We replaced the Asp18–Ile19 dipeptide of the C-terminal ET analogue Ph–Ph–CH2–O–N CH–CO–Phe–Asp–Ile–Ile–Trp–OH by alkyl spacers of various lengths to investigate the role of the aminoacidic central portion of the molecule and to define the N-terminal and C- terminal pharmacophoric regions of this analogue. The side-chains of the central dipeptide have been shown to be irrelevant for the binding of the molecule to the receptor, but the ...