3- And 4-imidazol-1-yl-methyl substituted biphenyl compounds (named as meta- and para-substituted compounds) were synthesized bearing additional substituents in 3'-/4'-position as inhibitors of P450 17 (17alpha-hydroxylase-C17,20-lyase). P450 17 is the key enzyme of androgen biosynthesis. Its inhibition is a novel therapeutic strategy for treatment of prostate cancer (PC). Twenty-nine compounds were synthesized by Ar-Mg-Br, Negishi or Suzuki aryl-aryl cross coupling and tested toward human and rat enzyme. Most of the compounds showed moderate to excellent activity against one of the enzymes (0.087 microM < or = IC50 < or = 7.7 microM (ketoconazole: 0.74 microM) for the human enzyme, 0.63 microM < or = IC50 < or = 32 microM (ketoconazole: 67 microM) for the rat enzyme). Interestingly, strong species differences were observed. In addition compounds were tested for inhibition toward P450 arom. The 3-imidazol-1-yl-methyl substituted compounds showed good inhibitory activity of P450 arom, while for the 4-substituted compounds negligible inhibition was found. For the most active group of P450 17 inhibitors, (i.e. the 4-imidazol-1-yl-methyl substituted compounds) a QSAR study was performed for inhibition of the human enzyme leading to the result that a hydrophilic substituent in 3'-/4'-position is very important. The most promising compounds (with respect to activity toward both enzymes) were tested in vivo using SD-rats for reduction of plasma testosterone concentrations 2 and 6 h after single i.p. application. The fluorine substituted compound 8c decreased the testosterone plasma concentration to castration level (after 2 h; 5 mg/kg) showing a biological half live of about 6 h.