Three new crown ester-linked bipyridine homologues with three, four or five ethylene glycol units, which are bulky and soluble in both hydrophilic and lipophilic media, were synthesized. The reaction of the appropriate macrocycles with $K_2PtCl_4$ in water gave yellow cisplatin analogues 6-8 in good yield. These complexes were converted to carboplatin analogues by exchange of the leaving group. All the compounds were characterized by elemental analysis and various spectroscopic methods. Carboplatin analogues 9-11 showed good solubility in both hydrophilic and lipophilic media. The crystal structures of 7, 9, and 11 were determined by x-ray diffraction. X-ray structures indicate that two pyridine rings of the bipyridyl ligand in three compounds can not attain the coplanar state owing to the steric bulkiness of the substituents in 3,3'- positions. The solvolysis reactions of 6-8 in DMSO, characterized by $^1H$, $^{13}C$, and $^{195}Pt$ NMR spectra, leads to the unprecedented example for the complete release of the free crown ester-linked bipyridines, yielding the formation of $cis-[Pt(Me_2SO)_2Cl_2]$. Cisplatin analogs, 7 and 8 showed a moderate and significant cytotoxic effect on both murine leukemia L1210 and P388 even though they do not have any NH proton.
The structure of $[{Pt(DMB)(\mu-OH)}_2]_2(F_3CSO_3)4\cdot2H2_O$ (13) has revealed that two conformational isomers are self-assembled by different hydrogen bonding modes, resulting in new type of co-crystallization of monomer and its polymer. Conformer 13a has the expected methylol conformation in which two methylol substituents are oriented as far as possible to minimize steric interaction between themselves. Each OH group in trans position is hydrogen bonded to oxygen atom of two triflates, which prevents the approach of other molecules for further hydrogen bonding. In contrast to 13a, the orientations of oxygen atoms of methylol groups in conformer 13b are directed to same way. Furthermore, conformer 13b self-assembles to form one dimensional linear polymer through the formation of intermolecular hydrogen bonding between the two methylol OH groups of neighboring monomers.
Three o-carborane-linked bipyridyl ligands were synthesized. Potential BNCT reagents containing cisplatin analogs, 26, 27 and 32 were prepared by displacement of the weakly bound benzonitrile ligands in $cis-[Pt(PhCN)_2Cl_2]$ by the corresponding ligands 23, 24 and 25, respectively. Carboplatin analogs containing o-carborane cages were synthesized in order to increase water solubility of cisplatin analogs. cis-Coordinated DMSO molecules of Pt(Ⅱ) complexes in which leaving groups are carboxylate groups such as CBDCA and oxalate, were replaced by the corresponding bipyridine derivatives including o-carborane cages. Three platinum compounds 30, 31 and 34 showed a little increased hydrophilicity in comparison to the corresponding cisplatin analogs as expected.
Cesium fluoride is found to be a good fluoride ion source for deboronation in the course of searching the effective and mild degradation method of o-carborane. Cesium fluoride degraded ortho-closo-carborane and derivatives quantitatively in ethanol under reflux condition and cesium salt form of nido-carboranes were obtained easily in high yield. Deboronation reaction proceeded effectively at 2 molar ratio of cesium fluoride per o-carborane cage or higher. o-Carborane ester-linked bipyridine, 23 was deboronated successfully using cesium fluoride in ethanol/THF without breaking susceptible ester bond due to weak nucleophilicity of fluoride ion. Cesium salt type of nido-carboranes have much higher water solubility than corresponding tetrabutylammonium salt form, therefore they could be converted to other salt of mono anions.