The synthesis, characterization and preliminary biological evaluation of triazole complexes of palladium

Van Niekerk, Annick (2017-03)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Palladium based anti-cancer agents have been identified as potential replacements for known platinum based chemotherapeutics. However, only a limited number of these compounds have managed to progress beyond the laboratory due to a lack of understanding surrounding their mode of action and structure activity relationships. Hence, the aim of this study was to synthesize a small library of trans-Pd(II)-1-substituted-4-phenyl-1,2,3-triazolyl and N,N’-bidentate Pd(II)-1-substituted- 4-pyridyl-1,2,3-triazolyl complexes for evaluation against human breast cancer cell lines. The DNA interaction modes of the active compounds were investigated with DNA migration and DNA titration studies. A number of known (1a – 3a, 7a – 9a, 1b – 3b, 7b, 9b) and novel (4a – 6a, 4b – 6b, 8b) 1-substituted- 4-phenyl-1,2,3-triazole and 1-substituted-4-pyridyl-1,2,3-triazole ligands were synthesized, in moderate to good yields. The N-bound substituents were varied in order to investigate the effects of sterics, electronics and hydrophilicity on the cytotoxicity of the resulting complexes. All ligands were characterized using FTIR, 1H NMR and 13C NMR spectroscopy, as well as ESI-MS spectrometry. Elemental analysis was also employed to confirm the purity of the compounds. Complexation of 1a – 9a to Pd(II) yielded the trans-Pd(II)-phenyl-1,2,3-triazolyl complexes (T1a – T9a) in moderate to good yields. It was observed that these compounds dissociate in DMSO and an NMR study was conducted to confirm that ligand exchange indeed takes place. Complexation of ligands 1b – 9b to Pd(II) yielded the N,N’-bidentate-Pd(II)-pyridyl-1,2,3-triazolyl complexes (N1b – N9b) in moderate to good yields. Unlike the trans-Pd(II)-1-substituted-4-phenyl-1,2,3-triazolyl complexes, the N,N’-bidentate-Pd(II)-pyridyl-1,2,3-triazolyl complexes displayed no signs of ligand exchange in DMSO. Characterization of all complexes was carried out using FTIR, 1H and 13C NMR spectroscopy, ESI-MS and elemental analysis. The kinetic solubility in a 2 % (V/V) DMSO/PBS solution of all complexes was determined using a turbidimetric assay. It was found that all complexes were moderately soluble with the exception of complexes T2a, T7a, T9a and N1b. The cytotoxicity of these complexes were thus evaluated as suspensions. Owing to the ligand dissociation observed for complexes T1a – T9a, the cytotoxicity observed for the treatment of cells with these complexes cannot be ascribed to the activity of the original complexes but rather to a mixture of species in solution. The cytotoxicity of the complexes was evaluated employing a MTT Assay (3-(4,5-dimethylthiazol-2- yl)-2,5-diphenylterazolium bromide assay) against breast adenocarcinoma cell lines MCF-7 and MDA-MB-231. Complex T8a displayed moderate cytotoxicity against MCF-7 (IC50 = 40.69 (± 1.1) μM), while none of the other complexes displayed any anti-cancer activity at the complex concentrations tested. Subsequently, evaluation of the ligands against MCF-7 showed that ligands 1a – 4a displayed moderate cytotoxicity while 7a displayed anti-cancer activity (IC50 = 13.02 (± 1.2) μM) which is comparable to that of cisplatin. A structure-activity relationship in favour of the smaller N-bound substituents was established. DNA migration and titration studies revealed that ligands 1a – 4a displayed moderate intercalative character. Complex T8a displayed covalent binding in the DNA migration study, similar to that observed for cisplatin. Ligand 7a displayed weak intercalation based on the DNA migration study, but the DNA titration study revealed a potential multi-mode binding character. The affinity of the ligands towards DNA did not correlate directly with the IC50 values obtained. This potentially indicates that the pharmacological target of the cytotoxic ligands is probably not DNA, and thus requires further investigation.

