A compound of the formula (I): ##STR1## wherein R.sub.1 is a hydrogen atom or lower alkyl; R.sub.2 is a lower alkoxy, lower alkylamino, lower cycloalkyl, optionally substituted phenyl or optionally substituted heterocyclic group; R.sub.3 is an optionally substituted phenyl; R.sub.4 is an optionally substituted phenyl, optionally substituted cycloalkyl, optionally substituted alkyl or optionally substituted heterocyclic group, or a pharmaceutically acceptable salt thereof, which has a high affinity for gastrin receptors and/or CCK-B receptors but not for CCK-A receptors, and is useful for treating diseases associated with gastrin receptors and/or CCK-B receptors without inducing the side effects associated with CCK-A receptors.