Design and synthesis of C-terminal modified cyclic peptides as VEGFR1 antagonists

Abstract

Previously designed cyclic peptide antagonist c[YYDEGLEE]-NH2 disrupts the interaction between vascular endothelial growth factor (VEGF) and its receptors (VEGFRs). It represents a promising tool in the fight against cancer and age-related macular degeneration. We described in this paper the optimization of the lead peptide by C-terminal modification. A new strategy for the synthesis of cyclic peptides is developed, improving the cyclisation efficiency. At 100 µM, several new peptides with an aromatic group flexibly linked at C-terminal end showed significantly increased receptor binding affinities in competition ELISA test. The most active peptide carrying a coumarin group may be a useful tool in anti-angiogenic biological studies.

Figure 1

Complex of a VEGF-A dimer with two D2 domains of VEGFR1. The two VEGF-A monomers are presented in red and in blue, the two D2 are in gold. The binding sites on VEGF are circled [10].

Figure 2

(a) Docking model of peptide 1 (in cyan) with the VEGFR1 D2 domain (in gold) [25]. The C-terminal amide is indicated by an arrow. (b) Optimization of peptide 1. Peptide 2 with Tyr replaced by a Lys retains peptide’s receptor binding affinity but with improved solubility and creates a potential labeling site [26]. New peptides are designed with C-terminal substitutions expected to create interactions with Phe172 and Leu174 (circled in pink) belonging to the VEGFR1 D2 domain.

Scheme 1

(a) SPPS with HBTU/DIEA coupling method. (b) 2% TFA with 5% TIPS in CH₂Cl₂. (c) HBTU/HOBt/DIEA in DMF. (d) TFA with 2.5% TIPS and 2.5% water.

Scheme 2

(a) R-NH₂, HBTU/HOBt/DIEA in DMF. (b) 50% TFA in CH₂Cl₂, 1 h.

Scheme 3

(a) SPPS with HBTU/DIEA coupling method. (b) 2% TFA with 5% TIPS in CH₂Cl₂. (c) DIC/HOAt in DMF 1–3 days. (d) 50% TFA in CH₂Cl₂ 2 h.