Alkaloids from Eschscholzia c alifornica and Their Capacity to Inhibit Binding of [3H]8-Hydroxy-2-(di-N-propylamino)tetralin to 5-HT1A Receptors in Vitro

A 70% ethanol extract of California poppy (Eschscholzia californica) was able to bind to 5-HT1A and 5-HT7 receptors at 100 μg/mL. The subsequent isolation procedure yielded the known alkaloids californidine (1), escholtzine (2), N-methyllaurotetanine (3), caryachine (4), and O-methylcaryachine (5), along with a new pavine alkaloid, 6S,12S-neocaryachine-7-O-methyl ether N-metho salt (7). The structure of 7 was determined by spectroscopic data interpretation, while the absolute stereochemistry was determined by means of circular dichroism. From the results obtained from the radioligand-binding assay of the pure compounds, including the commercially available protopine (6), it was evident that the activity on the 5-HT1A receptor was at least partly due to the presence of the aporphine alkaloid 3, which showed the highest inhibition of [3H]8-hydroxy-2-(di-N-propylamino)tetralin ([3H]8-OH-DPAT) binding with an EC50 value of 155 nM and a K i of 85 nM.