Provided are compounds, the use of the said compounds in treatment, for example treatment of microbial infections, particularly by Gram negative bacteria. The compounds are polymyxin-based and are represented by the formula (I): and pharmaceutically acceptable salts thereof, where X is -NHC(O)-, -C(O)-, -OC(O)-, -CH2- or -SO2- R5 represents C0-12 alkyl(C4-6 heterocyclyl), or C2-12 alkyl or C0-12 alkyl(C3-8 cycloalkyl). and the alkyl or cycloalkyl bears one, two or three hydroxyl groups, or a -NR6R7 group, or one -NR6R7 group and one or two hydroxyl groups and R1 to R4 and R6 to R8 are as defined in the description.本發明提供化合物,該等化合物於治療之用途,例如用於治療微生物感染、尤其革蘭氏陰性細菌(Gram negative bacteria)之微生物感染。該等化合物係基於多黏菌素且係由下式(I)代表:及其醫藥上可接受之鹽,其中X係-NHC(O)-、-C(O)-、-OC(O)-、-CH2-或-SO2-;R5代表C0-12烷基(C4-6雜環基)、或C2-12烷基或C0-12烷基(C3-8環烷基),且該烷基或環烷基具有一個、兩個或三個羥基,或-NR6R7基團,或一個-NR6R7基團及一個或兩個羥基;且R1至R4及R6至R8係如說明書中所定義。
