The invention concerns a compound of the formula (I):
wherein, for example:
R1 is of the formula —NHC(═O)Rb wherein Rb is, for example, (1-4C)alkyl;
R2 and R3 are hydrogen or fluoro;
R2 and R3 are hydrogen or fluoro;
D is O;
R4 and R5 are hydrogen, (1-4C)alkyl or AR-oxymethyl;
AR is phenyl or phenyl(1-4C)alkyl;
R6 is hydrogen;
>A—B— is of the formula >C═C(Ra)—, >CHCHRa—, or >C(OH)CHRa— (> represents two single bonds) wherein Ra is hydrogen or (1-4C)alkyl;
and pharmaceutically-acceptable salts thereof; processes for their preparation; pharmaceutical compositions containing them and their use as antibacterial agents.