A compound of Formula I: or its stereoisomers, pharmaceutically acceptable salts, complexes, hydrates, solvates, tautomers, polymorphs, racemic mixtures, optically active forms and pharmaceutically active derivative thereof, wherein R1 is hydrogen or a substituent； R2 is hydrogen or a substituent； X is -NH, -NC1-6 alkyl, O, or CR3R4； R3 and R4 are hydrogen or a substituent； Y1 is N or CR5； R5 is hydrogen or a substituent； Y2 is N or CH； Y3 is N or CR6； R6 is hydrogen or a substituent； Z1 is NH when Z2 is C1-6 alkylene； or Z1 is C1-6 alkylene when Z2 is NH； n is 1 or 2； W is CH2 wherein dotted line (----) represents no bond； W is O when dotted line (----) represents either a bond or no bond Ring A is a nitrogen-containing heterocyclic ring system. The compounds of Formula I are useful as antimicrobial agents.
