Constrained analogues of phenylalanine have been conceptually designed for analyzing the binding pockets of Phe7 (S7) and Phea (Sa), two aromatic residues important for the pharmacological properties of SP, ie, L-tetrahydroisoquinoleic acid, L-diphenylalanine, L-9- fluorenylglycine (Flg), 24ndanylglycine, the diastereomers of Ll-indanylglycine (Ing) and Ll- benz [flindanylglycine (Bfi), and the 2 and E isomers of dehydrophenylalanine (AZPhe, ...