Cyclization of RGD Peptides by Suzuki-Miyaura Cross-Coupling

Halogenated l- or d-tryptophan obtained by biocatalytic halogenation was incorporated into RGD peptides together with a variety of alkyl or aryl boronic acids. Suzuki-Miyaura cross-coupling either in solution or on-resin results in side chain-to-tail-cyclized RGD peptides, for example, with biaryl moieties, providing a new dimension of structure-activity relationships. An array of RGD peptides differing in macrocycle size, the presence of d-amino acid, N-methylation, or connectivity between the indole moiety and the boronic acid showed that, in particular, connectivity exhibits a major impact on affinities toward integrins, for example, α_Vβ₃. Structure-activity relationship studies yielded peptides with affinities toward α_Vβ₃ in the low nanomolar range, good selectivity, and high plasma stability. Structural characteristics of representative molecules have been investigated by molecular dynamics simulations, which allowed understanding the observed activity differences.