A plant extract library was screened for GABA(A) receptor activity making use of a two-microelectrode voltage clamp assay on Xenopus laevis oocytes. An ethyl acetate extract of black pepper fruits [Piper nigrum L. (Piperaceae) 100 microg/mL] potentiated GABA-induced chloride currents through GABA(A) receptors (composed of alpha(1), beta(2), and gamma(2S) subunits) by 169.1 +/- 2.4%. With the aid of an HPLC-based activity profiling approach, piperine (5) was identified as the main active compound, together with 12 structurally related less active or inactive piperamides (1-4, 6-13). Identification was achieved by on-line high-resolution mass spectrometry and off-line microprobe 1D and 2D NMR spectroscopy, using only milligram amounts of extract. Compound 5 induced a maximum potentiation of the chloride currents by 301.9 +/- 26.5% with an EC(50) of 52.4 +/- 9.4 microM. A comparison of the modulatory activity of 5 and other naturally occurring piperamides enabled insights into structural features critical for GABA(A) receptor modulation. The stimulation of chloride currents through GABA(A) receptors by compound 5 was not antagonized by flumazenil (10 microM). These data show that piperine (5) represents a new scaffold of positive allosteric GABA(A) receptor modulators targeting a benzodiazepine-independent binding site.

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In a screening of Iranian plants for antiprotozoal activity, an n-hexane extract of the roots of Salvia sahendica potently inhibited the growth of Plasmodium falciparum K1 strain. Subsequent HPLC-based activity profiling led to the identification of seven known and one new abietane-type diterpenoid. Structure elucidation was achieved by analysis of spectroscopic data including 1D and 2D NMR. The absolute configuration of sahandol (7) and sahandone (8) were assigned by comparison of experimental ECD spectra with calculated ECD data, using time-dependent density functional theory and methanol as the solvent. In vitro biological activity against P. falciparum and Trypanosoma brucei rhodesiense STIB 900 strain and cytotoxicity in rat myoblast (L6) cells were determined. The IC50 values of the compounds ranged from 0.8 µM to over 8.8 µM against P. falciparum, and from 1.8 µM to over 32.3 µM against T. brucei rhodesiense. The cytotoxic IC50 values ranged from 0.5-15.5 µM. Selectivity indices for P. falciparum were 0.1 to 18.2, and 0.1 to 1.2 for T. brucei rhodesiense.

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