Challenges and Opportunities for the Application of Boron Clusters in Drug Design

Palladium-catalyzed intramolecular dehydrogenative coupling of BH and OH: synthesis of carborane-fused benzoxaboroles

A Pd-catalyzed intramolecular dehydrogenative coupling of BH and OH for the construction of cage B–O bonds was developed to afford C,B-carborane-fused heterocycles.

Ir-catalyzed selective dehydrogenative cross-coupling of aryls with o-carboranes via a mixed directing-group strategy

Ir-catalyzed highly selective B–H/C–H cross dehydrogenative coupling between o-carboranes and (hetero)aryls has been achieved using a mixed directing-group strategy.

Halogen⋯halogen interactions in decahalo-closo-carboranes: CSD analysis and theoretical study

We theoretically (PBE0-D3/def2TZVP) and experimentally (CSD analysis) demonstrate the importance of “like–like” halogen interactions for the stability of several decahalo-closo-carborane dimers.

Application of Nitroimidazole-Carbobane-Modified Phenylalanine Derivatives as Dual-Target Boron Carriers in Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) has received extensive attention as noninvasive cell-level oncotherapy for treating solid cancer tumors. However, boron-containing drugs such as l-boronophenylalanine (BPA) and sodium borocaptate have low boron content and/or poor tumor-targeting ability, limiting their application. In this study, we designed and synthesized a series of nontoxic, dual-target boron carriers (B139, B142, and B151) with the ability to accumulate specifically in tumor cells. We found that the B139 uptake into hypoxic tumor regions was high, with a 70-fold boron content compared to BPA. In addition, in vivo observation showed that B139 can be trapped in tumor cells for a prolonged period and maintains an effective therapeutic concentration, with a peak boron concentration of 50.7 μg/g and a high tumor: blood boron ratio of >3, achieving ideal BNCT conditions. Cytotoxicity evaluation in mice further proved that B139 is safe and reliable. Therefore, B139 has great potential for BNCT application as a dual-target, safe, and efficient boron carrier.

De Novo Carborane-Containing Macrocyclic Peptides Targeting Human Epidermal Growth Factor Receptor

l-Carboranylalanine (^LCba) is a unique artificial amino acid containing a cluster of 10 boron atoms. Since the three-dimensional aromaticity and charge distributions of the carborane side chain are quite different from any side chains of proteinogenic amino acids, there is no report whether ^LCba can be a substrate for the translation machinery. Here, we report studies on the ribosomal incorporation of ^LCba into peptide via initiation and elongation using the flexizyme-assisted translation system. Our results indicate that only the initiation step could tolerate ^LCba incorporation, but the elongation steps could not, very likely due to its steric bulkiness of the side chain. Based on this knowledge, we have designed a library of macrocyclic peptides initiated by α-N-(2-choloroacetyl)-l-carboranylalanine (ClAc-^LCba) and selected molecules capable of binding to human epidermal growth factor receptor (hEGFR). Two peptides that were forwarded to deeper studies exhibited affinities with K_D values at 16 and 20 nM against hEGFR. Computational modeling of one of the peptides suggested that the carborane side chain might be directly involved in the interaction with the hydrophobic β-sheet core in the EGF binding site of hEGFR, which is consistent with the mutational data where replacing ^LCba residue with ^LPhe completely eliminated the binding activity. Cell lines that stably express hEGFR could be stained by incubation with the C-terminal fluorescein-labeled peptides, whereas hEGFR-negative cells could not be stained. This study provides a general strategy for the de novo discovery of carborane-containing macrocyclic peptides targeting various tumor biomarker proteins, potentially applicable to boron neutron capture therapy.

Versatile, one-pot introduction of nonahalogenated 2-ammonio-decaborate ions as boron cluster scaffolds into organic molecules; host-guest complexation with γ-cyclodextrin

We report the modification of the 2-ammonio group at halogenated decaborate ions with 2,3-epoxypropane, the product of which reacts readily with nucleophiles to form previously inaccessible coupling of polyhedra with organic molecules and materials. We demonstrate that these ions present a good binding motif in supramolecular chemistry.

