Peptide platinum complexes and methods of use thereof

A purified peptide platinum complex comprising the formula (I):

• or a pharmaceutically acceptable salt thereof,
• wherein
• R1 and R2 are independently —N(R6)2, —NH3+, or R1 and R2 are each —NH2 and join through an C2-C6 alkylene or C3-C7 cycloalkylene group to form a bidentate diamine ligand;
• R3 is a peptide ligand, with the proviso that R3 cannot be an amino acid;
• R4 is a peptide ligand, an inorganic ligand, —CN or —OC(O)R5, with the proviso that R4 cannot be an amino acid;
• R5 is C1-C24 alkyl;
• and
• each R6 is independently —H, —C1-C6 alkyl, —C3-C7 cycloalkyl or -aryl.

A method for making a platinum complex of formula (I),

• comprising allowing a complex of formula (II),
• to react with at least about 2 molar equivalents of a compound of formula (II),
• wherein
• R1 and R2 are independently —N(R6)2, —NH3+, or R1 and R2 are each —NH2 and join through an C2-C6 alkylene or C3-C7 cycloalkylene group to form a bidentate diamine ligand;
• R3 is a peptide ligand, with the proviso that R3 cannot be an amino acid;
• R4 is a peptide ligand, an inorganic ligand, —CN or —OC(O)R5, with the proviso that R4 cannot be an amino acid;
• R5 is C1-C24 alkyl;
• each R6 is independently —H, —C1-C6 alkyl, —C3-C7 cycloalkyl or -aryl;
• and halo is —F, —Cl, —Br, —I or —At.