Mapping the X+1 binding site of the Grb2-SH2 domain with α,α-disubstituted cyclic α-amino acids

A series of phosphopeptides containing α,α-disubstituted cyclic α-amino acids (Acnc, 3 ≤n≤ 7; n refers to the number of carbons in the ring) at the X+1 position of Ac-Tyr(PO3H2)-X+1-Asn-NH2 has been synthesised and their inhibitory activity as antagonists of the Grb2-SH2 domain has been determined in competitive binding assays. The SAR data obtained have been interpreted by using models constructed from the X-ray structure of the ligand-bound Grb2-SH2 domain. The used of α,α-disubstituted cyclic α-amino acids to map the binding pockets of proteins expands the classical alanine scan concept and takes advantage of the known conformational preferences of these amino acids.