Synthesis of naphthalimide-carborane and metallacarborane conjugates: Anticancer activity, DNA binding ability

The development of 1,8-naphthalimide derivatives as DNA-targeting anticancer agents is a rapidly growing area and has resulted in several derivatives entering into clinical trials. One of original recent developments is the use of boron clusters: carboranes and metallacarboranes in the design of pharmacologically active molecules. In this direction several naphthalimide-carborane and metallacarborane conjugates were synthesized in the present study. Their effect on a cancer cell line - cytotoxicity, type of cell death, cell cycle, and ROS production were investigated. The tested conjugates revealed different activities than the leading members of the naphthalimides family, namely mitonafide and pinafide. These derivatives could induce G0/G1 arrest and promote mainly apoptosis in HepG2 cell line. Our investigations demonstrated that the most promising molecule is N-{[2-(3,3'-commo-bis(1,2-dicarba-3-cobalta(III)-closo-dodecaborate-1-yl)ethyl]-1'-aminoethyl)}-1,8-naphthalimide] (17). It was shown that 17 exhibited cytotoxicity against HepG2 cells, activated cell apoptosis, and caused cell cycle arrest in HepG2 cells. Further investigations in HepG2 cells revealed that compound 17 can also induce ROS generation, particularly mitochondrial ROS (mtROS), which was also proved by increased 8-oxo-dG level in DNA. Additionally to biological assays the interaction of the new compounds with ct-DNA was studied by CD spectra and melting temperature, thus demonstrating that these compounds were rather weak classical DNA intercalators.

Metallacarborane Sulfamides: Unconventional, Specific, and Highly Selective Inhibitors of Carbonic Anhydrase IX

Carbonic anhydrase IX (CAIX) is a transmembrane enzyme that regulates pH in hypoxic tumors and promotes tumor cell survival. Its expression is associated with the occurrence of metastases and poor prognosis. Here, we present nine derivatives of the cobalt bis(dicarbollide)(1-) anion substituted at the boron or carbon sites by alkysulfamide group(s) as highly specific and selective inhibitors of CAIX. Interactions of these compounds with the active site of CAIX were explored on the atomic level using protein crystallography. Two selected derivatives display subnanomolar or picomolar inhibition constants and high selectivity for the tumor-specific CAIX over cytosolic isoform CAII. Both derivatives had a time-dependent effect on the growth of multicellular spheroids of HT-29 and HCT116 colorectal cancer cells, facilitated penetration and/or accumulation of doxorubicin into spheroids, and displayed low toxicity and showed promising pharmacokinetics and a significant inhibitory effect on tumor growth in syngenic breast 4T1 and colorectal HT-29 cancer xenotransplants.

