Chiral cyclobutane scaffoldstheir application in the the development of new functionalized organogelators, organocatalysts and MRI contrast agents /

Resumen

In this thesis, different systems containing a cyclobutane-based scaffold were synthesized and studied as gelators, catalysts or contrast agents. Results of this thesis are divided in three chapters. 1) Two peptide-based low molecular weight gelators previously studied in our group were functionalized with a terpyridine derivative. The influence of this added moiety was determined in the final gelation behavior. This study was performed by tube inversion test, scanning electron microscopy, circular dichroism and theoretical calculations, suggesting that the aggregation of both compounds followed a helical-like structure. These new gelators were complexed with some metal ions in order to obtain metallogelators, but the obtained complexes were not able to gelate any solvent, confirming that the rational design of metallogelators is still a big challenge. 2) Different new hybrid tripeptides containing two proline units and a cyclobutane-based amino acid were synthesized and studied as organocatalysts for aldol reactions. Noteworthy, the enantioselectivity in aldol reactions was reversed in the presence of water. Results were rationalized by conformational and mechanistic studies using NMR, circular dichroism and theoretical calculations. The almost quantitative yields and good enantioselectivities achieved under easy reaction conditions, confers these peptide catalysts with interesting properties to be employed in aldol reactions and to be further explored in other chemical processes. 3) Two new linear ligands containing a cyclobutane-based diamine were synthesized and complexed with different paramagnetic metal ions. The thermodynamic stability, kinetic inertness, and the hydration number of these complexes were investigated using different techniques. They were studied as potential contrast agents for magnetic resonance imaging (MRI) using different NMR methodologies. Overall, results suggested that one of them is a good and safe candidate to be used as contrast agent for clinical MRI.