CHAPTER 4: Multivalent Glycocalixarenes: Synthesis and Molecular Recognition

The introduction of carbohydrate moieties at either the lower or upper rim of calixarenes provides a special class of glycoconjugates that are referred to as glycocalixarenes or calixsugars. The most commonly employed scaffolds are calix[4]arenes, but substrates with larger cavities such as calix[8]arenes are also occasionally employed. The assembly of calixsugars is carried out with the use of different carbon–carbon and carbon–heteroatom bond-forming reactions so that the carbohydrate units are linked to the calixarene scaffolds through a variety of tethers. The ligation means employed are (1) the Mitsunobu reaction, (2) O-glycosylation, (3) S-alkylation, (4) amide bond formation, (5) palladium-catalyzed coupling, (6) Wittig olefination, (7) Cu(i)-catalyzed azide–alkyne cycloaddition, (8) nucleophilic substitution in tosyltetrazoles, (9) isothiocyanate–amine addition and (10) thiol–ene coupling. In addition to the synthetic efforts, molecular recognition studies have also been carried out, mainly towards plant and human lectins.