Bioderived Rotaxanes via Dynamic Covalent Boron Chemistry

We report on the use of vicinal diols as a template for synthesis of mechanically interlocked molecules. Vicinal diols are prevalent in bio(macro)molecules such as carbohydrates, RNA as well as polyhydroxylated natural products, and a range of methods exists for recognition and selective binding to these motifs. Here we use dynamic covalent boron chemistry to reversibly attach a V-shaped boronic acid pincer ligand with two alkene-appended arms to a linear diol-containing thread. Following condensation of the pincer ligand with the thread, ring-closing metathesis establishes a quasi[1]rotaxane architecture along with a non-entangled isomer in a 1:2 ratio. Advanced NMR spectroscopy and mass spectrometry unambiguously assigned the isomers and revealed that the quasi[1]rotaxane was in equilibrium with its hydrolyzed free [2]rotaxane form. The boron handle could also be selectively oxidized to kinetically trap the rotaxane in place. This study demonstrates that prevalent biomolecular motifs can be used as templates for establishing mechanical bonds, meaning it might be possible to interlock unmodified native biomolecules and biopolymers for future biomedical applications.