AFRIKAANSE OPSOMMING: Kankerteenmiddels gebaseer op palladium is geïdentifiseer as moontlike plaasvervangers vir die bestaande platinum baseerde chemoterapeutiese middels. Tenspyte hiervan het slegs ‘n beperkte hoeveelheid palladium verbindings verder as die laboratorium gevorder, vermoedelik weens ‘n gebrek aan kennis rondom hul metode van aktiwiteit en struktuur-aktiwiteit verhoudings. Dus, die doel van hierdie studie was om ‘n reeks trans-Pd(II)-1-gesubstitueerde-4-feniel-1,2,3-triasoliel en N,N’-bidentate Pd(II)-1-gesubstitueerde-4-piridiel-1,2,3-triasoliel komplekse te evalueer as potensiële kankerteenmiddels, teen menslike borskanker sellyne. Die interaksie van die aktiewe verbindings met DNS is ook ondersoek deur middel van DNS migrasie en DNS titrasie studies. A aantal bekende (1a – 3a, 7a – 9a, 1b – 3b, 7b, 9b) en nuwe (4a – 6a, 4b – 6b, 8b) 1- gesubstitueerde-4-feniel-1,2,3-triasool and 1-gesubstitueerde-4-piridiel-1,2,3-triasool ligande was gesintetiseer, in matige tot goeie opbrengs. Die N-gebonde substituente is gevarieer om die effek van steriese hindernis, elektroniese interaksies en hidrofiliesiteit op die sitotoksisiteit van die komplekse te ondersoek. Al die ligande is gekarakteriseer deur van FTIR, 1H KMR en 13C KMR spektroskopie, asook ESI-MS spektrometrie gebruik te maak. Die suiwerheid van die verbindings is deur mikroanaliese bepaal. Kompleksering van 1a – 9a aan ‘n Pd(II) sentrum, het die trans-Pd(II)-feniel-1,2,3-triasoliel komplekse (T1a – T9a) in matige to goeie opbrengs opgelewer. Daar is waargeneem dat hierdie komplekse in DMSO ligand uitruiling met die oplosmiddel ondergaan en ‘n KMR studie het bevestig dat liganduitruiling inderdaad wel in oplossing plaasvind. Kompleksering van ligande 1b – 9b aan ‘n Pd(II) sentrum, het die N,N’-bidentate-Pd(II)-piridiel-1,2,3-triasoliel komplekse (N1b – N9b) in matige tot goeie opbrengs opgelewer. Anders as in die geval van die trans-Pd(II)-feniel-1,2,3-triasoliel komplekse, toon die N,N’-bidentate-Pd(II)-piridiel-1,2,3-triasoliel komplekse geen tekens van liganduitruiling in DMSO nie. Alle komplekse is deur middel van FTIR, 1H en 13C KMR spektroskopie, ESI-MS spektrometrie en mikroanaliese gekarakteriseer. Die kinetiese oplosbaarbeid van al die komplekse in ‘n 2 % DMSO/PBS oplossing is met ‘n turbidimetriese toets vasgestel. Al die komplekse is matig oplosbaar met die uitsluiting van komplekse T2a, T7a, T9a en N1b. Die sitotoksisiteit van hierdie komplekse is dus bepaal met suspensies. As gevolg van die liganduitruiling wat vir komplekse T1a – T9a waargeneem is, kan die sitotoksisiteit wat vir hierdie komplekse bepaal is, nie die aktiwiteit van die oorspronklike komplekse toegeskryf word nie, maar eerder aan ‘n mengsel van spesies teenwoordig in die oplossing. Die sitotoksisiteit van die komplekse is ge-evalueer met ‘n MTT toets teen twee bors adenokarsinoom sellyne, MCF-7 en MDA-MB-231. Kompleks T8a het gematigde sitotoksisiteit teen MCF-7 (IK50 = 40.69 (± 1.1) μM) getoon, terwyl nie een van die ander komplekse enige antikanker aktiwiteit by die konsentrasies wat getoets is toon nie. Daaropvolgende evaluasie van die ligande teen MCF-7 het aan die lig gebring dat ligande 1a – 4a gematigde sitotoksisiteit toon, terwyl ligand 7a antikanker aktiwiteit (IK50 = 13.02 (± 1.2) μM) vergelykbaar aan dié van sisplatien toon. ‘n Struktuur-aktiwiteit verhouding ten gunste van die kleiner substituente is vasgestel. DNS migrasie en titrasie studies het gewys dat ligande 1a – 4a gematigde interkalasie met DNS ondergaan. Kompleks T8a het kovalente binding aan DNS in die DNS migrasie studie getoon, soortgelyk aan dit gevind vir sisplatien. Ligand 7a het swak interkalasie in die DNS migrasie studie getoon, maar die DNS titrasie studie het getoon dat 7a moontlik ‘n veelvoudige binding karakter het. Die affiniteit van die ligande teenoor DNS stem nie ooreen met die IK50 waardes wat in die MTT toets bepaal is nie. Dit dui moontlik aan dat DNS nie die farmakologiese teiken van die sitotoksiese ligande is nie, en dat verdere ondersoek benodig word.

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