Fluxional Boron Clusters: From Theory to Reality

Isolated boron clusters exhibit many intriguing properties, which have only recently been unfolding with the hand-in-hand advancement of state-of-the-art experimental and theoretical methods for the analyses of their electronic structure, chemical reactivity, and nuclear dynamics. A fascinating property that a number of these clusters display is fluxionality, a dynamical phenomenon associated with the delocalized nature of the chemical bonding and related to the continuous exchange between interatomic neighbors. The electron-deficient nature of boron is the driving force behind its extraordinary ability to form multicenter bonds, and this in turn leads to fluxional behavior only when an appropriate combination of topology and bonding is present. The first instance of fluxionality in boron clusters, the quasi-planar anion B₁₉^-, was reported in 2010. The rotational barrier of the inner B₆ unit spinning within the peripheral B₁₃ ring can be overcome even at low temperature, mimicking the characteristic motion of a rotary internal combustion engine, and hence, B₁₉^- was entitled a boron-based molecular Wankel engine. Shortly after that, it was found that other quasi-planar boron clusters, like B₁₃⁺ and B₁₈^2-, also exhibit an almost barrier-free rotation of internal planar moieties. The case of the B₁₃⁺ cation is special because, on the one hand, it was chosen to examine the way to initiate, control, and direct the internal rotation using circularly polarized laser radiation, and on the other hand, the experimental manifestation of fluxionality was first established for this system through infrared experiments. Nevertheless, fluxional behavior is not limited to planar or pure boron clusters. Larger boron clusters, such as the fullerene-analogue borospherenes B₄₀ and B₃₉^-, are also predicted to show pronounced dynamical behavior that is related to the interconversion between six- and seven-membered rings. Be₆B₁₁^-, a triple-layer cluster, is another particularly interesting system since it exhibits multifold fluxionality consisting of the revolution of the outer boron ring around the Be₆ core and the spinning of the two Be₃ rings with respect to each other. The essential criteria for dynamical behavior in boron clusters are (1) the absence of a localized two-center, two-electron (2c-2e) bond between two molecular regions that tend to rotate with respect to each other, (2) the absence of steric hindrances for rotation and reorganization, and (3) retention of the delocalized electronic structure throughout the rotation/reorganization process. The fulfillment of the above three conditions ensures that low energy barriers will be associated with the rotation or reorganization of molecular moieties. The first two points can be illustrated from the facts that a single localized C-B σ bond in CB₁₈ raises the rotational barrier by 27.0 kcal·mol^-1 and the expansion of the outer ring by a single boron atom in moving from B₁₂⁺ to B₁₃⁺ lowers the rotational barrier by 7.5 kcal·mol^-1. Alternatively, it is also possible to make a rigid boron cluster fluxional through doping, where the geometric and electronic changes caused by a suitable dopant, as in MB₁₂^- (M = Co, Rh, Ir) and B₁₀Ca, reduce the corresponding rotational barriers enough to achieve fluxionality. At present, there are 13 pure boron clusters (B₁₁^-/0/+, B₁₃^+/0/-, B₁₅^+/0/-, B₁₈^2-, B₁₉^-, and B₂₀^-/2-) and eight metal-doped boron clusters (B₁₀Ca, NiB₁₁^-, [B₂-Ta@B₁₈]^-, Be₆B₁₁^-, Be₆B₁₀^2-, and MB₁₈^- (M = K, Rb, Cs)) that have sufficiently small rotational barriers (less than ∼1.5 kcal·mol^-1) to exhibit fluxional behavior at low temperature. Some of the other reported boron clusters show more sizable barriers, and their dynamical behavior is manifested only at elevated temperatures. The research on such systems is driven by the notion that it ultimately will pave the way for the development of light-harvesting boron-based nanomotors/machines and robots, a reality that may not be that far away!

A self-catalyzed reaction of 1,2-dibenzoyl-o-carborane with hydrosilanes - formation of new hydrofuranes

The activation of Si-H bonds is a very important transformation both in organic and inorganic chemistry. Herein we report that 1,2-dibenzoyl-o-carborane (1) reacts with Si-H bonds, yielding new hydrofurane-type products. The mechanism of this Si-H bond activation was studied both experimentally and by DFT calculations, and supposedly proceeds in an FLP-type manner.

Metallacarboranes as a tool for enhancing the activity of therapeutic peptides

Metallacarboranes are anionic boron clusters with high affinity to serum albumin, ability to cross biological membranes, and no apparent toxicity in vitro and in vivo. Thus, conjugation with cobalt bis(1,2-dicarbollide), [COSAN]^- , ([3,3'-Co(1,2-C₂ B₉ H₁₁ )₂ ]^- ) may improve the properties of therapeutic peptides or proteins at both molecular and systemic levels. Here, we conjugated [COSAN]^- with the therapeutic peptide thymosin β4 (Tβ4), which has a pleiotropic activity that results in enhanced healing and regeneration of injured tissues. Using fluorescence quenching of human serum albumin and surface plasmon resonance techniques, we showed that the conjugates have a high affinity to human serum albumin. Using an in vitro wound closure assay, we showed that conjugation with [COSAN]^- enhances the activity of Tβ4 toward fibroblasts (MSU1.1 cell line). These results indicate an application of metallacarboranes in the development of analogs of various therapeutic peptides/proteins with superior pharmacological properties.

