N-Aminoacyl-3-amino-nido-carboranes as a Group of Boron-Containing Derivatives of Natural Amino Acids

Synthesis of Charge-Compensated nido-Carboranyl Derivatives of Sulfur-Containing Amino Acids and Biotin

A new group of charge-compensated nido-carboranyl derivatives of sulfur-containing amino acids and biotin has been synthesized in which the boron atom in position 9 or 10 of carborane is attached to a positively charged sulfur atom. The possibilities of obtaining symmetrical B(10)-substituted and asymmetric B(9)-substituted nido-carboranes were studied. Using the example of (S)-methionine and D-biotin derivatives, water-soluble S-substituted charge-compensated nido-carboranes with free functional groups were prepared. The results obtained open up prospects for the development of potential boron delivery agents for BNCT as well as new bioactive compounds containing a negatively charged nido-carboranyl fragment bearing a positive charge on the sulfur atom associated with the boron cluster.

Next generation of boron neutron capture therapy (BNCT) agents for cancer treatment

Boron neutron capture therapy (BNCT) is one of the most promising treatments among neutron capture therapies due to its long-term clinical application and unequivocally obtained success during clinical trials. Boron drug and neutron play an equivalent crucial role in BNCT. Nevertheless, current clinically used l-boronophenylalanine (BPA) and sodium borocaptate (BSH) suffer from large uptake dose and low blood to tumor selectivity, and that initiated overwhelm screening of next generation of BNCT agents. Various boron agents, such as small molecules and macro/nano-vehicles, have been explored with better success. In this featured article, different types of agents are rationally analyzed and compared, and the feasible targets are shared to present a perspective view for the future of BNCT in cancer treatment. This review aims at summarizing the current knowledge of a variety of boron compounds, reported recently, for the application of BCNT.

Synthesis of Novel Carborane-Containing Derivatives of RGD Peptide

Short peptides containing the Arg-Gly-Asp (RGD) fragment can selectively bind to integrins on the surface of tumor cells and are attractive transport molecules for the targeted delivery of therapeutic and diagnostic agents to tumors (for example, glioblastoma). We have demonstrated the possibility of obtaining the N- and C-protected RGD peptide containing 3-amino-closo-carborane and a glutaric acid residue as a linker fragment. The resulting carboranyl derivatives of the protected RGD peptide are of interest as starting compounds in the synthesis of unprotected or selectively protected peptides, as well as building blocks for preparation of boron-containing derivatives of the RGD peptide of a more complex structure.

Synthesis, In Silico, In Vivo, and Ex Vivo Evaluation of a Boron-Containing Quinolinate Derivative with Presumptive Action on mGluRs

In the brain, canonical excitatory neurotransmission is mediated by L-glutamate and its ionotropic (iGluR) and metabotropic (mGluR) receptors. The wide diversity of these often limits the development of glutamatergic drugs. This is due to the arduousness of achieving selectivity with specific ligands. In the present article, encouraged by reports of bioactive organoboron compounds, a diphenylboroxazolidone derived from quinolinate (BZQuin) was evaluated. BZQuin was synthesized with a yield of 87%. Its LD50 was 174 mg/kg in male CD-1 mice, as estimated by a modified Lorke’s method. BZQuin exerted a reduced ability to cause seizures when compared against its precursor, quinolinate. The latter suggested that it does not directly stimulate the ionotropic NMDA receptors or other ionic channels. The observation that the antiglutamatergic drugs riluzole and memantine displaced the BZQuin effect left the mGluRs as their possible targets. This is in line with results from molecular-docking simulations. During these simulations, BZQuin bound only to orthosteric sites on mGluR1, mGluR2, and mGluR7, with higher affinity than quinolinate. The survival of the neurons of mice previously administered with BZQuin or quinolinate was quantified in four neuroanatomical structures of the brain. The BZQuin effect was more appreciable in brain regions with a high expression of the previously mentioned mGluRs, while both antiglutamatergic drugs exerted a neuroprotective effect against it. Together, these results suggest that BZQuin exerts a positive influence on glutamatergic neurotransmission while selectively interacting with certain mGluRs.

Charge-Compensated Derivatives of Nido-Carborane

This review summarizes data on the main types of charge-compensated nido-carborane derivatives. Compared with organic analogs, onium derivatives of nido-carborane have increased stability due to the stabilizing electron-donor action of the boron cage. Charge-compensated derivatives are considered according to the type of heteroatom bonded to a boron atom.

Carborane-Containing Folic Acid bis-Amides: Synthesis and In Vitro Evaluation of Novel Promising Agents for Boron Delivery to Tumour Cells

The design of highly selective low-toxic, low-molecular weight agents for boron delivery to tumour cells is of decisive importance for the development of boron neutron capture therapy (BNCT), a modern efficient combined method for cancer treatment. In this work, we developed a simple method for the preparation of new closo- and nido-carborane-containing folic acid bis-amides containing 18-20 boron atoms per molecule. Folic acid derivatives containing nido-carborane residues were characterised by high water solubility, low cytotoxicity, and demonstrated a good ability to deliver boron to tumour cells in in vitro experiments (up to 7.0 µg B/10⁶ cells in the case of U87 MG human glioblastoma cells). The results obtained demonstrate the high potential of folic acid-nido-carborane conjugates as boron delivery agents to tumour cells for application in BNCT.

Advances in nonclassical phenyl bioisosteres for drug structural optimization

The phenyl group is the most prevalent ring system and plays an essential role as a pharmacophore or scaffold in marketed drugs. However, the indiscriminate employment of phenyl is also a major cause of poor physicochemical properties of active molecules. Nonclassical phenyl bioisosteres (NPBs) have emerged as effective replacements for phenyl in structural optimization due to their unique steric structures and physicochemical properties. Herein, the effects of widely reported NPBs on physicochemical properties and biological activities, including bicyclo[1.1.1]pentane (BCP), bicyclo[2.1.1]hexanes (BCH), bicyclo[2.2.2]octane (BCO), cubane (CUB) and closo-carboborane, are reviewed. Issues that require consideration while using NPBs and practical solutions to problems frequently encountered in structural optimization using NPBs are also discussed.