D4 dopamine receptor-selective compounds from the Chinese plant Phoebe chekiangensis

5-Hydroxy-indoline (1), tyramine (2), N-norarmepavine (3), and a novel glycosylated tetrahydroisoquinoline analog SCH 71450 (4) were all isolated from a methanol extract from the fruit of the Chinese plant Phoebe chekiangensis based on their activity in displacing D4 dopaminergic receptor ligand binding. These compounds and related natural products were evaluated for D4 receptor selectivity relative to D2 receptor binding displacement. Compounds 1 and 4 exhibited better D4 selectivity than standard dopaminergic antagonists including the clinically useful compound clozapine. GppNHp shifts in displacement curves indicated that compound 1 is an agonist while compound 4 is an antagonist.