Glycosyl-Templated Chiral Helix Stapling of Ethynylpyridine Oligomers by Alkene Metathesis between Inter-Pitch Side Chains

Ethynylpyridine polymers and oligomers consisting of 4-substituted pyridine rings linked by acetylene bonds at the 2- and 6-positions have been investigated. Ethynylpyridine oligomers covalently linked with a glycosyl chiral template form chiral helical complexes by intramolecular hydrogen bonding, in which the chirality of the template is translated to the helix. With a view to fixation of the chiral architecture, D/L-galactosyl- and D/L-mannosyl-linked ethynylpyridine oligomers have been developed with 4-(3-butenyloxy)pyridine units having alkene side chains. The helical structures are successfully stapled by alkene metathesis of the side chains. Subsequent removal of the chiral templates by acidolysis produces template-free stapled oligomers. The chiral, template-free, stapled oligomers show chiral helicity, which is resistant to polar solvents and heating. Stapling makes more happen: Ethynylpyridine oligomers have been prepared as helical structures by using a chiral template. These structures can be stapled by alkene metathesis of the side chains (see figure). Subsequent removal of the chiral template by acidolysis produces template-free stapled helical oligomers, which are resistant to polar solvents and heating.