Narrow Results

The synthesis and characterization of novel phthalocyanines containing o-carborane groups are described. These new tetrasubstituted phthalocyanines are of interest for the use in cancer therapy. The activities of the carboranyl substituted phthalocyanines were evaluated by the photooxidation of (S)-(−)-citronellol to give a high oxygen consumption comparable to the photosensitizers tetrasulfophthalocyanine zinc complexes.

Synthetic routes to mono- and di-carboranylpyrroles (1-5) bearing the carborane groups linked either directly to the 3- and/or 4-positions of the pyrrole ring or via one or two methylene spacers are described. Several X-ray structures of key intermediates are presented and discussed. Carboranylpyrroles can be cyclotetramerized to afford carboranylporphyrins in low to moderate yields, depending on the number of carborane cages and their linkage to the pyrrole ring. The best yields of porphyrin were obtained with pyrrole 3, bearing a two carbon spacer between the carborane and pyrrole units. The electrochemical polymerization of pyrroles 2 and 3 gave functionalized conducting polymer films with increased overoxidation resistance and thermal stability compared with unsubstituted polypyrrole. Dicarboranylpyrrole 4 did not electropolymerize under a variety of experimental conditions, whereas pyrrole 5 formed only soluble oligomers.

Various dipyrroles possess important motifs for construction of pyrrole-containing pigments. A series of 1,2-dipyrrolylethynes (4a–d) has been efficiently synthesized using an improved one-pot double Sonagashira coupling from trimethylsilylethyne and various 2-iodopyrroles. The resulting 1,2-dipyrrolylethynes were further transformed into novel indolyl-, ethenyl- and carboranyl-dipyrroles (5–7) using the Larock indole synthesis, stereoselective catalytic hydrogenation, or B₁₀H₁₄. Indolyl-dipyrroles were found to selectively bind fluoride ions using one pyrrolic and the indolyl NHs, whereas the carboranyl- and ethenyl-dipyrroles are potentially valuable precursors for the synthesis of porphyrin isomers and expanded pigments.

Condensation of amino groups in 5-(4-aminophenyl)-10,15,20-triphenylporphyrin and 5,10,15,20-tetrakis(4-aminophenyl)porphyrin with pentafluorobenzaldehyde resulted in corresponding Schiff bases and was shown to be a convenient route for the preparation of fluorinated porphyrin derivatives. Compounds thus obtained were easily transformed into the corresponding amines using sodium borohydride. Fluorinated carboranyl porphyrins were prepared via the nucleophilic substitution of the para-fluorine atom of pentafluorophenyl-substituted amine porphyrin derivatives with carborane S-nucleophiles. The alternative synthetic route to the fluorinated carboranyl porphyrins included the condensation of para-carboranyl-substituted tetrafluorobenzaldehyde with corresponding meso-aminoporphyrins. All prepared porphyrins were characterized by different spectroscopic techniques such as UV-vis, IR, ¹H, ¹¹B, ¹⁹F NMR and mass spectra.

A series of new BODIPY conjugates containing maleimide or carborane-succinimide-triazole functional groups were prepared from synthetically available azido-substituted BODIPYs. The structure of new synthesized compounds was characterized by UV-vis, IR, NMR and mass spectrometry. The crystal structures of BODIPY-maleimide conjugates were determined by single crystal X-ray diffraction study. The carborane-containing BODIPYs can be promising agents for photodynamic and boron neutron capture therapy.

Boron is a unique element with electron-deficient properties. In nature, it appears as boric acid and inorganic borates rather than in elemental form. Boron chemistry has been well developed, and a tremendous amount of new boron-containing compounds and materials have been reported. Consequently, boron has found a wide range of applications in fine chemistry, material science, new energy generation and drug development. In particular, boron-based small molecule drugs have attracted enormous attention in recent decades, of which some have been approved by the FDA for clinical use. As a result, boron-containing compounds have been employed in both chemotherapy and radiotherapy to treat different types of patients. Naturally, boron has two main isotopes, boron-11 and boron-10. Boron-10 is capable of absorbing thermal neutrons and initiating a nuclear fission reaction. The reaction generates and releases linear high-energy alpha (α) particles that can destroy tumor cells, so the concept has been utilized in boron neutron capture therapy and nuclear power plants, to treat cancer patients and reduce neutron leakage, respectively. Since the book aims to update and analyze advances in boron-based medicinal chemistry, this chapter first introduces basic boron chemistry and provides a brief overview of the clinical applications and perspectives of organoboron compounds typically involved in disease treatments.