**5. Conclusion**

Natural products with GABA receptors activity were identified in the literatures and discussed in this chapter. Depending on the number of related compounds and test systems used, it was possible to draw in the vicinity of conclusions regarding their structure–activity relationships. As most of the studies examined flavones, and these studies mainly applied radio ligand binding assays, substitution patterns responsible for increased receptor affinity could be associated with one flavone even with diazepam-like Ki values. As far as receptor regulation is concerned, flavones are either non-competitive antagonists or partial agonists. However, certain compounds also exhibited anxiolytic or anticonvulsant effects. Other phenolic compounds addressed in this study were, for example, coumarins, where prenylated compounds demonstrated higher stimulation of the receptor. The association of phenyl residues and pronounced receptor modulation has also been observed for flavanes, isoflavonoids, and chalcones and may be of interest to the production of GABA(A) receptor modulators. Besides, the structural features required for the positive or negative regulation of the polyacetylene and monoterpene receptors as well as the effect of deglycosylation on certain triterpenes have been highlighted. Very few studies have been found on the subtype-specificity of natural products. One example is the enhanced modulation of isopimar and sandaropimaric acid receptors after the exchange of α1-subunit for α2 or α3-subunits. Neolignane honokiol must also be stated in this sense, although the effect was more dependent

on the GABA(A) receptor subunits. Data obtained from recorded in vivo studies may be helpful in this regard, as many compounds have been known to exhibit anxiolytic effects without exhibiting sedative or muscle relaxant properties.