Off-Cycle Processes in Pd-Catalyzed Cross-Coupling of Carboranes

Off-cycle processes in catalytic reactions can dramatically influence the outcome of the chemical transformation and affect its yield, selectivity, rate, and product distribution. While the generation of off-cycle intermediates can complicate reaction coordinate analyses or hamper catalytic efficiency, the generation of such species may also open new routes to unique chemical products. Recently, we reported the Pd-mediated functionalization of carboranes with a range of O-, N-, and C-based nucleophiles. By utilizing a Pd-based catalytic system supported by a biaryl phosphine ligand developed by Buchwald and co-workers, we discovered an off-cycle isomerization process ("cage-walking") that generates four regioisomeric products from a single halogenated boron cluster isomer. Here we describe how several off-cycle processes affect the regioisomer yield and distribution during Pd-catalyzed tandem cage-walking/cross-coupling. In particular, tuning the transmetallation step in the catalytic cycle allowed us to incorporate the cage-walking process into Pd-catalyzed cross-coupling of sterically unencumbered substrates, including cyanide. This work demonstrates the feasibility of using tandem cage-walking/cross-coupling as a unique low-temperature method for producing regioisomers of mono-substituted carboranes.

11B NMR Chemical Shift Predictions via Density Functional Theory and Gauge-Including Atomic Orbital Approach: Applications to Structural Elucidations of Boron-Containing Molecules

¹¹B nuclear magnetic resonance (NMR) spectroscopy is a useful tool for studies of boron-containing compounds in terms of structural analysis and reaction kinetics monitoring. A computational protocol, which is aimed at an accurate prediction of ¹¹B NMR chemical shifts via linear regression, was proposed based on the density functional theory and the gauge-including atomic orbital approach. Similar to the procedure used for carbon, hydrogen, and nitrogen chemical shift predictions, a database of boron-containing molecules was first compiled. Scaling factors for the linear regression between calculated isotropic shielding constants and experimental chemical shifts were then fitted using eight different levels of theory with both the solvation model based on density and conductor-like polarizable continuum model solvent models. The best method with the two solvent models yields a root-mean-square deviation of about 3.40 and 3.37 ppm, respectively. To explore the capabilities and potential limitations of the developed protocols, classical boron-hydrogen compounds and molecules with representative boron bonding environments were chosen as test cases, and the consistency between experimental values and theoretical predictions was demonstrated.

New keys for old locks: carborane-containing drugs as platforms for mechanism-based therapies

Icosahedral carboranes in medicine are still an emerging class of compounds with potential beneficial applications in drug design. These highly hydrophobic clusters are potential "new keys for old locks" which open up an exciting field of research for well-known, but challenging important therapeutic substrates, as demonstrated by the numerous examples discussed in this review.

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

Advances in the field of boron chemistry have expanded the application of this element in Medicinal Chemistry. Boron-containing compounds represent a new class for medicinal chemists to use in their drug designs. Bortezomib (Velcade^®), a dipeptide boronic acid approved by the FDA in 2003 for treatment of multiple myeloma, paved the way for the discovery of new boron-containing compounds. After its approval, two other boron-containing compounds have been approved, tavaborole (Kerydin^®) for the treatment of onychomicosis and crisaborole (Eucrisa^®) for the treatment of mild to moderate atopic dermatitis. A number of boron-containing compounds have been described and evaluated for a plethora of therapeutic applications. The present review is intended to highlight the recent advances related to boron-containing compounds and their therapeutic applications. Here, we focused only in those most biologically active compounds with proven in vitro and/or in vivo efficacy in the therapeutic area published in the last years.

Comparative study of inorganic, boron-rich cluster and organic, phenyl adenosine modifications: synthesis and properties

Background: Nucleoside analogs are important class of chemotherapeutics. One of the original openings in the nucleoside medicinal chemistry was derivatives comprising a boron cluster component. Results: A series of adenosine derivative pairs containing inorganic boron cluster or alternatively its mimic, organic phenyl modification were synthesized and their physicochemical and biological properties compared. Marked effects of boron clusters, which are qualitatively and quantitatively different from the phenyl group effects, were detected. The studied characteristics include syn/ anti conformation, lipophilicity, cytotoxicity and antiviral activity, as well as phosphorylation by adenosine kinase. Conclusion: The obtained results demonstrate usefulness of the boron clusters for tuning properties of biomolecules and prove their potential as modifying units in design of future therapeutics based on nucleoside structures.

