Metallacarborane Derivatives Effective against Pseudomonas aeruginosa and Yersinia enterocolitica

Bis(Dicarbollide) Complexes of Transition Metals: How Substituents in Dicarbollide Ligands Affect the Geometry and Properties of the Complexes

The interaction between different types of substituents in dicarbollide ligands and their influence on the stabilization of various rotational conformers (rotamers) of transition metal bis(dicarbollide) complexes [3,3'-M(1,2-C2B9H11)2]- are considered. It has been shown that the formation of intramolecular CH···X hydrogen bonds between dicarbollide ligands is determined by the size of the proton acceptor atom X rather than its electronegativity. Due to the stabilization of rotamers with different dipole moments, intramolecular hydrogen bonds between ligands in transition metal bis(dicarbollide) complexes can have a significant impact on the biological properties of their derivatives. In the presence of external complexing metals, weak intramolecular CH···X hydrogen bonds can be broken to form stronger X->M donor-acceptor bonds. This process is accompanied by the mutual rotation of dicarbollide ligands and can be used in sensors and molecular switches based on transition metal bis(dicarbollide) complexes.

Metallacarboranes in Medicinal Chemistry: Current Advances and Future Perspectives

Metallacarboranes, exemplified by cobalt bis(dicarbollide) ([COSAN]-), have excelled their historical metallocene analogue label to become promising in drug design, medical studies, and fundamental biological research. Serving as a unique platform for conjugation with biomolecules, they also constitute an auspicious building block for biologically active derivatives and a carrier for cellular transport of membrane-impermeable cargos. Modified [COSAN]- exhibits specific antimicrobial, antiviral, and anticancer actions showing promise for preclinical trials. Contributing to the ongoing development in medicinal chemistry, metallacarboranes offer desirable physicochemical properties and low acute toxicity. This article presents a critical look at metallacarboranes in the context of their application in medicinal chemistry, emphasizing [COSAN]- as a potential game-changer in drug design and biomedical sciences. As medicinal chemistry seeks innovative building blocks, metallacarboranes emerge as an important novelty with versatile solutions and promising implications.

Synthetic routes to carbon substituted cobalt bis(dicarbollide) alkyl halides and aromatic amines along with closely related irregular pathways

Carbon substituted cobalt bis(dicarbollide) alkyl halides [(1-X-(CH2)n-1,2-C2B9H10)(1,2-C2B9H11)-3,3'-Co]Me4N (X = Br, I; n = 1-3) are prepared in high yields (>90%) from their corresponding alcohols without side skeletal substitutions. These species offer access to the synthesis of aromatic cobalt bis(dicarbollide) amines, however only for particular terminal halogen substitution, the propylene pendant arm, and under appropriately controlled reaction conditions. Thus, the compounds substituted at cage carbon atoms with a propylene linker and terminal aromatic amine groups could be prepared. In other cases, numerous irregular reaction pathways occur, undoubtedly as a consequence of the bulky anionic boron cage in close proximity to the reaction site. Among them, an unusual intramolecular hydroboration forming rigidified carbon-to-boron bridged isomeric anions with an asymmetric structure that correspond to formulae [(1,8'-μ-C2H4)-(1,2-C2B9H10)(1',2'-C2B9H10)-3,3'-Co]- and [(1,7'-μ-C2H4)-(1,2-C2B9H10)(1',2'-C2B9H10)-3,3'-Co]- is described herein and the former isomer is structurally characterized. This product with a restrained geometry is widely accessible through nucleophile and/or thermally induced decomposition of (pseudo)halides attached to the cage via an ethylene linker. Surprisingly enough, also doubly bridged isomeric species [(1,8-μ-C2H4-1,2-C2B9H9)2-3,3'-Co]- and [(1,7-μ-C2H4-1,2-C2B9H9)2-3,3'-Co]- are available in good yield using these methods. Furthermore, other more typical side reactions are discussed, i.e. nucleophilic reactions of propyl halides with Me3N formed apparently by disproportionation of Me4N+ at higher temperatures or with pyridine used as a base.

