Efficient Modulation of γ-Aminobutyric Acid Type A Receptors by Piperine Derivatives

Piperine activates TRPV1 (transient receptor potential vanilloid type 1 receptor) receptors and modulates gamma-aminobutyric acid type A receptors (GABA(A)R). We have synthesized a library of 76 piperine analogues and analyzed their effects on GABA(A)R by means of a two-microelectrode voltage-clamp technique. GABA(A)R were expressed in Xenopus laevis oocytes. Structure-activity relationships (SARs) were established to identify structural elements essential for efficiency and potency. Efficiency of piperine derivatives was significantly increased by exchanging the piperidine moiety with either N,N-dipropyl, N,N-diisopropyl, N,N-dibutyl, p-methylpiperidine, or N,N-bis(trifluoroethyl) groups. Potency was enhanced by replacing the piperidine moiety by N,N-dibutyl, N,N-diisobutyl, or N,N-bistrifluoroethyl groups. Linker modifications did not substantially enhance the effect on GABA(A)R. Compound 23 [(2E,4E)-5-(1,3-benzodioxol-5-yl)-N,N-dipropyl-2,4-pentadienamide] induced the strongest modulation of GABA(A) (maximal GABA-induced chloride current modulation (IGABA-max = 1673% +/- 146%, EC50 = 51.7 +/- 9.5 mu M), while 25 [(2E,4E)-5-(1,3-benzodioxol-5-yl)-N,N-dibutyl-2,4-pentadienamide] displayed the highest potency (EC50 = 13.8 +/- 1.8 mu M, IGABA-max = 760% +/- 47%). Compound 23 induced significantly stronger anxiolysis in mice than piperine and thus may serve as a starting point for developing novel GABA(A)R modulators.