Metal-Binding Q-Proline Macrocycles

Herein, we introduce the efficient synthesis of Q-proline (Q-Pro) based, metal-binding macrocycles (QPM), which can display up to nine functional groups. Synthesis of eight QPM was achieved through standard Fmoc-SPPS and peptoid chemistry. QPM are disordered in the absence of a metal cation, as evidenced by NMR and a crystal structure of QPM-3 obtained through racemic crystallization. Addition of metal cations cause these macrocycles to adopt ordered, uniform core structures regardless of the functional groups. Alkylation of QPM allows for addition of reactive functional groups as the final step in a synthesis. Interestingly, the addition of secondary functional groups to the hydantoin amide position (R₂) converts the proline ring from Cg-endo to Cg-exo, due to steric interactions.