Structural Patterns Enhancing the Antibacterial Activity of Metallacarborane-Based Antibiotics

Healthcare systems heavily rely on antibiotics to treat bacterial infections, but the widespread presence of multidrug-resistant bacteria puts this strategy in danger. Novel drugs capable of overcoming current resistances are needed if our ability to treat bacterial infections is to be maintained. Boron clusters offer a valuable possibility to create a new class of antibiotics and expand the chemical space of antibiotics beyond conventional carbon-based molecules. In this work, we identified two promising structural patterns providing cobalta bis(dicarbollide)(COSAN)-based compounds with potent and selective activity toward Staphylococcus aureus (including clinical strains): introduction of the α-amino acid amide and addition of iodine directly to the metallacarborane cage. Furthermore, we found that proper hydrophilic-lipophilic balance is crucial for the selective activity of the tested compounds toward S. aureus over mammalian cells. The patterns proposed in this paper can be useful in the development of metallacarborane-based antibiotics with potent antibacterial properties and low cytotoxicity.

Chemistry of Carbon-Substituted Derivatives of Cobalt Bis(dicarbollide)(1-) Ion and Recent Progress in Boron Substitution

The cobalt bis(dicarbollide)(1-) anion (1-), [(1,2-C2B9H11)2-3,3'-Co(III)](1-), plays an increasingly important role in material science and medicine due to its high chemical stability, 3D shape, aromaticity, diamagnetic character, ability to penetrate cells, and low cytotoxicity. A key factor enabling the incorporation of this ion into larger organic molecules, biomolecules, and materials, as well as its capacity for "tuning" interactions with therapeutic targets, is the availability of synthetic routes that enable easy modifications with a wide selection of functional groups. Regarding the modification of the dicarbollide cage, syntheses leading to substitutions on boron atoms are better established. These methods primarily involve ring cleavage of the ether rings in species containing an oxonium oxygen atom connected to the B(8) site. These pathways are accessible with a broad range of nucleophiles. In contrast, the chemistry on carbon vertices has remained less elaborated over the previous decades due to a lack of reliable methods that permit direct and straightforward cage modifications. In this review, we present a survey of methods based on metalation reactions on the acidic C-H vertices, followed by reactions with electrophiles, which have gained importance in only the last decade. These methods now represent the primary trends in the modifications of cage carbon atoms. We discuss the scope of currently available approaches, along with the stereochemistry of reactions, chirality of some products, available types of functional groups, and their applications in designing unconventional drugs. This content is complemented with a report of the progress in physicochemical and biological studies on the parent cobalt bis(dicarbollide) ion and also includes an overview of recent syntheses and emerging applications of boron-substituted compounds.

Half-Sandwich Nickelacarboranes Derived from [7-(MeO(CH2)2S)-7,8-C2B9H11]−

New carboranyl thioethers 1-MeO(CH2)nS-1,2-C2B10H11 (n = 2, 3) were prepared by the alkylation of the trimethylammonium salt of 1-mercapto-ortho-carborane with 1-bromo- 2-methoxyethane and 1-bromo-3-methoxypropane, respectively. Their deboronation with cesium fluoride in ethanol gave the corresponding nido-carboranes Cs[7-MeO(CH2)nS-7,8-C2B9H11] (n = 2, 3). The reactions of Cs[7-MeO(CH2)2S-7,8-C2B9H11] with various nickel(II) phosphine complexes [(dppe)NiCl2] and [(R’R2P)2NiCl2] (R = R’ = Ph, Bu; R = Me, R’ = Ph; R = Ph, R’ = Me, Et) were studied and a series of nickelacarboranes 3,3-dppe-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 and 3,3- (R’R2P)2-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 (R = R’ = Bu; R = Me, R’ = Ph; R = Ph, R’ = Me, Et) was prepared. The molecular crystal structure of 3,3-dppe-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 was determined by single-crystal X-ray diffraction.

