| abstract |
A compound pf general formula (I): n nwherein, for example,n X 1 and X 2 independently represent a hydrogen atom. R a represents a hydrogen atom or a protecting group for a hydroxyl group. R b and R c form an optionally protected ā(CāO)ā together with the 3-position carbon atom attached to R b and R c , and the broken line forms a single bond or double bond together with the solid line, or a pharmaceutically acceptable salt of the compound or a prodrug thereof. |