Compounds of the formula I ##STR00001## wherein X represents hydrogen or hydroxy; Y represents oxygen or sulphur or oxidized sulphur selected from the groups S(O) and S(O.sub.2); R.sup.1 and R.sup.2, which may be the same or different, represent hydrogen or a residue after removal of 1 hydrogen atom from a straight, branched or cyclic, saturated or unsaturated, C.sub.1 C.sub.6-hydrocarbon; or R.sup.1 and R.sup.2, together with the carbon atom to which they are attached (marked with an asterisk in formula I), bearing the group X, form a C.sub.3 C.sub.8 carbocyclic ring; Q represents a diradical residue after removal of 2 hydrogen atoms from a straight, branched or cyclic, saturated or unsaturated C.sub.1 C.sub.8-hydrocarbon; and R.sup.3 represents hydrogen or a residue after removal of 1 hydrogen atom from a straight, branched or cyclic, saturated or unsaturated C.sub.1 C.sub.6-hydrocarbon; may be used for the preparation of a medicament for the treatment and/or prophylaxis of osteoporosis and related bone disorders.