Investigation of zwitterionic 7-ammonium-7,9-nido-m-carborane

Zwitterionic ammonium-substituted nido m-carborane (7-NH₃-7,9-nido-carborane), a novel boron moiety for boron neutron capture therapy, was synthesized and its chemical properties were investigated. This boron cluster system showed unique properties by reacting with carbonyl groups of ketones and aldehydes to generate the corresponding iminium-substituted nido m-carboranes.     

Synthesis of Zwitter-Ionic Conjugate of Nido-Carborane with Cholesterol

9-HC≡CCH₂Me₂N-nido-7,8-C₂B₉H₁₁, a previously described carboranyl terminal alkyne, was used for the copper(I)-catalyzed azide-alkyne cycloaddition with azido-3β-cholesterol to form a novel zwitter-ionic conjugate of nido-carborane with cholesterol, bearing a 1,2,3-triazol fragment. The conjugate of nido-carborane with cholesterol, containing a charge-compensated group in the linker, can be used as a precursor for the preparation of liposomes for BNCT (Boron Neutron Capture Therapy). The solid-state molecular structure of a nido-carborane derivative with the 9-Me₂N(CH₂)₂Me₂N-nido-7,8-C₂B₉H₁₁ terminal dimethylamino group was determined by single-crystal X-ray diffraction.     

Synthesis of boron-containing derivatives of pyropheophorbide <Emphasis Type="ItalicUnderline">a</Emphasis> and investigation of their photophysical and biological properties

Proceeding from pyropheophorbide a and 9-hydroxymethyl-m-carborane, 1-hydroxymethyl-o-carborane, and 3-amino-o-carborane new carboranylchlorins were prepared, and their photophysical and biological properties were investigated.     

Palladium-Catalyzed Alkynylation of 2-Iodo-<Emphasis Type="Italic">p</Emphasis>-carboranes and 9-Iodo-<Emphasis Type="Italic">m</Emphasis>-carboranes

Palladium-catalyzed reaction of ethynyl-substituted pyridine and quinoline derivatives with 2-iodo-p-carborane and 9-iodo-m-carborane gives the corresponding pyridylethynyl- and quinolylethynyl-substituted carboranes. Carborane-containing steroids in which the carborane fragment is linked to the steroid skeleton through acetylene bridge were synthesized by the Sonogashira reaction.     

New synthetic method of 1,2-diaryl-1,2-dicarba-closo-dodecaboranes employing aromatic nucleophilic substitution (SNAr) reaction

Aromatic nucleophilic substitution (S_NAr) reaction of 1-phenyl-o-carborane with 4-nitrofluorobenzene in the presence of NaH or KO^tBu proceeded smoothly to give 1-(4-nitrophenyl)-2-phenyl-o-carborane; similar reaction affords various 1,2-diaryl-o-carboranes, which are useful precursors for macromolecular construction and drug design.     

Synthesis of a Tyr-octreotate conjugated closo-carborane [HC2B10H10]: a potential compound for boron neutron capture therapy

A novel Tyr³-octreotate conjugated closo-carborane as a potential compound for boron neutron capture therapy was obtained via Fmoc solid phase peptide synthesis. The boron cluster [C₂B₁₀H₁₁] was introduced through the reaction of 6,9-bis(acetonitrile)decaborane and 5-hexynoic acid yielding a new closo-carborane conjugated carboxylic acid which was coupled subsequently with solid phase conjugated Tyr³-octreotate. The final boron-containing peptide was purified by preparative reverse phase HPLC and structural identity was proved applying MALDI-TOF mass spectrometry.     

Synthesis of (m-carboran-9-yl)ferrocene and (m-carboran-9-yl)cymantrene

Cross-coupling reactions of 9-iodo-m-carborane with ferrocenylzinc chloride or cymantrenylzinc chloride catalyzed by (Ph₃P)₂PdCl₂ result in the formation of (m-carbo ran-9-yl)ferrocene and (m-carboran-9-yl)cymantrene, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 542–543, March, 1998.     

Synthesis of novel carborane-containing terminal alkynes

Lithiation of 1-bromomethyl-o-carborane with lithium diisopropylamide (LDA) in THF results in the in situ formation of 1-lithio-2-bromomethyl-o-carborane, the reaction of which with 3-trimethylsilylprop-2-ynal gives 2-(2-trimethylsilylethynyl)-3,4-(о-carborano)-2,5-dihydrofuran. Subsequent base-catalyzed desilylation furnishes new terminal alkynes of closoand nido-carborane series.     

