Carborane carboxylic acid derivatives

Some triorganotin carboxylate structures, in particular those containing two RsSn moieties, deserve additional comment because their structures are more varied. For example, rare types of organotin carboxylates include derivatives of carborane-carboxylic acids [ (l,7-C2BioHn-l-COO)Bu2Sn 20]2 (structure of type A) [451]. The bis(triphenyltin) derivative of phenylmaleic acid, 145, contains only four-coordinate tetrahedral tin (Sn O 2.077 and 2.090 A) and is not associated, but in the bis(triphenyltin) citraconate, 146, one tin atom participates in the supramolecular association, 147, and polymer-chain formation and becomes five-coordinate (trigonal pyramidal Sn-O 2.193 A, Sn O 2.397 A) whereas the second remains four-coordinate (Sn-O 2.089 A), as a part of a dangling side chain [441]. 

The use of nanocontainers, such as low-density lipoproteins (LDL) or liposomes is the important approach directed to selective delivery of therapeutics into tumors. One of the observed differences between tumor cells and their normal counterparts is the rate of metabolism of low-density lipoproteins (LDLs). The LDL vesicle comprises a phospholipids/cholesterol shell with a diameter of approximately 15-20 nm, filled with cholesteryl and glyceryl esters of long-chain alkyl carboxylic acids. This difference is based on the increased need that tumor cells possess for cholesterol to facilitate new membrane formation. The overexpression of the LDL receptors on the tumor cell membrane is responsible for its LDL accretion. This provides a basis for cellular differentiation and the targeting of tumor cells with boron if cholesteryl esters of the LDL core are replaced with a boron species that would simulate cholesterol in its physiochanical properties. This concept was proposed by Kahl in the early 1990s. The initial compounds synthesized were esters of carborane carboxylic acid with various fatty acid alcohols [80]. Later, some other derivatives of cholesterol were synthesized [81,82] and LDLs were proposed as tumor delivery agents for carborane-containing porphyrins [83]. 

Januszko, A. Kaszynski, R Drzewinski, W. Ring effect on helical twisting power of optically active mesogenic esters derived from benzene, bicyclo[2.2.2]octane, and p-carborane carboxylic acids, J. Mater. Chem. 2006,16,452- 61. 

Other carboranylporphyrins and boronated chlorine eg for PDT, in which porphyrin is linked to the carboranyl moiety via the boron or the carbon atoms have also been reported by OTshevskaya et al. In arecent work, boronated amide derivatives starting from 5,10,15,20-tetra(p-aminophenyl) porphyrin and 9-o- and 9-m-carborane carboxylic acid chlorides were prepared. Also, the reaction of 2-formyl-5,10,15,20-tetraphenylporphyrin with the lithium salt of 1,2-c/oso-C2BjoHj2, and... 

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