Compuestos de formula I donde: uno de Y1 o Y2 representa N y el otro representa NR5, O o S, o bien uno de Y1 o Y2 representa S y el otro representaCR5, donde R5 representa hidrogeno o C1-4 alquilo; m representa 0, 1 o 2; R1 y R3 representa hidrogeno, C1-6 alquilo, C2-6 alquenilo, C2-6 alquinilo, C1-6alcoxi, C1-6 haloalquilo, C3-7 cicloalquilo, C3-7 cicloalquilC1-4 alquilo, arilo, arilC1-4 alquilo, arilC1-4 alcoxi, arilC3-7 cicloalquilo, heteroarilo,heteroarilC1-4 alquilo, R6SO2NR2-,R6CONR2-, R6OCONR2-, R2R7NCONR2-, R2R7N-, R6SO2NR2C1-4 alquilo, R6CONR2C1-4 alquilo, R6OCONR2C1-4 alquilo-R2R7NCONR2C1-4 alquilo, R6SO2C1-4 alquilo, R2R7NSO2C1-4 alquilo, R2R7NCOC1-4 alquilo, R6COC1-4 alquilo, R7OOCC1-4 alquilo, R6OC1-4 alquilo, o R2R7NC1-4alquilo; A representa CO-2 alquileno opcionalmente sustituido; R2 representa hidrogeno n C1-4 alquilo; B representa carboxi o un éster o amidametabolicamente lábil del mismos; y R4 representa un grupo de formula (i) o (ii). R6 representa C1-6 alquilo, C2-6 alquenilo, C2-6 alquinilo, C1-6haloalquilo, C1-4 alcoxiC1-4 alquilo, C1-7 cicloalquilo, C3-7 cicloalquilC1-4 alquilo, arilo, arilC1-4, alquilo, arilcarboniloC1-4, alquilo, heteroarilo, oheteroalrilC1-4, alquilo, R7 representa halogeno o cualquiera de los significados descitos para R6, R8 representa halogeno o C1-4 alquilo; prepresenta 1 o 2. X1 representa un grupo de formula: N,CH>N-CH2-, o >CH-CH2-; X2 representa un grupo de formula: N,CH-CH2-N<, -CH2-<CH,-NH-<CH o -O-<CH;X3 representa N o CH, con la condicion de que cuando X3 sea N no puede ser un grupo: N, -CH2-<N, -NH-<CH o -O-<CH; uno de Z1 o Z2 representa Z y el otrorepresenta CH2, con la condicion de que cuando X3 representa N, entonces Z2ha de ser CH2; Z representa un grupo de formula: HN<, C1-6 alquilo <N.Compounds of formula I where: one of Y1 or Y2 represents N and the other represents NR5, O or S, or one of Y1 or Y2 represents S and the other represents CR5, where R5 represents hydrogen or C1-4 alkyl; m represents 0, 1 or 2; R1 and R3 represent hydrogen, C1-6alkyl, C2-6alkenyl, C2-6alkynyl, C1-6alkoxy, C1-6haloalkyl, C3-7cycloalkyl, C3-7cycloalkylC1-4alkyl, aryl, arylC1-4alkyl, arylC1-4alkoxy, arylC3-7 cycloalkyl, heteroaryl, heteroarylC1-4alkyl, R6SO2NR2-, R6CONR2-, R6OCONR2-, R2R7NCONR2-, R2R7N-, R6SO2NR2C1-4R2C2R2C1R2C1R2C1R2C2 alkyl, R6SO2C1-4 alkyl, R2R7NSO2C1-4 alkyl, R2R7NCOC1-4 alkyl, R6COC1-4 alkyl, R7OOCC1-4 alkyl, R6OC1-4 alkyl, or R2R7NC1-4alkyl; A represents CO-2 optionally substituted alkylene; R2 represents hydrogen n C1-4 alkyl; B represents carboxy or an ester or amidametabolically labile thereof; and R4 represents a group of formula (i) or (ii). R6 represents C1-6alkyl, C2-6alkenyl, C2-6alkynyl, C1-6haloalkyl, C1-4alkoxyC1-4alkyl, C1-7cycloalkyl, C3-7cycloalkylC1-4alkyl, aryl, arylC1-4alkyl, C 1-4 arylcarbonyl, alkyl, heteroaryl, C 1-4 heteroaryl, alkyl, R7 represents halogen or any of the meanings for R6, R8 represents halogen or C1-4 alkyl; it represents 1 or 2. X1 represents a group of formula: N, CH> N-CH2-, or> CH-CH2-; X2 represents a group of the formula: N, CH-CH2-N <, -CH2- <CH, -NH- <CH or -O- <CH; X3 represents N or CH, with the proviso that when X3 is N there is no it can be a group: N, -CH2- <N, -NH- <CH or -O- <CH; one of Z1 or Z2 represents Z and the other represents CH2, with the proviso that when X3 represents N, then Z2 must be CH2; Z represents a group of the formula: HN <, C1-6 alkyl <N.