Super arming of a glycosyl donor using a molecular lever

Ring-System-Based Conformational Switches and their Applications in Sensing and Liposomal Drug Delivery

In the past decades, a great number of stimuli-responsive systems have been developed to be used as drug-delivery systems with high sensitivity and selectivity in targeted therapy. Despite promising results, the current stimuli-responsive systems suffer from the complexity of preparation, as most novel stimuli-responsive systems are based on polymers. Small molecules have often been neglected as candidates for application for stimuli-responsive systems. Recently, structures based on six-membered ring molecules or bicyclic molecules have been developed into conformational switches working through conformational interconversion. These single conformational switches have significantly reduced the complexity of material preparation compared to polymers or copolymers. In this review, we focus on ring-system-based conformational switches that are involved in sensors and smart drug-delivery systems. We hope that this review will shed light on ring-system-based single conformational switches for use in the development of stimuli-responsive systems.

1 Introduction2 Conformation Switches Based On Bispidine Derivatives3 Conformation Switches Based On Cycloalkanes4 Conformation Switches Based On Carbohydrates5 Conclusion

Conformationally Switchable Glycosyl Donors

Glycosyl donors functionalized with 2,2'-bipyridine moieties on the 3-OH and 6-OH or the 2-OH and 4-OH undergo a conformational change when forming 1:1 complexes with Zn²⁺ ions. The pyranoside ring of the zinc complexes adopted axial-rich skew boat conformations. The reactivities of the two glycosyl donors were investigated by performing a series of glycosylations in the presence or absence of Zn²⁺ ions. These glycosylations suggested a decrease in reactivity when binding Zn²⁺. The conformational effect of binding Zn²⁺ was therefore studied using a third glycosyl donor, unable to undergo conformational changes when binding Zn²⁺. From competition experiments, it was observed that the binding-induced conformational change increased the reactivity slightly compared to the glycosyl donor unable to undergo a conformational change.