Antimicrobial agents

A method for treating a bacterial infection in a mammal comprising administering to the mammal an effective amount of a bicyclic heteroaromatic ring compound of formula I:

• wherein:
• two of X1 to X8 are N and the remaining of X1 to X8 are CH;
• and
• the bicyclic heteroaryl ring is a) substituted on a first ring carbon with a group R1 and substituted on a second ring carbon with a group R2;
• or is b) substituted on a ring carbon with a group R1 and substituted on a ring nitrogen with R3 to form the corresponding ammonium salt that has a suitable counter ion X−;
• or is c) substituted on a ring carbon with a group R4;
• R1 is phenyl that is optionally substituted with one or more groups independently selected from halo, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C1-C6)alkoxycarbonyl, —C(═O)NReRf, and phenyl that is optionally substituted with one or more halo, (C1-C6)alkyl, or (C3-C6)cycloalkyl;
• R2 is —NRcRd, —N+(Ra)3Z−, —C(═NRa)—NRcRd, —NRa—C(═NRa)—NRcRd, —NRa—C(═NRa)—Ra, —NRa—NRa—C(═NRa)—NRcRd, —C(H)═N—NRa—C(═NRa)—NRcRd, —C(═O)—NRa—C(═NRa)—NRcRd, —C(═O)—NRa—C(═NRa)—Ra, or Rb;
• or R2 is (C1-C6)alkyl that is substituted with —NRcRd, —N+(Ra)3Z−, —C(═NRa)—NRcRd, —NRaC(═NRa)—NRcRd, —NRa—C(═NRa)—Ra, —NRa—NRa—C(═NRa)—NRcRd, —C(H)═N—NRa—C(═NRa)—NRcRd, —C(═O)—NRa—C(═NRa)—NRcRd, —C(═O)—NRa—C(═NRa)—Ra, or Rb;
• R3 is (C1-C6)alkyl;
• each R4 is independently phenyl that is substituted with one or more R2 or —C(═O)NRmRn and that is also optionally substituted with one or more halo, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C1-C6)alkoxycarbonyl, or phenyl that is optionally substituted with one or more halo, (C1-C6)alkyl, or (C3-C6)cycloalkyl;
• each Ra is independently H, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C3-C6)cycloalkyl(C1-C6)alkyl, aryl, heteroaryl, aryl(C1-C6) alkyl or heteroaryl(C1-C6) alkyl;
• each Rb is independently selected from imidazoyl, piperazinyl, triazole, and piperazinyl that is optionally substituted with (C1-C6)alkyl;
• each Rc and Rd is independently selected from H, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C3-C6)cycloalkyl(C1-C6)alkyl, aryl, heteroaryl, aryl(C1-C6)alkyl and heteroaryl(C1-C6)alkyl wherein any (C1-C6)alkyl of Rc and Rd is optionally substituted with one or more hydroxy or amino;
• or Rc and Rd together with the nitrogen to which they are attached form a aziridino, azetidino, morpholino, piperazino, pyrrolidino or piperidino;
• each Re and Rf is independently selected from H, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C3-C6)cycloalkyl(C1-C6)alkyl, aryl, heteroaryl, aryl(C1-C6)alkyl and heteroaryl(C1-C6)alkyl wherein any (C1-C6)alkyl is optionally substituted with one or more hydroxy or amino;
• or Re and Rf together with the nitrogen to which they are attached form a aziridino, azetidino, morpholino, piperazino, pyrrolidino or piperidino;
• each Rm and Rn is independently selected from H, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C3-C6)cycloalkyl(C1-C6)alkyl, aryl, heteroaryl, aryl(C1-C6)alkyl and heteroaryl(C1-C6)alkyl wherein any (C1-C6)alkyl of Rm and Rn is optionally substituted with one or more amino;
• or Rm and Rn together with the nitrogen to which they are attached form a aziridino, azetidino, morpholino, piperazino, pyrrolidino or piperidino;
• and
• each Z− is independently a suitable counter ion;
• or a pharmaceutically acceptable salt thereof.