Synthesis of B-organo-substituted 1,2-, 1,7-, and 1,12-dicarbaclosododecarboranes(12)

A convenient new method is proposed for the synthesis of 9-organo-substituted o- and m-carboranes and 2-organo-substituted p-carborane by the substitution of iodine in 9-iodine-o-, 9-iodine-m-, and 2-iodine-p-carboranes by an organic group from an organomagnesium compound in the presence of catalytic amounts of phosphine complexes of palladium. For the first time the halogen in boron halogen carboranes has been substituted by an organic group.     

Synthesis of podands with nido-carboranyl groups as a basis for construction of crown ethers with an incorporated metallacarborane moiety

The reactions of the dioxane derivative of 7,8-dicarba-nido-undecaborate anion (nido-carborane), [10-O(CH₂CH₂)₂O-nido-7,8-C₂B₉H₁₁], with a series of O,O′-dinucleophiles (pyrocatechol, resorcinol, hydroquinone, and ethylene glycol) were studied. The nido-carborane-based podand was obtained, which can be used for assembling of crown ethers with an inserted metallacarborane moiety.     

NMR study of 1-aryl-1,2-dicarba-closo-dodecaboranes: intramolecular C-H?O hydrogen bonding in solution

Dicarba-closo-dodecaborane(12) (carborane) has recently received much attention as a building block for supramolecular assemblies and bioactive compounds. Among carborane isomers, 1,2-dicarba-closo-dodecaborane(12) (o-carborane) has unique chemical properties, including the ability of the o-carborane C-H hydrogens to form hydrogen bonds. To evaluate intramolecular hydrogen bond formation between the o-carborane C-H hydrogen and various hydrogen bond acceptors in solution, we have designed and synthesized 1-aryl-o-carboranes 2. Intramolecular hydrogen bonding ability was evaluated by means of ¹H NMR measurement of the o-carborane C-H hydrogen signal of 2. The 1-(2-methoxyphenyl)-o-carborane derivative 2m appeared to form an intramolecular hydrogen bond between o-carborane C-H hydrogen and the oxygen atom acting as a hydrogen bonding acceptor. In this study, we present evidence for hydrogen bond formation in solution between the o-carborane C-H and hydrogen bond acceptors positioned with appropriate geometry.     

Synthesis of Carborane Derivatives of 2-(2-Carboxyvinyl)-25,10,15,20-tetraphenylporphine

New carboranyl-containing porphyrins were synthesized from 2-(2-carboxyvinyl)-5,10,15,20-tetraphenylporphine and 9-hydroxymethyl-m-carborane, 1-hydroxymethyl-o-carborane, and 3-amino-o-carborane. Physical properties of the products were studied.     

New B-substituted derivatives of m-carborane, p-carborane, and cobalt bis(1,2-dicarbollide) anion

The Pd-catalyzed cross-coupling reactions of B-I bond in m- and p-carboranes and cobalt bis(1,2-dicarbollide) anion with organomagnesium and organozinc compounds were studied. Carboranyl derivatives of furan, thiophene, indole, pyridine and quinoline were synthesized. 2-Pyridylethynyl and 3-quinolylethynyl derivatives of p-carborane were prepared by Pd-catalyzed cross-coupling reactions using corresponding alkynes or their magnesium derivatives.     

Synthesis of Closo-1,7-Carboranyl Alkyl Amines

Of the three closo-carborane isomers (C₂B₁₀H₁₂), closo-1,2-carborane has been used most widely in the synthesis of carboranyl amines. However, closo-1,2-carboranes are prone to deboronation to nido-7,8-carborane under various conditions including attack by basic amino groups. In order to overcome this problem, closo-1,7-carboranyl ethyl-, propyl-, and butylamine were synthesized, which should be more stable towards basic deboronation than their closo-1,2-carboranyl counterparts. These closo-1,7-carboranyl amines (5, 18 and 19) were synthesized using two different methods, both starting from the corresponding closo-1,7-carboranyl alkyl iodides (3, 14 and 15). One of the carboranyl alkyl amine (5) was conjugated with folic acid to form a closo-1,7-carborane-folic acid bioconjugate (20).     

