Tricyclic nitrogen containing compounds as antibacterial agents

A compound of formula (I) or a pharmaceutically acceptable salt and/or N-oxide thereof:

• wherein:
• Z1 and Z2 are independently selected from CH and N;
• R1a and R1b are independently selected from hydrogen;
• halogen;
• cyano;
• (C1-6)alkyl;
• (C1-6)alkylthio;
• trifluoromethyl;
• trifluoromethoxy;
• carboxy;
• hydroxy optionally substituted with (C1-6)alkyl or (C1-6)alkoxy-substituted(C1-6)alkyl;
• (C1-6)alkoxy-substituted(C1-6)alkyl;
• hydroxy (C1-6)alkyl;
• an amino group optionally N-substituted by one or two (C1-6)alkyl, formyl, (C1-6)alkylcarbonyl or (C1-6)alkylsulphonyl groups;
• and aminocarbonyl wherein the amino group is optionally substituted by (C1-4)alkyl;
• provided that R1a and R1b are H when Z2 or Z1 is N, respectively;
• R2 is hydrogen, or (C1-4)alkyl, or together with R6 forms Y as defined below;
• A is a group (i):
• in which:
• R3 is as defined for R1a and R1b or is oxo and n is 1 or 2:
• or A is a group (ii)
• W1, W2 and W3 are CR4R8
• or W2 and W3 are CR4R8 and W1 represents a bond between W3 and N.
• X is O, CR4R8, or NR6;
• one R4 is as defined for R1a and R1b and the remainder and R8 are hydrogen or one R4 and R8 are together oxo and the remainder are hydrogen;
• R6 is hydrogen or (C1-6)alkyl;
• or together with R2 forms Y;
• R7 is hydrogen;
• halogen;
• hydroxy optionally substituted with (C1-6)alkyl;
• or (C1-6)alkyl;
• Y is CR4R8CH2;
• CH2CR4R8;
• (C═O);
• CR4R8;
• CR4R8(C═O);
• or (C═O)CR4R8;
• or when X is CR4R8, R8 and R7 together represent a bond;
• U is selected from CO, and CH2 and
• R5 is an optionally substituted bicyclic carbocyclic or heterocyclic ring system (B):
• containing up to four heteroatoms in each ring in which
• at least one of rings (a) and (b) is aromatic;
• X1 is C or N when part of an aromatic ring, or CR14 when part of a non-aromatic ring;
• X2 is N, NR13, O, S(O)x, CO or CR14 when part of an aromatic or non-aromatic ring or may in addition be CR14R15 when part of a non aromatic ring;
• X3 and X5 are independently N or C;
• Y1 is a 0 to 4 atom linker group each atom of which is independently selected from N, NR13, O, S(O)x, CO and CR14 when part of an aromatic or non-aromatic ring or may additionally be CR14R15 when part of a non aromatic ring;
• Y2 is a 2 to 6 atom linker group, each atom of Y2 being independently selected from N, NR13, O, S(O)x, CO, CR14 when part of an aromatic or non-aromatic ring or may additionally be CR14R15 when part of a non aromatic ring;
• each of R14 and R15 is independently selected from:
• H;
• (C1-4)alkylthio;
• halo;
• carboxy(C1-4)alkyl;
• (C1-4)alkyl;
• (C1-4)alkoxycarbonyl;
• (C1-4)alkylcarbonyl;
• (C1-4)alkoxy (C1-4)alkyl;
• hydroxy;
• hydroxy(C1-4)alkyl;
• (C1-4)alkoxy;
• nitro;
• cyano;
• carboxy;
• amino or aminocarbonyl optionally mono- or di-substituted by (C1-4)alkyl;
• or
• R14 and R15 may together represent oxo;
• each R13 is independently H;
• trifluoromethyl;
• (C1-4)alkyl optionally substituted by hydroxy, (C1-6)alkoxy, (C1-6)alkylthio, halo or trifluoromethyl;
• (C2-4)alkenyl;
• (C1-4)alkoxycarbonyl;
• (C1-4)allylcarbonyl;
• (C1-6)alkylsulphonyl;
• aminocarbonyl wherein the amino group is optionally mono or disubstituted by (C1-4)alkyl;
• and
• each x is independently 0, 1 or 2.