Combining magnetic nanoparticles and icosahedral boron clusters in biocompatible inorganic nanohybrids for cancer therapy

The potential biomedical applications of the MNPs nanohybrids coated with m-carboranylphosphinate (1-MNPs) as a theranostic biomaterial for cancer therapy were tested. The cellular uptake and toxicity profile of 1-MNPs from culture media by human brain endothelial cells (hCMEC/D3) and glioblastoma multiform A172 cell line were demonstrated. Prior to testing 1-MNPs' in vitro toxicity, studies of colloidal stability of the 1-MNPs' suspension in different culture media and temperatures were carried out. TEM images and chemical titration confirmed that 1-MNPs penetrate into cells. Additionally, to explore 1-MNPs' potential use in Boron Neutron Capture Therapy (BNCT) for treating cancer locally, the presence of the m-carboranyl coordinated with the MNPs core after uptake was proven by XPS and EELS. Importantly, thermal neutrons irradiation in BNCT reduced by 2.5 the number of cultured glioblastoma cells after 1-MNP treatment, and the systemic administration of 1-MNPs in mice was well tolerated with no major signs of toxicity.

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.

Highly selective palladium-catalyzed one-pot, five-fold B-H/C-H cross coupling of monocarboranes with alkenes

Palladium-catalyzed dehydrogenative B-H/C-H cross coupling of monocarborane anions with alkenes is reported, allowing for the first time the isolation of selectively penta-alkenylated boron clusters. The reaction cascade is regioselective for the cage positions, leading directly to B2-6 functionalization. Under mild and convenient conditions, styrenes, benzylic alkenes and aliphatic alkenes are demonstrated to be viable coupling partners with exclusive vinyl-type B-C bond formation. Multiple subsequent transformations provide access to directing group-free products, chiral derivatives and penta-alkylated cages. The five-fold coupling, combined with the latter reactions, represents a powerful methodology for the straightforward synthesis of new classes of boron clusters.

Slow-spin relaxation of a low-spin S = 1/2 FeIII carborane complex

In this communication, we report the first evidence of slow-spin relaxation of a low-spin FeIII carborane complex. Iron S = 1/2 complexes showing such behaviour are particularly appealing as qubit candidates because they fulfil some of the main requirements to reach long decoherence times, such as moderate magnetic anisotropy, small spin, metal element mainly with zero-nuclear spin and furthermore, large versatility to introduce chemical modifications.

Synthesis of 9-borafluorene analogues featuring a three-dimensional 1,1'-bis(o-carborane) backbone

The synthesis of [1,1'-bis(o-carboranyl)]boranes was achieved through the deprotonation of 1,1'-bis(o-carborane) reagents followed by salt metathesis with (iPr)2NBCl2. X-ray crystallography confirms planar central BC4 rings and Gutmann-Beckett studies reveal an increase in Lewis acidity at the boron center in comparison to their biphenyl congener, 9-borafluorene.

Boron-Containing Probes for Non-optical High-Resolution Imaging of Biological Samples

Boron has been employed in materials science as a marker for imaging specific structures by electron energy loss spectroscopy (EELS) or secondary ion mass spectrometry (SIMS). It has a strong potential in biological analyses as well; however, the specific coupling of a sufficient number of boron atoms to a biological structure has proven challenging. Herein, we synthesize tags containing closo‐1,2‐dicarbadodecaborane, coupled to soluble peptides, which were integrated in specific proteins by click chemistry in mammalian cells and were also coupled to nanobodies for use in immunocytochemistry experiments. The tags were fully functional in biological samples, as demonstrated by nanoSIMS imaging of cell cultures. The boron signal revealed the protein of interest, while other SIMS channels were used for imaging different positive ions, such as the cellular metal ions. This allows, for the first time, the simultaneous imaging of such ions with a protein of interest and will enable new biological applications in the SIMS field.

