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Design and development of novel bismuth compounds as potential contrast agents for diagnostic imaging and antibiotics against helicobacter pylori
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posted on 06.02.2017by Busse, Madleen
The primary aim of this research project was to synthesise and characterise novel hetero- and homoleptic bismuth(III) complexes and bismuth(III)-oxo-clusters using different ligand systems such as carboxylates (Chapter 2), sulfonates (Chapter 3), amino arenesulfonates (Chapter 4) and alpha-amino acids (Chapter 5).
The synthesis of bismuth(III) carboxylato complexes was investigated using the solvent-free (SF) and solvent-mediated (SM) methods. A variety of salicylic, thiosalicylic, nicotinic and mercaptonicotinic acids were applied and resulted in the formation of eighteen new hetero- and homoleptic bismuth(III) complexes including [PhBi(5SMSal)(H2O)4][5SMSal] (5SMSal = Methyl-5-sulfosalicylate), 2-10, [PhBi(O2CBSM)2] (MSBCO2 = 2-(methylthio)benzoate), 2-17, [Bi(O2CN)3] (NCO2 = nicotinate), 2-19 and [Bi2(O2CNS)3] (NSCO2 = 2-mercaptonicotinate), 2-23.
In studying the formation of heteroleptic bismuth(III) sulfonates, nine new compounds were successfully synthesised and structurally characterised by X-ray crystallography. Highlights include the bis-phenylbismuth(III) sulfonate polymer [Ph2Bi(O3SC)] (CSO3 = S-(+)-10-camphorsulfonate), 3-1 and the mono-phenylbismuth(III) sulfonate complex [PhBi(O3SN)] (NSO3 = 1,5-naphthalenedisulfonate), 3-10. Applying the SF methodology resulted in four new homoleptic bismuth(III) complexes, while the SM method afforded the unexpected formation of the dimeric [Bi2(H2O)2(SO4)2(OH)2], 3-15 and the Bi8-cluster compound [Bi8(O3SM)20(SO4)2], 3-16. Changing the bismuth(III) source to Bi2O3 resulted in the formation of two new bismuth(III)-oxo/hydroxo-clusters. Single crystals suitable for X-ray diffraction were isolated and resulted in a novel structural motif of the three cluster chain [Bi18O12(OH)12(O3SC)18(H2O)2]x 13H2O, 3-17, and a cluster of even higher nuclearity [Bi38O45(O3SM)24(H2O)14]x(meta-xylene), 3-20.
Next, the coordination chemistry of seven new silver(I) amino arenesulfonato complexes was investigated, which were then subsequently used to access nine new hetero- and homoleptic bismuth(III) amino arenesulfonates through metathesis reactions, e.g. the tris-(meta-aminobenzenesulfonato) bismuth(III) complex [Bi(O3SBAm)3], 4-11 and the mono-phenylbismuth(III) 2-pyridinesulfonate [PhBi(O3SP)2], 4-20a. A second synthetic pathway utilising [Bi(OtBu)3] was used to synthesise the homoleptic bismuth(III) amino arenesulfonato complexes and the results obtained for both methods were compared.
Moving to the alpha-amino acids, four different methods (SF and SM, Ag2O and [Bi(OtBu)3] methods) were studied to access the bismuth(III) complexes. The investigation of the synthesis of bismuth(III) complexes of monoprotic alpha-amino acids resulted in the formation of four new bismuth(III) compounds, e.g. [Bi(Phe)3] (Phe = (S)-2-amino-3-phenylpropanoato), 5-1, while polyprotic alpha-amino acids resulted in three new bismuth(III) compounds such as [Bi2(Glu)3] (Glu = L-glutamate), 5-8. The stability and bismuth(III)-oxo-cluster formation of the tris-substituted bismuth(III) complexes of alpha-amino acids in aqueous solution was investigated using electrospray ionisation mass spectrometry (ESI-MS).
The synthesised bismuth(III) compounds of sulfonates (Chapter 3), amino arenesulfonates (Chapter 4) and alpha-amino acids (Chapter 5) were assessed for their activity against Helicobacter pylori (H. pylori) strains (251, B128 and 26695). Their activity was compared with standard bismuth carboxylate compounds and commercially available bismuth(III) products [bismuth subsalicylate (BSS), colloidal bismuth subcitrate (CBS) and ranitidine bismuth subcitrate (RBC)]. Most complexes proved to be highly active against H. pylori and gave significantly lower minimum inhibitory concentration (MIC) values than the commercially available bismuth(III) products BSS, CBS and RBC.