Analogs of bradykinin with restricted conformational freedom

Three analogs of bradykinin have been synthesized which bear an alpha-methyl group in the place of an alpha proton at position, 4, 5, or 8. Such analogs possess restricted conformational freedom and are of interest for three reasons. (1) They may provide information about the receptor-bound conformation of the peptide. (2) They may provide a route to antagonists of the native peptide. (3) They may be degraded slowly by proteolytic enzymes. None of the analogs described here antagonized the action of bradykinin, but one exhibited tissue specificity and decreased pulmonary inactivation in the rat.