Carboranes hydrophobic

C2B9H12, the isomers m- and p-carborane (see Chapter 3.2), the cioso-dodecaborate system B,2H,22 (see Chapter 2.1.5.6), and an arachno-azanonaborane system BXN H n (see Chapter 3.4.4.3). All these dusters have in common the fact that they are stable in aqueous solution, and thereby would allow administration to patients via the blood stream. Their chemistry, and thus the way in which they can be attached to organic molecules, as well as their physiologically relevant parameters of hydrophobicity, vary considerably, however. For a review of the chemistry of BNCT, see Refs. [9-11]. 

The extreme hydrophobicity, or in other words, the low water solubility, of the carborane cage is a major disadvantage in terms of biodistribution. However, 0-C2B10 can be readily converted into a water-soluble degradation product. 0-C2B10 reacts with strong nucleophiles such as alkoxides, aliphatic amines and fluoride anion to... 

The octahedron 24 has a very large internal cavity, capable of enclosing multiple neutral guests [62]. Guests have included carboranes, adamantane, adamantols and 1,3,5-trimethoxybenzene. In all of these cases a host guest ratio of 1 4 is observed with no lower ratios. The hydrophobic cavity that the cage possesses promotes the encapsulation of the above guests in D20 solution. Tri(tert-butyl)benzene was only observed to be encapsulated in a 1 1 ratio. The size of this... 

A New Medicinal Application of Boron Clusters. Potent Nuclear Receptor Ligands Bearing Carborane as a Hydrophobic Pharmacophore... 

Figure 3 displays the synthesis of a hydrophilic carboracycle whose water-solubility is based upon the presence of eight sulfonate substituents and accompanying sodium cations. The properties of this system and other similar hydrophilic species are the subjects of ongoing research. Variables of interest are the size of the hydrophobic cavity, linker structure and the identity of the hydrophilic groups attached to the carborane cages. 

The main problem with the use of carboranes in BNCT is their high hydrophobity. Thus we synthesized a triethyleneglycol carborane derivative by the following route ... 

While the synthesis of a variety of single macrocycles containing 1,2- and 1,7-CaBioHio carboranylene linkers has been described, more recent work has focused upon functionalization of the carborane cages from which these hydrophobic species are comprised and the discovery of methods by which such molecules could be made water-soluble. Water solubility would place a hydrophobic cavity bounded by carborane cages in aqueous media and provide a means to support the solubilization of hydrophobic hydrocarbon or carborane-rich structures. Derivatization of B-vertices of carboracycles derived from 1,2- or l.T-CaBioHio carboranylene groups is easily accomplished by well established methods. ... 

Another, similar, vesicle is the low-density hpoprotein (LDL), which is a major carrier of cholesterol. Cancer cells avidly absorb LDL as a source of cholesterol for their rapidly dividing cells. The LDL can be isolated and their cholesterol core replaced by hydrophobic carboranes. In vitro studies of hamster V-79 cancer cells have shown that such boronated LDLs resulted in intercellular concentrations of 240 (tg B/cell, which is about lOx the amount needed for effective BNCT. The use of drug laden vesicles, such as liposomes or LDLs, also take advantage of a general phenomenon of the enhanced permeability and retention (EPR) effect. ... 

Carboranes, in general, and icosahedral carboranes, in particular, in their neutral and anionic forms are also known for their exceptional characteristics such as low nucleophihcity, high hydrophobicity, and their electron-withdrawing properties having highly polarizable o-aromatic character [48,49]. 

The incorporation of a large number of boron atoms into a tumor for boron neutron capture therapy (BNCT) has been accorded considerable interest over the last few years [67]. It is known that if boron-containing cells are exposed to a neutron flux, they are destroyed without causing irreparable harm to adjacent healthy tissue. In the context of SERMs, for example, Endo et al. have prepared complex 18 [ 1 - (hydroxymethyl) -12- (4-hydroxyphenyl) -1,12-dicarba-closo-dodeca-borane] in which the hydrophobic carborane cage mimics the C and D rings of estradiol (Scheme 3.7) [68]. 

Carboranes and numerous metallacarboranes are characterized by exceptional lipophilicity or amphiphilicity. These properties make them particularly suitable for use as hydrophobic components in biologically active molecules, particularly those which interact hydrophobically with... 

The hydrophobicity of dicarbadodecaboranes can be reduced by the presence of a dipole moment, which is strongly dependent on the position of the carbon atoms in the carborane cage. 

Consequently, the hydrophobicity of dicarbadodecaborane (C2B]oH,2) (1-3) isomers increases in the following order l,2-dicarba-cZo5 o-dodecaborane (ort/ o-carborane) (1) electrophilic boron atom in hydrophobic, neutral c/oio-carborane results in the formation of more hydrophilic, anionic n/tZo-carboranes (CjBpHfj). 

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