Selective blockade of the serotonin 5-HT(2A) receptor is a useful therapeutic approach for a number of disorders, including schizophrenia, insomnia and ischaemic heart disease. A series of aporphines were docked into a homology model of the rat 5-HT(2A) receptor using AutoDock. Selected compounds with high in silico binding affinities were screened in vitro using radioligand-binding assays against rat serotonin (5-HT(1A) and 5-HT(2A)) and dopamine (D1 and D2) receptors. (R)-Roemerine and (±)-nuciferine were found to have high affinity for the 5-HT(2A) receptor (K(i) = 62 and 139 nM, respectively), with (R)-roemerine showing 20- to 400-fold selectivity for the 5-HT(2A) receptor over the 5-HT(1A), D1 and D2 receptors. Investigation into the ligand-receptor interactions suggested that the selectivity of (R)-roemerine is due to it having stronger H-bonding and dipole-dipole interactions with several of the key residues in the 5-HT(2A) receptor-binding site.
A 96-well microplate filtration based 5-HT(2A) receptor-radioligand binding assay was optimized and adopted to carry out a bioassay-guided fractionation of the methanol extract of the leaves of Litsea sessilis. This purification led to the isolation of two compounds identified as (+)-boldine (1) and (+)-dehydrovomifoliol (2). (+)-Boldine binds to 5-HT(2A) receptors at high concentrations with a K(i) value of 2.16 microm. However, (+)-dehydrovomifoliol showed minimal competitive inhibition on the binding of [(3)H]ketanserin to the same receptor with a K(i) value of 2.06 mm. These results suggest that (+)-boldine influences the activity of 5-HT(2A) receptors through competitive binding as an agonist or antagonist.
Compounds with activity at serotonin (5-hydroxytryptamine) 5-HT2 and α1 adrenergic receptors have potential for the treatment of central nervous system disorders, drug addiction or overdose. Isolaureline, dicentrine and glaucine enantiomers were synthesized, and their in vitro functional activities at human 5-HT2 and adrenergic α1 receptor subtypes were evaluated. The enantiomers of isolaureline and dicentrine acted as antagonists at 5-HT2 and α1 receptors with (R)-isolaureline showing the greatest potency (pKb = 8.14 at the 5-HT2C receptor). Both (R)- and (S)-glaucine also antagonized α1 receptors, but they behaved very differently to the other compounds at 5-HT2 receptors: (S)-glaucine acted as a partial agonist at all three 5-HT2 receptor subtypes, whereas (R)-glaucine appeared to act as a positive allosteric modulator at the 5-HT2A receptor.