Half- and mixed-sandwich metallacarboranes for potential applications in medicine

Today, medicinal chemistry is still clearly dominated by organic chemistry, and commercially available boron-based drugs are rare. In contrast to hydrocarbons, boranes prefer the formation of polyhedral clusters via delocalized 3c2e bonds, such as polyhedral dicarba-closo-dodecaborane(12) (closo-C2B10H12). These clusters have remarkable biological stability, and the three isomers, 1,2- (ortho), 1,7- (meta), and 1,12-dicarba-closo-dodecaborane(12) (para), have attracted much interest due to their unique structural features. Furthermore, anionic nido clusters ([7,8-C2B9H11]2−), derived from the neutral icosahedral closo cluster 1,2-dicarba-closo-dodecaborane(12) by deboronation followed by deprotonation are suitable ligands for transition metals and offer the possibility to form metallacarboranes, for example via coordination through the upper pentagonal face of the cluster. The isolobal analogy between the cyclopentadienyl(–1) ligand (Cp−) and [C2B9H11]2− clusters (dicarbollide anion, Cb2−) is the motivation in using Cb2− as ligand for coordination to a metal center to design compounds for various applications. This review focuses on potential applications of half- and mixed-sandwich-type transition metal complexes in medicine.

Improved synthesis of icosahedral carboranes containing exopolyhedral B-C and C-C bonds

Carboranes are boron-rich molecular clusters possessing electronic characteristics that allow for orthogonal approaches to vertex-selective modifications. We report improved functionalization methods utilizing orthogonal chemistry to achieve efficient substitution at electron-rich B-vertices and electron-poor C-vertices of carborane. Functionalization of B-vertices with alkyl and (hetero)aryl groups using the corresponding Grignard reagents has been improved through the use of a Pd-based precatalyst featuring an electron-rich biaryl phosphine ligand, resulting in reduced reaction times. Importantly, this method is tolerant towards alkyl-based Grignard reagents containing β-hydrogens. Furthermore, a transition metal-free approach to the substitution of carborane C-vertices with (hetero)aryl substrates has been developed under nucleophilic aromatic substitution (SNAr) conditions. The selective substitution of carboranes afforded by these methods holds potential for the rational synthesis of heterofunctionalized boron clusters with substituents on both boron and carbon-based vertices.

Icosahedral boron clusters as modifying entities for biomolecules

INTRODUCTION

Icosahedral boron clusters have unique properties useful in medicinal chemistry: rigidity, chemical stability, and three-dimensional aromaticity. Furthermore, these abiotic compounds have low toxicity and are stable in the biological environment. All these features ultimately give them the ability to interact with biological molecules in a different mode than organic compounds.

AREAS COVERED

In the present article, we aim to introduce boron clusters as a class of entities suitable for modifications of biomolecules to obtain a specific biological effect. We will focus on icosahedral boron clusters, as well as metallacarboranes, and their biological activity and interaction with the biological environment.

EXPERT OPINION

Boron clusters are suitable for altering structural and functional features of biomolecules and can be used in the development of new drugs and drug delivery systems. The high affinity of boron clusters, especially metallacarboranes, to albumin creates a new possibility to use them to optimize the pharmacokinetics of biologically active peptides. Boron clusters have high potential in biological and medicinal applications. Due to their peculiar properties, they can be used to optimize parameters critical for the biological activity of therapeutic substances and their affinity toward biological targets.

