Patent ID: 8530662

Claim:
A compound represented by the following formula (II) or a salt thereof; wherein R4 represents an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkoxy group, an aryloxy group, a formyl group, a carboxyl group, an acetyl group, a propionyl group, a butyryl group, a valeryl group, an isovaleryl group, a pivaloyl group, a lauroyl group, a myristoyl group, a benzoyl group, a naphthoyl group, a methoxycarbonyl group, an ethoxycarbonyl group, a tert-butoxycarbonyl group, a n-decyloxycarbonyl group, a n-hexadecyloxycarbonyl group, a phenoxycarbonyl group, a naphthyloxycarbonyl group, a methylsulfonyl group, an ethylsulfonyl group, a propylsulfonyl group, a butylsulfonyl group, a pentylsulfonyl group, a hexylsulfonyl group, an octylsulfonyl group, a dodecylsulfonyl group, a hexadecylsulfonyl group, a phenylsulfonyl group, a naphthylsulfonyl group, a carbamoyl group, a sulfamoyl group, a thiol group, an alkylthio group, an arylthio group, a methylthiocarbonyl group, an ethylthiocarbonyl group, a butylthiocarbonyl group, an octylthiocarbonyl group, a decylthiocarbonyl group, a tetradecylthiocarbonyl group, an octadecylthiocarbonyl group, a phenylthiocarbonyl group, a naphthylthiocarbonyl group, a ureido group, an amino group, an acetylamino group, an ethylcarbonylamino group, a tert-butylcarbonylamino group, a n-octylcarbonylamino group, a n-hexadecylcarbonylamino group, a benzoylamino group, a naphthoylamino group, a methoxycarbonylamino group, an ethoxycarbonylamino group, a n-octyloxycarbonylamino group, a n-hexadecyloxycarbonylamino group, a cyano group, or a heterocycle residue, R5 represents a hydrogen atom or an alkyl group, and R6 represents a hydrogen atom, an alkyl group, a formyl group, a carboxyl group, an aryl-substituted alkoxycarbonyl group, a carbamoyl group or a sulfamoyl group.