Spatially Directional Resorcin[4]arene Cavitand Glycoconjugates for Organic Catalysis in Aqueous Media

Resorcin[4]arenes and their rigid structures “cavitands” offer a unique molecular structure scaffolds suitable for attaching and orienting multi-ligands on their upper rims. Their remarkable structure properties, the relative ease of chemical modification on their either rims or through the multiple phenolic hydroxyl (-OH) groups, manipulating their cavity size and the role of spatial directionality provided by their cores, led synthetic chemist to explore their utilities in the synthesis of valuable resorcin[4]arene/cavitand assemblies with wide range of applications in many research areas such as supramolecular chemistry, host-guest chemistry, glycoconjugates, polymer chemistry, host-guest chemistry, micro-reactors in chemical catalysis and others. In particular, in the field of glycoconjugates, the synthesis of multi-directional glycoresorcin[4]arenes have found valuable uses in glycobiology, i.e. lectins and cells recognitions. Recently, the spatial directionality of β-D-glucopyranoside based on the resorcin[4]arene rigid structure “cavitand” was first described by our group in the synthesis of resorcin[4]arene cavitand glycoconjugates (RCGs). The efficacy of RCGs was established as phase catalysts in order to evaluate their abilities catalyzing different organic transformations in aqueous environment as a green approach in organic syntheses. RCGs showed a variety of advantages such as low catalytic loading and faster conversions for water-insoluble hydrophobic substrates in aqueous media. This dissertation consists of four chapters. Chapter 1 describes the design and the synthesis of a family of spatially directional resorcin[4]arene cavitand glycoconjugates (RCGs) by coupling β-D-glucopyranose moieties on the resorcin[4]arene cavitand upper rims via multiple 1,4-disubstituted 1,2,3-triazolethe linkages achieved from the well-known click reaction, the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The multiple directional β-D-glucopyranoside units on the cavitand cores are capable of multiple H-bond interactions resulting in a significant molecular host system, i.e. “pseudo-saccharide cavity” capable of accommodating different guest molecules, especially hydrophobic organic species, in aqueous environment raising the advantages of these amphiphilies for appreciable applications as molecular vessels and micro-reactors in an ideal atmosphere “water”. In Chapter 2, the utility of RCGs as efficient phase transfer catalysts for thiocyanation and thiazole formation in water is described. The catalytic activity (1 mol% loading) of RCGs enhancing the formation of both thiocyanate and thioazole species in aqueous media is a direct evidence of their capability acting as micro-reactors in water. Also, the recoverability and the reusability of RCGs for thiocyanation and thizaole formation have been examined. Additionally, the influence of the flexibility/rigidity and the orientation of the multiple β-D-glucopyranose moieties on the RCGs’ catalytic efficciency in thiocyanation and thiazole formation has been investigated. In Chapter 3, the design and the synthesis of an octopus-like structure resorcin[4]arene glycoconjugate (RG) is described. RG consists of eight β-D-glucopyranoside units attached to a flexible open system resorcin[4]arene core. The flexibility of the resorcin[4]arene assembly and the presence of the multiple β-D-glucopyranosides provides a wider-type of pseudo-saccharide bucket capable of encapsulating larger molecules in aqueous environment. RG was evaluated for catalyzing the CuAAC in water without the use of any added organic solvent. RG was remarkably efficient in catalyzing the CuAAC reactions in aqueous atmosphere for a variety of small/bulky and hydrophilic/hydrophobic azido and alkyne substrates. In Chapter 4, the construction of resorcin[4]arene cavitand based-carcerands (RCCs) via tandem CuAAC reactions is described. The CuAAC reaction was utilized as an efficient coupling method for the complimentary azido- and alkyne-cavitand halves via multiple 1,4-disubstituted 1,2,3-triazole linkers. Unlike the most reports of covalently linked carcerand synthesis, which are accomplished at very dilute concentration, the fast kinetics of the CuAAC reaction enabled carcerand synthesis at much higher concentration and in high yield