Structure and reactivity of noble metal complexes of saccharide and glycoside derivatives relevant to the biological actions

• Main Author: Alba, Laurenzo De Vera
• Format: text
• Language: English
• Published: Animo Repository 2021
• Subjects: Metal complexes; Saccharides; Glycosides; Precious metals; Amino sugars; Chemistry
• Online Access: https://animorepository.dlsu.edu.ph/etdd_chem/2; https://animorepository.dlsu.edu.ph/cgi/viewcontent.cgi?article=1002&context=etdd_chem
• Institution: De La Salle University

This research involves the synthesis and characterization of various sugar-containing complexes of noble metals with biological relevance. The first parts of the study explore the formation of Pt(II), Pd(II), and Cu(II) complexes based on an “Oqn” ligand which is derived from an aminosugar and 8-hydroxy-2-quinolinecarboxaldehyde (HQA) linked together by either a Schiff base or an amine group. The complexes studied were: imine-type Oqn complexes of Pt(II) (complexes 1-3), imine-type Oqn complexes of Pd(II) (4-6), amine-type Oqn complexes of Pt(II) (7) and Pd(II) (8), imine- and amine-type Oqn complexes of Cu(II) (9-13), and several related Pt(II), Pd(II), and Cu(II) complexes of HQA (14-17). These compounds were characterized by various methods including X-ray crystallography, nuclear magnetic resonance spectroscopy, UV-visible spectroscopy, and protein interaction studies whenever applicable. Initial cytotoxicity tests carried out on several of these compounds indicate their potential for use as anticancer agents. The final part of the thesis investigated the synthesis and crystallization of a novel Ag(I) complex of O-acetylsinigrin (Ag·SinAc) as the first example of a glucosinolate-metal complex. It was found that Ag forms an unstable complex with sinigrin, which rapidly decomposes to form an Ag-aglycone compound by breaking the glycosidic C-S bond. For the Ag·SinAc complex, the crystal structure shows η2-coordination with the ethylene moiety and an overall coordination polymer structure composed of a hollow 1D chain with an Ag-containing central structure. Ag·SinAc degradation into the Ag-aglycone can be induced by heat. Computational studies for heterolytic bond dissociation enthalpies and electron charge transfer using optimized structures show that metals, especially Ag, are able to activate the glycosidic C-S bond through polarization. Additionally, the Ag appears to stabilize the aglycone leaving group. It is proposed that a similar mechanism exists as the role of arginine (Arg259) within the naturally occurring myrosinase enzyme which hydrolyzes sinigrin, in the stabilization of the aglycone leaving group. Thus, the Ag-sinigrin system may be a biomimetic model for the myrosinase-catalyzed decomposition of sinigrin.