Complications and Treatments of Pseudomonas aeruginosa Infection After Rhinoplasty With Implants: A Clinical Study

BACKGROUND

Pseudomonas aeruginosa is an opportunistic pathogen, and because of its specificity, its treatments appear tricky in postrhinoplasty infections with internal implants. This study summarizes the clinical characteristics and treatment of this type of infections to provide some reference for clinical work.

METHODS

We retrospectively analyzed 10 patients who were diagnosed with a nasal infection of P. aeruginosa after implant nasal augmentation. The results of the bacterial culture and drug sensitivity test of the patients' wound secretions were summarized and analyzed. We summarized the characteristics of the patients' infection and the treatments, and we also summarized the patients' prognosis.

RESULTS

In these 10 cases, their implants included rib cartilage and ear cartilage alone, as well as their own cartilage combined with expanded polytetrafluoroethylene and silicone. All patients developed wound infections within 1 month after rhinoplasty, with bacterial cultures of P. aeruginosa . Prolonged use of sensitive antibiotics, as well as wound dressing changes, failed to keep the infection well under control. Patients whose implant was removed and thoroughly debrided within 1 week of infection did not experience any serious complications. In patients who were infected for >1 week before surgery to remove the implants, complications such as nasal column necrosis and nasal contracture occurred, and later the nasal repair was performed after multiple surgeries.

CONCLUSIONS

For bacterial infections in postrhinoplasty wounds with implants, we recommend early bacterial culture. If the infection is clearly P. aeruginosa , the implant should be removed and thoroughly debrided as soon as possible to avoid serious complications.

LEVEL OF EVIDENCE

Level IV.

Advanced Tool for Chiral Separations of Anionic and Zwitterionic (Metalla)carboranes: Supercritical Fluid Chromatography

The continuous expansion of research in the field of stable carboranes and their wide potential in the drug design require carrying out fundamental studies regarding their chiral separations. Although supercritical fluid chromatography (SFC) is a viable technique for fast enantioseparations, no investigation concerning boron cluster compounds has been done yet. We aimed at the development of a straightforward method enabling chiral separations of racemic mixtures of anionic cluster carboranes and metallacarboranes that represent an analytical challenge. The fast gradient screening testing nine polysaccharide-based columns was used. The key parameters affecting the selectivity were the type of chiral selector, the type of alcohol, and the base in cosolvent. Moreover, the addition of acetonitrile or water to the cosolvent was identified as an effective tool for decreasing the analysis time while preserving the resolution. After the optimization, the chiral separations of 19 out of 20 selected compounds were achieved in less than 10 min. These results demonstrate the clear advantage of SFC over chiral separations using HPLC in terms of both analysis time and structural variety of successfully separated compounds.

Metallacarborane Derivatives as Innovative Anti-Candida albicans Agents

Infections caused by Candida species have increased significantly in the past decades and are among the leading causes of morbidity and mortality worldwide, resulting in serious public health problems. Currently, conventional antifungals are often ineffective as Candida spp. have developed growing resistance to systemic drugs. Since inorganic metallacarboranes are known to affect cellular events, new derivatives of these abiotic compounds were tested against Candida albicans. Compounds based on cobalt bis-dicarbollide [COSAN] were studied on Candida albicans strains, including a panel of 100 clinical isolates. The presented data prove that metallacarborane derivatives are effective against clinical isolates of Candida albicans, even those resistant to systemic drugs, and show synergistic potential in combination with amphotericin B, and low toxicity against human cells and Danio rerio embryos. This paper is a consequential step in the investigations of the broad spectrum and valuable future medical applications of metallacarboranes, especially in the fight against drug-resistant pathogens.

