Recent developments in boron neutron capture therapy

Neutron-Absorption Properties of B/Cu Composites

Copper has high electrical and thermal conductivity, which is frequently employed in structural and functional materials. In this research, powder metallurgy was used to incorporate boron nanosheets into metal matrix composites to create boron dispersion-enhanced copper matrix composites. The neutron-absorption characteristics of composite materials were investigated, as well as the link between neutron-absorption cross-section and neutron energy. The results told us that the morphology of the second phase on the particle surface is closely related to the size of Cu-B particles, copper and boron correspond atomically to each other on the interface without dislocation or lattice distortion, forming a completely coherent interface, and that the neutron absorption cross-section decreases exponentially as neutron energy increases. In low-energy neutrons with energies less than 0.1 eV, the increase of boron content and ¹⁰B abundance in Cu-B alloy will enhance the neutron-absorption capacity of the alloy. Boron dispersion-strengthened copper matrix composites have good neutron-absorption capacity, and the microstructure and size of boron do not affect the neutron-absorption performance of composites with the same content of boron. The hardness of the B-dispersion-strengthened Cu matrix composite obtained by nanoindentation test is about 3.04 GPa. Copper matrix composites with boron dispersion reinforcement exhibit high hardness and neutron-absorption characteristics.

Tuning a modular system - synthesis and characterisation of a boron-rich s-triazine-based carboxylic acid and amine bearing a galactopyranosyl moiety

Introduction of a bis(isopropylidene)-protected galactopyranosyl moiety in s-triazine-based boron-rich carboxylic acids and amines results in soluble and suitable coupling partners for tumour-selective biomolecules with applications as selective agents for boron neutron capture therapy (BNCT). Bearing either a carboxylic acid or primary amine as a functional group, these compounds are highly versatile and thus largely extend the possible coupling strategies with suitable biomolecules. Modification of the gastrin-releasing peptide receptor (GRPR) selective agonist [d-Phe⁶, β-Ala¹¹, Ala¹³, Nle¹⁴]Bn(6-14) with the carboxylic acid derivative yielded a bioconjugate with an optimal receptor activation and internalisation profile. This demonstrates the great potential of this approach for the development of novel boron delivery agents.

Enlargement of a Modular System-Synthesis and Characterization of an s-Triazine-Based Carboxylic Acid Ester Bearing a Galactopyranosyl Moiety and an Enormous Boron Load

The amount of boron accumulated in tumor tissue plays an important role regarding the success of the boron neutron capture therapy (BNCT). In this article, we report a modular system, combining readily available starting materials, like glycine, 1,3,5-triazine and the well-known 9-mercapto-1,7-dicarba-closo-dodecaborane(12), as well as α-d-galactopyranose for increased hydrophilicity, with a novel boron-rich tris-meta-carboranyl thiol.

Modular triazine-based carborane-containing carboxylic acids - synthesis and characterisation of potential boron neutron capture therapy agents made of readily accessible building blocks

Based on a modular combination of s-triazine, the well-known 9-mercapto-1,7-dicarba-closo-dodecaborane(12) and commercially available carboxylic acids, namely thioglycolic acid, glycine, and N_α-Boc-l-lysine, several carboxylic acid derivatives were synthesised and fully characterised. The thioglycolic acid derivative was introduced into a peptide hormone by solid phase peptide synthesis. High activity and selective internalisation into peptide receptor-expressing cells was observed. With a very high boron content of twenty boron atoms, these derivatives are interesting as selective Boron Neutron Capture Therapy (BNCT) agents.

Influence of fluorine substituents on the NMR properties of phenylboronic acids

The paper presents results of a systematic NMR studies on fluorinated phenylboronic acids. All possible derivatives were studied. The experimental (1)H, (13)C, (19)F, (11)B, and (17)O spectral data were compared with the results of theoretical calculations. The relation between the calculated natural bond orbital parameters and spectral data (chemical shifts and coupling constants) is discussed. The first examples of (10)B/(11)B isotopic effect on the (19)F spectra and (4)JFO scalar coupling in organic compounds are reported.

