Scheme 3. Recent applications of β′-substituted MAs. Left: S. Thayumanavan and coworkers have performed in-depth kinetic studies on the addition–elimination reaction of these species and demonstrated their applications for crosslinkable gels, and as click handles.⁶⁸ Centre: Y. Kohsaka and coworkers have shown different applications of β′-substituted MAs in polymer materials. One of them involves the fully reversible crosslinking of MA-based materials.⁷⁵ Right: J. L. Bernardes and coworkers have demonstrated the chemoselective modification of native proteins on the most nucleophilic lysine residue(s) with a β′-substituted MA as a reactive click handle.⁷².