A series of indole derivatives with varied substituents on the α, β-unsaturated double bond were synthesized and evaluated for their ability to inhibit rat prostatic 5α-reductase. Compounds possessing an ethyl substituent at the β-position of the double bond showed potent inhibitory activity. Among them,(Z)-4-{2-[[3-[1-(4, 4'-difluorobenzhydryl) indol-5-yl]-2- pentenoyl] amino] phenoxy} butyric acid (16, KF20405) showed the maximum potency ...