of N-coordinated boron atoms, the...

Boron-based hybrids as novel scaffolds for the development of drugs with neuroprotective properties

Novel boron-based compounds (BBCs) were synthesized and evaluated as potential candidates for the development of novel drugs against Alzheimer's disease (AD). The neuroprotective profile of novel BBCs was evaluated using Aβ1-42-treated-SH-SY5Y cells while their antioxidant activity was evaluated by total antioxidant capacity (TAC) and total oxidative status (TOS) assays. Results showed that BLA (a novel boron-based hybrid containing an antioxidant portion) inhibited cell death induced by Aβ1-42-exposure in differentiated SH-SY5Y cells, resulting in an increase in cell viability by 25-33% (MTT assay) and by 63-71% (LDH assay) in a concentration range of 25-100 μM. Antioxidant assays demonstrated a good capability of BLA to counteract the oxidative status. Moreover, BLA possessed a significant ability to inhibit acetylcholinesterase (AChE) (22.96% at 50 μM), an enzyme whose enzymatic activity is increased in AD patients. In the present work, absorption and distribution properties of boron-based hybrids were predicted using Pre-ADMET software. In vitro preliminary results suggested that boron-based hybrids could be new structural scaffolds for the development of novel drugs for the management of AD.

A Boron-Containing Compound Acting on Multiple Targets Against Alzheimer's Disease. Insights from Ab Initio and Molecular Dynamics Simulations

Given the multifactorial nature and pathogenesis of Alzheimer's disease, therapeutic strategies are addressed to combine the benefits of every single-target drug into a sole molecule. Quantum mechanics and molecular dynamics (MD) methods were employed here to investigate the multitarget action of a boron-containing compound against Alzheimer's disease. The antioxidant activity as a radical scavenger and metal chelator was explored by means of density functional theory. The most plausible radical scavenger mechanisms, which are hydrogen transfer, radical adduct formation, and single-electron transfer in aqueous and lipid environments, were fully examined. Metal chelation ability was investigated by considering the complexation of Cu(II) ion, one of the metals that in excess can even catalyze the β-amyloid (Aβ) aggregation. The most probable complexes in the physiological environment were identified by considering both the stabilization energy and the shift of the λ^max induced by the complexation. The excellent capability to counteract Aβ aggregation was explored by performing MD simulations on protein-ligand adducts, and the activity was compared with that of curcumin, chosen as a reference.

The Emergence and Evolution of Borophene

Neighboring carbon and sandwiched between non-metals and metals in the periodic table of the elements, boron is one of the most chemically and physically versatile elements, and can be manipulated to form dimensionally low planar structures (borophene) with intriguing properties. Herein, the theoretical research and experimental developments in the synthesis of borophene, as well as its excellent properties and application in many fields, are reviewed. The decade-long effort toward understanding the size-dependent structures of boron clusters and the theory-directed synthesis of borophene, including bottom-up approaches based on different foundations, as well as up-down approaches with different exfoliation modes, and the key factors influencing the synthetic effects, are comprehensively summarized. Owing to its excellent chemical, electronic, mechanical, and thermal properties, borophene has shown great promise in supercapacitor, battery, hydrogen-storage, and biomedical applications. Furthermore, borophene nanoplatforms used in various biomedical applications, such as bioimaging, drug delivery, and photonic therapy, are highlighted. Finally, research progress, challenges, and perspectives for the future development of borophene in large-scale production and other prospective applications are discussed.

Effects of boron-containing compounds in the fungal kingdom

BACKGROUND

The number of known boron-containing compounds (BCCs) is increasing due to their identification in nature and innovative synthesis procedures. Their effects on the fungal kingdom are interesting, and some of their mechanisms of action have recently been elucidated.

METHODS

In this review, scientific reports from relevant chemistry and biomedical databases were collected and analyzed.

