New tricyclic compound or its salt and antimicrobial agent comprising the same

PURPOSE: To obtain a new compound useful as an antimicrobial agent, an agent for fish diseases, an agricultural chemical and a preservative for foods. CONSTITUTION: The objective compound of formula I [R 1 is H or carboxy- protecting group; R 2 is (substituted)lower alkyl, (substituted)OH or nitro; R 3 is (substituted)lower alkyl; X is halogen; Y is halogen or (substituted)cyclic amino], e.g. ethyl-1-[N-{2,2-bis(t-butyloxycarbonyl)ethyl}-N-methyl]amino-5,6,7,8- tetrafluoro-1,4-dihydro-4-oxyquinoline-3-carboxylate. This compound of formula I is obtained by starting from a compound of formula II (R 2a is halogen or nitro; Z 1 and Z 2 are releasable groups; Y 1 is halogen) and passing the compound of formula II through a compound of formula III (R 11 and R 12 are H or carboxy- protecting group), etc. COPYRIGHT: (C)1993,JPO&Japio