Synthesis of Dendritic Glycoclusters and Their Applications for Supramolecular Gelation and Catalysis

Abstract

Glycoclusters with three, four, and six arms of glycosyl triazoles were designed, synthesized, and characterized. The self-assembling properties of these molecules and their catalytic activity as ligands in copper-catalyzed azide and alkyne cycloaddition (CuAAC) reactions were studied. The compounds with a lower number of branches exhibit excellent gelation properties and can function as supramolecular gelators. The resulting gels were characterized using optical microcopy and atomic force microscopy. The glycoconjugates containing six branches showed significant catalytic activity for copper sulfate mediated cycloaddition reactions. In aqueous solutions, 1 mol % of glycoclusters to substrates was efficient at accelerating these reactions. Several trimeric compounds were found to be capable of forming co-gels with the catalytically active hexameric compounds. Using the organogels formed by the glycoconjugates as supramolecular catalysts, efficient catalysis was demonstrated for several CuAAC reactions. The metallogels with CuSO4 were also prepared as gel columns, which can be reused for the cycloaddition reactions several times. These include the preparation of a few glycosyl triazoles and aryl triazoles and isoxazoles. We expect that these sugar-based soft biomaterials will have applications beyond supramolecular catalysis for copper-catalyzed cycloaddition reactions. They may also be useful as ligands or gel matrixes for other metal-ion catalyzed organic reactions.

Recently Developed Carbohydrate Based Gelators and Their Applications

“…Biphasic metallogel reaction mixtures and metallogel columns were utilized to carry out several CuAAC and isoxazole synthesis reactions, using a variety of substrates as shown in Figure 43. The metallogels were successfully reused for up to six reaction cycles, showing the reusability of these soft catalytic materials [88]. The gels formed in this study may have applications in other catalytic reactions using copper ions, as well as catalytic reactions that require alternative metal ions.…”

“…The design rationale of these compounds is based on the concept of multivalency, where individual functional units may perform synergistically when tethered. Dendritic structures have been shown to be effective in the generation of LMOGs [87,88]. Dendrimers have the advantage of uniform molecular weight compared to polymers and can also allow one to introduce desired functionalities into the structure.…”

“…The results of this study showed that linking three to four small molecules to a central core to create trimeric and tetrameric conjugates can be a rational approach to designing supramolecular gelators. More recently, we have designed and synthesized twelve dendritic glycoclusters containing three, four and six glycosyl triazole branches [88]. The clusters with fewer branches were found to be effective supramolecular gelators and the hexameric glycoclusters were found to efficiently accelerate copper sulfate mediated cycloaddition reactions.…”

“…The clusters with fewer branches were found to be effective supramolecular gelators and the hexameric glycoclusters were found to efficiently accelerate copper sulfate mediated cycloaddition reactions. The glycoconjugates 63 [88] and 64-66 were also effective gelators for alcohols and aqueous mixtures ( Figure 42). Combining the efficient trimeric gelators and hexameric catalysts led to the formation of stable co-metallogels that could be used as supramolecular catalysts.…”

Synthesis of Carbohydrate Based Macrolactones and Their Applications as Receptors for Ion Recognition and Catalysis

“…Using Cu (I) catalyzed azide-alkyne cycloaddition reactions (CuAAC), the “click chemistry”, many classes of 1,4-disubstituted 1,2,3-triazole derivatives have been synthesized and studied. There are also many studies towards the effective transformation of [3+2] azide-alkyne cycloaddition reactions, and triazole functions have been used as ligands for catalysis, including the CuAAC reactions [ 22 , 23 , 24 , 25 , 26 ]. Besides being medicinally important, the macrocycles containing the 1,2,3-triazole moieties are also useful in forming host-guest complexes and recognitions for ions [ 27 , 28 , 29 , 30 ].…”