Palladium, platinum and gold complexes: a synthetic approach towards the discovery of anticancer agents

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dc.contributor.advisor Prof. James Darkwa Prof. D. Jasper G. Rees en
dc.contributor.author Keter, Frankline Kiplangat
dc.date.accessioned 2010-03-10T06:28:55Z
dc.date.available 2010-03-10T06:28:55Z
dc.date.issued 2010-03-10T06:28:55Z
dc.date.submitted 2008-01
dc.identifier.uri http://hdl.handle.net/10210/3074
dc.description Ph.D. en
dc.description.abstract Ligands bis(pyrazolyl)acetic acid (L1) and bis(3,5-dimethylpyrazolyl)acetic acid (L2) were synthesised by reacting pyrazoles and dibromoacetic acid under phase transfer conditions, by using benzyltriethylammonium chloride as the catalyst. Ligands L1 and L2 were characterised by a combination of 1H, 13C{1H} NMR, IR spectroscopy and microanalysis. Esterification of L1 and L2 led to formation of bis(pyrazolyl)ethyl acetate (L3) and bis(3,5-dimethylpyrazolyl)ethyl acetate (L4). Ligands L3 and L4 were also characterised by a combination of 1H, 13C{1H} NMR, IR spectroscopy and microanalysis. Subsequently, new pyrazolyl palladium(II) and platinum(II) compounds, [PdCl2(L1)] (1), [PdCl2(L2)] (2), [PtCl2(L1)] (3a) and [PtCl2(L2)] (4) were prepared by reacting bis(pyrazolyl)acetic acid ligands (L1-L2) with K2[PdCl4] or K2[PtCl4] respectively. The structures of complex 1 and 2 reveal distorted square planar geometries. The bond angles of N-Pd-N, N-Pd-Cl, N-Pd-Cl, for 1 and 2 are between 85.8(3)o and 90.81(4)o). The platinum compound, K2[Pt4Cl8(L1)2(deprotonated-L1)2].2H2O (3b), crystallised from aqueous solutions containing 3a when such solutions were left to stand overnight. Each platinum coordination environment consists of two cis-Cl ligands and one K2-N^N(L1) unit (L1 = bis(pyrazolyl)acetic acid), with two ligand moieties in 3b that are deprotonated with two K+ counter ions. Reaction of bis(pyrazolyl)acetic acid ligands (L1-L2) with [HAuCl4].4H2O gave gold(III) complexes [AuCl2(L1)]Cl (5a) and [AuCl2(L2)]Cl (6a). The spectroscopic, mass spectroscopy and microanalysis data were used to confirm the formation of the desired complexes. However, attempts to crystallise 5a and 6a led to formation of [AuCl2(pz)(pzH)] (5b) and [AuCl2(3,5-Me2pz)(3,5-Me2pzH)] (6b). This was confirmed by the structural characterisation of 5b, which has a distorted square-planar geometry. When complexes 1-6a were screened for their anti-tumour activity against CHO-22 cells, they showed no appreciable biological activities against CHO-22 cells. Substitution reactions of complexes 1-6a with L-cysteine performed to probe any relationship between the observed antitumour activities and the rates of ligand substitution of these complexes were inconclusive. Dithiocarbamate ligands L5-L8 were synthesised as potassium salts by introducing a CS2 group in positions 1 of pyrazole, 3,5-dimethylpyrazole, indazole and imidazole. The reaction of L5-L8 with [AuCl(PPh3)], [Au2Cl2(dppe)], [Au2Cl2(dppp)] and [Au2Cl2(dpph)], led to isolation of complexes [Au(L)(PPh3)] (13-16), [Au2(L)2(dppe)] (17a-19), [Au2(L)2(dppp)] (20-22) and [Au2(L)2(dpph)] (23-25) (dppe = bis(diphenylphosphino)ethane, dppp = bis(diphenylphosphino)propane, dpph = bis(diphenylphosphino)hexane; L = anions of L5-L8). The mononuclear molecular structure of 15 features a near linear geometry with a P(1)-Au(1)-S(1) angle of 175.36(2) o. The binuclear gold(I) complexes 20-22 and 23-25 have two P-Au-S moieties as evident in the solid state structure of 25. Attempts to crystallise complex 17a led to the formation of a gold(I) cluster complex [Au18S8(dppe)6]2+ (17b) as confirmed by X-ray crystallography. Cluster 17b features weak Au···Au interactions (2.9263(7)-3.1395(7) Å). Complexes 13-16 and 20-25 were tested in vitro for anticancer activity on HeLa cells. The activities of gold(I) complexes 13-16 were comparable to that of cisplatin. Dinuclear gold(I) complexes 20-25 also showed appreciable antitumour activity against HeLa cells. However, the dpph gold(I) compounds (23-25) were highly active, with 24 showing the highest activity against HeLa cells (IC50 = 0.1 μM). The tumour specificity (TS) factors for 23 and 24 were 31.0 and 70.5, respectively. en
dc.language.iso en en
dc.subject Palladium compounds en
dc.subject Platinum compounds en
dc.subject Gold compounds en
dc.subject Complex compounds synthesis en
dc.subject Cancer treatment en
dc.subject Palladium - Therapeutic use en
dc.subject Gold - Therapeutic use en
dc.subject Platinum - Therapeutic use en
dc.title Palladium, platinum and gold complexes: a synthetic approach towards the discovery of anticancer agents en
dc.type Thesis en

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