Compounds of formula (I) or formula (II) have dopaminergic activity: wherein: R1 is a carboxyl, carboxyl ester, or carboxamide group; R2 is a group —C(═O)—NR3R4, or —S(═O)2—NR3R4; R3 and R4 are independently selected from hydrogen, optionally substituted C1-C6 alkyl, (C1-C5 fluoroalkyl)-CH2—, -Q, and —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(═O)—; and R7 is C1-C6 alkyl, C1-C6 fluoroalkyl or cyclopropyl.