The present invention relates to compounds of the formulae Ia and Ib, wherein G, R10, R30, R40, R50 and R60 have the meanings indicated in the claims, which are valuable pharmaceutical active compounds. They are inhibitors of the protease cathepsin A, and are useful for the treatment of diseases such as atherosclerosis, heart failure, renal diseases, liver diseases or inflammatory diseases, for example. The invention furthermore relates to processes for the preparation of the compounds of the formulae Ia and Ib, their use and pharmaceutical compositions comprising them.