Synthesis and in vitro antiviral activity of lipophilic pyrimidine nucleoside/carborane conjugates

Compounds based on Adamantyl-substituted Amino Acids and Peptides as Potential Antiviral Drugs Acting as Viroporin Inhibitors

The discussion has revolved around the derivatives of amino acids and peptides containing carbocycles and their potential antiviral activity in vitro against influenza A, hepatitis C viruses, and coronavirus. Studies conducted on cell cultures reveal that aminoadamantane amino acid derivatives exhibit the capacity to hinder the replication of viruses containing viroporins. Furthermore, certain compounds demonstrate potent virucidal activity with respect to influenza A/H5N1 and hepatitis C virus particles. A conceptual framework for viroporin inhibitors has been introduced, incorporating carbocyclic motifs as membranotropic carriers in the structure, alongside a functional segment comprised of amino acids and peptides. These components correspond to the interaction with the inner surface of the channel's pore or another target protein.

New type of RNA virus replication inhibitor based on decahydro-closo-decaborate anion containing amino acid ester pendant group

In this work, a synthetic approach to prepare an example of new class of the derivatives of the closo-decaborate anion with amino acids detached from the boron cluster by pendant group has been proposed and implemented. Compound Na₂[B₁₀H₉–O(CH₂)₄C(O)–His–OMe] was isolated and characterized. This compound has an inorganic hydrophobic core which is the 10-vertex boron cage and the –O(CH₂)₄C(O)–His–OMe organic substituent. It has been shown to possess strong antiviral activity in vitro against modern strains of A/H1N1 virus at 10 and 5 µg/mL. The compound has been found to be non-cytotoxic up to 160 µg/mL. At the same time, the compound has been found to be inactive against SARS-CoV-2, indicating specific activity against RNA virus replication. Molecular docking of the target derivative of the closo-decaborate anion with a model of the transmembrane region of the M2 protein has been performed and the mechanism of its antiviral action is discussed.

The Boron Advantage: The Evolution and Diversification of Boron’s Applications in Medicinal Chemistry

In this review, the history of boron’s early use in drugs, and the history of the use of boron functional groups in medicinal chemistry applications are discussed. This includes diazaborines, boronic acids, benzoxaboroles, boron clusters, and carboranes. Furthermore, critical developments from these functional groups are highlighted along with recent developments, which exemplify potential prospects. Lastly, the application of boron in the form of a prodrug, softdrug, and as a nanocarrier are discussed to showcase boron’s emergence into new and exciting fields. Overall, we emphasize the evolution of organoboron therapeutic agents as privileged structures in medicinal chemistry and outline the impact that boron has had on drug discovery and development.

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.

Sonogashira Coupling of the Ethynyl Monocarborane [CB11H11-12-CCH]–

The Sonogashira cross coupling between the monocarborane cluster 12-ethynylmonocarba-closo-dodecaborate [CB11H11-12-CCH]– and bromoarenes under Pd catalysis has been developed, providing access to aryl carboranyl alkynes in yields of 42–95%. The transformations...

Synthesis and evaluation of adenosine derivatives as A1, A2A, A2B and A3 adenosine receptor ligands containing boron clusters as phenyl isosteres and selective A3 agonists

A series of adenosine and 2'-deoxyadenosine pairs modified with a 1,12-dicarba-closo-dodecaborane cluster or alternatively with a phenyl group at the same position was synthesized, and their affinity was determined at A1, A2A, A2B and A3 adenosine receptors (ARs). While AR affinity differences were noted, a general tendency to preferentially bind A3 AR over other ARs was observed for most tested ligands. In particular, 5'-ethylcarbamoyl-N6-(3-phenylpropyl)adenosine (18), N6-(3-phenylpropyl)-2-chloroadenosine (24) and N6-(3-phenylpropyl)adenosine (40) showed nanomolar A3 affinity (Ki 4.5, 6.4 and 7.5 nM, respectively). Among the boron cluster-containing compounds, the highest A3 affinity (Ki 206 nM) was for adenosine derivative 41 modified at C2. In the matched molecular pairs, analogs bearing boron clusters were found to show lower binding affinity for adenosine receptors than the corresponding phenyl analogs. Nevertheless, interestingly, several boron cluster modified adenosine ligands showed significantly higher A3 receptor selectivity than the corresponding phenyl analogs: 7vs. 8, 15vs. 16, 17vs. 18.