Synthesis and Antibacterial Activity Studies of the Conjugates of Curcumin with closo-Dodecaborate and Cobalt Bis(Dicarbollide) Boron Clusters

A series of novel conjugates of cobalt bis(dicarbollide) and closo-dodecaborate with curcumin were synthesized by copper(I)-catalyzed azide-alkyne cycloaddition. These conjugates were tested for antibacterial activity. It was shown that all derivatives are active when exposed to Bacillus cereus ATCC 10702 and are not active against Gram-negative microorganisms and Candida albicans at the maximum studied concentration of 1000 mg/L. The conjugate of alkynyl-curcumin with azide synthesized from the tetrahydropyran derivative of cobalt bis(dicarbollide) exhibited activity against Gram-positive microorganisms: Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212 and the clinical isolate MRSA 17, that surpassed curcumin by 2–4 times.

Cobalt Bis-Dicarbollide Enhances Antibiotics Action towards Staphylococcus epidermidis Planktonic Growth Due to Cell Envelopes Disruption

The emergence of antibiotic resistance in opportunistic pathogens represents a huge problem, the solution for which may be a treatment with a combination of multiple antimicrobial agents. Sodium salt of cobalt bis-dicarbollide (COSAN.Na) is one of the very stable, low-toxic, amphiphilic boron-rich sandwich complex heteroboranes. This compound has a wide range of potential applications in the biological sciences due to its antitumor, anti-HIV-1, antimicrobial and antibiofilm activity. Our study confirmed the ability of COSAN.Na (in the concentration range 0.2–2.48 µg/mL) to enhance tetracycline, erythromycin, and vancomycin action towards Staphylococcus epidermidis planktonic growth with an additive or synergistic effect (e.g., the combination of 1.24 µg/mL COSAN.Na and 6.5 µg/mL TET). The effective inhibitory concentration of antibiotics was reduced up to tenfold most efficiently in the case of tetracycline (from 65 to 6.5 µg/mL). In addition, strong effect of COSAN.Na on disruption of the cell envelopes was determined using propidium iodide uptake measurement and further confirmed by transmission electron microscopy. The combination of amphiphilic COSAN.Na with antibiotics can therefore be considered a promising way to overcome antibiotic resistance in Gram-positive cocci.

Carboranes as unique pharmacophores in antitumor medicinal chemistry

Carborane is a carbon-boron molecular cluster that can be viewed as a 3D analog of benzene. It features special physical and chemical properties, and thus has the potential to serve as a new type of pharmacophore for drug design and discovery. Based on the relative positions of two cage carbons, icosahedral closo-carboranes can be classified into three isomers, ortho-carborane (o-carborane, 1,2-C2B10H12), meta-carborane (m-carborane, 1,7-C2B10H12), and para-carborane (p-carborane, 1,12-C2B10H12), and all of them can be deboronated to generate their nido- forms. Cage compound carborane and its derivatives have been demonstrated as useful chemical entities in antitumor medicinal chemistry. The applications of carboranes and their derivatives in the field of antitumor research mainly include boron neutron capture therapy (BNCT), as BNCT/photodynamic therapy dual sensitizers, and as anticancer ligands. This review summarizes the research progress on carboranes achieved up to October 2021, with particular emphasis on signaling transduction pathways, chemical structures, and mechanistic considerations of using carboranes.