RESULTS

It is notable that several BCC actions in fungi induce social and economic benefits for humans. In fact, boric acid was traditionally used for multiple purposes, but some novel synthetic BCCs are effective antifungal agents, particularly in their action against pathogen species, and some were recently approved for use in humans. Moreover, most reports testing BCCs in fungal species suggest a limiting effect of these compounds on some vital reactions.

CONCLUSIONS

New BCCs have been synthesized and tested for innovative technological and biomedical emerging applications, and new interest is developing for discovering new strategic compounds that can act as environmental or wood protectors, as well as antimycotic agents that let us improve food acquisition and control some human infections.

R, José M. SQ, D. FGE, Marvin A. SU. Docking Simulations Exhibit Bortezomib and other Boron-containing Peptidomimetics as Potential Inhibitors of SARS-CoV-2 Main Protease

Background::

Treatment of the COVID19 pandemic requires drug development. Boron- containing compounds are attractive chemical agents, some of them act as proteases inhibitors.

Objective::

The present study explores the role of boronic moieties in molecules interacting on the binding site of the SARS-CoV-2 main protease.

Methods::

Conventional docking procedure was applied by assaying boron-free and boron-containing compounds on the recently reported crystal structure of SARS-CoV-2 main protease (PDB code: 6LU7). The set of 150 ligands includes bortezomib and inhibitors of coronavirus proteases.

Results::

Most of the tested compounds share contact with key residues and pose on the cleavage pocket. The compounds with a boron atom in their structure are often estimated to have higher affinity than boron-free analogues.

Conclusion::

Interactions and the affinity of boron-containing peptidomimetics strongly suggest that boron-moieties increase affinity on the main protease, which is tested by in vitro assays. A Bis-boron-containing compound previously tested active on SARS-virus protease and bortezomib were identified as potent ligands. These advances may be relevant to drug designing, in addition to testing available boron-containing drugs in patients with COVID19 infection.

Biochemical and histomorphological findings in Swiss Wistar rats treated with potential boron-containing therapeutic - K2[B3O3F4OH]

BACKGROUND

Boron and boron containing compounds are known for their biological and protective roles being non-toxic and non-mutagenic in low concentrations. Male rats were exposed to halogenated boroxine (HB), dipotassium-trioxohydroxytetrafluorotriborate K₂[B₃O₃F₄OH], a potential new boron-containing therapeutic, aiming to determine concentrations with no adverse effects on selected serum biochemical parameters and histomorphological features.

METHODS

HB was prepared by reacting potassium hydrofluoride (KHF₂) with boric acid in molar ratios 2:3 at room temperature and its primary structure contains 4 fluorine atoms substituted in 6-membered ring. In concentrations of 10, 25, 35 and 45 mg/kg, HB was administered intraperitoneally as a single dose. Biochemical parameters were observed 24 and 96 h following the treatment. Effects of HB on biochemical blood parameters were also observed 24 h following continuous nine days application in concentrations of 10 mg/kg intraperitoneally and 50 mg/kg per os. Histomorphological observation of kidneys, liver, spleen, lungs and heart was performed for all treated animals.

RESULTS

Administration of single high dose of HB (35 mg/kg-45 mg/kg) effected high levels of urea and creatinine, which indicated renal injury that appeared to be temporary. Possible cause of concern is pancreatic injury indicated by elevated levels of serum amylase in the groups of animals that received the highest dosages of the substance. Histopathological examination of selected tissues revealed mild to moderate lesions in the kidneys and livers associated with administration of HB.

CONCLUSION

Observation of biochemical serum parameters or histopathology of examined tissues revealed no adverse effects of HB either after the administration of single dose lower than 35 mg/kg or following repeated administration at 10 mg/kg. These dosages should be further considered for potential therapeutic applications.

