Cetrorelix Impurity 21

AC-3- (2-naphthyl) -D-Ala-4-Cl-D-Phe-3- (3-Pyridyl) -D-Ala-Ser-Tyr-D-Cit-Leu-Arg-Pro-Pro-D-Ala-NH2; (S) -1- (((R) -2- ((S) -2- ((S) -2- ((R) -2- ((R) -2- ((R) -2-acetamido-3- (naphthalen-2-yl) propanamido) -3- (4-chlorophenyl) propanamido) -3- (pyridin-3-yl) propanamido) -3-hydroxypropanamido) -3- (4-hydroxyphenyl) propanamido) -5-ureidopentanoyl) -L-leucyl-L-arginyl-L-prolyl) -N- ((R) -1-amino-1-oxopropan-2-yl) pyrrolidine-2-carboxamide