Herein we describe the synthesis of a series of new potent tachykinin NK(2) receptor antagonists by the modulation of the C- and N-terminal moieties of ibodutant (MEN 15596, 1). The N-terminal benzo[b]thiophene ring was replaced by different substituted naphthalenes and benzofurans, while further modifications were evaluated at the C-terminal tetrahydropyran moiety. Most compounds demonstrated a high affinity for the human NK(2) receptor and high in vitro antagonist potency, indicating that a wide range of substituents at both termini can be incorporated in the molecule without detrimental effects on the interactions with the NK(2) receptor. Selected compounds were tested in vivo confirming their activity as NK(2) antagonists. In particular, after both iv and id administration to guinea pig, compound 61 b was able to antagonize NK(2)-induced colonic contractions with a potency and duration-of-action fully comparable to the reference compound 1 (MEN 15596, ibodutant).