THE APPLICATION OF SPIROLIGOMERS TOWARDS MOLECULAR RECOGNITION AND ORGANOCATALYSIS

Abstract

This thesis presents the development of bis-amino acid-based spiroligomer applications in the areas of molecular recognition and organocatalysis. By taking advantage of the high degree of functionality and chirality of the unique bis-amino acid building blocks, spiroligomer backbones can be synthesized with predefined shapes, functioning as molecular hosts or as enzyme active-site-like pockets. Firstly, we demonstrated that spiroligomers can be designed to act as anion receptors. We designed a collection of spiroligomers that each display two urea groups. The spiroligomer that displayed the two urea groups in a way that they pointed at each other acts as an anion receptor and binds hydrogen pyrophosphate H2PPi anion (H2P2O72−), as demonstrated by an NMR titration experiment. Other spiroligomers that displayed the two ureas demonstrated a variety of behaviors including self-association and gel formation. In later work we explored the use of spiroligomers to develop catalysts. We attempted to design bipyridine/TEMPO-based bifunctional catalysts but they failed to achieve a faster alcohol oxidation rate than the background reaction. We then demonstrated the successful incorporation of metal-salen functional groups into spiroligomers in Chapter 4. Several bis-amino acid-based metal-salen complexes were synthesized and examined as asymmetric catalysts. Although only moderate enantio-selectivity was detected from synthesized Mn-salen catalyzed epoxidation reactions, it provides the first direct evidence that chiral bis-amino acid backbone can act as a chiral pocket that influence substrate selection and the stereochemical outcome of reactions.