tricyclic antibiotic. compound of formula (I): wherein a1 represents -o-, -s- or -n-r3； a2 represents -ch-2 ~, -o-, -n-r4, -c (= o) -or -ch (o-r4) -； a 3 represents C 3-8 C 8 cycloalkylene； saturated and unsaturated 4- to 8-membered heterocyclodiyl having 1, 2 or 3 heteroatoms selected from nitrogen, oxygen and sulfur, group a3 which is unsubstituted or substituted； a4 represents C 1 -C 4 alkylene, C 2 C 4 alkylene, C = o or a group selected from C 2 H 4 NH, C 2 H 4-s- being attached to the adjacent nr5- group via carbon atom； eg are aryl or heteroaryl which are unsubstituted or substituted and R 1 and R 2 independently represent hydrogen or a substituent selected from hydroxy, halogen, mercapto, cyano, nitro, C 1 -C 2. C6-6 alkyl, C6-6 alkoxy, C6-6 alkylthio, C6-6 alkylcarbonyloxy, C6-6 alkylsulfonyloxy, C 1-1 C 6 -heteroalkylcarbonyloxy, C 5- C 6 -heterocyclylcarbonyloxy, C 1-6 C 6 -heteroalkoxy, wherein the heteroalkyl, heteroalkoxy or heterocyclyl groups comprise 1, 2 or 3 heteroatoms selected from nitrogen, oxygen and sulfur, substituents in which the alkyl moieties are unsubstituted or yet substituted； R3, R4 and R5 independently of one another represent hydrogen or C1-6 alkyl； x1 and x2 independently represent a nitrogen atom or cr2, contact that at least one of x1 and x2 represents a nitrogen atom； m is 1； and the (ch2) m portion is optionally substituted by C1-4 alkyl； hydrogen, carboxy, hydroxy, C1-C4-alkoxy, C1-C4-alkylcarbonyloxy, amino, mono- or di-C1-C4-alkyl) amino or acylamino n is 0, 1 or 2 pharmaceutically acceptable salts thereof are valuable for use as a medicament for treating bacterial infections.antibiótico tricíclico. composto de fórmula (i): em que a1 representa -o-, -s- ou -n-r3； a2 represneta -ch~ 2~, -o-, -n-r4, -c(=o)-ou -ch(o-r4)-； a3 representa c~ 3~-c~ 8~cicloalquileno； heterociclodiíla saturada e insaturada de 4 a 8 elementos com 1, 2 ou 3 heteroátomos selecionados de nitrogênio, oxigênio e enxofre, grupo a3 o qual é não substituído
