Divergent polyester dendronization of macrocycles as a platform for the enhancement of supramolecular applications
Description
Rigid, macrocyclic compounds have initiated an ever-increasing interest spanning beyond the boundaries of supramolecular chemistry and to other fields/sectors of chemical research. Due to their construction and composition, these molecules possess an ability to encapsulate guests of varying sizes, which designates these molecules as essential candidates for host-guest chemistry and molecular recognition; concepts of which can be extended to yield immense benefit. In addition to encapsulation affinity, resorcinol-based deep-cavity cavitands are capable of dimerizing around small guests, forming capsules in order to more efficiently protect a hydrophobic guest from an aqueous environment. In order to probe their potential as drug-delivery vehicles, deep-cavity cavitands were modified with peripheral hydroxyl functionality to impart water solubility and biocompatibility. Divergent dendronization was the proposed method for the surface modification because this technique provided a procedure that would ensure complete functionalization of the substrate while delivering clean products in quantitative yields. The bis(hydroxymethyl) propanoic acid monomer was effective in facilitating the step-wise increase in the size and functionality of the cavitand surface, thereby providing water-solubility at physiological pH. The cavitand was fitted with three generations or layers of poly(ester) dendrons, but maintained the ability to encapsulate small and larger guests such as cyclohexane and dodecane respectively. In order to further modify the surface of cavitands, copper-catalyzed 'click' chemistry was used to graft a variation of dendritic and polymeric side chains from the surface. Click chemistry was chosen because of its abilities to offer high yielding, clean products, while displaying tolerance to a range of functional groups. Previously prepared samples of azide-terminated poly(ester) dendrons, calixarene, cyclodextrin, and poly(caprolactone) were attached to the cavitand surface, and the change in solubility was monitored. In addressing the size restriction of the cavitand core, larger or expanded, rigid macrocycles were prepared from biphenyl substrates via click chemistry. 3 ,3'-dihydroxybenzidine was converted to a biphenyl diazide, and designated as the monomer unit for the fully conjugated macrocyclic target