Pyrrolidine 3-carboxylic acid, or β-proline (Fig. 1) is a constrained β-amino acid commonly used in the design of peptides with enhanced stability towards hydrolysis by proteases. 6 β-Proline is also a potent agonist of the strychnine-sensitive glycine receptor, 7 serves as a building block for the preparation of novel inhibitors of bacterial DNA gyrase 8 and forms the central moiety of a conformationally restricted, highly potent fibrinogen receptor antagonist. 9 In addition, ...