HPLC-based activity profiling for GABAA receptor modulators from Homalomena occulta rhizomes using zebrafish larval locomotor activity assay

Gamma-aminobutyric acid type A (GABAA) receptors are the major inhibitory neurotransmitter receptors in the central nervous system, and a key target for numerous clinically important drugs used to treat anxiety, insomnia and epilepsy. A dichloromethane extract from rhizomes of Homalomena occulta (Lour.) Schott (Araceae) potentiated GABA-induced chloride currents in a two-microelectrode voltage clamp assay with Xenopus laevis oocytes expressing human GABAA receptors. The same extract was tested in a zebrafish larval locomotor activity assay in which larval locomotion is provoked with the GABAA receptor antagonist pentylenetetrazol (PTZ) [1]. A significant lowering of PTZ-provoked locomotion was observed in larvae pretreated with the extract for 3h. GABAergic activity in the extract was tracked by HPLC-based activity profiling. Reduced larval locomotion was observed with the microfraction collected between 24 – 27 min (A). Compounds in this time window were purified by a combination of normal and reverse phase chromatography, and their structures were established by 1D and 2D NMR and HRMS. Compounds were identified as 3-substituted phenols bearing alkyl/alkenyl chains or benzo-alkyl/benzo-alkenyl moieties as represented in 1 and 2, respectively (B).