New 3-, 8-disubstituted pyrazolo[5,1-c][1,2,4]benzotriazines useful for studying the interaction with the HBp-3 area (hydrogen bond point area) in the benzodiazepine site on the gamma-aminobutyric acid type A (GABAA) receptor

The pharmacophoric model using ADLR procedure, based on pyrazolo[5,1-c][1,2,4]benzotriazine system, studied in our laboratory, allowed us to identify the essential interaction points (HBp-1, HBp-2, and Lp-1) and the important areas for affinity modulation (HBp-3 and Lp-2) for binding recognition at benzodiazepine (Bzs) site of GABAA receptors (GABAA-Rs). In this work ADLR method is used to rationalize the affinity data of 23 new compounds and to improve the knowledge on HBp-3 area, hydrogen bond area. Among these new compounds emerge the pyrrolo derivatives (18, 25, 28, 34, and 37) for their good affinity value (14.9 > Ki(nM) > 63.0). In the orientations proposed by ADLR, the NH moiety of the pyrrole ring, independently of the position in the pyrazolobenzotriazine core, fits in HBp-3 area and points out the acceptor feature of this hydrogen bond area, already known as donor area. Unexpectedly, the oxygen atom of the furane ring does not form efficient hydrogen bond with the same area, probably for an imperfect distance. The size of substituent at position 8 is important but not necessary for the receptor recognition, in fact the interdependence between the features of the 3- and 8-substituent’s is again verified, (i.e., compound 20 vs 32).