Anthracycline conjugates, process for its preparation and its use as antitumor compounds

An anthracycline derivative of Formula (IIc) Ant-L- (Z) m-X (IIc) in which Ant is selected from the structure: ** Formula ** in which the wavy line indicates the binding to L; L is a connector selected from -N (R) -, -N (R) m (C1-C12 alkylene) -, -N (R) m (C2-C8 alkenylene) -, - N (R) m (C2 alkynylene -C8) -, -N (R) m (CH2CH2O) n-, and the structure: ** Formula ** in which the wavy lines indicate the junctions to Ant and Z; and Z is an optional spacer selected from -CH2C (O) -, -CH2C (O) NR (C1-C12 alkylene) -, and the structures: ** Formula ** X is a reactive functional group selected from maleimide, thiol, amino, bromide, p-toluenesulfonate, iodide, hydroxyl, carboxyl, pyridyl disulfide, and N-hydroxysuccinimide; R is H, C1-C12 alkyl or C6-C20 aryl; R1 and R2 are independently selected from an amino acid side chain; Z1 is selected from - (C1-C12 alkylene) -, - (C2-C8 alkenylene) -, - (C2-C8 alkynylene) - and - (CH2CH2O) n-; m is 0 or 1; and n is from 1 to 6; or wherein the anthracycline derivative is selected from the structures: ** Formula ** in which Z is C1-C12 alkylene, ** Formula **