The present invention provides a VDAC regulator comprising a compound represented by the formula (I): ##STR00001## wherein R.sup.1 is a halogen atom, an optionally substituted heterocyclic group, an optionally substituted hydroxyl group, an optionally substituted thiol group or an optionally substituted amino group; A is an optionally substituted acyl group, an optionally substituted heterocyclic group, an optionally substituted hydroxyl group or an optionally esterified or amidated carboxyl group; B is an optionally substituted aromatic group; X is an oxygen atom, a sulfur atom or an optionally substituted nitrogen atom; and Y is a divalent hydrocarbon group or heterocyclic group; a salt thereof or a prodrug thereof, which is useful as an agent for the prophylaxis or treatment of Down's syndrome and the like.