Bioactive Glasses: A Promising Therapeutic Ion Release Strategy for Enhancing Wound Healing

The morbidity, mortality, and burden of burn victims and patients with severe diabetic wounds are still high, which leads to an extensively growing demand for novel treatments with high clinical efficacy. Biomaterial-based wound treatment approaches have progressed over time from simple cotton wool dressings to advanced skin substitutes containing cells and growth factors; however, no wound care approach is yet completely satisfying. Bioactive glasses are materials with potential in many areas that exhibit unique features in biomedical applications. Today, bioactive glasses are not only amorphous solid structures that can be used as a substitute in hard tissue but also are promising materials for soft tissue regeneration and wound healing applications. Biologically active elements such as Ag, B, Ca, Ce, Co, Cu, Ga, Mg, Se, Sr, and Zn can be incorporated in glass networks; hence, the superiority of these multifunctional materials over current materials results from their ability to release multiple therapeutic ions in the wound environment, which target different stages of the wound healing process. Bioactive glasses and their dissolution products have high potency for inducing angiogenesis and exerting several biological impacts on cell functions, which are involved in wound healing and some other features that are valuable in wound healing applications, namely hemostatic and antibacterial properties. In this review, we focus on skin structure, the dynamic process of wound healing in injured skin, and existing wound care approaches. The basic concepts of bioactive glasses are reviewed to better understand the relationship between glass structure and its properties. We illustrate the active role of bioactive glasses in wound repair and regeneration. Finally, research studies that have used bioactive glasses in wound healing applications are summarized and the future trends in this field are elaborated.

Advances in Discovery of PDE10A Inhibitors for CNS-Related Disorders. Part 1: Overview of the Chemical and Biological Research

Phosphodiesterase 10A (PDE10A) is a double substrate enzyme that hydrolyzes second messenger molecules such as cyclic-3',5'-adenosine monophosphate (cAMP) and cyclic-3',5'-guanosine monophosphate (cGMP). Through this process, PDE10A controls intracellular signaling pathways in the mammalian brain and peripheral tissues. Pharmacological, biochemical, and anatomical data suggest that disorders in the second messenger system mediated by PDE10A may contribute to impairments in the central nervous system (CNS) function, including cognitive deficits as well as disturbances of behavior, emotion processing, and movement. This review provides a detailed description of PDE10A and the recent advances in the design of selective PDE10A inhibitors. The results of preclinical studies regarding the potential utility of PDE10A inhibitors for the treatment of CNS-related disorders, such as schizophrenia as well as Huntington's and Parkinson's diseases are also summarized.

Effects of boron-containing compounds on immune responses: review and patenting trends

INTRODUCTION

Boron-containing compounds induce effects on immune responses. Such effects are interesting to the biomedical field for the development of therapeutic tools to modulate the immune system.

AREAS COVERED

The scope of BCC use to modify immune responses is expanding, mainly with regard to inflammatory diseases. The information was organized to demonstrate the breadth of reported effects. BCCs act as modulators of innate and adaptive immunity, with the former including regulation of cluster differentiation and cytokine production. In addition, BCCs exert effects on inflammation induced by infectious and noninfectious agents, and there are also reports regarding their effects on mechanisms involving hypersensitivity and transplants. Finally, the authors discuss the beneficial effects of BCCs on pathologies involving various targets and mechanisms.

EXPERT OPINION

Some BCCs are currently used as drugs in humans. The mechanisms by which these BCCs modulate immune responses, as well as the required structure-activity relationship for each observed mechanism of action, should be clarified. The former will allow for the development of improved immunomodulatory drugs with extensive applications in medicine. Patenting trends involve claims concerning the synthesis and actions of identified molecules with a defined profile regarding cytokines, cell differentiation, proliferation, and antibody production.

Turning fear of boron toxicity into boron-containing drug design

BACKGROUND

Despite the historical employment of boron-containing compounds (BCCs) with medicinal purposes, the reported cases of BCC toxicity in humans during the twentieth century were driving us towards an "boron-withdrawal" period. Fortunately, the use of boric acid for specific purposes remains, and the discovery of natural BCCs with biological action attractive for therapeutic purposes as well as the introduction of some new BCCs for clinical use have reactivated the interest in studying the properties of these BCCs.

