A pyrimidone derivative represented by formula (I) or a salt thereof, or a
solvate thereof or a hydrate thereof having inhibitory activity against
tau protein kinase 1: 1
wherein R.sup.1 represents a C.sub.1-C.sub.12 alkyl group which may be
substituted; R represents, for example, a group represented by the
following formula (II): 2
wherein R2 and R.sup.3 independently represent a hydrogen atom or a
C.sub.1-C.sub.8 alkyl group; R.sup.4 represents a benzene ring which may
be substituted, a naphthalene ring which may be substituted, an indan
ring which may be substituted, a tetrahydronaphthalene ring which may be
substituted, or an optionally substituted heterocyclic ring having 1 to 4
hetero atoms selected from the group consisting of oxygen atom, sulfur
atom and nitrogen atom, and having 5 to 10 ring-constituting atoms in
total.
