Antiviral agents and uses thereof

A compound of formula (I), or a pharmaceutically acceptable salt thereof:

• wherein,
• R1 is selected from the group consisting of COOH, or a salt thereof, C(O)NR9R10, C(O)OR11 wherein R9, R10 and R11 are independently selected from the group consisting of hydrogen and optionally substituted C1-C6 alkyl;
• R3 is selected from the group consisting of N-linked triazole substituted at one or both ring carbon atoms, optionally substituted N-linked tetrazole, optionally substituted N-linked indole, optionally substituted N-linked isoindole, and optionally substituted N-linked benzotriazole;
• R4 is NHC(O)R17 wherein R17 is selected from the group consisting of C1-C6 alkyl, C1-C6 haloalkyl and C3-C6 cycloalkyl;
• R6, R7 and R8 are independently selected from the group consisting of OH, NH2, C1-C6 alkyl, NR18R18′, C1-C6 alkoxy, —OC(O)R18, —NH(C═O)R18, and S(O)nR18, wherein n=0-2 and each R18 and R18′ are independently hydrogen or optionally substituted C1-C6 alkyl.