METHODS

We carried out a structured search of bibliographic databases for scientific peer-reviewed research literature regarding boron toxicity and linked that information to that about BCCs in drug design and development. A deductive qualitative content analysis methodology was applied to analyse the interventions and findings of the included studies using a theoretical outline.

RESULTS

This review recapitulates the following on a timeline: the boron uses in medicine, the data known about the toxicological profiles of some BCCs, the pharmacological properties of some BCCs that are employed in cancer and infectious disease therapies, and the known properties of BCCs recently introduced into clinical assays as well as the identification of their structure-activity relationships for toxicity and therapeutic use. Then, we discuss the use of new approaches taking advantage of some toxicological data to identify potent and efficient BCCs for prevention and therapy while limiting their toxic effects.

CONCLUSION

Data for boron toxicity can be strategically used for boron-containing drug design.

Theoretical Coupling and Stability of Boronic Acid Adducts with Catecholamines

Background:

Catecholamines combined with boric/boronic acids are attractive chemical agents in drug design because some of their adducts have shown interesting biological activity. Scant information exists about their stability.

Objective:

The aim of the present theoretical study was to explore the role of boron in molecules that combine catecholamines and boric/boronic acids, with a particular interest in examining stability.

Method:

The methodology was based on the US GAMESS program using DFT with the B3LYP exchange-correlation functional and the 6-31G (d,p) split-valence basis set.

Results:

According to the current findings, the boron-containing compounds (BCCs) exhibit weaker bonding to the hydroxyls on the ethylamine moiety than to those in the aromatic ring. The strongest binding site of a hydroxyl group was often found to be in meta-position (relative to ethylamine moiety) for boron-free compounds and in para-position for BCCs. Nonetheless, the methyl substituent in the amino group was able to induce changes in this pattern. We analyzed feasible boronsubstituted structures and assessed the relative strength of the respective C-B bonds, which allowed for the identification of the favorable points for reaction and stability.

Conclusion:

It is feasible to form adducts by bonding on the amine and catechol sides of catecholamines. The presence of boron stabilizes the adducts in para-position. Since some of these BCCs are promising therapeutic agents, understanding the mechanisms of reaction is relevant for drug design.

The Fructoborates: Part of a Family of Naturally Occurring Sugar-Borate Complexes-Biochemistry, Physiology, and Impact on Human Health: a Review

Sugar-borates (SBs) are mono- or di-sugar-borate esters (SBEs) comprised of one or two monosaccharide molecules linked to a boron (B) atom. SBEs occur naturally in commonly consumed herbs, vegetables, fruits, seeds, and nuts and, other than greatly varying levels of B found in local drinking water, are the primary natural dietary sources of B-containing molecules in humans. To date, the most studied SBE is calcium fructoborate (CaFB). CaFB represents an important example of how organic B-containing molecules are significantly distinct from their inorganic counterparts. During these past two decades, CaFB has been researched for its physical and biochemical characteristics, safety, and clinical outcomes. Results of these researches are presented and discussed herein. CaFB has been characterized using Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), high-performance thin-layer chromatography (HPTLC), nuclear magnetic resonance (NMR), liquid chromatography-multistage accurate mass spectrometry (LC-MSn), X-ray diffraction (XRD), Raman spectroscopy, and inductively coupled plasma (ICP) in non-biological and biological specimens. Potential health benefits of CaFB have been clinically investigated in pilot and efficacy studies demonstrating (i) significant reductions in knee discomfort and improved flexibility within 7, 14, and 90 days and (ii) significant effect on blood levels of inflammatory, cardiovascular, and other biomarkers. These studies support the use of CaFB as a dietary supplement for the management of joint discomfort. CaFB is presented here in order to illustrate how physiological benefits are imparted by distinct organic boron-containing molecules rather than solely by the element B itself. Considering recent National Health and Nutrition Examination Survey (NHANES) data reporting increases in age-related joint pain and an increasing elderly demographic, SBEs offer potential for safe, natural, and effective management of joint discomfort and improved mobility in human and animal health applications. Several of these studies may also open new opportunities for use of SBEs for health benefits beyond joint health.

