Compounds having neutral endopeptidase (NEP) and/or human soluble endopeptidase (hSEP) inhibitory activity corresponding to the formula I, wherein the substituents R.sup.1, R.sup.2, R.sup.3 and R.sup.4 have the meanings given in the description and also pharmaceutical compositions containing these compounds, in particular pharmaceutical compositions suitable for treating or inhibiting cardiovascular diseases, sexual dysfunction and/or adverse conditions associated with apoptosis.