A compound of the formula: ##STR1##

wherein R¹ and R² each is H or a hydrocarbon group which may be substituted, or R¹ and R² form a 3- to 8-membered carbo or heterocyclic ring which may be substituted; R³ is H, a lower alkyl which may be substituted or an aromatic group which may be substituted; R⁴ is (1) an aromatic group which may be substituted, (2) an aliphatic hydrocarbon group substituted by an aromatic group which may be substituted, which hydrocarbon group may be further substituted or (3) an acyl; X and Y each is oxygen or sulfur which may be oxidized; and ring A is a benzene ring which may be further substituted, or a salt thereof, is useful for an agent for suppressing neurodegeneration.