A compound represented by formula (la) or its pharmacologically acceptable salt or solvate, or their diastereomer mixture with respect to the carbon atom attached with wherein R5a and Req, which are different from each other, represent a hydrogen atom or hydroxyl, RWax and Rm f which are different from each other, represent a hydrogen atom or hydroxyl, n is an integer of 1 to 4, and the steric configuration of carbon atom attached with represents R or S.