An ethyl acetate extract of Curcuma kwangsiensis S.G. Lee & C.F. Liang (Zingiberaceae) rhizomes (100 lg/
ml) enhanced the GABA-induced chloride current (IGABA) through GABAA receptors of the a1b2c2S subtype
by 79.0 ฑ 7.0%. Potentiation of IGABA was measured using the two-microelectrode voltage-clamp technique
and Xenopus laevis oocytes. HPLC-based activity profiling of the crude extract led to the identification
of 11 structurally related labdane diterpenoids, including four new compounds. Structure elucidation
was achieved by comprehensive analysis of on-line (LC-PDA-ESI-TOF-MS) and off-line (microprobe 1D
and 2D NMR) spectroscopic data. The absolute configuration of the compounds was established by comparison
of experimental and calculated ECD spectra. Labdane diterpenes represent a new class of plant
secondary metabolites eliciting positive GABAA receptor modulation. The highest efficiency was observed
for zerumin A (maximum potentiation of IGABA by 309.4 ฑ 35.6%, and EC50 of 24.9 ฑ 8.8 lM).
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