Efficient blue light emitting materials based on m-carborane–anthracene dyads. Structure, photophysics and bioimaging studies

Linking m-carborane to the anthracene dye produces an exceptional enhancement of the fluorescence properties, with quantum efficiencies close to 100% in solution. Dyads were internalized by HeLa cells through endocytosis showing intense blue emission.

Effects of boron-containing compounds on cardiovascular disease risk factors - A review

Boron is considered to be a biological trace element but there is substantial and growing support for it to be classified as an essential nutrient for animals and humans, depending on its speciation. Boron-containing compounds have been reported to play an important role in biological systems. Although the exact biochemical functions of boron-containing compounds have not yet been fully elucidated, previous studies suggest an active involvement of these molecules in the mediation of inflammation and oxidative stress. Chronic inflammation and oxidative stress are known to amplify the effects of the main cardiovascular risk factors: smoking, diet, obesity, arterial hypertension, dyslipidemia, type 2 diabetes (as modifiable risk factors), and hyperhomocysteinemia and age (as independent risk factors). However, the role of boron-containing compounds in cardiovascular systems and disease prevention has yet to be established. This paper is a review of boron-containing compounds' existence in nature and their possible functions in living organisms, with a special focus on certain cardiovascular risk factors that may be diminished by intake of these compounds, leading to a reduction of cardiovascular morbidity and/or mortality.

Profile of three boron-containing compounds on the body weight, metabolism and inflammatory markers of diabetic rats

It has been reported that boron induces changes in carbohydrate and lipid metabolism, body weight and inflammatory processes. This is relevant to the biomedical field due to the requirement for developing therapeutic tools with potential application in metabolic disorders affecting humankind. However, most of the reported data from both humans and animals were obtained after boron was administered as borax or boric acid. In this work, we determined the effects of boric, cyclohexylboronic (CHB) and phenylboronic (PBA) acids (10 mg/kg of body weight/daily for two weeks) on the body weight, metabolism and inflammatory markers in the blood of control, fat-feeding and experimental diabetic rats. In particular, we observed the effects of the administration of these compounds on glycaemia and cholesterol, triglyceride, insulin, IL-6 and C-reactive protein levels, as well as visceral fat and body weight. We found different profiles for each boron-containing compound: boric acid induced decreasing body weight, insulin and IL-6 levels; CHB administration induced an increase in body weight and cholesterol but decreased IL-6 levels; and PBA administration induced a decrease in visceral fat and glucose and insulin levels. These results can improve the understanding of boron as a metabolic regulator and help develop new potential strategies to use compounds with this trace element for therapeutic purposes.

Structural and biological overview of Boron-containing amino acids in the medicinal chemistry field

Amino acids are the basic structural units of proteins as well as the precursors of many compounds with biological activity. The addition of boron reportedly induces changes in the chemical-biological profile of amino acids.

METHODS

We compiled information on the biological effect of some compounds and discuss the structure-activity relationship of the addition of boron. The specific focus presently is on borinic derivatives of α-amino acids, the specific changes in biological activity caused by the addition of a boron-containing moiety, and the identification of some attractive compounds for testing as potential new drugs.

RESULTS

Borinic derivatives of α-amino acids have been widely synthesized and tested as potential new therapeutic tools. The B-N (1.65 A°) or B-C (1.61 A°) or B-O (1.50 A°) bond is often key for the stability at different pHs and temperatures and activity of these compounds. The chemical features of synthesized derivatives, such as the specific moieties and the logP, polarizability and position of the boron atom are clearly linked to their pharmacodynamic and pharmacokinetic profiles. Some mechanisms of action have been suggested or demonstrated, while those responsible for other effects remain unknown.