Electrochemistry of Cobalta Bis(dicarbollide) Ions Substituted at Carbon Atoms with Hydrophilic Alkylhydroxy and Carboxy Groups

In this study we explore the effect on the electrochemical signals in aqueous buffers of the presence of hydrophilic alkylhydroxy and carboxy groups on the carbon atoms of cobalta bis(dicarbollide) ions. The oxygen-containing exo-skeletal substituents of cobalta bis(dicarbollide) ions belong to the perspective building blocks that are considered for bioconjugation. Carbon substitution provides wider versatility and applicability in terms of the flexibility of possible chemical pathways. However, until recently, the electrochemistry of compounds substituted only on boron atoms could be studied, due to the unavailability of carbon-substituted congeners. In the present study, electrochemistry in aqueous phosphate buffers is considered along with the dependence of electrochemical response on pH and concentration. The compounds used show electrochemical signals around −1.3 and +1.1 V of similar or slightly higher intensities than in the parent cobalta bis(dicarbollide) ion. The signals at positive electrochemical potential correspond to irreversible oxidation of the boron cage (the C2B9 building block) and at negative potential correspond to the reversible redox process of (CoIII/CoII) at the central atom. Although the first signal is typically sharp and its potential can be altered by a number of substituents, the second signal is complex and is composed of three overlapping peaks. This signal shows sigmoidal character at higher concentrations and may be used as a diagnostic tool for aggregation in solution. Surprisingly enough, the observed effects of the site of substitution (boron or carbon) and between individual groups on the electrochemical response were insignificant. Therefore, the substitutions would preserve promising properties of the parent cage for redox labelling, but would not allow for the further tuning of signal position in the electrochemical window.

Structurally rigidified cobalt bis(dicarbollide) derivatives, a chiral platform for labelling of biomolecules and new materials

We report the difunctional modification of an anionic cobalta bis(dicarbollide)(1-) cluster with a B(8,8')-oxygen bridging unit that provides structural rigidity and an organic alkylazide substituent(s) on the carbon atoms of the metallacarborane cage. These ions present a good binding motif for incorporation into organic molecules using Huisgen-Sharpless (2+3) cycloaddition reactions. In addition, the compounds are chiral, as verified by separation of enantiomers using HPLC on chiral stationary phases (CSPs) and provide a high electrochemical peak in the window located outside of typical signals of biomolecules.

Physiologically Active Compounds Based on Membranotropic Cage Carriers–Derivatives of Adamantane and Polyhedral Boron Clusters (Review)

Data on compounds based on cage structures―boron clusters (polyhedral boron hydrides, carboranes, metallacarboranes) and compounds of the adamantane series, which possess physiological activity, have been generalized. The main emphasis is placed on the antiviral activity of the compounds. The mechanism of the possible action of the replication inhibitors of influenza A virus strains is considered, the molecular model of viroporin inhibitors is discussed. The proposed model consists of a cage hydrophobic core that performs the function of a membranotropic carrier (a boron cluster or adamantane fragment), into which physiologically active functional groups are introduced. The relationship between the structure of the cage compound with the introduced substitute and the biologically active properties of this molecular structure has been analyzed.

Nematicidal activity of naphthalimide-boron cluster conjugates

Distinctive biological properties characterize 1,8-naphthalimides and their derivatives. This study presents and compares the activity of a series of compounds where 1,8-naphthalimide fragment was attached either to carborane or metallacarborane...

Synthesis of Boronated Amidines by Addition of Amines to Nitrilium Derivative of Cobalt Bis(Dicarbollide)

A series of novel cobalt bis(dicarbollide) based amidines were synthesized by the nucleophilic addition of primary and secondary amines to highly activated B-N+≡C-R triple bond of the propionitrilium derivative [8-EtC≡N-3,3'-Co(1,2-C2B9H10)(1',2'-C2B9H11)]. The reactions with primary amines result in the formation of mixtures of E and Z isomers of amidines, whereas the reactions with secondary amines lead selectively to the E-isomers. The crystal molecular structures of E-[8-EtC(NMe2)=HN-3,3'-Co(1,2-C2B9H10)(1',2'-C2B9H11)], E-[8-EtC(NEt2)=HN-3,3'-Co(1,2- C2B9H10)(1',2'-C2B9H11)] and E-[8-EtC(NC5H10)=HN-3,3'-Co(1,2-C2B9H10)(1',2'-C2B9H11)] were determined by single crystal X-ray diffraction.