Poster Presentation RACI Biomolecular Division Conference 2013

Proteases are involved in almost all physiological processes such as apoptosis and immune response. They play key roles in not only humans but also many disease-causing micro-organisms. Abnormality of the proteases would often result in complex and severe diseases, thus have always been popular targets for drug development.

It is known that proteases universally bind to substrates in a β-strand conformation¹ . This poster describes the design and synthesis of a series of novel macrocyclic peptido-mimetic inhibitors for cathepsins and α-chymotrypsin. The macrocyclic constraints were introduced by ring-closing metathesis and force the compounds to adopt the desired conformation. Instead of linking the P₁ side chain to P₃, the macrocycles are placed between P₂ and P₄ residues, leaving the P₁ residue available for further modifications (Figure 1). One example (compound B, Figure 1) was identified as a potent inhibitor of cathepsin L and S, with IC₅₀ of 3nM and 1.7nM respectively. Another macrocycle (compound A, Figure 1) showed high potency against α-chymotrypsin with an IC₅₀ of 52.1nM. By replacing the aldehyde carbon with a C¹³ atom and conducting NMR experiments, the inhibitor was identified to covalently attach to the enzyme and form a hemiacetal with the active site serine. The structure of the enzyme-inhibitor complex was solved by high-resolution X-ray crystallography (Figure 2) which revealed the inhibitor was bound within the active site in a β-strand fashion.

Figure 1. P1-P3 constrained peptide compared to P2-P4 constrained peptide.    

Figure 2. X-ray crystal structure of compound A (Figure 1) binding to the active site of α-chymotrypsin.