A compound of the formula (I):
##STR1##
wherein R1 is hydroxy and the like; R2 is optionally
substituted lower alkyl and the like; R3 is hydrogen atom and the like;
R4 is optionally substituted arylene and the like; R5 is
CC and the like; R6 is optionally substituted
naphtyl and the like
its optically active substance, its prodrug, their pharmaceutically acceptable
salt, or solvate thereof.