CONCLUSION

The increasing number of synthetic borinic derivatives of α-amino acids as well as the recently reported crystal structures are providing new insights into the stability of these compounds at different pHs and temperatures, their interactions on drug targets, and the ring formation of five-membered heterocycles. Further research is required to clarify the ways to achieve specific synthesis, the mechanisms involved in the observed biological effect, and the toxicological profile of this type of boron-containing compounds (BCCs).

More than boric acid: Increasing relevance of boron in medicine

Although boron has been a chemical element of interest since the ancient times, only a few boron-containing compounds (BCCs) had been used for medicinal purposes before the 21^st century. Among these, only boric acid has been explored in multiple therapeutic applications. Hence, it is common to extrapolate from boric acid to all BCCs, supposing a similar biological effect. However, boric acid is just one of dozens of BCCs in nature and thousands available from chemical synthesis. Nowadays, there is a boom in research on new BCCs as potential tools in the prevention, diagnosis and therapy of human disease. We herein discuss the new role of BCCs in drug development, with emphasis on the compounds for which a mechanism of action has been proposed or demonstrated. Because of data gathered in recent years, BCCs have expanded beyond the well-known fields of antimicrobial and antineoplastic agents, now being explored for their possible use as enzyme inhibitors, regulators of protein expression and modulators of the immune response, as well as in biomaterials. We suggest that translational medicine can accelerate the medicinal applications of BCCs, which is especially important for the human diseases that are generating a high global burden.

Several effects of boron are induced by uncoupling steroid hormones from their transporters in blood

Boron is increasingly added to food supplements due to multiple effects that have been reported in mammals after boric acid administration. Among these effects are inflammatory process control, bone and muscle strength enhancement, protein expression regulation, and a decreased risk of developing some pathologies in which these processes are key, such as osteoporosis, dermatological inflammatory non-infectious maladies and diseases affecting the central nervous system. Experimental data have suggested that steroid hormone levels in plasma change after boric acid administration, but a clear mechanism behind these variations has not been established. We analyzed possibilities for these changes and hypothesized that boric acid disrupts the interactions between steroid hormones and several carriers in plasma. In particular, we proposed that there is an uncoupling of the interactions between sex hormone binding globulin (SHBG) and estrogens and testosterone and that there are alterations in the binding of hydrophobic ligands by other carrier proteins in plasma. Further experimental and computational studies are required to support the hypothesis that boric acid and probably other boron-containing compounds can displace steroid hormones from their plasma carriers. If such phenomena are confirmed, boron administration with a clear mechanism could be employed as a therapeutic agent in several diseases or physiological events that require modulation of steroid hormone levels in plasma.

Rhodium-catalyzed asymmetric hydroboration of γ,δ-unsaturated amide derivatives: δ-borylated amides

γ,δ-Unsaturated amides in which the alkene moiety bears an aryl or heteroaryl substituent undergo regioselective rhodium-catalyzed δ-borylation by pinacolborane to afford chiral secondary benzylic boronic esters. The results contrast the γ-borylation of γ,δ-unsaturated amides in which the disubstituted alkene moiety bears only alkyl substituents; the reversal in regiochemistry is coupled with a reversal in the sense of π-facial selectivity.

A solid-phase approach for the synthesis of α-aminoboronic acid peptides

A solid-phase synthesis of α-aminoboronic acid peptides using a 1-glycerol polystyrene resin is described.

Small molecules targeting LapB protein prevent Listeria attachment to catfish muscle

Listeria monocytogenes is a Gram-positive foodborne pathogen and the causative agent of listeriosis. L. monocytogenes lapB gene encodes a cell wall surface anchor protein, and mutation of this gene causes Listeria attenuation in mice. In this work, the potential role of Listeria LapB protein in catfish fillet attachment was investigated. To achieve this, boron-based small molecules designed to interfere with the active site of the L. monocytogenes LapB protein were developed, and their ability to prevent L. monocytogenes attachment to fish fillet was tested. Results indicated that seven out of nine different small molecules were effective in reducing the Listeria attachment to catfish fillets. Of these, three small molecules (SM3, SM5, and SM7) were highly effective in blocking Listeria attachment to catfish fillets. This study suggests an alternative strategy for reduction of L. monocytogenes contamination in fresh and frozen fish products.