Synthesis and solution properties of sulfate-type hybrid surfactants with a benzene ring

Nine novel sulfate-type hybrid surfactants, C_mF_2m+1C₆H₄CH(OSO₃Na)C_nH_2n+1 (FmPHnOS: m=4, 6, 8; n=3, 5, 7; C₆H₄: p-phenylene), with a benzene ring in their molecules were synthesized. Alkanoyl chlorides were allowed to react with iodobenzene in the presence of aluminum chloride to give the corresponding aromatic ketones. The reaction of the ketones with perfluoroalkyl iodides yielded 1-[4-(perfluoroalkyl)phenyl]-1-alkanones as intermediates. The intermediates were allowed to react with methanol in tetrahydrofuran in the presence of sodium borohydride to yield 1-[4-(perfluoroalkyl)phenyl]-1-alkanols. The desired hybrid surfactants were obtained by the reaction of 1-[4-(perfluoroalkyl)phenyl-1-alkanols with sulfur trioxide/pyridine complex in pyridine and by the subsequent neutralization of the products with sodium hydroxide solution. When compared with the conventional hybrid surfactants, C_mF_2m+1C₆H₄COCH(SO₃Na)C_nH_2n+1 (FmHnS: m=4, 6; n=2, 4, 6; C₆H₄: p-phenylene), the new hybrid surfactants thus synthesized were found to have a comparable ability to lower the surface tension of water and a high hydrophilicity. The cmc of FmPHnOS obeyed Kleven’s rule and their occupied areas per molecule increased with increasing m and n with the values between 0.66 and 1.05 nm². The aggregation number for FmPHnOS micelles ranged from 6 to 45 and the hydrodynamic radius of the micelles was in the range of 1.4-3.1 nm.     

Influence of Electronic Environment on the Radiative Efficiency of 9-Phenyl-9H-carbazole-Based ortho-Carboranyl Luminophores

The photophysical properties of closo-ortho-carboranyl-based donor–acceptor dyads are known to be affected by the electronic environment of the carborane cage but the influence of the electronic environment of the donor moiety remains unclear. Herein, four 9-phenyl-9H-carbazole-based closo-ortho-carboranyl compounds (1F, 2P, 3M, and 4T), in which an o-carborane cage was appended at the C3-position of a 9-phenyl-9H-carbazole moiety bearing various functional groups, were synthesized and fully characterized using multinuclear nuclear magnetic resonance spectroscopy and elemental analysis. Furthermore, the solid-state molecular structures of 1F and 4T were determined by X-ray diffraction crystallography. For all the compounds, the lowest-energy absorption band exhibited a tail extending to 350 nm, attributable to the spin-allowed π–π* transition of the 9-phenyl-9H-carbazole moiety and weak intramolecular charge transfer (ICT) between the o-carborane and the carbazole group. These compounds showed intense yellowish emission (λ_em = ~540 nm) in rigid states (in tetrahydrofuran (THF) at 77 K and in films), whereas considerably weak emission was observed in THF at 298 K. Theoretical calculations on the first excited states (S₁) of the compounds suggested that the strong emission bands can be assigned to the ICT transition involving the o-carborane. Furthermore, photoluminescence experiments in THF‒water mixtures demonstrated that aggregation-induced emission was responsible for the emission in rigid states. Intriguingly, the quantum yields and radiative decay constants in the film state were gradually enhanced with the increasing electron-donating ability of the substituent on the 9-phenyl group (‒F for 1F < ‒H for 2P < ‒CH₃ for 3M < ‒C(CH₃)₃ for 4T). These features indicate that the ICT-based radiative decay process in rigid states is affected by the electronic environment of the 9-phenyl-9H-carbazole group. Consequently, the efficient ICT-based radiative decay of o-carboranyl compounds can be achieved by appending the o-carborane cage with electron-rich aromatic systems.     

Synthesis of azomethines based on 4-formylphenyl m-carboranyl-C-methanoate

A preparative method for the synthesis of m-carborane azomethines via the condensation of mcarborane-C-4-formylphenyl methanoate with aliphatic, cycloaliphatic, and aromatic amines was developed.     

Reactions of lithium derivatives of o- and m-carboranes with 5,6-benzocoumarin and 5,6-benzo-3-ethoxycarbonylcoumarin

Reactions of lithium derivatives o- and m-carborane with 5,6-benzocoumarin and 5,6-benzo-3-ethoxycarbonylcoumarin have been studied.     

Large inclusion constants of ��-cyclodextrin with carborane derivatives

Complexation of some o-, m- and p-carborane derivatives with ??-cyclodextrin was investigated using phenolphthalein in pH 10.5 (0.05 mol dm^?3) borate buffer. Some carborane derivatives indicated large inclusion constants K_ass > 1 × 10⁵ dm³ mol^?1.     

Esters of isoxazole- and isothiazolecarboxylic acids and oximes of β-isatin, isoxazole- and ferrocene-containing ketones and carborane alcohols

Oximes of β-isatin, isoxazole- and ferrocene-containing ketones, o- and m-carborane alcohols react with isoxazol- and isothiazolecarboxylic acid chlorides in the presence of triethylamine to afford the corresponding esters.