Peptide bicycles that inhibit the Grb2 SH2 domain

Developing short peptides into useful probes and therapeutic leads remains a difficult challenge. Structural rigidification is a proven method for improving the properties of short peptides. In this work, we report a strategy for stabilizing peptide macrocycles by introducing side-chain-to-side-chain staples to produce peptide bicycles with higher affinity, selectivity, and resistance to degradation. We have applied this strategy to G1, an 11-residue peptide macrocycle that binds the Src homology 2 (SH2) domain of growth-factor-bound protein 2 (Grb2). Several homodetic peptide bicycles were synthesized entirely on-resin with high yields. Two rounds of iterative design produced peptide bicycle BC1, which is 60 times more potent than G1 and 200 times more selective. Moreover, BC1 is completely intact after 24 hours in buffered human serum, conditions under which G1 is completely degraded. Our peptide-bicycle approach holds promise for the development of selective inhibitors of SH2 domains and other phosophotyrosine (pTyr)-binding proteins, as well as inhibitors of many other protein-protein interactions.     

Polar Hinges as Functionalized Conformational Constraints in (Bi)cyclic Peptides

Two polar hinges for cyclization of peptides have been developed, leading to bicyclic peptides and cyclized peptides with improved solubility and biological activity. Increasingly, we note that a good aqueous solubility of peptides is an absolute prerequisite, not only to allow handling and purification of our target peptides but also being crucial for biological activity characteristics. Compared to earlier hinges, the 1,1′,1“‐(1,3,5‐triazinane‐1,3,5‐triyl)tris(2‐bromoethanone) (TATB) and 2,4,6‐tris(bromomethyl)‐s‐triazine (TBMT), each containing three nitrogen atoms are structurally similar but chemically very different. Both were accessible in a one‐step fashion from bromoacetonitrile. TATB and TBMT are very suitable for the preparation of more soluble bicyclic peptides. Azide‐modified TATB and TBMT derivatives provide hinges for the preparation of cyclized peptides for incorporation on scaffolds to afford protein mimics.