The invention relates to compounds of formula (II), and pharmaceutically acceptable salts thereof, wherein R1 to R4 are as defined in the claims. The invention further relates to their use as inhibitors of 17β-HSD1 and in treatment or prevention of steroid hormone dependent diseases or disorders, such as steroid hormone dependent diseases or disorders requiring the inhibition of the 17β-HSD1 enzyme and/or requiring the lowering of the endogenous estradiol concentration. The present invention also relates to the preparation of the aforementioned compounds and pharmaceutical compositions comprising as an active ingredient(s) one or more of the aforementioned compounds or pharmaceutically acceptable salts thereof.