Raman cell imaging with boron cluster molecules conjugated with biomolecules

Raman spectroscopic measurements and theoretical calculation revealed that the Raman bands corresponding to the B–H stretching vibrations of two types of simple icosahedral boron clusters, ortho-carborane 3 and closo-dodecaborate 4 appeared at approximately 2450–2700 cm⁻¹, and did not overlap with those of cellular components. Although ortho-carborane 3 possesses a possible property as a Raman probe, it was difficult to measure Raman imaging in the cell due to its poor water solubility. In fact, ortho-carborane derivative 6, which internally has an alkyne moiety, exhibited very weak Raman signals of the C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C stretching and the B–H stretching vibrations were barely detected at a 400 ppm boron concentration in HeLa cells. In contrast, closo-dodecaborate derivatives such as BSH (5) were found to be a potential Raman imaging probe cluster for target molecules in the cell. BSH-conjugated cholesterol 7 (BSH-Chol) was synthesized and used in Raman imaging in cells. Raman imaging and spectral analysis revealed that BSH-based Raman tags provide a versatile platform for quantitative Raman imaging.

We performed Raman cell imaging using boron clusters.

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.

Carborane-linked 2'-deoxyuridine 5'-O-triphosphate as building block for polymerase synthesis of carborane-modified DNA

5-[(p-Carborane-2-yl)ethynyl]-2'-deoxyuridine 5'-O-triphosphate was synthesized and used as a good substrate in enzymatic construction of carborane-modified DNA or oligonucleotides containing up to 21 carborane moieties in primer extension reactions by DNA polymerases.

Antiproliferative activity of (η6-arene)ruthenacarborane sandwich complexes against HCT116 and MCF7 cell lines

Three [(η⁶-arene)RuC₂B₉H₁₁] complexes (arene = p-cymene (2), biphenyl (3) and 1-Me-4-COOEt-C₆H₄ (4)) were synthesised according to modified literature procedures and fully characterised. 2-4 were found to be moderately active against two types of tumour cell lines (HCT116 and MCF7), with IC₅₀ values in the low micromolar range. However, viability of normal, healthy cells (MRC-5 cell line, MLEC and mouse macrophages) was not affected by treatment with 2-4, indicating high selectivity of the metallacarborane complexes towards tumour cell lines, compared to the unselective antitumour agent cisplatin and other potential Ru^II drugs. Moreover, flow cytometric analysis suggested that 4 induces cell death via a caspase-dependent apoptotic mechanism. DFT calculations of the frontier molecular orbitals showed that the HOMO-LUMO gap in 2-4 is smaller than in the corresponding cyclopentadienyl complexes 2-Cp-4-Cp (e.g. 5.47 (2) vs. 6.31 eV (2-Cp)). In order to assess the stability of 2-4, particularly the ruthenium-dicarbollide bond, energy decomposition analysis (EDA) of 2-4, together with the respective cyclopentadienyl analogues 2-Cp-4-Cp, was performed. EDA suggests that the ruthenium(ii)-dicarbollide bond in the three complexes is mostly ionic and far stronger than the ruthenium(ii)-arene bond.

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

There are two branches in boron medicinal chemistry: the first focuses on single boron atom compounds, and the second utilizes boron clusters. Boron clusters and their heteroatom counterparts belong to the family of cage compounds. A subset of this extensive class of compounds includes dicarbadodecaboranes, which have the general formula C2B10H12, and their metal biscarboranyl complexes, metallacarboranes, with the formula [M(C2B10H12)2(-2)]. The unique properties of boron clusters have resulted in their utilization in applications such as in pharmacophores, as scaffolds in molecular construction, and as modulators of bioactive compounds. This Perspective presents an overview of the properties of boron clusters that are pertinent for drug discovery, recent applications in the design of various classes of drugs, and the potential use of boron clusters in the construction of new pharmaceuticals.

Recent developments with boron as a platform for novel drug design

INTRODUCTION

After decades of development, the medicinal chemistry of compounds that contain a single boron atom has matured to the present status of having equal rights with other branches of drug discovery, although it remains a relative newcomer. In contrast, the medicinal chemistry of boron clusters is less advanced, but it is expanding and may soon become a productive area of drug discovery.

AREAS COVERED

The author reviews the current developments of medicinal chemistry of boron and its applications in drug design. First generation boron drugs that bear a single boron atom and second generation boron drugs that utilize boron clusters as pharmacophores or modulators of bioactive molecules are discussed. The advantages and gaps in our current understanding of boron medicinal chemistry, with a special focus on boron clusters, are highlighted.

EXPERT OPINION

Boron is not a panacea for every drug discovery problem, but there is a good chance that it will become a useful addition to the medicinal chemistry tool box. The present status of boron resembles the medicinal chemistry status of fluorine three decades ago; indeed, currently, approximately 20% of pharmaceuticals on the market contain fluorine. The fact that novel boron compounds, especially those based on abiotic polyhedral boron hydrides, are currently unfamiliar could be advantageous because organisms may be less prone to developing resistance against boron cluster-based drugs.