SEARCH FOR SELECTIVE ANTAGONISTS AT α1-ADRENORECEPTOR SUBTYPES: WB-4101 RELATED COMPOUNDS

The development of subtype selective α1 ligands is intensively pursued in order to obtain more effective and safer agents for the treatment of cardiovascular pathologies such as hypertension and arrhythmia, but also and particularly of benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS). One of the oldest and most potent α1 antagonists is represented by WB-4101, a 2-aminomethyl-1,4-benzodioxane derivative which is slightly selective for α1A and, to a minor extent, for α1D-ARs with respect to α1B-AR and 5-HT1A serotoninergic receptor. Many structural modifications of WB-4101 have been done to improve both affinity and selectivity.1-4 Some evidences, resulting from mutagenesis and docking studies, suggest that the benzodioxane moiety and the 2,6-dimethoxyphenoxy residue of WB-4101 are, respectively, involved in conferring α1a selectivity and high α1 affinity. Consistently with these findings, our recent researches have demonstrated that removal of one or both ortho-methoxy substituents adversely affects the affinity for the three α1-AR subtypes, but not that for the 5-HT1A receptor.3 On the basis of these indications, we synthesized a number of S and R analogues of WB-4101, characterized by different substitutions at the benzodioxane and/or phenoxy fragment, in order to modulate and, hopefully, to improve the activity and selectivity profile of the parent compound. In particular, we considered derivatives with benzodioxane 8-substituted with F,4 Cl, OH or OMe 4 or fused with a cyclohexane to give a tetrahydronaphthodioxane polycycle.2 On the other hand, 2,6-dimethoxyphenyl residue was replaced by ortho methoxy substituted 1-naphthyl 2 or biphenyl systems. Finally, hybrid structures were designed combining some of the above modifications. After binding assays, which demonstrated the better α1a, α1b, α1d and 5-HT1A affinity of the S enantiomers, these latter were tested in functional assays on isolated tissues, finding that almost all were able to discriminate among the α1-AR subtypes. 1. Bolognesi M.L., Budriesi R., Cavalli A., Chiarini A., Gotti R., Leonardi A., Minarini A., Poggesi E., Recanatini M., Rosini M., Tumiatti V., Melchiorre C. J.Med.Chem. 1999, 42, 4214-4224. 2. Bolchi C., Catalano P., Fumagalli L., Gobbi M., Pallavicini M., Pedretti A., Villa L., Vistoli G., Valoti E. Bioorg.Med.Chem. 2004, 12, 4937-51. 3. Fumagalli L., Bolchi C., Colleoni S., Gobbi M., Moroni B., Pallavicini M., Pedretti A., Villa L., Vistoli G., Valoti E. Bioorg.Med.Chem. 2005, 13, 2547-2559. 4. Valoti E., Pallavicini M., Villa L., Pezzetta D. J.Org.Chem. 2001, 66, 1018-1025.