Peptidomimetics containing the spiroazepinoindolinone scaffold were designed and synthesized in order to ascertain their antiproliferative activity on the DU-145 human prostatic carcinoma cell line. Ethyl 2'-oxa-1,2,3,5,6,7-hexahydrospiro[4H-azepine-4,3'-3H-indole]-1'-carboxylate scaffold was functionalized at nitrogen azepino ring with Aib-(l/d)Trp-OH dipeptides. Combining the different stereochemistries of the scaffold and the tryptophan, diastereoisomeric peptidomimetics were prepared and tested. Their biological activity was evaluated by proliferation studies proving that the isomer containing S spiroazepino-indolinone scaffold and l tryptophan is the most active compound. Docking studies confirmed that the active peptidomimetic could bind the GHSR-1a receptor with docking scores comparable with those of well-known agonists even though with a somewhat different binding mode.