Compounds of formula (I) ##STR00001## wherein R.sup.1 is a phenylcarbonylmethyl group wherein the phenyl moiety is substituted, and R.sup.2 to R.sup.4 are defined as in the claims, or the prodrugs or salts thereof, particularly the physiologically acceptable salts thereof, pharmaceutical compositions containing these compounds, and methods of treating type I and type II diabetes mellitus, arthritis, obesity, allograft transplantation and calcitonin-induced osteoporosis using these compounds.