Antiproliferative compounds, conjugates thereof, methods therefor, and uses thereof

A method for treating a cancer in a subject suffering from such cancer, comprising administering to the subject a therapeutically effective amount of a compound having a structure represented by formula (II), or a conjugate thereof with a ligand that is an antibody,

• wherein
• n is 0, 1, or 2;
• R1, R2 and R3 are independently H, unsubstituted or substituted C1-C10 alkyl, unsubstituted or substituted C2-C10 alkenyl, unsubstituted or substituted C2-C10 alkynyl, unsubstituted or substituted aryl, unsubstituted or substituted heteroaryl, unsubstituted or substituted (CH2)1-2O(C1-C10 alkyl), unsubstituted or substituted (CH2)1-2O(C2-C10 alkenyl), unsubstituted or substituted (CH2)1-2O(C2-C10 alkynyl), (CH2)1-2OC(═O)(C1-C10 alkyl), unsubstituted or substituted (CH2)1-2OC(═O)(C2-C10 alkenyl), unsubstituted or substituted (CH2)1-2OC(═O)(C2-C10 alkynyl), unsubstituted or substituted C(═O)(C1-C10 alkyl), unsubstituted or substituted C(═O)(C2-C10 alkenyl), unsubstituted or substituted C(═O)(C2-C10 alkynyl), unsubstituted or substituted cycloaliphatic, unsubstituted or substituted heterocycloaliphatic, unsubstituted or substituted arylalkyl, or unsubstituted or substituted alkylaryl;
• R4 is
• R5 is H, C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, CO(C1-C5 alkyl), CO(C2-C5 alkenyl), or CO(C2-C5 alkynyl);
• or a pharmaceutically acceptable ester thereof, a pharmaceutically acceptable amide thereof at the carboxyl group of R4 with the α-amino group of an α-amino acid, or a pharmaceutically acceptable salt thereof.