Identification of dihydrostilbenes in Pholidota chinensis as a new scaffold for GABAA receptor modulators.

A dichloromethane extract of stems and roots of Pholidota chinensis (Orchidaceae) enhanced GABA-induced chloride currents (IGABA) by 132.75±36.69% when tested at 100μg/mL in a two-microelectrode voltage clamp assay, on Xenopus laevis oocytes expressing recombinant α1β2γ2S GABAA receptors. By means of an HPLC-based activity profiling approach, the three structurally related stilbenoids coelonin (1), batatasin III (2), and pholidotol D (3) were identified in the active fractions of the extract. Dihydrostilbene 2 enhanced IGABA by 1512.19±176.47% at 300μM, with an EC50 of 52.51±16.96μM, while compounds 1 and 3 showed much lower activity. The relevance of conformational flexibility for receptor modulation by stilbenoids was confirmed with a series of 13 commercially available stilbenes and their corresponding semisynthetic dihydro derivatives. Dihydrostilbenes showed higher activity in the oocyte assay than their corresponding stilbenes. The dihydro derivatives of tetramethoxy-piceatannol (12) and pterostilbene (20) were the most active among these derivatives, but they showed lower efficiencies than compound 2. Batatasin III (2) showed high efficiency but no significant subunit specificity when tested on the receptor subtypes α1β2γ2s, α2β2γ2s, α3β2γ2s, α4β2γ2s, α5β2γ2s, α1β1γ2s, and α1β3γ2s. Dihydrostilbenes represent a new scaffold for GABAA receptor modulators.