The invention provides novel analogues of enacyloxin Ha and their pharmaceutically acceptable salts, metabolites, isomers (e.g. stereoisomers) and prodrugs. Such compounds are effective in the treatment of infections caused by Gram-negative bacteria such as Acinetobacter baumannii. Compounds in accordance with the invention include those of formula (A), and their pharmaceutically acceptable salts, metabolites, isomers (e.g. stereoisomers) and prodrugs: In formula (A): X is 0 or NRx (where R* is either H or C1-3 alkyl, e.g. CH3)； R1 is a 5- or 6-membered, saturated or unsaturated, carbocyclic ring optionally substituted by one or more substituents, or R1 is an optionally substituted straight-chained or branched C-1-6 alkyl group (e.g. C1-3 alkyl group)； R2 is H, F, CI, Br, I or CH3； R3 is H or OH； R8 is a straight-chained or branched C1-8 alkyl group (e.g. a C1-6 aikyl group)； Y is one of the following groups: (wherein each * denotes the point of attachment of the group to the remainder of the molecule； R9 is H, F, CI, Br or I； R4 and R5 are independently selected from H and OH, or R4 and R5 together are =0, preferably R4 is H and R5 is OH； R6 is H, F, CI, Br, I or CH3； R7 is H and R7' is OH, or R7 and R7' together are =0, preferably R7 is H and R7' is OH)； and each— independently represents an optional bond (i.e. each of C2-C3, C4-C5, C6-C7, C8-C9 and C10-C11 are independently either C-C (single) or C=C (double) bonds).L'invention concerne de nouveaux analogues d'énacyloxine Ha et leurs sels, métabolites, isomères (par exemple, stéréo-isomères) et promédicaments pharmaceutiquement acceptables. Ces composés sont efficaces dans le traitement d'infections causées par des bactéries Gram négatif telles que Acinetobacter baumannii. Les composés selon l'invention comprennent ceux de formule (A), et leurs sels, métabolites, isomères (par exemple stéréoisomères) et promédicaments pharmaceutiquement acceptables : dans la formule (A) : x est 0 ou NRx (où R* est soit H soit un
