Isoquinoline Alkaloids Isolated from Corydalis yanhusuo and Their Binding Affinities at the Dopamine D1 Receptor

Bioactivity-guided fractionation of Corydalis yanhusuo has resulted in the isolation of eight known isoquinoline alkaloids - tetrahydropalmatine, isocorypalmine, stylopine, corydaline, columbamine, coptisin, 13-methylpalmatine, and dehydrocorybulbine. The tertiary alkaloids were further analyzed by chiral HPLC to determine the ratios of d-and l-isomers. The isolated compounds were screened for their binding affinities at the dopamine D1 receptor. Isocorypalmine had the highest affinity (Ki = 83 nM). The structure-affinity relationships of these alkaloids are discussed.