Synthesis of biologically active boron-containing compounds

Boron-containing compounds which possess unique and attractive properties have received increasing attention from the pharmaceutical industry and academia recently. They have shown interesting and useful biological activities, including antibacterial, antifungal, antiparasitic, antiviral, and anti-inflammatory activities. In this review, the synthetic strategies for various boron-containing compounds, including peptidyl boronic acids, benzoxaboroles, benzoxaborines, benzodiazaborines, amine carboxyboranes, and amine cyanoboranes are summarized. Representative structures of each structural class and recently developed biologically active boron-containing compounds are used as examples in this review.

Not all boronic acids with a five-membered cycle induce tremor, neuronal damage and decreased dopamine

Several striatal toxins can be used to induce motor disruption. One example is MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), whose toxicity is accepted as a murine model of parkinsonism. Recently, 3-Thienylboronic acid (3TB) was found to produce motor disruption and biased neuronal damage to basal ganglia in mice. The aim of this study was to examine the toxic effects of four boronic acids with a close structural relationship to 3TB (all having a five-membered cycle), as well as boric acid and 3TB. These boron-containing compounds were compared to MPTP regarding brain access, morphological disruption of the CNS, and behavioral manifestations of such disruption. Data was collected through acute toxicity evaluations, motor behavior tests, necropsies, determination of neuronal survival by immunohistochemistry, Raman spectroscopic analysis of brain tissue, and HPLC measurement of dopamine in substantia nigra and striatum tissue. Each compound showed a distinct profile for motor disruption. For example, motor activity was not disrupted by boric acid, but was decreased by two boronic acids (caused by a sedative effect). 3TB, 2-Thienyl and 2-furanyl boronic acid gave rise to shaking behavior. The various manifestations generated by these compounds can be linked, in part, to different levels of dopamine (measured by HPLC) and degrees of neuronal damage in the basal ganglia and cerebellum. Clearly, motor disruption is not induced by all boronic acids with a five-membered cycle as substituent. Possible explanations are given for the diverse chemico-morphological changes and degrees of disruption of the motor system, considering the role of boron and the structure-toxicity relationship.

Scope of translational medicine in developing boron-containing compounds for therapeutics

The ubiquitousness of naturally occurring boron-containing compounds (BCCs) has led to their constant contact with humankind. Recently, many synthetic BCCs have been elaborated for a broad spectrum of purposes, especially boric, boronic and borinic acids. Although BCCs were once employed primarily as antiseptics and later as antibiotics, they have become an increasingly relevant therapeutic tool. Nevertheless, this potential of BCCs has been drastically limited due to some unfortunate intra-hospital accidents in the 1940s and 1950s. The increasing use of BCCs as insecticides, antimicrobials, and other agents is providing new insights into their role in the physiology of several living species and in the pathophysiology of humans. It is becoming clear that BCCs act through a wide range of mechanisms, as do their corresponding boron-free counterparts. When comparing BCCs and similar boron-free compounds, in many cases the former show advantages in the medical field. The current mini-review focuses on how BCCs have been developed by means of translational medicine, a process connecting biomedical research with clinical applications. This process of discovery is currently in an exponential stage.

Morin P, Westcott SA. Synthesis, characterization, and anticancer properties of iminophosphineplatinum(II) complexes containing boronate esters

Three new iminophosphines containing pinacol-derived boronate esters have been prepared and ligated to dichloridoplatinum(II) fragments. All compounds have been characterized fully, including an X-ray diffraction study carried out for the platinum complex 8, which is derived from 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline. These three new platinum complexes, along with the non-boron containing control, have been examined for their initial cytotoxic properties against two glioma cell lines using the MTT method.