Abstract: Compounds of formula (I) have activity in alleviating the effects of impaired dopaminergic signaling, for example in the treatment of Parkinsons Disease: wherein: R1 is a carboxyl, carboxyl ester, or carboxamide group; R2 and R3 are independently hydrogen, or a group —C(?O)R6 or —C(?O)OR6 wherein R6 is C1-C6 alkyl, or a group —CH2Q wherein Q is an optionally substituted monocyclic cycloalkyl or heterocyclyl ring of 3 to 6 ring atoms; R7 is (i) optionally substituted phenyl or monocyclic heteroaryl, or (ii) a radical of formula —CHR4R5; R4 is (a) optionally substituted C1-C4 alkyl, C1-C4 alkoxy, C2-C4 alkenyl, C2-C4 alkenyloxy, or C2-C4 alkynyl, or (b) —CH2XCH3, —CH2CH2XCH3, or —CH2XCH2CH3, wherein X is —O—, S, or —NR7 wherein R7 is hydrogen, methyl or ethyl; or —CH2Q or CH2OQ wherein Q is as defined in relation to R6; and R5 is hydrogen, methyl, ethyl, or methyl substituted by 1, 2 or 3 fluoro atoms; or R4 and R5 taken together with the carbon atom to which they are attached form an optionally substituted