The invention provides a homocysteine synthase inhibitor useful for the prophylaxis or treatment of diseases involving homocysteine synthase. The homocysteine synthase inhibitor is a compound of the formula (I)
wherein each symbol is as defined herein, or a pharmacologically acceptable salt thereof, or a solvate thereof.
The invention provides a therapeutic drug for ischemic stroke. The therapeutic drug has the formula (I)
wherein each symbol is as defined herein, or a pharmacologically acceptable salt thereof, or a solvate thereof, as an active ingredient.