Compounds represented by the formula: wherein R1 and R2 are hydrogen atom, a hydrocarbon group or a heterocyclic group, or R1 and R2 may form, together with the adjacent carbon atom, a 3- to 8-membered homocyclic or heterocyclic ring, W indicates (i) a group represented by the formula: wherein ring B indicates a 5- to 7-membered ring, or (ii) a group represented by the formula: wherein R4 indicates (1) an aliphatic hydrocarbon group, which may be substituted with an aromatic group, or (2) an acyl group containing an aromatic group, R5 is hydrogen atom, a C1-6 alkyl, or an acyl group, provided that, when W is Wa, R3 is hydrogen atom, a hydrocarbon group or a heterocyclic group, when W is Wb, R3 indicates a C6-14 aryl group, or salts thereof or prodrugs thereof have an excellent action to inhibit neurodegeneration and the like as well as an excellent brain penetrability and are low in the toxicity, thereby being useful as prophylactic or therapeutic drugs for nerve degenerative diseases and the like.