Polymyxin Impurity 8

(S) -N- ((S) -4-amino-1- (((S) -1- (((S) -4-amino-1-oxo-1- (((3S,6S,9S,12S,15R,18S,21S) -6,9,18-tris (2-aminoethyl) -15-benzyl-3- ((R) -1-hydroxyethyl) -12-isobutyl-2,5,8,11,14,17,20-heptaoxo-1,4,7,10,13,16,19-heptaazacyclotricosan-21-yl) amino) butan-2-yl) amino) -3-hydroxy-1-oxopropan-2-yl) amino) -1-oxobutan-2-yl) -6-methyloctanamide