--R1 or gag-CO--NH--R3 --CO--O--R1 wherein gag-O--, gag-CO-- and R3 are as defined above and R1 --O-- is represented by the formula: ##STR25## wherein R13 is a hydrogen atom or halogen atom or a lower alkyl or halo-lower alkyl group, R14 is a hydrogen or halogen atom or a cyano, carboxyl, lower alkoxycarbonyl, lower alkyl or halo-lower alkyl group, and R15 is a lower alkylene group; or ##STR26## w