Compounds of formula (I) or formula (II) have dopaminergic activity: wherein: R1 is a carboxyl, carboxyl ester, or carboxamide group； R2 is a group &mdash；C(&boxH；O)&mdash；NR3R4, or &mdash；S(&boxH；O)2&mdash；NR3R4； R3 and R4 are independently selected from hydrogen, optionally substituted C1-C6 alkyl, (C1-C5 fluoroalkyl)-CH2&mdash；, -Q, and &mdash；CH2Q, wherein Q is an optionally substituted monocyclic carbocyclic or heterocyclic ring of (3) to (6) ring atoms； or R3 and R4 together with the nitrogen to which they are attached form an optionally substituted monocyclic cycloalkyl or non-aromatic heterocyclic ring of (3) to (8) ring atoms； R5 is hydrogen, or a natural or non-natural alpha amino acid residue linked via a peptide bond； R6 is hydrogen or a group R7C(&boxH；O)&mdash；； and R7 is C1-C6 alkyl, C1-C6 fluoroalkyl or cyclopropyl.