Metal-catalyzed cross-coupling chemistry with polyhedral boranes

Over the past several decades, metal-catalyzed cross-coupling has emerged as a very powerful strategy to functionalize carbon-based molecules. More recently, some of the cross-coupling methodologies have been adapted to inorganic compounds including boron-rich clusters. The development of this chemistry relies on the ability to synthesize halogenated boron-rich clusters which can serve as electrophilic cross-coupling partners with nucleophilic substrates in the presence of a metal catalyst. While the cross-coupling chemistry with boron-clusters is conceptually reminiscent of that of its hydrocarbon counterparts, several key aspects including the spheroidal bulk of clusters and the distinct nature of boron-halogen/boron-heteroatom bonds make this chemistry unique. The utility of metal-catalyzed cross-coupling can be extended to several classes of polyhedral boranes including neutral and anionic carboranes, metallaboranes, and carbon-free boranes. Importantly, cross-coupling enables a suite of boron-heteroatom (C, N, O, P, S) couplings to prepare boron cluster-based systems that can be used for ligand design, medicinal chemistry, and materials applications.

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.

Synthesis and Structural Characterization of Amidine, Amide, Urea and Isocyanate Derivatives of the Amino-closo-dodecaborate Anion [B12H11NH₃]. Molecules 2018;23:molecules23123137. [PMID: 30501105 PMCID: PMC6321512 DOI: 10.3390/molecules23123137]

The synthesis and structural characterization of new derivatives of [B₁₂H₁₂]²⁻ is of fundamental interest and is expected to allow for extended applications. Herein we report on the synthesis of a series of amidine, amide, urea and isocyanate derivatives based on the amino-closo-dodecaborate anion [B₁₂H₁₁NH₃]⁻. Their structures have been confirmed by spectroscopic methods, and nine crystal structures are presented.

DNA Modified with Boron⁻Metal Cluster Complexes [M(C₂B₉H11)₂]-Synthesis, Properties, and Applications

Together with tremendous progress in biotechnology, nucleic acids, while retaining their status as "molecules of life", are becoming "molecular wires", materials for the construction of molecular structures at the junction between the biological and abiotic worlds. Herein, we present an overview of the approaches for incorporating metal centers into nucleic acids based on metal⁻boron cluster complexes (metallacarboranes) as the metal carriers. The methods are modular and versatile, allowing practical access to innovative metal-containing DNA for various applications, such as nucleic acid therapeutics, electrochemical biosensors, infrared-sensitive probes, and building blocks for nanoconstruction.

Comparative Study of Carborane- and Phenyl-Modified Adenosine Derivatives as Ligands for the A2A and A3 Adenosine Receptors Based on a Rigid in Silico Docking and Radioligand Replacement Assay

Adenosine receptors are involved in many physiological processes and pathological conditions and are therefore attractive therapeutic targets. To identify new types of effective ligands for these receptors, a library of adenosine derivatives bearing a boron cluster or phenyl group in the same position was designed. The ligands were screened in silico to determine their calculated affinities for the A2A and A3 adenosine receptors. An virtual screening protocol based on the PatchDock web server was developed. In the first screening phase, the effects of the functional group (organic or inorganic modulator) on the adenosine ligand affinity for the receptors were determined. Then, the lead compounds were identified for each receptor in the second virtual screening phase. Two pairs of the most promising ligands, compounds 3 and 4, and two ligands with lower affinity scores (compounds 11 and 12, one with a boron cluster and one with a phenyl group) were synthesized and tested in a radioligand replacement assay for affinity to the A2A and A3 receptors. A reasonable correlation of in silico and biological assay results was observed. In addition, the effects of a phenyl group and boron cluster, which is new adenosine modifiers, on the adenosine ligand binding were compared.

The closo-Dodecaborate Dianion Fused with Oxazoles Provides 3D Diboraheterocycles with Selective Antimicrobial Activity

The synthesis and application of icosahedral boron cluster compounds has been studied extensively since their discovery several decades ago; however, two aspects of their chemistry have received little attention: The possibility to form inorganic/organic fused boraheterocycles and their potential to act as antimicrobial agents. This work comprises the preparation of a class of 3D diborabenzoxazole analogues with the closo-dodecaborate in place of the benzene moiety. The presented synthetic procedures provide access to a wide range of diboraheterocycles under mild conditions. These 3D heterocycles exhibit strong and selective antimicrobial activity against Neisseria gonorrhoeae, a widespread bacterial pathogen that has shown increasing incidences of multidrug resistance and for which the development of new antimicrobial compounds is urgently needed.