Subtle modifications to a thieno[2,3-d]pyrimidine scaffold yield negative allosteric modulators and agonists of the dopamine D ₂ receptor

We recently described a structurally novel series of negative allosteric modulators (NAMs) of the dopamine D ₂ receptor (D ₂ R) based on thieno[2,3-d]pyrimidine 1, showing it can be structurally simplified to reveal low molecular weight, fragment-like NAMs that retain robust negative cooperativity, such as 3. Herein, we report the synthesis and functional profiling of analogues of 3, placing specific emphasis on examining secondary and tertiary amino substituents at the 4-position, combined with a range of substituents at the 5/6-positions (e.g. aromatic/aliphatic carbocycles). We identify analogues with diverse pharmacology at the D ₂ R including NAMs with sub-μM affinity (9h) and, surprisingly, low efficacy partial agonists (9d and 9i).