Novel pro-drugs ##STR1## the variables are as defined in the specification. New and unnatural dipeptoids of .alpha.-substituted Trp-Phe derivatives useful as agents in the treatment of obesity, hypersecretion of gastric acid in the gut, gastrin-dependent tumors, or as antipsychotics are disclosed. Further, the dipeptoids are antianxiety agents and antiulcer agents. They are agents useful for preventing the response to the withdrawal from chronic treatment or with use of nicotine, diazepam, alcoh...