Propane-1,3-dione derivative or its salt

Disclosed is a compound of formula (I), or a pharmaceutically acceptable salt thereof, wherein A is optionally substituted benzene, optionally substituted pyridine, or thiophene, B is benzene or thiophene, R1 is H or -CO-lower alkyl, or R1 and R2 may together form optionally substituted dioxolane, and wherein the rest of the substituents are as described in the specification. Also disclosed is the use of the compound as a GnRH receptor antagonist for treating prostate cancer, breast cancer, endometriosis, uterine leiomyoma, or prostatic hypertrophy.