Exploring the Power of Metal-Free Click Transformations toward the Synthesis of Highly Functionalized Dendrimers for Applications in Drug Delivery

Dendrimers hold immense promises for biomedical applications due to their precisely defined architecture, monodispersity, multivalent surface, and nanoscale dimensions. However, their clinical translation remains constrained by synthetic complexity and purity concerns. Copper-catalyzed Click Chemistry has shown immense potential to construct highly functionalized dendrimers but faces limitations in biological applications due to copper contamination. While metal-free click reactions such as strain-promoted azide-alkyne cycloaddition (SPAAC), thiol-ene coupling, and inverse electron-demand Diels-Alder (IEDDA) have emerged as biocompatible alternatives, their application to the construction of densely functionalized dendrimers remains rare. Here, we report the first integrated metal-free click strategy to construct a second-generation dendrimer (Glucose-60-D) bearing 60 peripheral glucose units using a synergistic sequence of thiol-ene, SPAAC, and IEDDA reactions. This triple-click approach enabled the efficient assembly of a dendrimer bearing 240 surface hydroxyl groups with excellent monodispersity and purity, confirmed by structural, spectroscopic, and chromatographic analyses. Biocompatibility studies across five mammalian cell lines demonstrated excellent cytotolerance at high doses, and mechanistic studies revealed GLUT-mediated uptake as the dominant internalization pathway. In vivo fluorescence imaging studies further demonstrated selective colocalization with microglia and neurons at the site of injury in a pediatric mouse model of traumatic brain injury demonstrating the potential of the Glucose-60-D as a targeted drug delivery nanoplatform. Collectively, this work presents the first demonstration of a divergent, orthogonal, and entirely metal-free click-chemistry approach for constructing a complex dendritic nanocarrier with robust translational potential for drug delivery.