Non-intercalative, deoxyribose binding of boric acid to calf thymus DNA

The present study characterizes the effects of the boric acid binding on calf thymus DNA (ct-DNA) by spectroscopic and calorimetric methods. UV-Vis absorbance spectroscopy, circular dichroism (CD) spectroscopy, transmission electron microscopy (TEM), isothermal titration calorimetry (ITC), and Fourier transform infrared (FT-IR) spectroscopy were employed to characterize binding properties. Changes in the secondary structure of ct-DNA were determined by CD spectroscopy. Sizes and morphologies of boric acid-DNA complexes were determined by transmission electron microscopy (TEM). The kinetics of boric acid binding to calf thymus DNA (ct-DNA) was investigated by isothermal titration calorimetry (ITC). ITC results revealed that boric acid exhibits a moderate affinity to ct-DNA with a binding constant (K a) of 9.54 × 10(4) M(-1). FT-IR results revealed that boric acid binds to the deoxyribose sugar of DNA without disrupting the B-conformation at tested concentrations.

Putting Small Metallacarboranes to Work: A Review

The prospects for developing useful applications based on the chemistry of transition metal complexes of nido-2,3-RR'C2B4H42- and related small carborane ligands are reviewed, with primary emphasis on areas where their utility has been demonstrated in practice. Special attention is directed to the properties of small 6- and 7-vertex MC2B3 and MC2B4 clusters that distinguish them from their icosahedral metallacarborane congeners, and from structurally related metallocene sandwiches. A review with 43 references.

The Development of Photometric Sensors for Boronic Acids

Boronic acids bind certain 1,2- and 1,3-diols with high affinity through reversible formation of boronate esters. They have been utilized as the recognition moiety for artificial receptors, particularly receptors for carbohydrates that have cis-diol moieties. Therefore, sensors for boronic acids could serve as universal reporters for monitoring boronate formation. This paper reports the design and synthesis of a series of photometric chemosensors for phenylboronic acid using diethanolamine as the recognition moiety. Diethanolamine, which binds strongly to boronic acids, has been linked to three different types of optical reporters. A photoinduced electron transfer system based on the anthracene fluorophore has been used to create sensors that show up to a fivefold increase in fluorescent intensity in the presence of millimolar concentrations of phenylboronic acid. Sensor designs based on the restriction of free rotation of extended pi systems and on the perturbed electronic properties of azo dyes are also included. This work demonstrates that sensors based on several different designs can be used for the detection of boronic acids.

Coupling of Amino Carboranes to Carboxylic Acid Containing Substrates

The reactivity of the known amino carboranes 1-H(2)NCH(2)-1,2-C(2)B(10)H(11) and 7-H(3)N-7-CB(10)H(12) with carboxylic acid containing substrates was investigated. The reactions studied using the coupling reagent, 1,1'-carbonyldiimidazole, resulted in the preparation of a series of amides in moderate to high yield. The relative importance of this type of research resides in the fact that it allows the introduction of amino acids in close contact with the carborane cage. These compounds can constitute a new generation of substrates useful in boron neutron capture therapy. Our emphasis lies in the development of suitable synthetic schemes allowing the preparation of this type of compound. Experimental details and analytical data supporting the formulation of the prepared compounds are reported.

Synthesis and biological evaluation of boron-containing polyamines as potential agents for neutron capture therapy of brain tumors

New boron-containing spermidine/spermine (SPD/SPM) analogues have been synthesized: N5-[4-(2-aminoethyl-o-carboranyl)butyl] and N5-{4-[(2,3-dihydroxypropyl)-o-carboranyl]butyl} SPD/SPM derivatives (ASPD-5, ASPM-5, DHSPD-5, and DHSPM-5) as well as N5-{[4-(dihydroxyboryl)phenyl]methyl}spermidine (BBSPD-5). These boronated polyamines retain their ability to displace ethidium bromide from calf thymus DNA and are rapidly taken up in vitro by F98 rat glioma cells. The in vitro toxicities of ASPD-5, ASPM-5, DHSPD-5, and DHSPM-5 are lower than those previously reported for N5-[4-(o-carboranyl)butyl] SPD/SPM derivatives (SPD-5 and SPM-5) but similar to those of native SPD and SPM. Very low toxicity was also observed for BBSPD-5. In vivo studies of ASPD-5 and BBSPD-5 were performed in mice bearing intracerebral implants of the GL261 glioma and subcutaneous implants of the B16 melanoma. The biodistribution data found in both tumor models suggest that the polyamines synthesized to date do not appear to be suitable boron agents for BNCT.