Compounds represented by the general formula: [wherein R1 represents methoxy, ethyl, methylthio, etc., R2, R3 and R4 each represent hydrogen, a halogen, etc., R5 and R6 each represent —X5—X6—X7 (wherein X5 represents a single bond or —CO—, X6 represents a single bond, —NR3a, etc. and X7 and R3a each represent hydrogen, C1-10 alkyl, etc.), and Ar represents phenyl, pyridyl, etc.], salts thereof and hydrates of the foregoing.